Unilateral Versus Bilateral Percutaneous Pedicle Screw Fixation in Oblique Lumbar Interbody Fusion

Biomechanical changes of oblique lumbar interbody fusion with different fixation techniques in degenerative spondylolisthesis lumbar spine: a finite element analysis

OBJECTIVE

There is a dearth of comprehensive research on the stability of the spinal biomechanical structure when combining Oblique Lumbar Interbody Fusion (OLIF) with internal fixation methods. Hence, we have devised this experiment to meticulously examine and analyze the biomechanical changes that arise from combining OLIF surgery with different internal fixation techniques in patients diagnosed with degenerative lumbar spondylolisthesis.

METHODS

Seven validated finite element models were reconstructed based on computed tomography scan images of the L3-L5 segment. These models included the intact model, a stand-alone (S-A) OLIF model, a lateral screw rod (LSR) OLIF model, a bilateral pedicle screw (BPS) OLIF model, an unilateral pedicle screw (UPS) OLIF model, a bilateral CBT (BCBT) OLIF model, and an unilateral CBT(UCBT) OLIF model. The range of motion (ROM), as well as stress levels in the cage, L4 lower endplate, L5 upper endplate, and fixation constructs were assessed across these different model configurations.

RESULTS

S-A model had the highest average ROM of six motion modes, followed by LSR, UPS, UCBT, BPS and BCBT. The BCBT model had a relatively lower cage stress than the others. The maximum peak von Mises stress of the fixation constructs was found in the LSR model. The maximum peak von Mises stress of L4 lower endplate was found in the S-A model. The peak von Mises stress on the L4 lower endplate of the rest surgical models showed no significant difference. The maximum peak von Mises stress of the L5 upper endplate was found in the S-A model. The minimum peak von Mises stress of the L5 upper endplate was found in the BCBT model. No significant difference was found for the peak von Mises stress of the L5 upper endplate among LSR, BPS, UPS and UCBT models.

CONCLUSION

Among the six different fixation techniques, BCBT exhibited superior biomechanical stability and minimal stress on the cage-endplate interface. It was followed by BPS, UCBT, UPS, and LSR in terms of effectiveness. Conversely, S-A OLIF demonstrated the least stability and resulted in increased stress on both the cage and endplates. Combining OLIF with BCBT fixation technique enhanced biomechanical stability compared to BPS and presented as a less invasive alternative treatment for patients with degenerative lumbar spondylolisthesis.

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.

Can zoledronic acid reduce the risk of cage subsidence after oblique lumbar interbody fusion combined with bilateral pedicle screw fixation in the elderly population? A retrospective study

BACKGROUND

The objective of this study was to evaluate the potential of zoledronic acid for reducing the incidence of cage subsidence and enhancing interbody fusion rates following oblique lumbar interbody fusion (OLIF) surgery, particularly as the first reported evidence of the role of zoledronic acid combined with OLIF.

METHODS

A retrospective analysis was conducted on data from 108 elderly patients treated for degenerative lumbar diseases using OLIF combined with bilateral pedicle screw fixation from January 2018 to December 2021. Patients were divided into the zoledronic acid (ZOL) group (43 patients, 67 surgical segments) and the control group (65 patients, 86 surgical segments). A comparative analysis of the radiographic and clinical outcomes between the groups was performed, employing univariate and multivariate regression analyses to explore the relationships between cage subsidence and the independent variables.

RESULTS

Radiographic outcomes, including anterior height, posterior height, disc height, coronal disc angle, foraminal height, and lumbar lordosis, were not significantly different between the two groups. Similarly, no statistically significant differences were noted in the back visual analog scale (VAS) scores and Oswestry Disability Index (ODI) scores between the groups. However, at the 1-year follow-up, the leg VAS score was lower in the ZOL group than in the control group (P = 0.028). The ZOL group demonstrated a notably lower cage subsidence rate (20.9%) than did the control group (43.0%) (P < 0.001). There was no significant difference in the interbody fusion rate between the ZOL group (93.0%) and the control group (90.8%). Non-use of zoledronic acid emerged as an independent risk factor for cage subsidence (OR = 6.047, P = 0.003), along with lower bone mineral density, lower postoperative anterior height, and concave endplate morphology. The model exhibited robust discriminative performance, with an area under the curve (AUC) of 0.872.

CONCLUSION

The administration of zoledronic acid mitigates the risk of cage subsidence following OLIF combined with bilateral pedicle screw fixation in elderly patients; however, it does not improve the interbody fusion rate.

Biomechanical Comparison of Unilateral and Bilateral Pedicle Screw Fixation after Multilevel Lumbar Lateral Interbody Fusion

STUDY DESIGN

Human Cadaveric Biomechanical Study.

OBJECTIVES

Lumbar Lateral Interbody Fusion (LLIF) utilizing a wide cage has been reported as having favorable biomechanical characteristics. We examine the biomechanical stability of unilateral pedicle screw and rod fixation after multilevel LLIF utilizing 26 mm wide cages compared to bilateral fixation.

METHODS

Eight human cadaveric specimens of L1-L5 were included. Specimens were attached to a universal testing machine (MTS 30/G). Three-dimensional specimen range of motion (ROM) was recorded using an optical motion-tracking device. Specimens were tested in 3 conditions: 1) intact, 2) L1-L5 LLIF (4 levels) with unilateral rod, 3) L1-L5 LLIF with bilateral rods.

RESULTS

From the intact condition, LLIF with unilateral rod decreased flexion-extension by 77%, lateral bending by 53%, and axial rotation by 26%. In LLIF with bilateral rods, flexion-extension decreased by 83%, lateral bending by 64%, and axial rotation by 34%. Comparing unilateral and bilateral fixation, LLIF with bilateral rods reduced ROM by a further 23% in flexion-extension, 25% in lateral bending, and 11% in axial rotation. The difference was statistically significant in flexion-extension and lateral bending (P < .005).

CONCLUSIONS

Considerable decreases in ROM were observed after multilevel (4-level) LLIF utilizing 26 mm cages supplemented with both unilateral and bilateral pedicle screws and rods. The addition of bilateral fixation provides a 10-25% additional decrease in ROM. These results can inform surgeons of the incremental biomechanical benefit when considering unilateral or bilateral posterior fixation after multilevel LLIF.

Oblique lateral interbody fusion combined with unilateral versus bilateral posterior fixation in patients with osteoporosis

PURPOSE

To compare the clinical efficacy of oblique lateral interbody fusion (OLIF) combined with unilateral (UPSF) and bilateral pedicle screw internal fixation (BPSF) in patients with osteoporosis.

METHODS

Clinical data of 57 patients who underwent single-segment OLIF surgery with a clear diagnosis of osteoporosis from December 2018 to May 2021 were retrospectively analyzed, of which 27 patients underwent OLIF + UPSF and 30 patients underwent OLIF + BPSF. Surgical technique-related indexes were recorded, including operative time, operative blood loss and postoperative hospital stay; clinical outcome-related indexes included postoperative complications, Visual analogue scale (VAS) and Oswestry disability index (ODI) at preoperative, 1 week, 1 month, 3 months, and 12 months postoperative follow-up; and imaging outcome-related indexes included the measurement of preoperative and postoperative segmental lordosis (SL), and observation of the degree of cage subsidence and bone graft fusion.

RESULTS

The surgery was successfully performed in 57 patients, and there was no statistical difference in operative blood loss and postoperative hospital stay between UPSF group and BPSF group (P > 0.05). In terms of operative time, there was a significant difference (UPSF group: 92.30 ± 11.03 min, BPSF group: 119.67 ± 16.41, P < 0.05). Postoperative VAS and ODI scores exhibited significant improvement (P < 0.05). At the 12 months postoperative follow-up, the VAS and ODI scores in the BPSF group were significantly better than those in the UPS group (P < 0.05). Compared with the preoperative images, the SL was significantly improved in both groups after surgery (P < 0.05). At 6 months postoperatively, the fusion rate in the UPSF group was significantly lower than that in the BPSF group (P < 0.05). At 1 year postoperatively, the fusion rate in the UPSF group was not significantly different from that in the BPSF group (P > 0.05). At 1 year postoperatively, the rate and degree of cage subsidence was higher in the UPSF group than in the BPSF group (P < 0.05).

CONCLUSION

In the long term, OLIF combined with bilateral posterior fixation applied to the osteoporosis patients is superior to OLIF surgery combined with unilateral posterior fixation in terms of clinical and imaging outcomes. It is effective in improving pain relief and functional improvement, accelerating bone graft fusion, and reducing cage subsidence compared with UPSF.

Comparing clinical and radiological outcomes between single-level OLIF and XLIF: A systematic review and meta-analysis

Background Context

Oblique lumbar interbody fusion (OLIF) and extreme lateral interbody fusion (XLIF) are 2 popular minimally invasive spinal fusion techniques with unique approach-related complication profiles. Accordingly, patient-specific anatomical factors, such as vascular anatomy or iliac crest height, greatly influence which technique to use. Previous studies comparing these approaches do not account for the inability of XLIF to access the L5-S1 disc space and therefore do not exclude this level in their analysis. The purpose of this study was to compare radiological and clinical outcomes of these techniques in the L1-L5 region.

Methods

A query of 3 electronic databases (PubMed, CINAHL plus, and SCOPUS) was performed, without time restriction, to identify studies that evaluated outcomes of single-level OLIF and/or XLIF between L1 and L5. Based on heterogeneity, a random effects meta-analysis was performed to evaluate the pooled estimation of each variable between the groups. An overlap of 95% confidence intervals suggests no statistically significant difference at the p<.05 level.

Results

A total of 1,010 patients (408 OLIF, 602 XLIF) were included from 24 published studies. Improvements in disc height (OLIF: 4.2 mm; XLIF: 5.3 mm), lumbar segmental (OLIF: 2.3°; XLIF: 3.1°), and lumbar lordotic angles (OLIF: 5.3°; XLIF: 3.3°) showed no significant difference. The rate of neuropraxia was significantly greater in the XLIF group at 21.2% versus 10.9% in the OLIF group (p<.05). However, the rate of vascular injury was higher in the OLIF cohort at 3.2% (95% CI:1.7-6.0) as compared to 0.0 (95% CI: 0.0-1.4) in the XLIF cohort. Improvements in VAS-b (OLIF: 5.6; XLIF: 4.5) and ODI (OLIF: 37.9; XLIF: 25.6) scores were not significantly different between the 2 groups.

Conclusions

This meta-analysis demonstrates similar clinical and radiological outcomes between single-level OLIF and XLIF from L1 to L5. XLIF had significantly higher rates of neuropraxia, whereas OLIF had greater rates of vascular injury.

A comparative study of robot-assisted and traditional surgeries in the treatment of thoracolumbar fractures based on 1-year follow-up observation

BACKGROUND: There are conflicting results for robot-assisted (RA) pedicle screw fixation compared with freehand (FH) pedicle screw fixation. OBJECTIVE: This study was designed to retrospectively compare the accuracy and efficacy of RA percutaneous pedicle screw fixation and traditional freehand FH pedicle screw fixation in the treatment of thoracolumbar fractures. METHODS: A total of 26 cases were assigned to the RA group, and 24 cases were assigned to the FH group. The operation time, bleeding volume, and visual analog scale (VAS) score 1 day after the operation, and the anterior/posterior (A/P) vertebral height ratio of the injured vertebrae at 3 days and at internal fixation removal 1 year after the operation were compared between the two groups. Pedicle screw position accuracy was assessed according to Gertzbein criteria. RESULTS: The operation times of the RA group and FH group were 138.69 ± 32.67 minutes and 103.67 ± 14.53 minutes, respectively, and the difference was statistically significant. The intraoperative blood loss was 49.23 ± 22.56 ml in the RA group and 78.33 ± 23.90 ml in the FH group, and the difference was statistically significant. There was a significant difference in the A/P vertebral height ratio of the injured vertebrae 3 days after the operation compared with before the operation in both groups (P < 0.05). There was a significant difference in the A/P vertebral height ratio of the injured vertebrae 3 days after the operation compared with that at fixation removal in both groups (P < 0.05). CONCLUSION: The application of RA orthopedic treatment for thoracolumbar fractures can achieve good fracture reduction.

OLIF versus ALIF: Which is the better surgical approach for degenerative lumbar disease? A systematic review

PURPOSE

The aim of this study was to compare the clinical and radiographical outcomes between OLIF and ALIF in treating lumbar degenerative diseases.

METHODS

We searched PubMed, Embase, Web of Science, and Cochrane Library for relevant studies. Changes in disc height (DH), segmental lordosis angle (SLA), lumbar lordosis (LL), visual analogue scale (VAS) score, and Oswestry disability index (ODI) between baseline and final follow-up, along with other important surgical outcomes, were assessed and analysed. Data on the global fusion rate and main complications were collected and compared.

RESULTS

Approximately, 2041 patients from 36 studies were included, consisting of 1057 patients who underwent OLIF and 984 patients who underwent ALIF. The results reveal no significant difference in DH, SLA, VAS score, and ODI between the two groups (all P > 0.05). The operation time, estimated blood loss, and length of hospital stay were also comparable between the two groups. Over 90% of the fusion rate was achieved in both groups. The OLIF group showed a higher complication rate than the ALIF group (OLIF 18.83% vs ALIF 7.32%).

CONCLUSIONS

OLIF leads to a higher complication rate, with the most notable complication being cage subsidence. Both OLIF and ALIF are effective treatments for degenerative lumbar diseases and have similar therapeutic effects. ALIF was expected to be more expensive for patients because of the necessity of involving vascular surgeons.

A biomechanical comparison of posterior fixation approaches in lumbar fusion using computed tomography based lumbosacral spine modelling

Extreme lateral interbody fusion (XLIF) may be performed with a standalone interbody cage, or with the addition of unilateral or bilateral pedicle screws; however, decisions regarding supplemental fixation are predominantly based on clinical indicators. This study examines the impact of posterior supplemental fixation on facet micromotions, cage loads and load-patterns at adjacent levels in a L4-L5 XLIF at early and late fusion stages. CT data from an asymptomatic subject were segmented into anatomical regions and digitally stitched into a surface mesh of the lumbosacral spine (L1-S1). The interbody cage and posterior instrumentation (unilateral and bilateral) were inserted at L4-L5. The volumetric mesh was imported into finite element software for pre-processing, running nonlinear static solves and post-processing. Loads and micromotions at the index-level facets reduced commensurately with the extent of posterior fixation accompanying the XLIF, while load-pattern changes observed at adjacent facets may be anatomically dependent. In flexion at partial fusion, compressive stress on the cage reduced by 54% and 72% in unilateral and bilateral models respectively; in extension the reductions were 58% and 75% compared to standalone XLIF. A similar pattern was observed at full fusion. Unilateral fixation provided similar stability compared to bilateral, however there was a reduction in cage stress-risers with the bilateral instrumentation. No changes were found at adjacent discs. Posterior supplemental fixation alters biomechanics at the index and adjacent levels in a manner that warrants consideration alongside clinical information. Unilateral instrumentation is a more efficient option where the stability requirements and subsidence risk are not excessive.

Successful outcomes of unilateral vs bilateral pedicle screw fixation for lumbar interbody fusion: A meta-analysis with evidence grading

BACKGROUND

Whether it’s better to adopt unilateral pedicle screw (UPS) fixation or to use bilateral pedicle screw (BPS) one for lumbar degenerative diseases is still controversially undetermined.

AIM

To make a comparison between UPS and BPS fixation as to how they work efficaciously and safely in patients suffering from lumbar degenerative diseases.

METHODS

We have searched a lot in the databases through 2020 with index terms such as “unilateral pedicle screw fixation” and “bilateral pedicle screw fixation.” Only randomized controlled trials and some prospective cohort studies could be found, yielding 15 studies. The intervention was unilateral pedicle screw fixation; Primarily We’ve got outcomes of complications and fusion rates. Secondarily, we’ve achieved outcomes regarding total blood loss, operative time, as well as length of stay. Softwares were installed and utilized for subgroup analysis, analyzing forest plots, sensitivity, heterogeneity, forest plots, publication bias, and risk of bias.

RESULTS

Fifteen previous cases of study including 992 participants have been involved in our meta-analysis. UPS had slightly lower effects on fusion rate [relative risk (RR) = 0.949, 95%CI: 0.910 to 0.990, P = 0.015], which contributed mostly to this meta-analysis, and similar complication rates (RR = 1.140, 95%CI: 0.792 to 1.640, P = 0.481), Δ visual analog scale [standard mean difference (SMD) = 0.178, 95%CI: -0.021 to 0.378, P = 0.080], and Δ Oswestry disability index (SMD = -0.254, 95%CI: -0.820 to 0.329, P = 0.402). In contrast, an obvious difference has been observed in Δ Japanese Orthopedic Association (JOA) score (SMD = 0.305, 95%CI: 0.046 to 0.563, P = 0.021), total blood loss (SMD = -1.586, 95%CI: -2.182 to -0.990, P = 0.000), operation time (SMD = -2.831, 95%CI: -3.753 to -1.909, P = 0.000), and length of hospital stay (SMD = -0.614, 95%CI: -1.050 to -0.179, P = 0.006).

CONCLUSION

Bilateral fixation is more effective than unilateral fixation regarding fusion rate after lumbar interbody fusion. However, JOA, operation time, total blood loss, as well as length of stay were improved for unilateral fixation.

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.

Oblique lateral interbody fusion combined with lateral plate fixation for the treatment of degenerative diseases of the lumbar spine: A retrospective study

Oblique lateral interbody fusion (OLIF) is a minimally invasive decompression technique used in the treatment of lumbar degenerative diseases (LDDs). It is usually combined with posterior pedicle screw fixation to decrease perioperative complications. Few studies have reported the efficacy of OLIF combined with lateral plate instrumentation (OLIF-LP) for the treatment of LDDs.The purpose of this retrospective study was to evaluate the clinical efficacy of OLIF combined with lateral plate instrumentation for the treatment of LDDs.From May 2020 to September 2020, the clinical data of 52 patients who underwent OLIF-LP were analyzed. The operation time, blood loss, and complications were recorded. The radiological parameters, visual analog scale score, and Oswestry Disability Index were evaluated.The average operation time, blood loss, and length of hospital stay were 75.41 ± 11.53 minutes, 39.57 ± 9.22 mL, and 7.22 ± 1.85 days, respectively. The visual analog scale score and Oswestry Disability Index both improved significantly after surgery (7.23 ± 1.26 vs 2.15 ± 0.87; 60.27 ± 7.91 vs 21.80 ± 6.32, P < .01). The postoperative disk height was 13.02 ± 8.83 mm, which was much greater than the preoperative value. The postoperative foraminal height improved significantly (16.18 ± 3.49 vs 21.54 ± 2.12 mm, P < .01), and the cross-sectional area improved from 88.95 ± 14.79 to 126.53 ± 8.83 mm2 (P < .001). The radiological fusion rate was 88% at the last follow-up. No major complications, such as ureteral injury, vascular injury, or vertebral body fracture, occurred.Use of the OLIF-LP technique can help avoid lumbar posterior surgery and minimize the operative time and blood loss. OLIF-LP can achieve 1-stage intervertebral fusion and instrumentation through a single small incision.

Poor Bone Quality, Multilevel Surgery, and Narrow and Tall Cages Are Associated with Intraoperative Endplate Injuries and Late-onset Cage Subsidence in Lateral Lumbar Interbody Fusion: A Systematic Review

BACKGROUND

A major complication of lateral lumbar interbody fusion (LLIF) is cage subsidence, which may lead to clinical problems, including loss of disc height correction, altered spinal alignment, recurrent pain, and vertebral body fracture. A thorough review of the current knowledge about the risk factors for the two types of cage subsidence after LLIF-intraoperative endplate injury and late-onset cage subsidence-could bring attention to well-established risk factors for clinical consideration while identifying any incompletely characterized factors that require further research to clarify.

QUESTIONS/PURPOSES

We performed a systematic review to answer the following questions: (1) Are bone quality and surrogates for bone quality, such as patient age and sex, associated with an increased likelihood of cage subsidence? (2) Are implant-related factors associated with an increased likelihood of cage subsidence?

METHODS

Two independent reviewers comprehensively searched Medline, Embase, Cochrane Library, PubMed, and Web of Science from 1997 to 2020 to identify all potential risk factors for cage subsidence after LLIF. Discrepancies were settled through discussion during full-text screening. Search terms included "lateral" AND "interbody fusion" AND "subsidence" OR "settling" OR "endplate injury" OR "endplate violation" WITHOUT "cervical" OR "transforaminal" OR "biomechanical." Eligible studies were retrospective or prospective comparative studies, randomized controlled trials, and case series with sample sizes of 10 patients or more reporting risk factors for cage subsidence or endplate injury after LLIF. Studies that involved cervical interbody fusions and biomechanical and cadaveric experiments were excluded. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was used to assess the studies' quality of evidence. The initial database review found 400 articles. Thirty-four articles with moderate- to very-low-quality evidence met the inclusion criteria for analysis. A total of 3233 patients (58% [1860] of whom were female) were included in this review. Two types of cage subsidence were reviewed: late-onset cage subsidence, which occurs gradually postoperatively, and intraoperative endplate injury, which is derived from iatrogenic endplate violation during endplate preparation or cage insertion. Among 20 studies with moderate quality of evidence according to the GRADE criteria, eight studies reported risk factors for cage subsidence related to bone mineral density and its surrogates and 12 studies focused on risk factors regarding implant factors, including cage dimension, cage material, construct length, and supplementary instrumentation.

RESULTS

Patients with a dual x-ray absorptiometry T-score of -1.0 or less, age older than 65 years, and female sex were considered to have a high risk of both types of cage subsidence. Regarding cage size, cage width ≥ 22 mm helped to avoid late-onset cage subsidence, and cage height ≤ 11 mm was recommended by some studies to avoid intraoperative endplate injuries. Studies recommended that multilevel LLIF should be conducted with extra caution because of a high risk of losing the effect of indirect decompression. Studies found that standalone LLIF might be sufficient for patients without osteoporosis or obesity, and supplementary instrumentation should be considered to maintain the postoperative disc height and prevent subsidence progression in patients with multiple risk factors. The effect of the bone graft, cage material, endplate condition, and supplementary instrumentation on cage subsidence remained vague or controversial.

CONCLUSION

Patients with poor bone density, patients who are older than 65 years, and female patients should be counseled about their high risk of developing cage subsidence. Surgeons should avoid narrow cages when performing LLIF to minimize the risk of late-onset cage subsidence, while being cautious of an aggressive attempt to restore disc height with a tall cage as it may lead to intraoperative endplate injury. For multilevel constructs, direct decompression approaches, such as posterior and transforaminal LIF, should be considered before LLIF, since the effect of indirect decompression may be difficult to maintain in multilevel LLIF because of high risks of cage subsidence. The effect of the cage material and supplementary instrumentation require stronger evidence from prospectively designed studies with larger sample size that randomly assign patients to polyetheretherketone (PEEK) or titanium cages and different fixation types. Future research on intraoperative endplate injuries should focus on the specific timing of when endplate violation occurs with the help of intraoperative imaging so that attempts can be made to minimize its occurrence.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Evaluation of the Stability of a Novel Lateral Plate Internal Fixation: An In Vitro Biomechanical Study

BACKGROUND

This study aims to evaluate the biomechanical stability of a novel lateral plate (NLP) that can be used in oblique lateral lumbar fusion (OLIF).

METHODS

In vitro biomechanical tests were performed on 6 fresh calf lumbar vertebrae specimens. The surgical segment was set at L3-L4. Each specimen was tested in the following order: intact state (INT); OLIF cage only/stand-alone (SA); cage supplemented with lateral screw-rod (LSR); cage supplemented with novel lateral plate (NLP); and cage supplemented with unilateral or bilateral pedicle screw-rod (UPS or BPS). A pure moment of ±7.5 Nm was applied to the specimen to produce 6 different motion directions, including flexion and extension, lateral bending, and axial rotation, and the range of motion (ROM) of L3-L4 in each direction was recorded.

RESULTS

In addition to flexion-extension, NLP reduced the ROM of SA (P < 0.05). In flexion-extension, the ROM of NLP was similar to those of SA and LSR (P > 0.05); compared to pedicle screw-rod (PSD), the ROM of NLP was higher (P < 0.05). In lateral bending, the ROM of NLP was close to that of LSR and PSD (P > 0.05). In axial rotation, the ROM of NLP was higher than that of PSD (P < 0.05), and close to that of LSR (P > 0.05).

CONCLUSIONS

NLP can enhance surgical segment stability in all directions of motion, similar to LSR, but weaker than UPS and BPS in flexion-extension and rotation.

Cadaveric biomechanical analysis of multilevel lateral lumbar interbody fusion with and without supplemental instrumentation

BACKGROUND

This study was to evaluate and compare the biomechanical features of multilevel lateral lumbar interbody fusion (LLIF) with or without supplemental instrumentations.

METHODS

Six human lumbar specimens were tested under multidirectional nondestructive moments (7.5 N·m), with a 6 degree-of-freedom spine simulator. The overall and intervertebral range of motion (ROM) were measured optoelectronically. Each specimen was tested under the following conditions at L2-5 levels: intact; stand-alone; cage supplemented with lateral plate (LP); cage supplemented with unilateral or bilateral pedicle screw/rod (UPS or BPS).

RESULTS

Compared with intact condition, the overall and intersegmental ROM were significantly reduced after multilevel stand-alone LLIF. The ROM was further reduced after using LP instrumentation. In flexion-extension (FE) and axial rotation (AR), pedicle screw/rod demonstrated greater overall ROM reduction compared to LP (P < 0.01), and bilateral greater than unilateral (P < 0.01). In lateral bending (LB), BPS demonstrated greater overall ROM reduction compared to UPS and LP (P < 0.01), however, UPS and LP showed similar reduction (P = 0.245). Intervertebral ROM reductions showed similar trend as the overall ones after using different types of instrumentation. However, at L2/3 (P = 0.57) and L3/4 (P = 0.097) levels, the intervertebral ROM reductions in AR were similar between UPS and LP.

CONCLUSIONS

The overall and intervertebral stability increased significantly after multilevel LLIF with or without supplemental instrumentation. BPS provided the greatest stability, followed by UPS and LP. However, in clinical practice, less invasive adjunctive fixation methods including UPS and LP may provide sufficient biomechanical stability for multilevel LLIF.