Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion

Prone Transpsoas Lumbar Interbody Fusion for Degenerative Disc Disease

Background

Prone transpsoas lumbar interbody fusion (PTP) is a newer technique to treat various spinal disc pathologies. PTP is a variation of lateral lumbar interbody fusion (LLIF) that is performed with the patient prone rather than in the lateral decubitus position. This approach offers similar benefits of lateral spinal surgery, which include less blood loss, shorter hospital stay, and quicker recovery compared with traditional open spine surgery. PTP offers additional benefits over traditional lateral positioning, with a more familiar patient position for spine surgeons, the ability to perform simultaneous posterior decompression and fusion without repositioning, and improved sagittal alignment.

Description

PTP is performed with the patient under general anesthesia and with use of somatosensory evoked potentials (SSEP) and electromyography (EMG) neuromonitoring. The patient is positioned prone with the aid of specialized patient positioners. Once the patient is positioned and draped, the disc space of interest is marked with use of fluoroscopic guidance. An incision is made, and blunt dissection is performed through the external oblique, internal oblique, and transversalis muscles. The psoas muscle is palpated, and dilators are placed at the target disc level under fluoroscopic guidance, with care taken to protect the peritoneum and lumbar plexus. Specialized retractors are then positioned. Anulotomy and disc removal, disc space preparation, trialing, and final interbody placement are performed. The procedure ends with obtaining hemostasis and closure of the incision.

Alternatives

Before surgery is performed, nonoperative treatment should be attempted, including the use of nonsteroidal anti-inflammatory drugs, physical therapy, and spinal injections. Surgical alternatives include posterior lumbar laminectomy with or without fusion, as well as other procedures in the anterior column, such as LLIF, anterior lumbar interbody fusion, oblique lumbar interbody fusion, transforaminal lumbar interbody fusion, and posterior lumbar interbody fusion. These alternatives must be considered, especially when working at the L4-S1 disc spaces, because of potential limitations to lateral surgery, such as in cases of high-riding iliac crests, a rising psoas, and previous abdominal surgery.

Rationale

Lateral spinal surgery evolved as a means to approach the anterior column of the spine in order to treat various spine disorders, such as degenerative disc disease, tumors, infection, and spinal deformity. With the PTP procedure, the patient is in the prone rather than the lateral decubitus position, which allows the psoas muscle to retract more posteriorly because it is under tension, pulling the lumbar plexus away from the target point of the procedure. In addition, the prone position results in improved sagittal alignment compared with the lateral position. With respect to sagittal alignment, the PTP procedure allows for more appropriate balancing, which improves clinical outcomes. The peritoneum is also farther away from the operative zone during PTP, providing a safer corridor away from the bowel and ureter. For these reasons, PTP can potentially lead to improved outcomes compared with a lateral procedure performed with the patient in the lateral decubitus position, while also minimizing the risk of bowel and bladder injury and neurapraxia. In addition, PTP eliminates the need for repositioning or staged procedures. For instance, posterior laminectomies and fusions can be efficiently performed with the patient in the prone position, possibly simultaneously with the PTP procedure, whereas repositioning and redraping would be required with a lateral approach.

Expected Outcomes

PTP has several advantages over traditional posterior spinal surgery. These include a shorter hospital stay, decreased blood loss, and faster return of mobility. Specifically compared with a lateral approach with the patient in the lateral decubitus position, PTP may result in better segmental lordosis and spinopelvic alignment. To date, overall outcomes are otherwise similar between lateral decubitus and prone transpsoas approaches.

Important Tips

Make sure to adjust the table to waist height and keep your elbows at 90° of flexion while working on localization of the disc space. When doing disc work through the retractor, either raise the bed or sit in a chair to make sure that the disc space is at eye level, so that you are not straining your neck.During dissection, utilize finger dissection and avoid the use of electrocautery as it can cause neurapraxia and result in flaccid oblique musculature and subsequent pseudohernia.To reduce the risk of peritoneal injury, a 2-incision technique can be performed: Place a finger in an accessory posterior incision (either a midline incision or the percutaneous screw incision) to initially palpate the tip of the transverse process. Next, slide your finger into the retroperitoneal space and feel the psoas medially. Place another finger through the lateral incision, and touch both fingers together to ensure you are in the retroperitoneal space with your dilators.Another trick is to start the incision more posteriorly, as gravity will force you more anteriorly during localization.When placing the cage, the goal is to have it as anterior as possible in order to gain maximal lordosis and to span the apophyseal ring to reduce the risk of subsidence. In addition, placement of the widest possible cage can help reduce subsidence, with 18-mm cages showing greater subsidence than 22-mm cages.

Acronyms and Abbreviations

PTP = prone transpsoas lumbar interbody fusionLLIF = lateral lumbar interbody fusionALIF = anterior lumbar interbody fusionOLIF = oblique lumbar interbody fusionTLIF = transforaminal lumbar interbody fusionMRI = magnetic resonance imagingNSAID = nonsteroidal anti-inflammatory drugCT = computed tomographyEMG = electromyographyAP = anteroposteriorK-wire = Kirschner wireIV = intravenousSSEP = somatosensory evoked potentials.

Development of a continuum-based, meshless, finite element modeling approach for representation of trabecular bone indentation

Implant subsidence into the underlying trabecular bone is a common problem in orthopaedic surgeries; however, the ability to pre-operatively predict implant subsidence remains limited. Current state-of-the-art computational models for predicting subsidence have issues addressing this clinical problem, often resulting from the size and complexity of existing subject-specific, image-based finite element (FE) models. The current study aimed to develop a simplified approach to FE modeling of subject-specific trabecular bone indentation resulting from implant penetration. Confined indentation experiments of human trabecular bone with flat- and sharp-tip indenters were simulated using FE analysis. A generalized continuum-level approach using a meshless smoothed particle hydrodynamics (SPH) approach and an isotropic crushable foam (CF) material model was developed for the trabecular bone specimens. Five FE models were generated with CF material parameters calibrated to cadaveric specimens spanning a range of bone mineral densities (BMD). Additionally, an alternative model configuration was developed that included consideration of bone marrow, with bone and marrow material parameters assigned to elements randomly according to bone volume (BV%) measurements of experimental specimens, owing to the non-uniform nature of trabecular bone tissue microstructure. Statistical analysis found significant correlation between the shapes of the numerical and experimental force-displacement curves. FE models accurately captured the bone densification patterns observed experimentally. Inclusion of marrow elements offered improved response prediction of the flat-tip indenter tests. Ultimately, the developed approach demonstrates the ability of a generalizable continuum-level SPH approach to capture bone variability using clinical bone imaging metrics without needing detailed image-based geometries, a significant step towards simplified subject-specific modeling of implant subsidence.

Comparison of Hounsfield Unit, Vertebral Bone Quality, and Dual-Energy X-Ray Absorptiometry T-Score for Predicting Cage Subsidence After Posterior Lumbar Interbody Fusion

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

To compare Hounsfield unit (HU), vertebral bone quality (VBQ), and dual-energy X-ray absorptiometry (DEXA) T-score in predicting cage subsidence (CS) after posterior lumbar interbody fusion.

METHODS

We retrospectively reviewed patients undergoing PLIF and measured L4 HU and VBQ. Baseline characteristics between CS and non-CS groups were compared. Multiple logistic regression analysis was used to identify risk factors for CS. Receiver operating characteristic (ROC) curves were used to explore the predictive value of variables for CS. Subgroup analysis was conducted for patients with available DEXA results.

RESULTS

Eighty-four patients were analyzed. The subsidence group was older, with lower L4 HU (92.6 (35.4) vs 130.8 (47.8), P < 0.001) and higher VBQ (3.30 (0.64) vs 2.99 (0.63), P = 0.041) compared to the non-CS group. Low L4 HU (OR 0.979, P = 0.022) was an independent risk factor for subsidence, while VBQ was not. ROC analysis indicated that L4 HU (AUC = 0.733, P < 0.001) exhibited superior predictive performance compared to VBQ (AUC = 0.643, P = 0.032). Subgroup analysis in patients with DEXA showed that the femoral neck T-score (AUC = 0.67, P = 0.037) could differentiate CS, with L4 HU exhibiting the highest predictive ability (AUC = 0.778, P < 0.001), both outperforming VBQ (AUC = 0.645, P = 0.075).

CONCLUSIONS

Among the three BMD parameters, only low L4 HU could be an independent risk factor for CS. Preoperative HU is mandatory in patients at risk for osteoporosis when undergoing spine surgery.

Advances in implants and bone graft types for lumbar spinal fusion surgery

The increasing prevalence of spinal disorders worldwide necessitates advanced treatments, particularly interbody fusion for severe cases that are unresponsive to non-surgical interventions. This procedure, especially 360° lumbar interbody fusion, employs an interbody cage, pedicle screw-and-rod instrumentation, and autologous bone graft (ABG) to enhance spinal stability and promote fusion. Despite significant advancements, a persistent 10% incidence of non-union continues to result in compromised patient outcomes and escalated healthcare costs. Innovations in lumbar stabilisation seek to mimic the properties of natural bone, with evolving implant materials like titanium (Ti) and polyetheretherketone (PEEK) and their composites offering new prospects. Additionally, biomimetic cages featuring precisely engineered porosities and interconnectivity have gained traction, as they enhance osteogenic differentiation, support osteogenesis, and alleviate stress-shielding. However, the limitations of ABG, such as harvesting morbidities and limited fusion capacity, have spurred the exploration of sophisticated solutions involving advanced bone graft substitutes. Currently, demineralised bone matrix and ceramics are in clinical use, forming the basis for future investigations into novel bone graft substitutes. Bioglass, a promising newcomer, is under investigation despite its observed rapid absorption and the potential for foreign body reactions in preclinical studies. Its clinical applicability remains under scrutiny, with ongoing research addressing challenges related to burst release and appropriate dosing. Conversely, the well-documented favourable osteogenic potential of growth factors remains encouraging, with current efforts focused on modulating their release dynamics to minimise complications. In this evidence-based narrative review, we provide a comprehensive overview of the evolving landscape of non-degradable spinal implants and bone graft substitutes, emphasising their applications in lumbar spinal fusion surgery. We highlight the necessity for continued research to improve clinical outcomes and enhance patient well-being.

Biomechanical Analysis of Lumbar Interbody Fusion Cages With Various Elastic Moduli in Osteoporotic and Non-osteoporotic Lumbar Spine: A Finite Element Analysis

STUDY DESIGN

Finite element analysis (FEA).

OBJECTIVE

This study aimed to explore the effects of cage elastic modulus (Cage-E) on the endplate stress in different bone conditions: osteoporosis (OP) and non-osteoporosis (non-OP). We also explored the correlation between endplate thickness and endplate stress.

METHODS

The FEA models of L4-L5 with lumbar interbody fusion were designed to access the effects of Cage-E on the endplate stress in different bone conditions. Two groups of the Young's moduli of bony structure were assigned to simulate the conditions of OP and non-OP, and the bony endplates were analyzed in 2 kinds of thicknesses: .5 mm and 1.0 mm, with the insertion of cages with different Young's moduli including .5, 1.5, 3, 5, 10, and 20 GPa. After model validation, an axial compressive load of 400 N and a flexion/extension moment of 7.5Nm was performed on the superior surface of L4 vertebral body in order to analyze the distribution of stress.

RESULTS

The maximum Von Mises stress in the endplates increased by up to 100% in the OP model compared with non-OP model under the same condition of cage-E and endplate thickness. In both OP and non-OP models, the maximum endplate stress decreased as the cage-E decreased, but the maximum stress in the lumbar posterior fixation increased as the cage-E decreased. Thinner endplate thickness was associated with increased endplate stress.

CONCLUSION

The endplate stress is higher in osteoporotic bone than non-osteoporotic bone, which explains part of the mechanism of OP-related cage subsidence. It is reasonable to reduce the endplate stress by reducing the cage-E, but we should balance the risk of fixation failure. Endplate thickness is also important when evaluating the cage subsidence risk.

Defining cage subsidence in anterior, oblique, and lateral lumbar spine fusion approaches: a systematic review of the literature

One of the most common complications of lumbar fusions is cage subsidence, which leads to collapse of disc height and reappearance of the presenting symptomology. However, definitions of cage subsidence are inconsistent, leading to a variety of subsidence calculation methodologies and thresholds. To review previously published literature on cage subsidence in order to present the most common methods for calculating and defining subsidence in the anterior lumbar interbody fusion (ALIF), oblique lateral interbody fusion (OLIF), and lateral lumbar interbody fusion (LLIF) approaches. A search was completed in PubMed and Embase with inclusion criteria focused on identifying any study that provided descriptions of the method, imaging modality, or subsidence threshold used to calculate the presence of cage subsidence. A total of 69 articles were included in the final analysis, of which 18 (26.1%) reported on the ALIF approach, 22 (31.9%) on the OLIF approach, and 31 (44.9%) on the LLIF approach, 2 of which reported on more than one approach. ALIF articles most commonly calculated the loss of disc height over time with a subsidence threshold of > 2 mm. Most OLIF articles calculated the total amount of cage migration into the vertebral bodies, with a threshold of > 2 mm. LLIF was the only approach in which most articles applied the same method for calculation, namely, a grading scale for classifying the loss of disc height over time. We recommend future articles adhere to the most common methodologies presented here to ensure accuracy and generalizability in reporting cage subsidence.

Endplate weakening during cage bed preparation significantly reduces endplate load capacity

PURPOSE

To analyze the effect of endplate weakness prior to PLIF or TLIF cage implantation and compare it to the opposite intact endplate of the same vertebral body. In addition, the influence of bone quality on endplate resistance was investigated.

METHODS

Twenty-two human lumbar vertebrae were tested in a ramp-to-failure test. One endplate of each vertebral body was tested intact and the other after weakening with a rasp (over an area of 200 mm2). Either a TLIF or PLIF cage was then placed and the compression load was applied across the cage until failure of the endplate. Failure was defined as the first local maximum of the force measurement. Bone quality was assessed by determining the Hounsfield units (HU) on CT images.

RESULTS

With an intact endplate and a TLIF cage, the median force to failure was 1276.3N (693.1-1980.6N). Endplate weakening reduced axial endplate resistance to failure by 15% (0-23%). With an intact endplate and a PLIF cage, the median force to failure was 1057.2N (701.2-1735.5N). Endplate weakening reduced axial endplate resistance to failure by 36.6% (7-47.9%). Bone quality correlated linearly with the force at which endplate failure occurred. Intact and weakened endplates showed a strong positive correlation: intact-TLIF: r = 0.964, slope of the regression line (slope) = 11.8, p < 0.001; intact-PLIF: r = 0.909, slope = 11.2, p = 5.5E-05; weakened-TLIF: r = 0.973, slope = 12.5, p < 0.001; weakened-PLIF: r = 0.836, slope = 6, p = 0.003.

CONCLUSION

Weakening of the endplate during cage bed preparation significantly reduces the resistance of the endplate to subsidence to failure: endplate load capacity is reduced by 15% with TLIF and 37% with PLIF. Bone quality correlates with the force at which endplate failure occurs.

The effect of polymethylmethacrylate augmentation on the primary stability of stand-alone implant construct versus posterior stabilization in oblique lumbar interbody fusion with osteoporotic bone quality- a finite element study

BACKGROUND CONTEXT

Oblique lumbar interbody fusion (OLIF) can provide an ideal minimally invasive solution for achieving spinal fusion in an older, more frail population where decreased bone quality can be a limiting factor. Stabilization can be achieved with bilateral pedicle screws (BPS), which require additional incisions and longer operative time. Alternatively, a novel self-anchoring stand-alone lateral plate system (SSA) can be used, where no additional incisions are required. Based on the relevant literature, BPS constructs provide greater primary biomechanical stability compared to lateral plate constructs, including SSA. This difference is further increased by osteoporosis. Screw augmentation in spinal fusion surgeries is commonly used; however, in the case of OLIF, it is a fairly new concept, lacking a consensus-based guideline.

PURPOSE

This comparative finite element (FE) study aimed to investigate the effect of PMMA screw augmentation on the primary stability of a stand-alone implant construct versus posterior stabilization in OLIF with osteoporotic bone quality.

STUDY DESIGN

The biomechanical effect of screw augmentation was studied inside an in-silico environment using computer-aided FE analysis.

METHODS

A previously validated and published L2-L4 FE model with normal and osteoporotic bone material properties was used. Geometries based on the OLIF implants (BPS, SSA) were created and placed inside the L3-L4 motion segment with increasing volumes (1-6 cm3) of PMMA augmentation. A follower load of 400 N and 10 Nm bending moment (in the three anatomical planes) were applied to the surgical FE models with different bone material properties. The operated L3-L4 segmental range of motion (ROM), the inserted cage's maximal caudal displacements, and L4 cranial bony endplate principal stress values were measured.

RESULTS

The nonaugmented values for the BPS construct were generally lower compared to SSA, and the difference was increased by osteoporosis. In osteoporotic bone, PMMA augmentation gradually decreased the investigated parameters and the difference between the two constructs as well. Between 3 cm3 and 4 cm3 of injected PMMA volume per screw, the difference between augmented SSA and standard BPS became comparable.

CONCLUSIONS

Based on this study, augmentation can enhance the primary stability of the constructs and decrease the difference between them. Considering leakage as a possible complication, between 3 cm3 and 4 cm3 of injected PMMA per screw can be an adequate amount for SSA augmentation. However, further in silico, and possibly in vitro and clinical testing is required to thoroughly understand the investigated biomechanical aspects.

CLINICAL SIGNIFICANCE

This study sheds light on the possible biomechanical advantage offered by augmented OLIF implants and provides a theoretical augmentation amount for the SSA construct. Based on the findings, the concept of an SSA device with PMMA augmentation capability is desirable.

The effect of different fixation systems on oblique lumbar interbody fusion under vibration conditions

Despite the fact that lower back pain caused by degenerative lumbar spine pathologies seriously affects the quality of life, however, there is a paucity of research on the biomechanical properties of different auxiliary fixation systems for its primary treatment (oblique lumbar interbody fusion) under vibratory environments. In order to study the effects of different fixation systems of OLIF surgery on the vibration characteristics of the human lumbar spine under whole-body vibration (WBV), a finite element (FE) model of OLIF surgery with five different fixation systems was established by modifying a previously established model of the normal lumbar spine (L1-S1). In this study, a compressive follower load of 500 N and a sinusoidal axial vertical load of ±40 N at the frequency of 5 Hz with a duration of 0.6 s was applied. The results showed that the bilateral pedicle screw fixation model had the highest resistance to cage subsidence and maintenance of disc height under WBV. In contrast, the lateral plate fixation model exerted very high stresses on important tissues, which would be detrimental to the patient's late recovery and reduction of complications. Therefore, this study suggests that drivers and related practitioners who are often in vibrating environments should have bilateral pedicle screws for OLIF surgery, and side plates are not recommended to be used as a separate immobilization system. Additionally, the lateral plate is not recommended to be used as a separate fixation system.

Can We Rely on Prophylactic Two-Level Vertebral Cement Augmentation in Long-Segment Adult Spinal Deformity Surgery to Reduce the Incidence of Proximal Junctional Complications?

Background and Objectives: Proximal junctional kyphosis (PJK) and failure (PJF), the most prevalent complications following long-segment thoracolumbar fusions for adult spinal deformity (ASD), remain lacking in defined preventive measures. We studied whether one of the previously reported strategies with successful results-a prophylactic augmentation of the uppermost instrumented vertebra (UIV) and supra-adjacent vertebra to the UIV (UIV + 1) with polymethylmethacrylate (PMMA)-could also serve as a preventive measure of PJK/PJF in minimally invasive surgery (MIS). Materials and Methods: The study included 29 ASD patients who underwent a combination of minimally invasive lateral lumbar interbody fusion (MIS-LLIF) at L1-2 through L4-5, all-pedicle-screw instrumentation from the lower thoracic spine to the sacrum, S2-alar-iliac fixation, and two-level balloon-assisted PMMA vertebroplasty at the UIV and UIV + 1. Results: With a minimum 3-year follow-up, non-PJK/PJF group accounted for fifteen patients (52%), PJK for eight patients (28%), and PJF requiring surgical revision for six patients (21%). We had a total of seven patients with proximal junctional fracture, even though no patients showed implant/bone interface failure with screw pullout, probably through the effect of PMMA. In contrast to the PJK cohort, six PJF patients all had varying degrees of neurologic deficits from modified Frankel grade C to D3, which recovered to grades D3 and to grade D2 in three patients each, after a revision operation of proximal extension of instrumented fusion with or without neural decompression. None of the possible demographic and radiologic risk factors showed statistical differences between the non-PJK/PJF, PJK, and PJF groups. Conclusions: Compared with the traditional open surgical approach used in the previous studies with a positive result for the prophylactic two-level cement augmentation, the MIS procedures with substantial benefits to patients in terms of less access-related morbidity and less blood loss also provide a greater segmental stability, which, however, may have a negative effect on the development of PJK/PJF.

Comparison of Long-term Follow-Up of n-HA PA66 Cage and PEEK Cage of Lumbar Interbody Fusion in Multi-level Degenerative Lumbar Diseases: A Stepwise Propensity Score Matching Analysis

OBJECTIVE

Previous studies have confirmed that the nanohydroxyapatite/polyamide-66 (n-HA/PA66) cage is an ideal alternative material for degenerative lumbar disease (DLD) comparable to the polyether ether ketone (PEEK) cage due to its similar radiographic fusion, subsidence rate, and clinical results. However, these studies were restricted to one-level surgery. The aim of this study was to analyze the long-term clinical and radiologic outcomes between n-HA PA66 cage and PEEK cage for patients with multi-level degenerative lumbar diseases (DLDs).

METHODS

We retrospectively reviewed all patients who underwent multi-level transforaminal lumbar interbody fusion (TLIF) from June 2010 to December 2016 with a minimum 6-year follow-up. Matched-pair analysis was performed using a 1-to-1 closest neighbor approach to match patients who received an n-HA PA66 cage with those who received a PEEK cage. Clinical outcomes and radiographic evaluations were compared between the two groups. The independent student's t-test and χ2 -test were applied to compare the differences between groups.

RESULTS

At the end of the propensity score matching (PSM) analysis, 48 patients from n-HA/PA66 group were matched to 48 patients in the PEEK group. No significant difference was observed in cage subsidence and bony fusion except for adjacent segment degeneration (ASD). The occurrence of ASD was 14.58% (7/48) in the n-HA/PA 66 group, which was significantly less than that in the PEEK group (33.33% [16/48]) (p = 0.031). Although the intervertebral space height (IH), segmental angle (SA) and lumbar lordosis (LL) significantly increased after surgery in both groups, there was no significant difference at any time point after surgery (p > 0.05). The visual analogue scale (VAS) and Oswestry disability index (ODI) scores significantly improved in both groups at 3m postoperative, 1y postoperative and at final follow-up. However, there were no significant differences in the VAS and ODI score at any time point (p > 0.05). The total complications and re-admission rate were not different between the two groups.

CONCLUSION

Overall, our data suggest that the outcomes of n-HA/PA66 cage group are comparable to those of the PEEK cage group, with a similar high fusion rate and low cage subsidence rate as PEEK cages, except its lower rate of ASD occurrence.

Predictors of Subsidence and its Clinical Impact After Expandable Cage Insertion in Minimally Invasive Transforaminal Interbody Fusion

STUDY DESIGN

Retrospective review of prospectively collected multisurgeon data.

OBJECTIVE

Examine the rate, clinical impact, and predictors of subsidence after expandable minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) cage.

SUMMARY OF BACKGROUND DATA

Expandable cage technology has been adopted in MI-TLIF to reduce the risks and optimize outcomes. Although subsidence is of particular concern when using expandable technology as the force required to expand the cage can weaken the endplates, its rates, predictors, and outcomes lack evidence.

MATERIALS AND METHODS

Patients who underwent 1 or 2-level MI-TLIF using expandable cages for degenerative lumbar conditions and had a follow-up of >1 year were included. Preoperative and immediate, early, and late postoperative radiographs were reviewed. Subsidence was determined if the average anterior/posterior disc height decreased by >25% compared with the immediate postoperative value. Patient-reported outcomes were collected and analyzed for differences at the early (<6 mo) and late (>6 mo) time points. Fusion was assessed by 1-year postoperative computed tomography.

RESULTS

One hundred forty-eight patients were included (mean age, 61 yr, 86% 1-level, 14% 2-level). Twenty-two (14.9%) demonstrated subsidence. Although statistically not significant, patients with subsidence were older, had lower bone mineral density, and had higher body mass index and comorbidity burden. Operative time was significantly higher ( P = 0.02) and implant width was lower ( P < 0.01) for subsided patients. Visual analog scale-leg was significantly lower for subsided patients compared with nonsubsided patients at a >6 months time point. Long-term (>6 mo) patient-acceptable symptom state achievement rate was lower for subsided patients (53% vs . 77%), although statistically not significant ( P = 0.065). No differences existed in complication, reoperation, or fusion rates.

CONCLUSIONS

Of the patients, 14.9% experienced subsidence predicted by narrower implants. Although subsidence did not have a significant impact on most patient-reported outcome measures and complication, reoperation, or fusion rates, patients had lower visual analog scale-leg and patient-acceptable symptom state achievement rates at the >6-month time point.

LEVEL OF EVIDENCE

Level 4.

Comparison of Intraoperative Endplate Injury between Mini-Open Lateral Lumbar Interbody Fusion (LLIF) and Transforaminal Lumbar Interbody Fusion (TLIF) and Analysis of Risk Factors: A Retrospective Study

OBJECTIVE

The study aimed to compare the incidence of intraoperative endplate injury in patients who underwent Transforaminal interbody fusion (TLIF) and mini-open lumbar interbody fusion (LLIF) surgery. The independent risk factors related to endplate injury in LLIF procedure were analyzed.

METHODS

A total of 199 patients who underwent LLIF (n = 106) or TLIF (n = 93) surgery from June 2019 to September 2021 were reviewed. The endplate injury was assessed by postoperative sagittal CT scan. A binary logistic analysis model were used to identify independent risk factors related to LLIF endplate injury based on univariate analysis.

RESULTS

There was an obvious difference in the occurrence of intraoperative endplate injury between LLIF (42/106, 39.6%) and TLIF group (26/93, 28%), although it did not reach the significant level. L1 CT value (OR = 0.985, 95% CI = 0.972-0.998), cage position (OR = 3.881, 95% CI = 1.398-10.771) and height variance (OR = 1.263, 95% CI = 1.013-1.575) were independent risk factors for endplate injury in LLIF procedure. According to the cage settlement patterns, there 5 types of A to E. The severity of the facet joint degeneration was positively related to the occurrence of endplate injury.

CONCLUSIONS

The incidence of intraoperative endplate injury is higher in LLIF than in TLIF procedures. Low bone quantity, cage posterior position and larger height variance are risk factors to induce endplate injury in LLIF surgery. The facet joint degeneration may be related to severe endplate injuries and even fractures.

Subsidence Performance of the Bioactive Glass-Ceramic (CaO-SiO2-P2O5-B2O3) Spacer in Terms of Modulus of Elasticity and Contact Area: Mechanical Test and Finite Element Analysis

OBJECTIVE

The objective of this study is to evaluate the subsidence performance of a bioactive glass-ceramic (CaO-SiO2-P2O5-B2O3) spacer in terms of its modulus of elasticity and contact area using mechanical tests and finite element analysis.

METHODS

Three spacer three-dimensional models (Polyether ether ketone [PEEK]-C: PEEK spacer with a small contact area; PEEK-NF: PEEK spacer with a large contact area; and Bioactive glass [BGS]-NF: bioactive glass-ceramic spacer with a large contact area) are constructed and placed between bone blocks for compression analysis. The stress distribution, peak von Mises stress, and reaction force generated in the bone block are predicted by applying a compressive load. Subsidence tests are conducted for three spacer models in accordance with ASTM F2267. Three types of blocks measuring 8, 10, and 15 pounds per cubic foot are used to account for the various bone qualities of patients. A statistical analysis of the results is conducted using a one-way Analysis of variance and post hoc analysis (Tukey's Honestly Significant Difference) by measuring the stiffness and yield load.

RESULTS

The stress distribution, peak von Mises stress, and reaction force predicted via the finite element analysis are the highest for PEEK-C, whereas they are similar for PEEK-NF and BGS-NF. Results of mechanical tests show that the stiffness and yield load of PEEK-C are the lowest, whereas those of PEEK-NF and BGS-NF are similar.

CONCLUSIONS

The main factor affecting subsidence performance is the contact area. Therefore, bioactive glass-ceramic spacers exhibit a larger contact area and better subsidence performance than conventional spacers.

Application of self-anchored lateral lumbar interbody fusion in lumbar degenerative diseases

STUDY DESIGN

This is a retrospective study.

OBJECTIVE

The aim of the study was to evaluate the efficacy of self-anchored lateral lumbar interbody fusion (SA-LLIF) in lumbar degenerative diseases.

METHODS

Forty-eight patients with lumbar degenerative disease between January 2019 and June 2020 were enrolled in this study. All patients complained of low back and leg pain, which were aggravated during standing activities and alleviated or disappeared during lying. After general anesthesia, the patient was placed in the right decubitus position. The anterior edge of the psoas major muscle was exposed through an oblique incision of approximately 6 cm, using an extraperitoneal approach. The psoas major muscle was then properly retracted dorsally to expose the disc. After discectomy, a suitable cage filled with autogenous bone graft from the ilium was implanted. Two anchoring plates were inserted separately into the caudal and cranial vertebral bodies to lock the cage. Clinical efficacy was evaluated using the visual analog scale (VAS) and Oswestry Disability Index (ODI). Lumbar lordosis, intervertebral disc height, spondylolisthesis rate, cage subsidence and fusion rate were also recorded.

RESULTS

A total of 48 patients were enrolled in this study, including 20 males and 28 females, aged 61.4 ± 7.3 (range 49-78) years old. Surgery was successfully performed in all patients. Lumbar stenosis and instability were observed in 22 cases, disc degenerative disease in eight cases, degenerative spondylolisthesis in nine cases, degenerative scoliosis in six cases, and postoperative revision in three cases. In addition, five patients were diagnosed with osteoporosis. The index levels included L2-3 in three patients, L3-4 in 13 patients, L4-5 in 23 patients, L2-4 in three patients, and L3-5 in six patients. The operation time was 81.1 ± 6.4 (range 65-102) min. Intraoperative blood loss was 39.9 ± 8.5 (range 15-72) mL. No severe complications occurred, such as nerve or blood vessel injuries. The patients were followed up for 11.7 ± 2.3 (range 4-18) months. At the last follow-up, the VAS decreased from 6.2 ± 2.3 to 1.7 ± 1.1, and the ODI decreased from 48.4% ± 11.2% to 10.9% ± 5.5%. Radiography showed satisfactory postoperative spine alignment. No cage displacement was found, but cage subsidence 2-3 mm was found in five patients without obvious symptoms, except transient low back pain in an obese patient. The lumbar lordosis recovered from 36.8° ± 7.9° to 47.7° ± 6.8°, and intervertebral disc height recovered from 8.2 ± 2.0 mm to 11.4 ± 2.5 mm. The spondylolisthesis rate decreased from 19.9% ± 4.9% to 9.4% ± 3.2%. The difference between preoperative and last follow-up was statistically significant (P<0.05).

CONCLUSION

SA-LLIF can provide immediate stability and good results for lumbar degenerative diseases with a standalone anchored cage without posterior internal fixation.

Clinical and radiographic outcomes of oblique lumbar interbody fusion with anterolateral screw and rod instrumentation in osteopenia patients: a retrospective study

PURPOSE

The purpose of this paper is to evaluate the clinical and radiographic outcomes of oblique lumbar interbody fusion (OLIF) to perform in L4/5 degenerative lumbar spondylolisthesis (DLS) patients who diagnosed with osteopenia.

METHODS

From December 2018 to 2021 March, 94 patients were diagnosed with degenerative spondylolisthesis underwent OLIF and divided into two groups with different bone mineral density. Anterolateral screw and rod instrumentation was applied in two groups. The primary outcomes were VAS, JOA and ODI. The secondary outcomes included disc height (DH), cross-sectional height of the intervertebral foramina (CSH), cross-sectional area of the dural sac (CSA), lumbar lordorsis (LL), pelvic titlt (PT), pelvic incidence (PI) and sacrum slop (SS).

RESULTS

All patients finished at least 1 years follow-up with 21.05 ± 4.42 months in the group A and 21.09 ± 4.28 months in the group B. The clinical symptoms were evaluated by VAS, JOA and ODI and 94 patients showed good outcomes at final follow-up (P < 0.05), with significant increases in DH, CSH and CSA. In group A, DH increased from 8.54 ± 2.48 to 11.11 ± 2.63 mm, while increased from 8.60 ± 2.29 to 11.23 ± 1.88 were recorded in group B. No statistical difference was found in DH between the two groups (P > 0.05). The cage subsidence was 1.14 ± 0.83 mm in group A and 0.87 ± 1.05 mm in group B (P > 0.05). There was no significant difference in the adjusted parameters of spino-pelvic between two groups (P > 0.05).

CONCLUSION

Oblique lumbar interbody fusion with anterolateral screw and rod instrumentation is feasible to be performed in osteopenia patients who diagnosed with degenerative spondylolisthesis.

The Role of Hounsfield Unit in Intraoperative Endplate Violation and Delayed Cage Subsidence with Oblique Lateral Interbody Fusion

STUDY DESIGN

Retrospective clinical case series.

OBJECTIVES

To investigate the risk factors for intraoperative endplate violations and delayed cage subsidence after oblique lateral interbody fusion (OLIF) surgery. Secondly, to examine whether low Hounsfield unit (HU) values at different regions of the endplate are associated with intraoperative endplate violation or delayed cage subsidence.

METHODS

61 patients (aged 65.1 ± 9.5 years; 107 segments) who underwent OLIF with or without posterior instrumentation from May 2015 to April 2019 were retrospectively studied. Intraoperative endplate violation was measured on sagittal reconstructed computerized tomography (CT) images immediate postoperatively, while delayed cage subsidence was evaluated using lateral radiographs and defined at 1-month follow-up or later. Demographic information and clinical parameters such as age, body mass index, bone mineral density, number of surgical levels, cage dimension, disc height restoration, visual analogue scale (VAS), and HU at different regions of the endplate were obtained.

RESULTS

Total postoperative cage subsidence was identified in 45 surgical levels (42.0%) in 26 patients (42.6%) up till postoperative 1-year follow-up. Low HU value at the ipsilateral epiphyseal ring was an independent risk factor for intraoperative endplate violation (P = .008) with a cut-off value of 326.21 HUs. Low HU values at the central endplate had a significant correlation with delayed cage subsidence in stand-alone cases (P = .013) with a cut-off value of 296.42 HUs. VAS scores were not different at 1 week postoperatively in cases with or without intraoperative endplate violation (3.12 ± .73 vs 2.89 ± .72, P = .166) and showed no difference at 1 year with or without delayed cage subsidence (1.95 ± .60 vs 2.26 ± .85, P = .173).

CONCLUSIONS

Intraoperative endplate violation and delayed cage subsidence are not uncommon with OLIF surgery. HUs of the endplate are good predictors for intraoperative endplate violation and cage subsidence since they can represent the regional bone quality of the endplate in contact with the implant. VAS improvements were not affected by intraoperative endplate violation or delayed cage subsidence at 1-year follow-up.

LEVEL OF EVIDENCE

Level III.

Subsidence of Interbody Cage Following Oblique Lateral Interbody Fusion: An Analysis and Potential Risk Factors

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

This study aimed to report the incidence and potential risk factors of polyetheretherketone (PEEK) cage subsidence following oblique lateral interbody fusion (OLIF) for lumbar degenerative diseases. We proposed also an algorithm to minimize subsidence following OLIF surgery.

METHODS

The study included a retrospective cohort of 107 consecutive patients (48 men and 59 women; mean age, 67.4 years) who had received either single- or multi-level OLIF between 2012 and 2019. Patients were classified into subsidence and non-subsidence groups. PEEK cage subsidence was defined as any violation of either endplate from the computed tomography scan in both sagittal and coronal views. Preoperative variables such as age, sex, body mass index, bone mineral density (BMD) measured by preoperative dual-energy X-ray absorptiometry, smoking status, corticosteroid use, diagnosis, operative level, multifidus muscle cross-sectional area, and multifidus muscle fatty degeneration were collected. Age-related variables (height and length) were also documented. Univariate and multivariate logistic regression analyses were used to analyze the risk factors of subsidence.

RESULTS

Of the 107 patients (137 levels), 50 (46.7%) met the subsidence criteria. Higher PEEK cage height had the strongest association with subsidence (OR = 9.59, P < .001). Other factors significantly associated with cage subsistence included age >60 years (OR = 3.15, P = .018), BMD <-2.5 (OR = 2.78, P = .006), and severe multifidus muscle fatty degeneration (OR = 1.97, P = .023).

CONCLUSIONS

Risk factors for subsidence in OLIF were age >60 years, BMD < -2.5, higher cage height, and severe multifidus muscle fatty degeneration. Patients who had subsidence had worse early (3 months) postoperative back and leg pain.

Postoperative cage migration and subsidence following TLIF surgery is not associated with bony fusion

Pseudarthrosis following transforaminal interbody fusion (TLIF) is not infrequent. Although cage migration and subsidence are commonly regarded as evidence of the absence of solid fusion, there is still no evidence of the influence of cage migration and subsidence on fusion. This study aimed to evaluate cage migration and subsidence using computed tomography (CT) DICOM data following lumbar interbody fusion. The effects of cage migration and subsidence on fusion and clinical outcomes were also assessed. A postoperative CT data set of 67 patients treated with monosegmental TLIF was analyzed in terms of cage position. To assess the effects of cage migration and subsidence on fusion, 12-month postoperative CT scans were used to assess fusion status. Clinical evaluation included the visual analog scale for pain and the Oswestry Disability Index. Postoperative cage migration occurred in 85.1% of all patients, and cage subsidence was observed in 58.2%. Radiological signs of pseudarthrosis was observed in 7.5% of the patients Neither cage migration nor subsidence affected the clinical or radiographic outcomes. No correlation was found between clinical and radiographic outcomes. The incidence of cage migration was considerable. However, as cage migration and subsidence were not associated with bony fusion, their clinical significance was considered limited.

Comparing Efficacy of Lumbar Disc Space Preparation via an Anterior-to-Psoas Approach Between Intraoperative Conventional Fluoroscopy and Computed Tomographic-Based Navigation System: A Cadaveric Study

OBJECTIVE

To compare the efficacy of intervertebral disc space preparation via an anterior-to-psoas (ATP) approach using conventional fluoroscopy (Flu) and computer tomography (CT)-based navigation by evaluating the disc remaining area.

METHODS

We equally assigned 24 lumbar disc levels from 6 cadavers into Flu and CT-based navigation (Nav) groups. Two surgeons performed disc space preparation using the ATP approach in both groups. Digital images of each vertebral endplate were obtained, and the remaining disc tissue was calculated in total and in quadrants. Operative time, number of attempts at disc removal, endplate violation area, number of endplate violation segments, and access angle were recorded.

RESULTS

The overall percentage of remaining disc tissue was significantly less in the Nav group than in the Flu group (32.7% vs. 43.3% respectively, P < 0.001). A significant difference was found in the posterior-ipsilateral (4.2% vs. 7.1%, P = 0.005) and posterior-contralateral (6.1% vs. 10.9%, P = 0.002) quadrants, respectively. No significant between-group difference was found concerning operative time, number of attempts at disc removal, endplate violation area, number of endplate violation segments, or access angle.

CONCLUSIONS

Intraoperative CT-based navigation may improve vertebral endplate preparation quality for an ATP approach, especially in the posterior quadrants. This technique may offer an effective alternative disc space and endplate preparation methods and may help enhance the fusion rates.

Development and validation of a risk prediction model for cage subsidence after instrumented posterior lumbar fusion based on machine learning: a retrospective observational cohort study

Background

Interbody cage subsidence is a common complication after instrumented posterior lumbar fusion surgery, several previous studies have shown that cage subsidence is related to multiple factors. But the current research has not combined these factors to predict the subsidence, there is a lack of an individualized and comprehensive evaluation of the risk of cage subsidence following the surgery. So we attempt to identify potential risk factors and develop a risk prediction model that can predict the possibility of subsidence by providing a Cage Subsidence Score (CSS) after surgery, and evaluate whether machine learning-related techniques can effectively predict the subsidence.

Methods

This study reviewed 59 patients who underwent posterior lumbar fusion in our hospital from 2014 to 2019. They were divided into a subsidence group and a non-subsidence group according to whether the interbody fusion cage subsidence occurred during follow-up. Data were collected on the patient, including age, sex, cage segment, number of fusion segments, preoperative space height, postoperative space height, preoperative L4 lordosis Angle, postoperative L4 lordosis Angle, preoperative L5 lordosis Angle, postoperative PT, postoperative SS, postoperative PI. The conventional statistical analysis method was used to find potential risk factors that can lead to subsidence, then the results were incorporated into stepwise regression and machine learning algorithms, respectively, to build a model that could predict the subsidence. Finally the diagnostic efficiency of prediction is verified.

Results

Univariate analysis showed significant differences in pre-/postoperative intervertebral disc height, postoperative L4 segment lordosis, postoperative PT, and postoperative SS between the subsidence group and the non-subsidence group (p < 0.05). The CSS was trained by stepwise regression: 2 points for postoperative disc height > 14.68 mm, 3 points for postoperative L4 segment lordosis angle >16.91°, and 4 points for postoperative PT > 22.69°. If the total score is larger than 0.5, it is the high-risk subsidence group, while less than 0.5 is low-risk. The score obtains the area under the curve (AUC) of 0.857 and 0.806 in the development and validation set, respectively. The AUC of the GBM model based on the machine learning algorithm to predict the risk in the training set is 0.971 and the validation set is 0.889. The AUC of the avNNet model reached 0.931 in the training set and 0.868 in the validation set, respectively.

Conclusion

The machine learning algorithm has advantages in some indicators, and we have preliminarily established a CSS that can predict the risk of postoperative subsidence after lumbar fusion and confirmed the important application prospect of machine learning in solving practical clinical problems.

Lateral interbody fusion without intraoperative neuromonitoring in addition to posterior instrumented fusion in geriatric patients: A single center consecutive series of 108 surgeries

Introduction

Lateral lumbar interbody fusion (LLIF) and lateral thoracic interbody fusion (LTIF), supported by intraoperative neuromonitoring (IONM), gained popularity as a mini-invasive alternatives for standard interbody fusion. The objective of this study was to investigate the clinical outcome in a large elderly patient cohort who underwent LTIF/LLIF without IONM.

Methods

This retrospective, single-center study enrolled elderly patients (≥70 years old) operated during the period from 2010 to 2016. Anterior lumbar interbody fusion (ALIF) in the L5/S1 segment was excluded from the analysis.

Results

The study enrolled 108 patients (63 males, 58.3%) with a mean age of 76.5 ​y/o. The mean follow-up was 14.4 ​± ​11.3 months. The mean time of the surgery was 92 ​± ​34.2 ​min. The mean blood loss was 62.2 ​ml. There were no vascular or visceral surgical complications. 39 medical complications were encountered in 24 (22%) patients. Less than 5% of patients presented with a new onset of motor weakness and less than 2% of the patients developed a new sensory deficit at the discharge. 46% of patients were lost in follow-up at 12 months.

Conclusions

IONM is not mandatory for LLIF/LTIF surgery in geriatric patients and has a low frequency of approach-related complications as well as neurological deterioration. Our results are comparable to the available literature. Regardless of the utilization of these mini-invasive, anterior approaches, in patients of advanced aged, the risk for major medical complications is high and is responsible for contributing to prolonged hospitalization.

Long-Term Durability of Stand-Alone Lateral Lumbar Interbody Fusion

BACKGROUND

The long-term durability of stand-alone lateral lumbar interbody fusion (LLIF) remains unknown.

OBJECTIVE

To evaluate whether early patient-reported outcome measures after stand-alone LLIF are sustained on long-term follow-up.

METHODS

One hundred and twenty-six patients who underwent stand-alone LLIF between 2009 and 2017 were included in this study. Patient-reported outcome measures included the Oswestry Disability Index (ODI), EuroQOL-5D (EQ-5D), and visual analog score (VAS) scores. Durable outcomes were defined as scores showing a significant improvement between preoperative and 6-week scores without demonstrating any significant decline at future time points. A repeated measures analysis was conducted using generalized estimating equations (model) to assess the outcome across different postoperative time points, including 6 weeks, 1 year, 2 years, and 5 years.

RESULTS

ODI scores showed durable improvement at 5-year follow-up, with scores improving from 46.9 to 38.5 ( P = .001). Improvements in EQ-5D showed similar durability up to 5 years, improving from 0.48 to 0.65 ( P = .03). VAS scores also demonstrated significant improvements postoperatively that were durable at 2-year follow-up, improving from 7.0 to 4.6 ( P < .0001).

CONCLUSION

Patients undergoing stand-alone LLIF were found to have significant improvements in ODI and EQ-5D at 6-week follow-up that remained durable up to 5 years postoperatively. VAS scores were found to be significantly improved at 6 weeks and up to 2 years postoperatively but failed to reach significance at 5 years. These findings demonstrate that patients undergoing stand-alone LLIF show significant improvement in overall disability after surgery that remains durable at long-term follow-up.

Perioperative Clinical Features and Long-term Prognosis After Oblique Lateral Interbody Fusion (OLIF), OLIF With Anterolateral Screw Fixation, or OLIF With Percutaneous Pedicle Fixation: A Comprehensive Treatment Strategy for Patients With Lumbar Degenerative Disease

OBJECTIVE

To compare the efficacy of oblique lateral interbody fusion (OLIF), OLIF combined with anterolateral screw fixation (OLIF-AF), and OLIF combined with percutaneous pedicle screw fixation (OLIF-PF) in the treatment of single-level or 2-level degenerative lumbar disease.

METHODS

Between January 2017 and 2021, 71 patients were treated with OLIF and combined OLIF. The demographic data, clinical outcomes, radiographic outcomes, and complications were compared among the 3 groups.

RESULTS

The operative time and intraoperative blood loss in the OLIF (p<0.05) and OLIF-AF (p<0.05) groups were lower than in the OLIF-PF group. Posterior disk height improvement in the OLIF-PF group was better than in the OLIF (p<0.05) and OLIF-AF (p<0.05) groups. In terms of foraminal height (FH), the OLIF-PF group was significantly better than the OLIF group (p<0.05), but there was no significant difference between the OLIF-PF and OLIF-AF groups (p>0.05) or between the OLIF and OLIF-AF groups (p>0.05). There were no significant differences in fusion rates, the incidence of complications, lumbar lordosis, anterior disc height, and cross-sectional area among the 3 groups (p>0.05). The OLIF-PF group had significantly lower rates of subsidence than the OLIF group (p<0.05).

CONCLUSION

OLIF remains a viable option with similar patient-reported outcomes and fusion rates compared with surgeries that include lateral and posterior internal fixation while greatly reducing the financial burden, intraoperative time, and intraoperative blood loss. OLIF has a higher subsidence rate than lateral and posterior internal fixation, but most subsidence is mild and has no adverse effect on clinical and radiographic outcomes.

The Impact of Cage and End plate-Related Factors on Cage Subsidence in Oblique Lateral Interbody Fusion

OBJECTIVES

To identify cage and end plate factors of cage subsidence (CS) in patients who underwent oblique lateral interbody fusion (OLIF) and their association with patient-reported outcomes.

METHODS

Sixty-one patients (43 women and 18 men), with a total of 69 segments (138 end plates) which underwent OLIF at a single academic institution between November 2018 and November 2020, were included. All the end plates were separated into CS and nonsubsidence groups. Cage-related parameters (cage height, cage width, cage insertion level, and cage position) and end plate-related parameters (position of end plate, Hounsfield unit value of the vertebra, end plate concave angle [ECA], end plate injury, and angular mismatch measured with cage/end plate angle [C/EA]) were compared and analyzed using logistic regression to predict CS. Receiver operating characteristic curve analysis was used to determine the cutoff points of the parameters.

RESULTS

Postoperative CS was identified in 50 of the 138 end plates (36.2%). The CS group had significantly lower mean Hounsfield unit values of the vertebra, higher rate of end plate injury, lower ECA, and higher C/EA than the nonsubsidence group. ECA and C/EA were identified as independent risk factors for developing CS. The optimal cutoff points for ECA and C/EA were 176.9° and 5.4°, respectively.

CONCLUSIONS

An ECA greater than 176.9° and a cage/end plate angular mismatch greater than 5.4° were found to be independent risk factors of postoperative CS after the OLIF procedure. These findings aid in preoperative decision-making and intraoperative technical guidance.

Implications of cage impactions in single-level OLIF treatment of degenerative spondylolisthesis

INTRODUCTION

Cage impactions (CI) of Oblique Lumbar Interbody Fusion (OLIF) appear to be a frequent mechanical complication with a potential functional impact.

OBJECTIVES

To determine the rate of CI occurrence, their risk factors and clinical implications in the case of combined single-level arthrodesis.

METHOD

A retrospective analysis of prospectively collected data was performed. All our patients with degenerative spondylolisthesis initially underwent OLIF combined with pedicle screw fixation (PSF). Intraoperative control with an image intensifier and a standard radiograph in the immediate postoperative period made it possible to assess the occurrence of CI, depending on the position of the implant. Secondary subsidence was sought on the standing radiological examination using EOS biplanar radiography during follow-up. The pelvic parameters were analyzed, as well as the occurrence of bone fusion. The clinical evaluation was made at≥1 year, by the Oswestry Disability Index (ODI), the walking distance (WD) and the Visual Analogue Scale (VAS).

RESULTS

In all, 130 patients out of the 131 included were analyzed. A CI occurred in 25.3% (n=33) of cases and of these, 94% (n=32) occurred intraoperatively. Postmenopausal women had more CI with an odds ratio (OR) of 5.8 (P=0.034). The "CI" group had a 9.5% lower ODI score than the "non-CI" group (P=0.0040), but both provided excellent ODI gains of 30.8±16 and 32.9±15.5% (P<0.0001). An "anterior" position of the implant allowed a greater gain in lumbar lordosis (P<0.001) but was associated with greater CI occurrence (P<0.001), with an OR of 6.75 (P=0.0018).

CONCLUSION

The occurrence of intraoperative cage impaction is a frequent event when performing OLIF. Postmenopausal women have an approximately 6 times greater risk of impaction than men, and patients with an "anterior" implant placement have a 7 times greater risk than with central placement. The negative impact of cage impactions on the clinical score (ODI) was significant after one year of follow-up.

LEVEL OF EVIDENCE

IV, non-comparative cohort study.

A retrospective study on application of a classification criterion based on relative intervertebral tension in spinal fusion surgery for lumbar degenerative diseases

Background

As an important part of spinal fusion procedure, the selection of fusion cage size is closely related to the curative effect of the surgery. It mainly depends on the clinical experience of surgeons, and there is still a lack of objective standards. The purpose of this study is to propose the concept of relative intervertebral tension (RIT) for the first time and its grading standards to improve the surgical procedures of lumbar interbody fusion.

Methods

This retrospective study was conducted from January 2018 to July 2019. A total of 83 eligible patients including 45 men and 38 women with lumbar degenerative disease underwent transforaminal lumbar interbody fusion (TLIF) were included in this study. A total of 151 fusion segments were divided into group A, group B and group C according to the grading standards of RIT. In addition, parameters of intervertebral space angle (ISA), intervertebral space height (ISH), intervertebral space foramen (IFH), fusion rates, cage-related complications and cage heights were also compared among the three groups.

Results

The ISA in group A was the smallest among three groups in contrast with group C with largest ISA at the final follow-up(P < 0.05). The group A presented the smallest ISH and IFH values(P < 0.05), compared with group B with the largest ISH and IFH values(P < 0.05). These two parameters in the group C were in-between. The fusion rates of group A, group B and group C were 100%, 96.3% and 98.8% at the final follow-up, respectively. No statistical difference in fusion rates and cage-related complications occurred among the three groups(P > 0.05), and a certain correlation between ISH and RIT was also observed.

Conclusions

The concept of RIT and the application of its clinical grading standards could simplify the surgical procedures of spinal fusion and reduce cage-related complications.

Design and evaluation of 3D-printed Sr-HT-Gahnite bioceramic for FDA regulatory submission: A Good Laboratory Practice sheep study

There is an unmet clinical need for a spinal fusion implant material that recapitulates the biological and mechanical performance of natural bone. We have developed a bioceramic, Sr-HT-Gahnite, which has been identified as a potential fusion device material. This material has the capacity to transform the future of the global interbody devices market, with follow on social, economic, and environmental benefits, rooted in its remarkable combination of mechanical properties and bioactivity. In this study, and in line with FDA requirements, the in vivo preclinical systemic biological safety of a Sr-HT-Gahnite interbody fusion device is assessed over 26 weeks in sheep under good laboratory practice (GLP). Following the in-life phase, animals are assessed for systemic biological effects via blood haematology and clinical biochemistry, strontium dosage analysis in the blood and wool, and histopathology examination of the distant organs including adrenals, brain, heart, kidneys, liver, lungs and bronchi, skeletal muscle, spinal nerves close to the implanted sites, ovaries, and draining lymph nodes. Our results show that no major changes in blood haematology or biochemistry parameters are observed, no systemic distribution of strontium to the blood and wool, and no macroscopic or histopathological abnormalities in the distant organs when Sr-HT-Gahnite was implanted, compared to baseline and control values. Together, these results indicate the systemic safety of the Sr-HT-Gahnite interbody fusion device. The results of this study extend to the systemic safety of other Sr-HT-Gahnite implanted medical devices in contact with bone or tissue, of similar size and manufactured using the described processes. STATEMENT OF SIGNIFICANCE: This paper is considered original and innovative as it is the first that thoroughly reports the systemic biological safety of previously undescribed bioceramic material, Sr-HT-Gahnite. The study has been performed under good laboratory practice, in line with FDA requirements for assessment of a new interbody fusion device, making the results broadly applicable to the translation of sheep models to the human cervical spine; and also the translation of Sr-HT-Gahnite as a biomaterial for use in additional applications. We expect this study to be of broad interest to the readership of Acta Biomaterilia. Its findings are directly applicable to researchers and clinicians working in bone repair and the development of synthetic biomaterials.

A triple minimally invasive surgery combination for subacute osteoporotic lower lumbar vertebral collapse with neurological compromise: a potential alternative to the vertebral corpectomy/expandable cage strategy

OBJECTIVE

Acute/subacute osteoporotic vertebral collapses (OVCs) in the lower lumbar spine with neurological compromise, although far less well documented than those in the thoracolumbar junction, may often pose greater treatment challenges. The authors clarified the utility of 3 familiar combined techniques of minimally invasive surgery for this condition as an alternative to the corpectomy/expandable cage strategy.

METHODS

This report included the authors' first 5 patients with more than 2 years (range 27-48 months) of follow-up. The patients were between 68 and 91 years of age, and had subacute painful L4 OVC with neurological compromise and preexisting lumbar spinal stenosis. The authors' single-stage minimally invasive surgery combination consisted of the following: step 1, balloon kyphoplasty for the L4 OVC to restore its strength, followed by L4-percutaneous pedicle screw (PPS) placement with patients in the prone position; step 2, tubular lateral lumbar interbody fusion (LLIF) at the adjacent disc space involved with endplate injury, with patients in the lateral position; and step 3, supplemental PPS-rod fixation with patients in the prone position.

RESULTS

Estimated blood loss ranged from 20 to 72 mL. Neither balloon kyphoplasty-related nor LLIF-related potentially serious complications occurred. With CT measurements at the 9 LLIF levels, the postoperative increases averaged 3.5 mm in disc height and 3.7 mm in bilateral foraminal heights, which decreased by only 0.2 mm and 0 mm at the latest evaluation despite their low bone mineral densities, with a T-score of -3.8 to -2.6 SD. Canal compromise by fracture retropulsion decreased from 33% to 23% on average. As indicated by MRI measurements, the dural sac progressively enlarged and the ligamentum flavum increasingly shrank over time postoperatively, consistent with functional improvements assessed by the physician-based, patient-centered measures.

CONCLUSIONS

The advantages of this method over the corpectomy/expandable cage strategy include the following: 1) better anterior column stability with a segmentally placed cage, which reduces stress concentration at the cage footplate-endplate interface as an important benefit for patients with low bone mineral density; 2) indirect decompression through ligamentotaxis caused by whole-segment spine lengthening with LLIF, pushing back both the retropulsed fragments and the disc bulge anteriorly and unbuckling the ligamentum flavum to diminish its volume posteriorly; and 3) eliminating the need for segmental vessel management and easily bleeding direct decompressions. The authors' recent procedural modification eliminated step 3 by performing loose PPS-rod connections in step 1 and their tight locking after LLIF in step 2, reducing to only once the number of times the patient was repositioned.

The predictive value of psoas and paraspinal muscle parameters measured on MRI for severe cage subsidence after standalone lateral lumbar interbody fusion

BACKGROUND CONTEXT

The effect of psoas and paraspinal muscle parameters on cage subsidence after minimally invasive techniques, such as standalone lateral lumbar interbody fusion (SA-LLIF), is unknown.

PURPOSE

This study aimed to determine whether the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae), and psoas FCSA normalized to the vertebral body area (FCSA/VBA) differ among levels with severe cage subsidence after SA-LLIF when compared to levels without severe cage subsidence.

STUDY DESIGN

Retrospective single center cohort study.

PATIENT SAMPLE

Patients who underwent SA-LLIF between 2008 and 2020 for degenerative conditions using exclusively polyetheretherketone (PEEK) cages, had a lumbar magnetic resonance imaging (MRI) scan within 12 months, a lumbar computed tomography (CT) scan within 6 months prior to surgery, and a postoperative clinical and radiographic follow-up at a minimum of 6 months were included.

OUTCOME MEASURES

Severe cage subsidence.

METHODS

MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA and FCSA/VBA at the L3-L5 pedicles. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8.0), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat and muscle. Mean volumetric bone mineral density (vBMD) at L1/2 was measured by quantitative CT. The primary endpoint was severe cage subsidence per level according to the classification by Marchi et al. Multivariable logistic regression analysis was performed using generalized linear mixed models. All analyses were stratified by biological sex.

RESULTS

95 patients (45.3% female) with a total of 188 operated levels were included in the analysis. The patient population was 92.6% Caucasian with a median age at surgery of 65 years. Overall subsidence (Grades 0-III) was 49.5% (53/107 levels) in men versus 58.0% (47/81 levels) in women (p=.302), and severe subsidence (Grades II-III) was 22.4% (24/107 levels) in men versus 25.9% (21/81 levels) in women (p=.608). In men, median psoas FCSA and psoas FCSA/VBA at L3 and L4 were significantly greater in the severe subsidence group when compared to the non-severe subsidence group. No such difference was observed in women. Paraspinal muscle parameters did not differ significantly between non-severe and severe subsidence groups for both sexes. In the multivariable logistic regression analysis with adjustments for vBMD and cage length, psoas FCSA at L3 (OR 1.002; p=.020) and psoas FCSA/VBA at L3 (OR 8.655; p=.029) and L4 (OR 4.273; p=.043) were found to be independent risk factors for severe cage subsidence in men.

CONCLUSIONS

Our study demonstrated that greater psoas FCSA at L3 and psoas FCSA/VBA at L3 and L4 were independent risk factors for severe cage subsidence in men after SA-LLIF with PEEK cages. The higher compressive forces the psoas exerts on lumbar segments as a potential stabilizer might explain these findings. Additional pedicle screw fixation might be warranted in these patients to avoid severe cage subsidence.

The Influence of Endplate Morphology on Cage Subsidence in Patients With Stand-Alone Oblique Lateral Lumbar Interbody Fusion (OLIF)

STUDY DESIGN

A retrospective study of prospectively collected radiographic and clinical data.

OBJECTIVE

This study aims to investigate the relationship between endplate morphology parameters and the incidence of cage subsidence in patients with mini-open single-level oblique lateral lumbar interbody fusion (OLIF).

METHODS

We included 119 inpatients who underwent OLIF from February 2015 to December 2017. A total of 119 patients with single treatment level of OLIF were included. Plain anteroposterior and lateral radiograph were taken preoperatively, postoperatively, and during follow-up. The correlation between disc height, endplate concave angle/depth, cage position and cage subsidence were investigated. Functional rating index (Visual Analogue Scale for pain, and Roland Morris Disability Questionnaire) were employed to assess clinical outcomes.

RESULTS

Cage subsidence was more commonly seen at the superior endplates (42/119, 35.29%) than at the inferior endplates (6/119, 5.04%) (p < 0.01). More importantly, cage subsidence was significantly less in patients with superior endplates that were without concave angle (3/20, 15%) than with concave angle (37/99, 37.37%) (p < 0.05). Cage subsidence correlated negatively with preoperative anterior disc height (r = -0.21, p < 0.05), but positively with disc distraction rate (r = 0.27, p < 0.01). Lastly, the distance of cage to the anterior edges of the vertebral body showed a positive correlation (r = 0.26, p < 0.01).

CONCLUSIONS

This study for the first time demonstrated that endplate morphology correlates with cage subsidence after OLIF. Since relatively flat endplates with smaller concave angle significantly diminish the incidence of subsidence, the morphology of cage surface should be taken into consideration when designing the next generation of cage. In addition, precise measurement of the disc height to avoid over-distraction, and more anteriorly placement of the cage is suggested to reduce subsidence.

A Systematic Review and Meta-Analysis of Silicon Nitride and Biomaterial Modulus as it Relates to Subsidence Risk in Spinal Fusion Surgery

Introduction

For decades, researchers and surgeons have sought to determine the optimal biomaterial for spinal fusion implants. Successful fusion is associated with improved quality of life while failures are often associated with costly and complex revisions. One common failure is subsidence. Biomaterials with higher modulus are thought to be related to subsidence risk but this has not been thoroughly investigated. The aim of this systematic review and meta-analysis is to assess silicon nitride and biomaterial modulus as they relate to subsidence risk in spinal fusions.

Methods

A systematic review was conducted using the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines. Databases searched included PubMed-Medline, Google Scholar, Embase, EBSCO, and Cochrane Library. Study quality was assessed according to the Newcastle-Ottawa Scale. A network meta-analysis was chosen, allowing for direct and indirect comparisons for multiple treatments using a Bayesian hierarchical framework with Markov chain Monte Carlo methods. Outcomes were reported as odds ratios with 95% confidence intervals. Heterogeneity between studies was evaluated using the I² test. A pairwise meta-analysis was also produced to compare the results of network analysis for consistency. Publication bias was assessed using a funnel plot, Egger test, and Begg test. All analyses were conducted using R (Project for Statistical Computing, ver. 4.0.4).

Results

The initial search yielded a total of 821 articles. After removal of duplicates and screening based on inclusion and exclusion criteria, 64 articles were available for review and 13 were selected for meta-analysis. Biomaterial implant types in the final studies included: silicon nitride (Si₃N₄), polyetheretherketone (PEEK), titanium (Ti), and two composites, nano-hydroxyapatite/polyamide 66 (n-HA/PA66) and a carbon fiber reinforced polymer (CFRP). A total of 1,192 patients were included in this analysis – 419 with titanium implants, 460 with PEEK, 96 with Si₃N₄, 332 with n-HA/PA66, and 35 with CFRP. Titanium had the highest rate of subsidence compared to other biomaterials. Pairwise analysis was consistent with these results. Both the Egger test (p = 0.28) and Begg test (p = 0.37) were found to be non-significant for publication bias.

Conclusions

Spinal fusion implants derived from Si₃N₄, compared to PEEK and titanium, do not appear to be correlated with increased subsidence risk.

Comparison of Long-Term Outcomes between the n-HA/PA66 Cage and the PEEK Cage Used in Transforaminal Lumbar Interbody Fusion for Lumbar Degenerative Disease: A Matched-Pair Case Control Study

OBJECTIVE

The nanohydroxyapatite/polyamide-66 (n-HA/PA66) cage is a novel bioactive nonmetal cage that is now used in some medical centers, while the polyetheretherketone (PEEK) cage is a typical device that has been widely used for decades with excellent clinical outcomes. This study was performed to compare the long-term radiographic and clinical outcomes of these two different cages used in transforaminal lumbar interbody fusion (TLIF).

METHODS

In this retrospective and matched-pair case control study, we included 200 patients who underwent TLIF from January 2010 to December 2014 with a minimum 7-year follow-up. One hundred patients who used n-HA/PA66 cages were matched with 100 patients who used PEEK cages for age, sex, diagnosis, and fusion level. The independent student's t-test and Pearson's chi-square test were used to compare the two groups regarding radiographic (fusion status, cage subsidence rate, segmental angle [SA], and interbody space height [IH]) and clinical (Oswestry Disability Index [ODI], and Visual Analog Scale [VAS] for back and leg) parameters preoperatively, postoperatively, and at the final follow-up.

RESULTS

The n-HA/PA66 and PEEK groups had similar fusion rates of bone inside and outside the cage at the final follow-up (95.3% vs 91.8%, p = 0.181, 92.4% vs 90.1%, p = 0.435). The cage union ratios exposed to the upper and lower endplates of the n-HA/PA66 group were significantly larger than those of the PEEK group (p < 0.05). The respective cage subsidence rates in the n-HA/PA66 and PEEK groups were 10.5% and 17.5% (p = 0.059). There were no significant differences between the two groups in the SA, IH, ODI scores, or VAS scores at any time point. The n-HA/PA66 group showed high fusion and low subsidence rates during long-term follow-up.

CONCLUSION

Both n-HA/PA66 and PEEK cages can achieve satisfactory long-term clinical and radiographic outcomes in TLIF. However, the n-HA/PA66 group showed significantly larger cage union ratios than the PEEK group. Therefore, the results indicated that the n-HA/PA66 cage is an ideal alternative material comparable to the PEEK cage in TLIF.

[Research progress of effect of cage height on outcomes of lumbar interbody fusion surgery]

Objective

To summarize the effect of cage height on outcomes of lumbar interbody fusion surgery and the importance of the cage height selection.

Methods

The related literature was widely reviewed to summarize the research progress on the complications caused by inappropriate height of the cage and the methods of selecting cage height.

Results

Inappropriate height of the cage can lead to endplate injury, cage subsidence, internal fixation failure, adjacent segmental degeneration, over-distraction related pain, insufficient indirect decompression, instability of operation segment, poor interbody fusion, poor sequence of spine, and cage displacement. At present, the selection of the cage height is based on the results of the intraoperative model test, which is reliable but high requirements for surgical experience and hard to standardize.

Conclusion

The inappropriate height of the cage may have an adverse impact on the postoperative outcome of patients. It is important to develop a selection standard of the cage height by screening the related influential factors.

MIS-TLIF or CLIF for single segmental lumbar degenerative disease

We aimed to compare the effect of minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) and Crenel lateral interbody fusion (CLIF) on single segmental lumbar degenerative disease. Patients with single segmental lumbar degenerative disease undergoing MIS-TLIF (n = 28) and CLIF (n = 28) were enrolled from April to October 2017. Preoperative medical history, anthropometric data, and clinical data were recorded. Visual analogue scores and Oswestry disability index (ODI) were assessed. Radiography was performed before and after surgery. X-ray films were evaluated according to the Bridwell method, visual analogue scores and ODI scores were evaluated. There were no significant differences in the gender, age, clinical diagnosis, involved segment or preoperative ODI score between 2 groups (P > .05). During 12-month follow-up, MIS-TLIF group had less intraoperative blood loss, drainage, postoperative bedridden time, and hospital stay (P < .05), but more operation time and radiation exposure time compared with CLIF group (P < .05). CLIF group reported less pain than MIS-TLIF group (P > .05). Both groups had similar lumbar fusion rate (P > .05). Overall, CLIF has less complications, less trauma and faster recovery for the treatment of single segmental lumbar degenerate disease when compared with MIS-TLIF. Evaluation of more patients and long-term follow-up are still needed to further validate our findings.

Can a bioactive interbody device reduce the cost burden of achieving lateral lumbar fusion?

OBJECTIVE

Intervertebral devices are increasingly utilized for fusion in the lumbar spine, along with a variety of bone graft materials. These various grafting materials often have substantial cost burdens for the surgical procedure, although they are necessary to overcome the limitations in healing capacity for many traditional interbody devices. The use of bioactive interbody fusion devices, which have demonstrable stimulatory capacity for the surrounding osteoblasts and osteoprogenitor cells and allow for osseointegration, may reduce this heavy reliance on osteobiologics for achieving interbody fusion. The objective of this study was to evaluate the rate of successful interbody fusion with a bioactive lateral lumbar interbody titanium implant with limited volume and low-cost graft material.

METHODS

The authors conducted a retrospective study (May 2017 to October 2018) of consecutively performed lateral lumbar interbody fusions with a bioactive 3D-printed porous titanium interbody device. Each interbody device was filled with 2-3 cm3/cage of a commercially available ceramic bone extender (β-tricalcium phosphate-hydroxyapatite) and combined with posterior pedicle screw fixation. No other biological agents or grafts were utilized. Demographic, clinical, and radiographic variables were captured. Fusion success was the primary endpoint of the study, with graft subsidence, fixation failure, and patient-reported outcomes (Oswestry Disability Index [ODI] and visual analog scale [VAS]-back and -leg pain scores) collected as secondary endpoints. The authors utilized a CT-based fusion classification system that accounted for both intervertebral through-growth (bone bridging) and ingrowth (integration of bone at the endplate-implant interface).

RESULTS

In total, 136 lumbar levels were treated in 90 patients. The mean age was 69 years, and 63% of the included patients were female. Half (50.0%) had undergone previous spinal surgery, and a third (33.7%) had undergone prior lumbar fusion. A third (33.7%) were treated at multiple levels (mean levels per patient 1.51). One year after surgery, the mean improvements in patient-reported outcomes (vs preoperative scores) were -17.8 for ODI (p < 0.0001), -3.1 for VAS-back pain (p < 0.0001), and -2.9 for VAS-leg pain (p < 0.0001). Bone bridging and/or appositional integrity was achieved in 99.3% of patients, including 97.8% who had complete bone bridging. No fixation loosening or implant failure was observed at any segment. Low-grade graft subsidence (Marchi grade ≤ I) occurred in 3 levels (2.2%), and intraoperative endplate violation occurred twice (1.5%). High-grade subsidence was not found. No implant failure or revision surgery for pseudarthrosis/subsidence was necessary.

CONCLUSIONS

The use of bioactive titanium interbody devices with a large surface footprint appears to result in a very high rate of effective fusion, despite the use of a small volume of low-cost biological material. This potential change in the osteobiologics required to achieve high fusion rates may have a substantially beneficial impact on the economic burden inherent to spinal fusion.

Radiographic and MRI evidence of indirect neural decompression after the anterior column realignment procedure for adult spinal deformity

OBJECTIVE

The anterior column realignment (ACR) procedure, which consists of sectioning the anterior longitudinal ligament/annulus and placing a hyperlordotic interbody cage, has emerged as a minimally invasive surgery (MIS) for achieving aggressive segmental lordosis enhancement to address adult spinal deformity (ASD). Although accumulated evidence has revealed indirect neural decompression after lateral lumbar interbody fusion (LLIF), whether ACR serves equally well for neural decompression remains to be proven. The current study intended to clarify this ambiguous issue.

METHODS

A series of 36 ASD patients with spinopelvic mismatch, defined as pelvic incidence (PI) minus lumbar lordosis (LL) > 10°, underwent a combination of ACR, LLIF, and percutaneous pedicle screw (PPS) fixation. This "MIS triad" procedure was applied over short segments with mean fusion length of 3.3 levels, and most patients underwent single-level ACR. The authors analyzed full-length standing radiographs, CT and MRI scans, and Oswestry Disability Index (ODI) scores in patients with minimum 1 year of follow-up (mean [range] 20.3 [12-39] months).

RESULTS

Compared with the preoperative values, the radiographic and MRI measurements of the latest postoperative studies changed as follows. Segmental disc angle more than quadrupled at the ACR level and LL nearly doubled. MRI examinations at the ACR level revealed a significant (p < 0.0001) increase in the area of the dural sac that was accompanied by significant (p < 0.0001) decreases in area and thickness of the ligamentum flavum and in thickness of the disc bulge. The corresponding CT scans demonstrated significant (all p < 0.0001) increases in disc height to 280% of the preoperative value at the anterior edge, 224% at the middle edge, and 209% at the posterior edge, as well as in pedicle-to-pedicle distance to 122%. Mean ODI significantly (p < 0.0001) decreased from 46.3 to 26.0.

CONCLUSIONS

The CT-based data showing vertebral column lengthening across the entire ACR segment with an increasingly greater degree anteriorly suggest that the corrective action of ACR relies on a lever mechanism, with the intact facet joints acting as the fulcrum. Whole-segment spine lengthening at the ACR level reduced the disc bulge anteriorly and the ligamentum flavum posteriorly, with eventual enlargement of the dural sac. ACR plays an important role in not only LL restoration but also stenotic spinal canal enlargement for ASD surgery.

Subsidence after lateral lumbar interbody fusion using a 3D-printed porous titanium interbody cage: single-institution case series

OBJECTIVE

Cage subsidence is a well-known phenomenon after lateral lumbar interbody fusion (LLIF), occurring in 10%-20% of cases. A 3D-printed porous titanium (pTi) cage has a stiffness that mimics the modulus of elasticity of native vertebrae, which reduces stress at the bone-hardware interface, lowering the risk of subsidence. In this study, the authors evaluated their institutional rate of subsidence and resultant reoperation in patients who underwent LLIF using a 3D-printed pTi interbody cage.

METHODS

This is a retrospective case series of consecutive adult patients who underwent LLIF using pTi cages from 2018 to 2020. Demographic and clinical characteristics including age, sex, bone mineral density, smoking status, diabetes, steroid use, number of fusion levels, posterior instrumentation, and graft size were collected. The Marchi subsidence grade was determined at the time of last follow-up. Outcome measures of interest were subsidence and resultant reoperation. Univariable logistic regression analysis was performed to assess the extent to which clinical and operative characteristics were associated with Marchi grade I-III subsidence. Significance was assessed at p < 0.05.

RESULTS

Fifty-five patients (38 with degenerative disc disease and 17 with adult spinal deformity) were treated with 97 pTi interbody cages with a mean follow-up of 18 months. The mean age was 63.6 ± 10.1 years, 60% of patients were female, and 36% of patients had osteopenia or osteoporosis. Patients most commonly underwent single-level LLIF (58.2%). Sixteen patients (29.1%) had posterior instrumentation. The subsidence grade distribution was as follows: 89 (92%) grade 0, 5 (5%) grade I, 2 (2%) grade II, and 1 (1%) grade III. No patients who were active or prior smokers and no patients with posterior instrumentation experienced graft subsidence. No clinical or operative characteristics were significantly associated with graft subsidence. One patient (1.8%) required reoperation because of subsidence.

CONCLUSIONS

In this institutional case series, subsidence of pTi intervertebral cages after LLIF occurred in 8% of operated levels, 3% of which were grade II or III. Only 1 patient required reoperation. These reported rates are lower than those reported for polyetheretherketone implants. Further studies are necessary to compare the impact of these cage materials on subsidence after LLIF.

Lumbar plexus safe working zones with lateral lumbar interbody fusion: a systematic review and meta-analysis

PURPOSE

Significant risk of injury to the lumbar plexus and its departing motor and sensory nerves exists with lateral lumbar interbody fusion (LLIF). Several cadaveric and imaging studies have investigated the lumbar plexus position with respect to the vertebral body anteroposterior plane. To date, no systematic review and meta-analysis of the lumbar plexus safe working zones for LLIF has been performed.

METHODS

This systematic review was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Relevant studies reporting on the position of the lumbar plexus with relation to the vertebral body in the anteroposterior plane were identified from a PubMed database query. Quantitative analysis was performed using Welch's t test.

RESULTS

Eighteen studies were included, encompassing 1005 subjects and 2472 intervertebral levels. Eleven studies used supine magnetic resonance imaging (MRI) with in vivo subjects. Seven studies used cadavers, five of which performed dissection in the left lateral decubitus position. A significant correlation (p < 0.001) existed between anterior lumbar plexus displacement and evaluation with in vivo MRI at all levels between L1-L5 compared with cadaveric measurement. Supine position was also associated with significant (p < 0.001) anterior shift of the lumbar plexus at all levels between L1-L5.

CONCLUSIONS

This is the first comprehensive systematic review and meta-analysis of the lumbar neural components and safe working zones for LLIF. Our analysis suggests that the lumbar plexus is significantly displaced ventrally with the supine compared to lateral decubitus position, and that MRI may overestimate ventral encroachment of lumbar plexus.

Unilateral versus bilateral pedicle screw fixation with transforaminal lumbar interbody fusion for treatment of lumbar foraminal stenosis

BACKGROUND CONTEXT

Transforaminal lumbar interbody fusion (TLIF) with bilateral pedicle screw fixation (BPSF) is an effective treatment for lumbar foraminal stenosis (LFS). However, the effects of TLIF with unilateral pedicle screw fixation (UPSF) on LFS treatment have not been clearly elucidated.

PURPOSE

We conducted this study to compare clinical outcomes and radiographic results of TLIF with UPSF and BPSF 2 years after the surgical treatment.

DESIGN

Prospective randomized study.

PATIENT SAMPLE

This study included 23 patients undergoing TLIF with UPSF and 25 patients undergoing TLIF with BPSF.

OUTCOME MEASURES

Clinical outcomes were evaluated by visual analog scale (VAS) for low back pain and leg pain and Oswestry Disability Index (ODI) score. Radiographic outcomes included foraminal height, disc space height, segmental lordosis, and final fusion rates.

METHODS

The clinical and radiographic outcomes were compared between the UPSF and BPSF group. The postoperative improvements were evaluated in either group. Intraoperative data such as duration of operation and estimated blood loss were collected. This study was registered at clinicaltrials.gov.

RESULTS

Analysis of the VAS and ODI scores showed significant improvements in clinical outcomes within each group. No significant differences between the 2 groups were noted in the improvements of the VAS and ODI scores. The mean operative duration and blood loss were significantly greater in the BPSF group than in the UPSF group. There were significant improvements in the height of the foramen and intervertebral space and segmental lordosis in both groups, while there was no significant difference between the groups in amount of the improvements. No significant difference was found in the final fusion rates.

CONCLUSIONS

TLIF is an appropriate procedure for LFS treatment. With balanced intervertebral support using a cage, UPSF could achieve similar and satisfactory effects on lumbar segmental stability and fusion compared to BPSF. The unilateral approach appears to be associated with slightly shorter operative time and less blood loss.

The Efficacy of Trabecular Titanium Cages to Induce Reparative Bone Activity after Lumbar Arthrodesis Studied through the 18f-Naf PET/CT Scan: Observational Clinical In-Vivo Study

Background: Titanium trabecular cages (TTCs) are emerging implants designed to achieve immediate and long-term spinal fixation with early osseointegration. However, a clear radiological and clinical demonstration of their efficacy has not yet been obtained. The purpose of this study was to evaluate the reactive bone activity of adjacent plates after insertion of custom-made titanium trabecular cages for the lumbar interbody with positron emission tomography (PET)/computed tomography (CT) 18F sodium fluoride (18F-NaF). Methods: This was an observational clinical study that included patients who underwent surgery for degenerative disease with lumbar interbody fusion performed with custom-made TTCs. Data related to the metabolic-reparative reaction following the surgery and its relationship with clinical follow-up from PET/CT performed at different weeks were evaluated. PET/CTs provided reliable data, such as areas showing abnormally high increases in uptake using a volumetric region of interest (VOI) comprising the upper (UP) and lower (DOWN) limits of the cage. Results: A total of 15 patients was selected for PET examination. Timing of PET/CTs ranged from one week to a maximum of 100 weeks after surgery. The analysis showed a negative correlation between the variables SUVmaxDOWN/time (r = −0.48, p = 0.04), ratio-DOWN/time (r = −0.53, p = 0.02), and ratio-MEAN/time (r = −0.5, p = 0.03). Shapiro−Wilk normality tests showed significant results for the variables ratio-DOWN (p = 0.002), ratio-UP (0.013), and ratio-MEAN (0.002). Conclusions: 18F-NaF PET/CT has proven to be a reliable tool for investigating the metabolic-reparative reaction following implantation of TTCs, demonstrating radiologically how this type of cage can induce reparative osteoblastic activity at the level of the vertebral endplate surface. This study further confirms how electron-beam melting (EBM)-molded titanium trabecular cages represent a promising material for reducing hardware complication rates and promoting fusion.

Intraoperative Endplate Injury Following Transforaminal Lumbar Interbody Fusion

OBJECTIVE

To investigate the incidence, distribution characteristics, risk factors, and clinical outcomes of intraoperative endplate injury following transforaminal lumbar interbody fusion (TLIF).

METHODS

Patients who underwent single-level TLIF from January 2018 to December 2020 were included. The patients were separated into endplate injury group (EI group) and no endplate injury group (non-EI group) by postoperative computed tomography scanning immediately. All patients' demographic, clinical, and radiographic parameters were analysed. Clinical outcomes were evaluated by visual analogue scale (VAS) for low back pain and Oswestry Disability Index (ODI).

RESULTS

576 patients were enrolled in this study. The rates of endplate injury were 19.6% (113 of 576) of patients and 9.9% (114 of 1152) of endplates. The rate of superior endplate injury was significantly higher than that of inferior endplate injury. The results illustrated that older age, lower disc height index (DHI), and taller cage height were independent risk factors for intraoperative endplate injury. The postoperative drain output, total blood loss, postoperative duration of drainage tube, and postoperative hospital stay in EI group were significantly more than those in non-EI group. There were no statistical differences in ODI and VAS scores at the same time point between two groups.

CONCLUSIONS

The rates of endplate injury were 19.6% of patients and 9.9% of endplates. The superior endplates are more susceptible to injury than inferior endplates. Older age, lower DHI, and taller cage height were independent risk factors for intraoperative endplate injury. Clinical outcomes were not affected by intraoperative endplate injury during early postoperative follow-up.

Pear-Shaped Disk as a Risk Factor for Intraoperative End Plate Injury in Oblique Lumbar Interbody Fusion

BACKGROUND

Intraoperative end plate injury can result in late-onset cage subsidence in oblique lumbar interbody fusion (OLIF). This study aimed to identify risk factors for intraoperative end plate injury and investigate whether a pear-shaped disk correlated with intraoperative end plate injury in OLIF.

METHODS

We retrospectively reviewed 102 levels in 82 patients (mean age 60.1 ± 10.0 years) who underwent OLIF for degenerative lumbar diseases. Intraoperative end plate injury was evaluated using midline sagittal computed tomography views at 3 days postoperatively and defined as cage breaching into an adjacent cortical end plate >2 mm. Patient demographics, surgical parameters, radiographic parameters, and cage-related parameters were recorded in all surgical levels. Evaluation of risk factors associated with intraoperative end plate injury was performed. Patient-reported outcome, fusion status, and late-onset cage subsidence were analyzed at a minimum of 1 year after the surgery.

RESULTS

Intraoperative end plate injury was observed in 26 levels (25.5%). Multivariate logistic regression analysis identified that bone mineral density (odds ratio [OR] = 0.978), preoperative segmental lordosis (OR = 0.790), and pear-shaped disk were risk factors (OR = 5.837) for intraoperative end plate injury. Intraoperative end plate injury occurred in 45.5% of levels with a pear-shaped disk compared with 16.0% of levels with no pear-shaped disk (P < 0.01). Late-onset cage subsidence was significantly more frequent in the injury group than the no-injury group. Patient-reported outcome and fusion status were unrelated to intraoperative end plate injury.

CONCLUSIONS

A pear-shaped disk is the greatest risk factor for intraoperative end plate injury following OLIF.

Radiographic Analysis of Pedicle Screw Retractor-Assisted Transforaminal Lumbar Interbody Fusion for Single-Segment Spondylolisthesis in Adults: A Retrospective Study and Technical Note

Objectives

The objective of this study was to introduce a retractor that can be temporarily installed on unilateral pedicle screws to achieve distraction‐reduction and nerve root protection, and to analyze the efficacy and safety of retractor‐assisted transforaminal lumbar interbody fusion (TLIF) in the treatment of lumbar spondylolisthesis.

Methods

This was a retrospective study of 125 patients who underwent retractor‐assisted TLIF for single‐segment spondylolisthesis from November 2017 to February 2021. Based on morphology, patients were divided into degenerative (N = 66) and isthmic groups (N = 59). Differences in demographics and preoperative characteristics between the groups were analyzed using the independent samples t‐test and χ² test. Changes in radiographic parameters (disc height, foramen height, spondylolisthesis degree, slippage length, and segmental lordosis) before and after surgery were compared using the paired samples t‐test. Logistic regression analysis was performed to analyze the relationship between facet joint angle (FJA) and degenerative lumbar spondylolisthesis (DLS).

Results

Unilateral screw retractor‐assisted TLIF significantly corrected spondylolisthesis and improved disc height and segmental lordosis (p < 0.05). There was no significant difference in foramen height between the two sides before and after operation (pre: 15.81 ± 3.58 mm vs 15.69 ± 3.68 mm, p = 0.599; post: 18.65 ± 2.31 mm vs 18.74 ± 2.26 mm, p = 0.516). The degree of spondylolisthesis in the DLS group before surgery was significantly lower than that in the isthmic spondylolisthesis group (17.70 ± 5.62% vs 25.18 ± 9.73%, p < 0.001), whereas a similar degree of correction could be achieved after surgery (5.91 ± 3.12% vs 7.16 ± 5.69%, p = 0.135). FJAs from L3/4 to L5/S1 were significantly smaller in patients with DLS than those in with isthmic spondylolisthesis (p < 0.05). Patients with facet sagittalization were more likely to have DLS (β: −0.101, odds ratio [OR]:0.904, 95% confidence interval [CI]: 0.874–0.934, p < 0.001), while the cut‐off FJA of L4/5 for predicting L4 spondylolisthesis was 53.19.

Conclusions

Pedicle screw retractor‐assisted TLIF is effective and safe in treating both degenerative and isthmic lumbar spondylolisthesis. The unilateral retractor has the capacity to maintain the disc height achieved by paddle distractors, which optimizes the nerve protection and distractor placement. Patients with an FJA on L4/5 <53.19 were more likely to have DLS.

Predictors of subsidence after lateral lumbar interbody fusion

OBJECTIVE

Lateral lumbar interbody fusion (LLIF) facilitates the restoration of disc height and the indirect decompression of neural elements. However, these benefits are lost when the graft subsides into the adjacent endplates. The factors leading to subsidence after LLIF are poorly understood. This article presents a case series of patients who underwent LLIF and reports factors correlating with subsidence.

METHODS

A retrospective review of a consecutive, prospectively collected, single-institution database of patients who underwent LLIF over a 29-month period was performed. The degree of subsidence was measured on the basis of postoperative imaging. The timing of postoperative subsidence was determined, and intraoperative fluoroscopic images were reviewed to determine whether subsidence occurred as a result of endplate violation. The association of subsidence with age, sex, cage size and type, bone density, and posterior instrumentation was investigated.

RESULTS

One hundred thirty-one patients underwent LLIF at a total of 204 levels. Subsidence was observed at 23 (11.3%) operated levels. True subsidence, attributable to postoperative cage settling, occurred for 12 (5.9%) of the levels; for the remaining 11 (5.4%) levels, subsidence was associated with intraoperative endplate violation noted on fluoroscopy during cage placement. All subsidence occurred within 12 weeks of surgery. Univariate analysis showed that the prevalence of true subsidence was significantly lower among patients with titanium implants (0 of 55; 0%) than among patients with polyetheretherketone cages (12 of 149; 8.1%) (p = 0.04). In addition, the mean ratio of graft area to inferior endplate area was significantly lower among the subsidence levels (0.34) than among the nonsubsidence levels (0.42) (p < 0.01). Finally, subsidence among levels with posterior fixation (4.4% [6/135]) was not significantly different than among those without posterior fixation (8.7% [6/69]) (p = 0.23). Multivariate analysis results showed that the ratio of cage to inferior endplate area was the only significant predictor of subsidence in this study (p < 0.01); increasing ratios were associated with a decreased likelihood of subsidence.

CONCLUSIONS

Overall, the prevalence of subsidence after LLIF was low in this clinical series. Titanium cages were associated with a lower prevalence of observed subsidence on univariate analysis; however, multivariate analysis demonstrated that this effect may be attributable to the increased surface area of these cages relative to the inferior endplate area.

Silicon Nitride as a Biomedical Material: An Overview

Silicon nitride possesses a variety of excellent properties that can be specifically designed and manufactured for different medical applications. On the one hand, silicon nitride is known to have good mechanical properties, such as high strength and fracture toughness. On the other hand, the uniqueness of the osteogenic/antibacterial dualism of silicon nitride makes it a favorable bioceramic for implants. The surface of silicon nitride can simultaneously inhibit the proliferation of bacteria while supporting the physiological activities of eukaryotic cells and promoting the healing of bone tissue. There are hardly any biomaterials that possess all these properties concurrently. Although silicon nitride has been intensively studied as a biomedical material for years, there is a paucity of comprehensive data on its properties and medical applications. To provide a comprehensive understanding of this potential cornerstone material of the medical field, this review presents scientific and technical data on silicon nitride, including its mechanical properties, osteogenic behavior, and antibacterial capabilities. In addition, this paper highlights the current and potential medical use of silicon nitride and explains the bottlenecks that need to be addressed, as well as possible solutions.

Biomechanical study of oblique lumbar interbody fusion (OLIF) augmented with different types of instrumentation: a finite element analysis

Background

To explore the biomechanical differences in oblique lumbar interbody fusion (OLIF) augmented by different types of instrumentation.

Methods

A three-dimensional nonlinear finite element (FE) model of an intact L3-S1 lumbar spine was built and validated. The intact model was modified to develop five OLIF surgery models (Stand-alone OLIF; OLIF with lateral plate fixation [OLIF + LPF]; OLIF with unilateral pedicle screws fixation [OLIF + UPSF]; OLIF with bilateral pedicle screws fixation [OLIF + BPSF]; OLIF with translaminar facet joint fixation + unilateral pedicle screws fixation [OLIF + TFJF + UPSF]) in which the surgical segment was L4–L5. Under a follower load of 500 N, a 7.5-Nm moment was applied to all lumbar spine models to calculate the range of motion (ROM), equivalent stress peak of fixation instruments (ESPFI), equivalent stress peak of cage (ESPC), equivalent stress peak of cortical endplate (ESPCE), and equivalent stress average value of cancellous bone (ESAVCB).

Results

Compared with the intact model, the ROM of the L4–L5 segment in each OLIF surgery model decreased by > 80%. The ROM values of adjacent segments were not significantly different. The ESPFI, ESPC, and ESPCE values of the OLIF + BPSF model were smaller than those of the other OLIF surgery models. The ESAVCB value of the normal lumbar model was less than the ESAVCB values of all OLIF surgical models. In most postures, the ESPFI, ESPCE, and ESAVCB values of the OLIF + LPF model were the largest. The ESPC was higher in the Stand-alone OLIF model than in the other OLIF models. The stresses of several important components of the OLIF + UPSF and OLIF + TFJF + UPSF models were between those of the OLIF + LPF and OLIF + BPSF models.

Conclusions

Our biomechanical FE analysis indicated the greater ability of OLIF + BPSF to retain lumbar stability, resist cage subsidence, and maintain disc height. Therefore, in the augmentation of OLIF, bilateral pedicle screws fixation may be the best approach.

Assessment of vertebral bone mineral density and stand-alone oblique lumbar interbody fusion for adjacent segment disease and primary lumbar degenerative diseases

PURPOSE

To evaluate the vertebral bone mineral density and the value of stand-alone oblique lumbar interbody fusion (SA OLIF) for the management of single-level adjacent segment disease (ASD) and primary lumbar degenerative diseases.

PATIENTS AND METHODS

Seventy-eight patients undergoing single-level SA OLIF was divided into index surgery group (n = 36) or revision surgery group (n = 42) at single center. The vertebral body Hounsfield units (HU) value was measured to assess bone mineral density of operated level by the preoperative CT. The following data were retrospectively collected and compared between the two groups: demographic, surgical data, clinical results, and complications.

RESULTS

No differences were found between the two groups in surgical data. The fusion segment HU values in the revision group were significantly higher than that in the index group (147.4 ± 35.3 vs 129.2 ± 38.4 p = .033). There were significant differences while comparing fusion segment HU values to L1-L4 horizontal plane (147.4 ± 35.3 vs 126.1 ± 28.4, p = .000) and L1 (147.4 ± 35.3 vs 126.8 ± 26.2, p = .000) in revision group, meanwhile, no statistically significant difference was observed in index group (p > .05). The cage subsidence was observed in the revision group (n = 2) and index group (n = 9) (p = .045). The patients with cage subsidence had significantly lower vertebral HU values.

CONCLUSION

SA OLIF is valid alternative to the traditional posterior approach in the management of ASD with good clinical outcomes at short-term follow-up. Increased HU values of fusion segment may play a role in the management of ASD by SA OLIF.

Clinical and Cost-Effectiveness of Lumbar Interbody Fusion Using Tritanium Posterolateral Cage (vs. Propensity-Matched Cohort of PEEK Cage)

Introduction

Surgical management of degenerative lumbar spine disorders is effective at improving patient pain, disability, and quality of life; however, obtaining a durable posterolateral fusion after decompression remains a challenge. Interbody fusion technologies are viable means of improving fusion rates in the lumbar spine, specifically various graft materials including autograft, structural allograft, titanium, and polyether ether ketone. This study assesses the effectiveness of Tritanium posterolateral cage in the treatment of degenerative disk disease.

Methods

Nearest-neighbor 1:1 matched control transforaminal lumbar interbody fusion with PEEK vs. Tritanium posterior lumbar (PL) cage interbody fusion patients were identified using propensity scoring from patients that underwent elective surgery for degenerative disk diseases. Line graphs were generated to compare the trajectories of improvement in patient-reported outcomes (PROs) from baseline to 3 and 12 months postoperatively. The nominal data were compared via the χ² test, while the continuous data were compared via Student's t-test.

Results

The two groups had no difference regarding either the 3- or 12-month Euro-Qol-5D (EQ-5D), numeric rating scale (NRS) leg pain, and NRS back pain; however, the Tritanium interbody cage group had better Oswestry Disability Index (ODI) scores compared to the control group of the PEEK interbody cage at both 3 and 12 months (p=0.013 and 0.048).

Conclusions

Our results indicate the Tritanium cage is an effective alternative to the previously used PEEK cage in terms of PROs, surgical safety, and radiological parameters of surgical success. The Tritanium cohort showed better ODI scores, higher fusion rates, lower subsidence, and lower indirect costs associated with surgical management, when compared to the propensity-matched PEEK cohort.