Accelerated degeneration of the segment adjacent to a lumbar fusion

Predictive factors of surgical adjacent segment disease in the cervical spine: A nested case-control study

STUDY DESIGN

Nested case-control study.

OBJECTIVE

Radiological adjacent segment degeneration is reported in a significant proportion of patients operated on following ACDF. Only a part of them will experience clinical symptoms, ultimately requiring a second cervical spine surgery (SASD). Our retrospective observational study, with prospective data collection, aims at considering the potential influence of cervical sagittal balance on post-ACDF second surgery based on postoperative imaging follow-up. Four key potential predictive factors were evaluated between cases and controls.

METHODS

Between January 1st, 2014, to January 1st, 2020, 1078 patients were operated on for ACDF in the Spine Department of Lille University Hospital. We identified 19 cases and 76 matched controls. Cases were defined as follow: >18 y/o, operated on for a second ACDF related to a SASD. Controls patients did not undergo a second cervical surgery during the study period.

RESULTS

The prevalence of SASD was 1.76%. Neither the cervical sagittal axis (p = 0.12), nor the cervical lordosis (p = 0.40) were related to SASD. However, we reported a strong tendency for the numbers of levels operated on and the postoperative local kyphosis to be risk factors of SASD (respectively p = 0.056 and p = 0.06).

CONCLUSION

We did not report a clear impact of the cervical spine balance parameters such as cervical lordosis or cSVA on the risk of second cervical surgery at 2 years. Though, we highlighted the potential correlation between the initial number of cervical spine levels operated on and the occurrence of sASD and the presence of early local kyphosis.

Evaluating surgical interventions for low-grade degenerative lumbar spondylolisthesis: a network meta-analysis of decompression alone, fusion, and dynamic stabilization

OBJECTIVE

This study aimed to investigate which of the decompression alone (DA), decompression with fusion (DF), and decompression with dynamic stabilization (DS) produced the most favorable outcome for patients with low-grade degenerative lumbar spondylolisthesis (LDLS).

MATERIAL AND METHOD

Pubmed, Embase, Cochrane, and Web of Science were searched for all studies published before October 1, 2023. A review and data analysis of all randomized controlled trials (RCTs) of three interventions was performed by Stata (version 17.0) and Review Manager (version 5.4).

RESULT

21 RCT studies with 3192 patients were included in the network meta-analysis. DA was superior to DF (MD = -92.05, P < 0.05; MD = -295.57, P < 0.05; MD = -2.19, P < 0.05; RR = 0.54, P < 0.05, respectively) and DS (MD = -35.69, P < 0.05; MD = -100.7, P < 0.05; MD = -295.57, P < 0.05; MD = -2.19, P < 0.05; RR = 0.54, P < 0.05, respectively) in reducing operative time, intraoperative blood loss, length of hospital stay, and postoperative adverse events. DS was superior to DF in reducing operative time, intraoperative blood loss, and length of hospital stay (MD = -56.35, P < 0.05; MD = -194.84, P < 0.05; MD = -1.12, P < 0.05, respectively). DF was superior to DA in reducing reoperations (RR = 0.55, p < 0.05). DF was superior to DA (MD = -1.44, p < 0.05) and DS (MD = -0.41, p < 0.05) in controlling the progression of olisthesis.

CONCLUSION

DA was the most favorable treatment for LDLS, reducing operative time, bleeding, hospital stay, and postoperative complications. DF outperformed DA in reducing reoperation rates. Although DS showed benefits in operative time and bleeding compared to DF, it did not offer a significant advantage over DA.

Efficacy and safety of allogeneic mesenchymal precursor cells with and without hyaluronic acid for treatment of chronic low back pain: A prospective, randomized, double blind, concurrent-controlled 36-month study

BACKGROUND CONTEXT

Low back pain (LBP) associated with degenerative disc disease (DDD) is a serious condition resulting in significant morbidity, disability, and reduced quality of life for millions of people each year. Patients who fail to improve with conservative/noninvasive treatments including physical therapy and nonopioid analgesic medications have limited options, which include opioid analgesics with their associated significant risks; epidural steroid injections with limited supporting evidence; or surgical interventions such as spine fusion or artificial disc replacement. A safe, minimally invasive, nonopioid treatment that provides prolonged improvement in pain, function, and quality of life is needed for such patients.

PURPOSE

Evaluate the efficacy and safety of a single injection of mesenchymal precursor cells (MPCs) with or without hyaluronic acid (HA) compared to an intradiscal saline injection through 36 months follow-up in subjects with chronic low back pain (CLBP) associated with moderate DDD (mDDD).

STUDY DESIGN/SETTING

A prospective, multicenter, randomized, double-blind, concurrent-controlled study conducted at 49 clinical sites.

SUBJECT SAMPLE

A total of 404 subjects with CLBP associated with mDDD at one level from L1 to S1 received MPCs without HA (MPC), MPCs with HA (MPC+HA), or saline control (control) treatment.

OUTCOME MEASURES

Subjects were clinically and radiographically evaluated at 1, 3, 6, 12, 18, 24, and 36 months postinjection. Clinical evaluation included adverse events, neurologic evaluation, laboratory tests, LBP intensity measured by Visual Analog Scale (VAS), Oswestry Disability Index (ODI) and EQ-5D-5L Index. Radiographic assessments used Magnetic Resonance (MR) imaging and X-ray imaging studies.

METHODS

The primary efficacy endpoint was a composite responder analysis for overall treatment success at both 12 and 24 months that was comprised of:[1] at least a 50% reduction from baseline in low back pain VAS score (average pain over 24 h);[2] at least a 15-point decrease from baseline in ODI score; and[3] no adjudicated posttreatment interventions at the treated level. To assess superiority, a Bayesian analysis used a probability threshold of 0.9875. Additional analyses were performed on a prespecified subpopulation of subjects with CLBP duration at baseline less than the median baseline duration of 68 months (CLBPLTM). Statistical assessments included least squares (LS) mean, LS mean change from baseline (CFB) using the mixed model for repeated measures (MMRM) and categorical responder analyses using stratified Cochran Mantel Haenszel row means score test with p<.05 defined as statistically significant. This study was conducted under a US Food and Drug Administration (FDA) Investigational New Drug (IND) application sponsored and funded by Mesoblast.

RESULTS

All treatment groups showed substantial improvement from baseline in LS Mean LBP and ODI. The primary efficacy endpoint for the trial did not reach significance for either treatment group compared to control in all subjects. Furthermore, none of the secondary endpoints showed a significant difference between treatment and control in all subjects. While the primary and secondary responder efficacy endpoints were not reached, MPC+HA significantly reduced LS mean LBP compared to control at 12 and 24 months in all subjects. The results observed in all subjects were enhanced for MPC+HA and MPC in the prespecified CLBPLTM subgroup with MPC+HA having significantly greater reduction in LBP at all time points compared to control and MPC having significantly greater reduction in LBP at 6, 12 and 36 months. In the CLBPLTM subgroup, MPC+HA also showed significantly greater proportion of pain responders at 12, 24 and 36 compared to control. MPC+HA also showed significantly greater function improvement at 12 and 18 months compared to control in the CLBPLTM subgroup. Furthermore, MPC+HA subjects in the CLBPLTM subgroup showed significantly greater improvement in quality of life (QOL) compared to control at 12, 24 and 36 months. MPC+HA baseline opioid users had greater reduction in daily average morphine equivalent dose (MED) compared to control at 6 through 36 months. Furthermore, significantly more MPC+HA baseline opioid users (27.8%) were not taking opioids at 36 months compared to (7.8%) control. The injection procedure and MPC treatment were well tolerated with no appreciable differences in Treatment Emergent Adverse Events (TEAEs). No Serious Adverse Events (SAEs) were related to the treatment or procedure. The number of subjects that received posttreatment interventions (PTI) at the treated level were comparable among groups.

CONCLUSIONS

While the primary and secondary efficacy endpoints were not met in all subjects, MPC+HA treatment showed a significant reduction in pain compared to control that was enhanced in subjects with CLBP duration less than 68 months. Intra-discal injection of MPC+HA is a minimally invasive nonopioid therapy that appears to be safe and demonstrates reduction in pain through 24 months compared to control with enhanced results in subjects with mDDD that have had CLBP less than 68 months.

Comparison of rostral facet joint violations in robotic- and navigation-assisted pedicle screw placement for adult lumbar spine instrumentation

BACKGROUND CONTEXT

Facet joint violation by pedicle screws may lead to adjacent-segment disease and postoperative pain. Previous studies have reported the incidence of rostral facet joint violation using various pedicle screw insertion techniques. However, the incidence of facet joint violations with robotic guidance has not been determined.

PURPOSE

To investigate and compare the incidence of rostral facet joint violation by pedicle screws under robotic guidance and computerized tomography (CT) navigation guidance.

STUDY DESIGN/SETTING

Retrospective matched cohort.

PATIENT SAMPLE

All patients who underwent robotic-assisted lumbar fusion at a major spine center up until 2023 were retrospectively identified and matched 1:3 to patients undergoing CT navigation guidance based by on age, sex, rostral vertebral level, and length of construct. Inclusion criteria consisted of age greater than 18 years, bilateral pedicle screw fixation, and presence of a postoperative CT scan of the lumbar spine or abdomen/pelvis at any point in the postoperative period.

OUTCOME MEASURES

Rostral facet joint violations.

METHODS

Descriptive statistics were used to compare cohorts: frequencies, chi-squared analysis for categorical variables, and t-test for continuous variables.

RESULTS

A total of 408 rostral pedicle screws were implanted in 204 patients (Robot: 102; Navigation: 306). Overall, 13 (12.3%) rostral facet joint violations were observed in the robot cohort and 75 (24.5%) in the navigation cohort (p=.01). Specifically, fewer robotic violations were observed at the L2 (3.5% vs 32.1%, p=.003) and L3 levels (3.9% vs 18.1%, p=.08) compared to navigation. No difference was observed at L4 and L5. Bilateral violations are significantly reduced with robotic approaches (5.3% vs 14.4%, p=.03). Lastly, more facet joint violations were observed during open approaches (robot: 18.8%, navigation: 27.3%) than percutaneous approaches (robot: 11.6%, navigation: 7.1%) in both groups (p<.001). The rate of L4 facet violations was 18.8% in the robotic cohort and 27.3% in the navigation cohort. The rate of L5 facet violations was 31.3% in the robotic cohort and 29.2% in the navigation cohort.

CONCLUSIONS

Use of robotic assistance in lumbar pedicle screws significantly reduced the rate of rostral facet joint violations compared to navigation guidance at L2 and L3 levels, but not at L4 and L5, with facet violations approaching nearly one-third of the patients at L5 screws. Rostral facet violations can play a significant role in adjacent segment degeneration and disease. Technical factors and trajectory issues likely play a role and addressing these components should minimize unintended facet violation and proximal adding on.

Endoscope-Assisted Revision Surgery after Lumbar Fusion with Pedicle Screw Fixation: A Case Series and Literature Review

BACKGROUND

Lumbar internal fixation and fusion can be subject to failure requiring revision surgery. Endoscopic revision surgery with minimal invasiveness may be a helpful therapeutic intervention in the management of certain fusion-related complications. According to the author's knowledge, there are few references to this technique in English literature.

OBJECTIVE

This study aimed to investigate the efficacy of endoscope-assisted revision surgery in patients with recurrent radiculopathy after lumbar fusion surgery, discuss the necessity of revision surgery, and review the relevant literature.

MATERIAL AND METHODS

We report a case series and review relevant literature. Information was gathered from the electronic medical record in our hospital. A total of 231 patients who underwent endoscopic spine procedures from January 2021 to October 2022 were reviewed. Three patients who underwent endoscopic decompressive procedures after lumbar fusion surgeries at a correspondence segment were identified, and the clinical courses and radiological findings of these patients were retrospectively reviewed.

RESULTS

The average interval from initial to revision surgery was 30.74 (range 10.50-48.00) months. The patients include one man and two women with an average age of 75.67 (range 68-81) years at the initial operation. Three patients developed symptoms of recurrent myelopathy after their initial surgery due to canal stenosis in the fusion segment and hyperostosis. All patients experienced symptom relief after revision surgery. At a mean follow-up time of 0.96 months, endoscopic decompression resulted in the average numerical rating scale (NRS) score for lower limb pain on the symptomatic side being reduced by 2.67. Patients rated their leg pain on average as 4.5 ± 0.5.

CONCLUSIONS

Endoscope-assisted revision surgery after lumbar fusion with pedicle screw fixation is a promising therapeutic strategy in treating recurrent radiculopathy. Spinal stenosis and hyperostosis are two of the most significant reasons for revision surgery. Resection of intraspinal lesions and endoscopic foraminal decompression appear to have promising outcomes. Certain fusion-related complications may be effectively treated with endoscope-assisted revision surgery. Further research should be conducted to investigate the clinical efficacy of revision surgery.

Comparative effectiveness of cortical bone trajectory screws and pedicle screws in the treatment of adjacent segment degeneration after lumbar fusion surgery: a systematic review and meta-analysis

PURPOSE

To compare the efficacy and safety of cortical bone trajectory (CBT) screw and pedicle screw (PS) internal fixation in the treatment of adjacent segment degeneration (ASD) after lumbar fusion.

METHODS

This study was registered on International Prospective Register of Systematic Reviews (PROSPERO) (ID: CRD42023484937). We searched PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wan Fang Database, and Wei Pu Database by computer to collect controlled clinical studies on the efficacy and safety of cortical bone trajectory (CBT) screw and pedicle screw (PS) internal fixation in the treatment of adjacent segment degeneration (ASD) after lumbar fusion from database establishment to November 2023. Two researchers screened the literature, extracted data and evaluated the risk of bias of the included studies, recorded the authors, and sample size, and extracted the intraoperative blood loss, operation time, Oswestry disability index (ODI), Visual analogue scale (VAS), disc height (DH), hospital length stay and complications in each study. Meta-analysis was performed using Revman 5.4 software provided by Cochrane Library.

RESULTS

A total of 6 cohort studies (CS) and 1 randomized controlled study with a total of 420 patients were included in this study, including 188 patients in the CBT group and 232 patients in the PS group. The CBT group had lower intraoperative blood loss than the PS group [mean difference (MD) = -129.38, 95% CI (-177.22, -81.55), P < 0.00001] and operation time was shorter than that of the PS group [MD = -1.42, 95% CI (-2.63, -0.20), P = 0.02]. Early postoperative back and leg pain improved more significantly in the CBT group [MD = -0.77, 95% CI (-1.35, -0.19), P = 0.01; MD = -0.24, 95% CI (-0.37, -0.10), P = 0.0005].

CONCLUSION

Compared with PS, CBT for adjacent segment degeneration after lumbar fusion has the advantages of less intraoperative blood loss, shorter operation time, and less back and leg pain in the early postoperative period.

In vivo study of a novel 3D-printed motion-preservation artificial cervical corpectomy construct: short-term imaging and biocompatibility evaluations in a goat model

BACKGROUND

Nonfusion technologies, such as motion-preservation devices, have begun a new era of treatment options in spine surgery. Motion-preservation approaches mainly include total disc replacement for anterior cervical discectomy and fusion. However, for multisegment fusion, such as anterior cervical corpectomy and fusion, the options are more limited. Therefore, we designed a novel 3D-printed motion-preservation artificial cervical corpectomy construct (ACCC) for multisegment fusion. The aim of this study was to explore the feasibility of ACCC in a goat model.

METHODS

Goats were treated with anterior C3 corpectomy and ACCC implantation and randomly divided into two groups evaluated at 3 or 6 months. Radiography, 3D CT reconstruction and MRI evaluations were performed. Biocompatibility was evaluated using micro-CT and histology.

RESULTS

Postoperatively, all goats were in good condition, with free neck movement. Implant positioning was optimal. The relationship between facet joints was stable. The range of motion of the C2-C4 segments during flexion-extension at 3 and 6 months postoperatively was 7.8° and 7.3°, respectively. The implants were wrapped by new bone tissue, which had grown into the porous structure. Cartilage tissue, ossification centres, new blood vessels, and bone mineralization were observed at the porous metal vertebrae-bone interface and in the metal pores.

CONCLUSIONS

The ACCC provided stabilization while preserving the motion of the functional spinal unit and promoting bone regeneration and vascularization. In this study, the ACCC was used for anterior cervical corpectomy and fusion (ACCF) in a goat model. We hope that this study will propel further research of motion-preservation devices.

Hybrid cortical bone trajectory and modified cortical bone trajectory techniques in transforaminal lumbar interbody fusion at L4-L5 segment: A finite element analysis

Background

The academia has increasingly acknowledged the superior biomechanical performance of the hybrid fixation technique in recent years. However, there is a lack of research on the hybrid fixation technique using BCS (Bilateral Cortical Screws) and BMCS (Bilateral Modified Cortical Screws). This study aims to investigate the biomechanical performance of the BCS and BMCS hybrid fixation technique in transforaminal lumbar interbody fusion (TLIF) at the L4-L5 segment in a complete lumbar-sacral finite element model.

Methods

Three cadaver specimens are used to construct three lumbar-sacral finite element models. The biomechanical properties of various fixation technologies (BCS-BCS, BMCS-BMCS, BMCS-BCS, and BCS-BMCS) are evaluated at the L4-5 segment with a TLIF procedure conducted, including the range of motion (ROM) of the L4-5 segment, as well as the stress experienced by the cage, screws, and rods. The testing is conducted under specific loading conditions, including a compressive load of 400 N and a torque of 7.5Nm, subjecting the model to simulate flexion, extension, lateral bending, and rotation.

Results

No significant variations are seen in the ROM at the L4-5 segment when comparing the four fixation procedures during flexion and extension. However, when it comes to lateral bending and rotation, the ROM is ordered in descending order as BCS-BCS, BCS-BMCS, BMCS-BMCS, and BMCS-BCS. The maximum stress experienced by the cage is observed to be highest within the BMCS-BCS technique during movements including flexion, extension, and lateral bending. Conversely, the BMCS-BMCS technique exhibits the highest cage stress levels during rotational movements. The stress applies to the screws and rods order the sequence of BCS-BCS, BCS-BMCS, BMCS-BCS, and BMCS-BMCS throughout all four working conditions.

Conclusion

The BMCS-BCS technique shows better biomechanical performance with less ROM and lower stress on the internal fixation system compared to other fixation techniques. BMCS-BMCS technology has similar mechanical performance to BMCS-BCS but has more contact area between screws and cortical bone, making it better for patients with severe osteoporosis.

Percutaneous microchannel unilateral approach bilateral micro decompression for adjacent segmental degeneration after lumbar fusion at 10 years: a case report and review of literature

Background

Adjacent segmental degeneration after lumbar fusion is one of the common long-term complications after lumbar fusion. With the continuous development of adjacent segmental degeneration, patients who fail conservative treatment often need reoperation to relieve symptoms. In recent years, the technique of bilateral microdecompression through unilateral approach under microchannel has been widely used in the treatment of lumbar degenerative diseases. However, the efficacy of this procedure for adjacent-segment degeneration after lumbar fusion has not been established. Here, we report a case of bilateral microscopic decompression via a unilateral approach through a microchannel in a patient with adjacent segmental degeneration after lumbar fusion.

Case report

A 70-year-old male patient was admitted to hospital because of lumbago accompanied by left lower extremity pain, numbness and weakness for 2 years, which aggravated for 2 months. Ten years ago, he underwent PLIF for lumbar spinal stenosis, and recovered well after the operation. According to imaging data and physical examination, the diagnosis was adjacent segmental degeneration after lumbar fusion. Bilateral microdecompression was performed through a unilateral approach under a microchannel. Good clinical outcomes was observed through 1-year postoperative follow-up.

Conclusions

This report reports the successful treatment of a patient with ASD 10 years after lumbar fusion. Bilateral microdecompression via a unilateral approach under a microchannel is a safe and effective method for the treatment of ASD after lumbar fusion with good surgical outcomes.

Bibliometric and Visualization Analysis of Biomechanical Research on Lumbar Intervertebral Disc

Background

Biomechanical research on the lumbar intervertebral disc (IVD) provides valuable information for the diagnosis, treatment, and prevention of related diseases, and has received increasing attention. Using bibliometric methods and visualization techniques, this study investigates for the first time the research status and development trends in this field, with the aim of providing guidance and support for subsequent research.

Methods

The Science Citation Index Expanded (SCI-Expanded) within the Web of Science Core Collection (WoSCC) database was used as the data source to select literature published from 2003 to 2022 related to biomechanical research on lumbar IVD. VOSviewer 1.6.19 and CiteSpace 6.2.R2 visualization software, as well as the online analysis platform of literature metrology, were utilized to generate scientific knowledge maps for visual display and data analysis.

Results

The United States is the most productive country in this field, with the Ulm University making the largest contribution. Wilke HJ is both the most prolific author and one of the highly cited authors, while Adams MA is the most cited author. Spine, J Biomech, Eur Spine J, Spine J, and Clin Biomech are not only the journals with the highest number of publications, but also highly cited journals. The main research topics in this field include constructing and validating three-dimensional (3D) finite element model (FEM) of lumbar spine, measuring intradiscal pressure, exploring the biomechanical effects and related risk factors of lumbar disc degeneration, studying the mechanical responses to different torque load combinations, and classifying lumbar disc degeneration based on magnetic resonance images (MRI), which are also the hot research themes in recent years.

Conclusion

This study systematically reviews the knowledge system and development trends in the field of biomechanics of lumbar IVD, providing valuable references for further research.

Long-term adjacent segment degeneration at average 21-year follow-up of posterior instrumented fusion for adolescent idiopathic scoliosis

INTRODUCTION

Posterior instrumented fusion for progressive adolescent idiopathic scoliosis (AIS) is generally considered to have good outcomes, but very long-term reviews are rare. Data on adjacent segment degeneration (ASD) following posterior instrumented thoracic fusion for AIS are lacking. The primary aim was to assess the incidence of ASD and to correlate this with radiographic measures and patient-reported outcome measures (PROMs). The secondary aim was to assess maintenance of curve correction at very long-term follow-up.

METHODS

This single-surgeon consecutive case series of 47 AIS patients was identified from a prospectively collated dataset. As the primary outcome, ASD was assessed radiographically using the Mimura grading system. Pulmonary function tests and PROMs were assessed along with secondary radiographic outcome measures.

RESULTS

Radiographic follow-up was achieved in 77% (36/47) of patients at an average of 21 years (range, 16.5-26.5 years) after surgery. Radiographic evidence of ASD was seen in 64%. PROMs showed a mean Oswestry disability index of 12.1% with an overall Scoliosis Research Society 22 score averaging at 3.7 out of 5. The Coronal Cobb Angle was corrected from an average of 57° preoperatively to 19° immediately postoperatively, deteriorating to 22° at final review, maintaining a 61% curve correction.

CONCLUSIONS

Radiographic evidence of ASD was found in 64% of the cohort. The patient-reported outcome measures were good, with few limitations to activities.

Biomechanical evaluation of the hybrid pedicle screw-cortical bone trajectory technique in transforaminal lumbar interbody fusion to adjacent segment degeneration-finite element analysis

BACKGROUND

Transforaminal lumbar interbody fusion is an effective surgical treatment of intervertebral disk herniation. However, its clinical efficacy for adjacent segment disk degeneration (ASDD) after hybrid bilateral pedicle screw - bilateral cortical screw (pedicle screw at L4 and cortical bone trajectory screw at L5) and hybrid bilateral cortical screw - bilateral pedicle screw (bilateral cortical screw at L4 and bilateral pedicle screw at L5) remains undiscovered. Therefore, the aim of this study is to evaluate the effect of the hybrid bilateral pedicle screw - bilateral cortical screw and hybrid bilateral cortical screw - bilateral pedicle screw on the adjacent segment via a 3-dimensional (3D) finite element (FE) analysis.

METHODS

Four human cadaveric lumbar spine specimens were provided by the anatomy teaching and research department of Xinjiang Medical University. Four finite element models of L1-S1 lumbar spine segment were generated. For each of these, four lumbar transforaminal lumbar interbody fusion models at L4-L5 segment with the following instruments were created: hybrid bilateral pedicle screw - bilateral cortical screw, bilateral cortical screw - bilateral cortical screw (bilateral cortical screw at both L4 and L5 segments), bilateral pedicle screw - bilateral pedicle screw (bilateral pedicle screw at both L4 and L5 segments), and hybrid bilateral cortical screw - bilateral pedicle screw. A 400-N compressive load with 7.5 Nm moments was applied for the simulation of flexion, extension, lateral bending, and rotation. The range of motion of L3-L4 and L5-S1 segments and von Mises stress of the intervertebral disc at the adjacent segment were compared.

RESULTS

Hybrid bilateral pedicle screw - bilateral cortical screw has the lowest range of motion at L3-L4 segment in flexion, extension, and lateral bending, and the highest disc stress in all motions, while the range of motion at L5-S1 segment and disc stress was lower than bilateral pedicle screw - bilateral pedicle screw in flexion, extension, and lateral bending, and higher than bilateral cortical screw - bilateral cortical screw in all motions. The range of motion of hybrid bilateral cortical screw - bilateral pedicle screw at L3-L4 segment was lower than bilateral pedicle screw - bilateral pedicle screw and higher than bilateral cortical screw - bilateral cortical screw in flexion, extension, and lateral bending, and the range of motion at L5-S1 segment was higher than bilateral pedicle screw - bilateral pedicle screw in flexion, lateral bending, and axial rotation. The disc stress at L3-L4 segment was lowest and more dispersed in all motions, and the disc stress at L5-S1 segment was higher than bilateral pedicle screw - bilateral pedicle screw in lateral bending and axial rotation, but more dispersed.

CONCLUSION

Hybrid bilateral cortical screw - bilateral pedicle screw decreases the impact on adjacent segments after spinal fusion, reduces the iatrogenic injury to the paravertebral tissues, and provides throughout decompression of the lateral recess.

Outcomes of patients undergoing single-level arthroplasty versus anterior lumbar interbody fusion

BACKGROUND

Compared to vertebral body fusion, artificial discs are thought to lessen the risks of adjacent segment disease and the need for additional surgery by maintaining spinal mobility as they mimic the intervertebral disc structure. No studies have compared the rates of postoperative complications and the requirement for secondary surgery at adjacent segments among patients who have undergone anterior lumbar interbody fusions (ALIF) versus those undergoing lumbar arthroplasty.

METHODS

An all-payer claims database identified 11,367 individuals who underwent single-level ALIF and lumbar arthroplasty for degenerative disc disease (DDD) between January 2010 and October 2020. Rates of complications following surgery, the need for additional lumbar surgeries, length of stay (LOS), and postoperative opioid utilization were assessed in matched cohorts based on logistic regression models. Kaplan-Meyer plots were created to model the probability of additional surgery.

RESULTS

Following 1:1 exact matching, 846 records of patients who had undergone ALIF or lumbar arthroplasty were analyzed. All-cause readmission within 30-30 days following surgery was significantly higher in patients undergoing ALIF versus arthroplasty (2.6% vs. 0.71%, p = 0.02). LOS was significantly lower among the patients who had undergone ALIF (1.043 ± 0.21 vs. 2.17 ± 1.7, p < .001).

CONCLUSIONS

ALIF and lumbar arthroplasty procedures are equally safe and effective in treating DDD. Our findings do not support that single-level fusions may biomechanically necessitate revisional surgeries.

Biomechanical Effect of Hybrid Dynamic Stabilization Implant on the Segmental Motion and Intradiscal Pressure in Human Lumbar Spine

The hybrid dynamic stabilization system, Dynesys-Transition-Optima, represents a novel pedicle-based construct for the treatment of lumbar degenerative disease. The theoretical advantage of this system is to stabilize the treated segment and preserve the range of motion within the adjacent segment while potentially decreasing the risk of adjacent segment disease following lumbar arthrodesis. Satisfactory short-term outcomes were previously demonstrated in the Dynesys-Transition-Optima system. However, long-term follow-up reported accelerated degeneration of adjacent segments and segmental instability above the fusion level. This study investigated the biomechanical effects of the Dynesys-Transition-Optima system on segment motion and intradiscal pressure at adjacent and implanted levels. Segmental range of motion and intradiscal pressure were evaluated under the conditions of the intact spine, with a static fixator at L4-5, and implanted with DTO at L3-4 (Dynesys fixator) and L4-5 (static fixator) by applying the loading conditions of flexion/extension (±7.5 Nm) and lateral bending (±7.5 Nm), with/without a follower preload of 500 N. Our results showed that the hybrid Dynesys-Transition-Optima system can significantly reduce the ROM at the fusion level (L4-L5), whereas the range of motion at the adjacent level (L3-4) significantly increased. The increase in physiological loading could be an important factor in the increment of IDP at the intervertebral discs at the lumbar spine. The Dynesys-Transition-Optima system can preserve the mobility of the stabilized segments with a lesser range of motion on the transition segment; it may help to prevent the occurrence of adjacent segment degeneration. However, the current study cannot cover all the issues of adjacent segmental diseases. Future investigations of large-scale and long-term follow-ups are needed.

Indications and timing of revision spine surgery in adults after adolescent surgery for idiopathic scoliosis

STUDY DESIGN

Retrospective case series.

PURPOSE

To characterize the indications and timing of revision spine surgery in adulthood after adolescent surgery for idiopathic scoliosis. Previous studies have shown that revision usually occurs within 3 months or more than 5 years after the index operation. It is not clear what the indications for and timeline to revision surgery are in these patients during adulthood.

METHODS

421 patients with idiopathic scoliosis were seen as adults over a 15-year period. 81 patients who had scoliosis surgery prior to age 18 were identified. This cohort was studied for indications and time from index to revision operation. Their clinical presentation and a description of their revision operation was also documented.

RESULTS

Of the 81 patients, 18 (22.2%) had a revision surgery as an adult. Indications for revision in order of prevalence were implant malposition, subjacent segment degeneration and stenosis, pseudoarthrosis, delayed deep wound infection, spondylolisthesis, and symptomatic implants. Revisions were indicated generally within 15 years or more than 30 years after the initial operation.

CONCLUSIONS

The timeline for revision spine surgery in idiopathic scoliosis was bimodal, with revisions occurring within 15 years or over 30 years after the initial operation. Implant malposition and subjacent segment degeneration were the most prevalent indications for adulthood revision.

LEVEL OF EVIDENCE

Prognostic-IV.

A Retrospective Comparative Study of Modified Percutaneous Endoscopic Transforaminal Discectomy and Open Lumbar Discectomy for Gluteal Pain Caused by Lumbar Disc Herniation

Introduction

This study aimed to demonstrate the safety and effectiveness of modified percutaneous endoscopic transforaminal discectomy (PETD) in the surgical management of single-segment lumbar disc herniation (LDH) gluteal pain and to determine whether it provides a better clinical outcome than open lumbar discectomy (OD).

Methods

A retrospective analysis of patients treated with modified PETD and OD for gluteal pain in LDH from January 2015 to December 2020 was conducted. Sample size was determined using a priori power analysis. Demographic information, surgical outcomes including procedure time (minutes), intraoperative blood loss (mL), hospital days, costs (RMB), fluoroscopy shots, recurrence and complications, etc., were recorded and analyzed. Prognostic outcomes were assessed using the visual analog scale (VAS), the Oswestry Disability Index (ODI), the Japanese Orthopedic Association Score (JOA) and modified MacNab criteria. The preoperative and postoperative VAS, ODI and JOA scores were recorded by two assistants. When the results were inconsistent, the scores were recorded again by the lead professor until all scores were consistently recorded in the data. MRI was used to assess radiological improvement and all patients received follow-ups for at least one year.

Results

The sample size required for the study was calculated by a priori analysis, and a total of 72 participants were required for the study to achieve 95% statistical test power. A total of 93 patients were included, 47 of whom underwent modified PETD, and 46 of whom underwent OD. In the modified PETD intragroup comparison, VAS scores ranged from 7.14 ± 0.89 preoperatively to 2.00 ± 0.58, 2.68 ± 0.70, 2.55 ± 0.69, 2.23 ± 0.81, and 1.85 ± 0.72 at 7 days, 1 month, 3 months, 6 months, and 12 months postoperatively. Patients showed significant pain relief postoperatively (P &lt; 0.01). According to the modified MacNab score, the excellent rate in the PETD group was 89.36%. There was no significant difference compared to the OD group (89.13%, P &gt; 0.05). Complication rates were lower (P &gt; 0.05) but recurrence rates were higher (P &gt; 0.05) in the modified PETD group than in the OD group. The modified PETD group had a faster operative time (P &lt; 0.01), shorter hospital stay (P &lt; 0.01), less intraoperative bleeding (P &lt; 0.01), and less financial burden to the patient (P &lt; 0.01) than the OD group. At 7 days postoperatively, the VAS score for low back pain was higher in the OD group than in the modified PETD group (P &lt; 0.01). The VAS and JOA scores at 1, 3, 6, and 12 months postoperatively were not significantly different between the modified PETD and OD groups (P &gt; 0.05), and the ODI was significantly different at 3 months postoperatively (P &lt; 0.05).

Conclusion

Modified PETD treatment is safe and effective for gluteal pain due to L4/5 disc herniation and has the advantages of a lower complication rate, faster postoperative recovery, shorter length of stay, fewer anesthesia risks and lower cost of the procedure compared with OD. However, modified PETD has a higher recurrence rate.

Application of a new anatomic hook-rod-pedicle screw system in young patients with lumbar spondylolysis: A pilot study

BACKGROUND

The pedicle screw-laminar hook system has strong fixation and is conducive to bone graft fusion for lumbar spondylolysis. However, the current pedicle screw-laminar hook fixation system is not specifically designed for lumbar spondylolysis.

AIM

To investigate the clinical effects of a new anatomical hook-rod-pedicle screw system in the treatment of lumbar spondylolysis in young adults.

METHODS

We designed a new anatomic hook-rod-pedicle screw system for young patients with lumbar spondylolysis. The isthmus and the corresponding pedicle screw entry point were exposed through the intermuscular approach. Autogenous iliac bone graft was obtained to bridge the isthmus defect, and then the anatomic hook-rod-pedicle screw system was used to fix the isthmus in 15 young patients.

RESULTS

At 24 mo follow-up, the visual analogue scale score of low back pain decreased from 6.73 ± 0.88 to 0.73 ± 0.59, and the Oswestry disability index score decreased from 58.20 ± 8.99 to 7.87 ± 4.97. Computed tomography showed bilateral isthmic bone healing in 14 cases and unilateral isthmic bone healing in 1 case. Magnetic resonance imaging showed that the lumbar disc signal of diseased segment and adjacent segments had no change compared with that before surgery. The pain visual analogue scale score of the donor site was 0.20 ± 0.41 at the last follow-up. According to the Modified Macnab score, the excellent and good rate was 100%.

CONCLUSION

The application of this new anatomical hook-rod-pedicle screw system to treat young patients with lumbar spondylolysis has the advantages of less trauma, a simple operation and satisfactory clinical effects.

Association between Occupation and Cervical Disc Degeneration in 1211 Asymptomatic Subjects

Magnetic resonance imaging (MRI) system has frequently observed degenerative changes in the cervical discs of healthy subjects. Although there are concerns regarding the link between an individual's occupation and intervertebral disc degeneration (IDD) in the cervical spine, whether the occupation affects IDD is still not clear. This study aimed to evaluate the occupation and IDD interplay using cervical spine MRI among a cohort of healthy individuals, and to evaluate any association between the type of labor and IDD. Using MRI, we prospectively measured at every level, the anteroposterior (AP) intervertebral disc diameter and disc height, in a cohort of 1211 healthy volunteers (606 (50%) male; mean age, 49.5 years). Using a minimum of 100 male and female each from the third to eighth decades of age (20-79 years), IDD was evaluated based on the modified Pfirrmann classification system to derive a disc degeneration score (DDS). We also measured the AP diameters of disc protrusion and of the dural sac as well as the spinal cord. The overall DDS and number of disc protrusions increased with age. Among 11 occupations, there were no significant differences in AP diameter of the dural sac as well as the spinal cord. For the four labor types (heavy object handling, same position maintenance, cervical extension position, and cervical flexion position), there were no significant differences in overall DDS and number of disc protrusions, with or without work. Also, among the four labor types, there were no significant differences in the AP diameter of the dural sac as well as the spinal cord. In this cross-sectional survey of cervical spine MRI data among healthy adult volunteers, occupation and type of labor might have no effect on IDD in the cervical spine.

Adjacent segments biomechanics following lumbar fusion surgery: a musculoskeletal finite element model study

PURPOSE

This study exploits a novel musculoskeletal finite element (MS-FE) spine model to evaluate the post-fusion (L4-L5) alterations in adjacent segment kinetics.

METHODS

Unlike the existing MS models with idealized representation of spinal joints, this model predicts stress/strain distributions in all passive tissues while organically coupled to a MS model. This generic (in terms of musculature and material properties) model uses population-based in vivo vertebral sagittal rotations, gravity loads, and an optimization algorithm to calculate muscle forces. Simulations represent individuals with an intact L4-L5, a preoperative severely degenerated L4-L5 (by reducing the disc height by ~ 60% and removing the nucleus incompressibility), and a postoperative fused L4-L5 segment with either a fixed or an altered lumbopelvic rhythm with respect to the intact condition (based on clinical observations). Changes in spine kinematics and back muscle cross-sectional areas (due to intraoperative injuries) are considered based on in vivo data while simulating three activities in upright/flexed postures.

RESULTS

Postoperative changes in some adjacent segment kinetics were found considerable (i.e., larger than 25%) that depended on the postoperative lumbopelvic kinematics and preoperative L4-L5 disc condition. Postoperative alterations in adjacent disc shear, facet/ligament forces, and annulus stresses/strains were greater (> 25%) than those found in intradiscal pressure and compression (< 25%). Kinetics of the lower (L5-S1) and upper (L3-L4) adjacent segments were altered to different degrees.

CONCLUSION

Alterations in segmental rotations mainly affected adjacent disc shear forces, facet/ligament forces, and annulus/collagen fibers stresses/strains. An altered lumbopelvic rhythm (increased pelvis rotation) tends to mitigate some of these surgically induced changes.

Quantitative Photoacoustic Reconstruction of the Optical Properties of Intervertebral Discs Using a Gradient Descent Scheme

The intervertebral discs (IVD) are among the essential organs of the human body, ensuring the mobility of the spine. These organs possess a high proportion of water. However, as the discs age, this content decreases, which can potentially lead to various diseases called degenerative disc diseases. This water content is therefore an important indicator of the well-being of the disc. In this paper, we propose photoacoustic imaging as a means of probing a disc and quantitatively recovering its molecular composition, which should allow concluding on its state. An adjoint-assisted gradient descent scheme is implemented to recover the optical absorption coefficient in the disc, from which, if spectroscopic measurements are performed, the molecular composition can be deduced. The algorithm was tested on synthetic measurements. A realistic numerical phantom was built from magnetic resonance imaging of an actual IVD of a pig. A simplified experiment, with a single laser source, was performed. Results show the feasibility of using photoacoustics imaging to probe IVDs. The influences of exact and approximate formulations of the gradient are studied. The impact of noise on the reconstructions is also evaluated.

Experimental measurements of micromotions of the cementless intervertebral disc prostheses in the cadaver bone

BACKGROUND

Sufficient primary stability is mandatory for successful bony prosthetic incorporation. Therefore, defined micromotion values of 150 μm should not be exceeded as higher values might compromise the ingrowth of bone trabeculae to the implant surface. The aim of this study was to evaluate the primary stability of different cementless disc prosthesis in a cadaver model.

METHODS

Four different implants with different anchoring and bearing concept were tested with a target level of L4/5. 26 specimens were randomly allocated to 1 of the 4 different implants with 6 speciments in each group. Two groups were formed depending on the anchoring (spikes vs. fin) and bearing concept (non-/semi- vs. constrained). Each implant was tested regarding primary stability in a hydraulic simulator allowing simultaneous polyaxial segment movements and axial loading. The measurements were recorded on the lower plate of the prosthesis.

FINDINGS

The majority of the implants showed micromotion values below 200 μm in all planes. Only one prosthesis presented borderline longitudinal amplitudes that were significant higher than the other planes. Furthermore, significant differences were observed in the sagittal plane when comparing spike and keel anchoring. Spike anchoring implants showed superior tresults to keel anchoring implants (40 μm vs. 55 μm; p = .039), while the non-/semi-constrained bearing concept was more advantageous compared to constrained group (40 μm vs. 63 μm; p = .001).

INTERPRETATION

Spike anchoring and non-constrained implants might provide better primary stability.

A comparison of long-term efficacy of K-rod-assisted non-fusion operation and posterior lumbar interbody fusion for single-segmental lumbar disc herniation

K-rod-assisted non-fusion surgery for the treatment of lumbar disc herniation has been proven to have short-term clinical efficacy. Meanwhile, its long-term effects have not been examined. To observed the long-term clinical efficacy of K-rod-assisted non-fusion operation, this study retrospectively analyzed 22 patients with lumbar disc (L4/5) herniation who underwent K-rod-assisted non-fusion operation (n = 13) or PLIF (n = 9). They were followed-up for more than 5 years. The operation times and blood loss were significantly reduced in the K-rod group compared to the PLIF group. At the last follow-up, the clinical outcomes of the K-rod group were improved compared to those of the PLIF group as observed by the VAS score, JOABPEQ, and ODI. Imaging outcomes at the last follow-up indicated that the loss of height in the L3/4 and L5/S1 intervertebral space, the ROM of L3/4 and L5/S1, and the incidence of adjacent segment degeneration in the PLIF group were significantly higher than those in the K-rod group. According to Pfirrmann grading, Modic changes, and UCLA grading, the incidence of adjacent segment degeneration was 55.6% in the PLIF group and 15.4% in the K-rod group. Changes in spino-pelvic parameters between the two groups were as follows: pelvic index remained unchanged, pelvic tilt angle increased, and lumbar lordosis and sacral slope decreased. Therefore, compared to PLIF, single-segment lumbar disc herniation using K-rod-assisted non-fusion surgery resulted in better long-term clinical efficacy. Our results demonstrate that this procedure can delay adjacent segment degeneration after lumbar surgery.

Is Pedicle-Based Hybrid Stabilization (PBHS) protecting posterior lumbar fixation from adjacent-segment failure? Finite element analysis and comparison of different systems

INTRODUCTION

Interbody fusion is a very common surgical treatment for degenerative disc diseases. It is necessary to explain the effect of Pedicle Based Hybrid Stabilization systems (PBHS) on the lumbar spine, as there is no consensus in the literature about their performance.

HYPOTHESIS

Topping off a fusion with a PBHS may provide some protection against adjacent segment failure.

MATERIAL AND METHODS

The biomechanical effect PBHS on fused and adjacent to fusion levels were investigated, including range of motion, bending stiffness, Von Mises stress A 3D Finite Element model of the L2-S1 spine was used and modified to simulate pre and postoperative changes during combined loading. Five models instrumented with different systems [Titanium and PEEK fusion; Dynesys hybrid system; NFlex hybrid stabilization and PEEK topping off fusion] were compared to those of healthy model.

RESULTS

After hybrid instrumentation, the L4-L5 level did not lose its motion completely, NFlex hybrid stabilization system maintained 82% of flexion at the adjacent to fusion level, reduced bending stiffness by 40% in axial rotation. Dynesys hybrid system represented more restricted motion than NFlex. PEEK topping off fusion system was the most rigid one among all three systems. It increased bending stiffness at the adjacent level and increased the axial motion by 25%. High risk of rod breakage was computed for PEEK topping off system as 48.8MPa in lateral bending.

CONCLUSION

Hybrid stabilization can delay adjacent segment failure and compensate lumbar spine mobility. However, it is clear that PBHS need to be further tested before being considered for clinical use.

LEVEL OF EVIDENCE

III; well-designed computational non-experimental study.

Effects of different pedicle screw insertion depths on sagittal balance of lumbar degenerative spondylolisthesis, a retrospective comparative study

BACKGROUND

Few reports to date have evaluated the effects of different pedicle screw insertion depths on sagittal balance and prognosis after posterior lumbar interbody and fusion (PLIF) in patients with lumbar degenerative spondylolisthesis (LDS).

METHODS

A total of 88 patients with single-level PLIF for LDS from January 2018 to December 2019 were enrolled. Long screw group (Group L): 52 patients underwent long pedicle screw fixation (the leading edge of the screw exceeded 80% of the anteroposterior diameter of vertebral body). Short screw group (Group S): 36 patients underwent short pedicle screw fixation (the leading edge of the screw was less than 60% of the anteroposterior diameter of vertebral body). Local deformity parameters of spondylolisthesis including slip degree (SD) and segment lordosis (SL), spino-pelvic sagittal plane parameters including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS) and lumbar lordosis (LL), Oswestry Disability Index (ODI), and Visual Analog Scale (VAS) for back pain of both groups were compared. Postoperative complications, including vertebral fusion rate and screw loosening rate, were recorded.

RESULTS

Except that PI in Group S at the final follow-up was not statistically different from the preoperative value (P > 0.05), other parameters were significantly improved compared with preoperative values one month after surgery and at the final follow-up (P < 0.05). There was no significant difference in parameters between Group L and Group S before and one month after surgery (P > 0.05). At the final follow-up, SD, SL, LL, PT and PI-LL differed significantly between the two groups (P < 0.05). Compared with the preoperative results, ODI and VAS in both groups decreased significantly one month after surgery and at the final follow-up (P < 0.05). Significant differences of ODI and VAS were found between the two groups at the final follow-up (P < 0.05). Postoperative complications were not statistically significant between the two groups (P > 0.05).

CONCLUSIONS

PLIF can significantly improve the prognosis of patients with LDS. In terms of outcomes with an average follow-up time of 2 years, the deeper the screw depth is within the safe range, the better the spino-pelvic sagittal balance may be restored and the better the quality of life may be.

Final Long-Term Reporting from a Randomized Controlled IDE Trial for Lumbar Artificial Discs in Single-Level Degenerative Disc Disease: 7-Year Results

BACKGROUND

This study compared 7-year safety and efficacy outcomes of activL and ProDisc-L lumbar total disc replacements in patients with symptomatic, single-level lumbar degenerative disc disease (DDD). The objectives are to report 7-year outcomes of the trial, evaluate the outcomes for patients lost to follow-up, and determine whether early outcomes predict long-term outcomes.

METHODS

This was a prospective, multicenter, randomized, controlled investigational device exemption study. Eligible patients with symptomatic, single-level lumbar DDD had failed ≥6 months of nonsurgical management. Patients (N = 283) were randomized to receive activL (n = 218) or ProDisc-L (n = 65). At 7 years, data were available from 206 patients (activL, 160; ProDisc-L, 46). Logistic regression models were fit to predict 7-year outcomes for patients lost to follow-up after 2 years.

RESULTS

At 7 years, the activL group was noninferior to the ProDisc-L group on the primary composite endpoint (P = .0369). Both groups showed significant reductions in back/leg pain severity and improvements in disability index and quality-of-life relative to baseline (P < .0001). In both groups, opioid use was significantly reduced at 7 years (0%) relative to baseline (P < .01), and the overall reoperation rates were low (4.6%). activL patients showed a significantly better range of motion (ROM) for flexion-extension rotation than ProDisc-L patients (P = .0334). A significantly higher proportion of activL patients did not report serious adverse events (activL, 62%; ProDisc-L, 43%; P = .011). Predictive modeling indicated that >70% of patients (depending on outcome) lost to follow-up after 2 years would show clinically significant improvement at 7 years if improvements were achieved at 2 years.

CONCLUSIONS

The benefits of activL and ProDisc-L are maintained after 7 years, with significant improvements from baseline observed in pain, function, and opioid use. activL is more effective at preserving ROM than ProDisc-L and has a more favorable safety profile. Improvements in other primary and secondary outcomes were similar between both disc designs.

LEVEL OF EVIDENCE

1.

Revision Surgery of Total Lumbar Disk Replacement: Review of 48 Cases

STUDY DESIGN

This was a retrospective clinical review.

OBJECTIVE

The objective of this study was to analyze failure mechanisms after total lumbar disk replacement (TDR) and surgical revision strategies in patients with recurrent low back pain (LBP).

SUMMARY AND BACKGROUND DATA

Several reports indicate that TDR revision surgery carries a major risk and that it should not be recommended. The clinical results of posterior instrumented fusion using the prosthesis like an interbody cage have not been well analyzed.

MATERIALS AND METHODS

From 2003 to 2018, 48 patients with recurrent LBP after TDR underwent revision surgery. The average age was 39 years (24-61 y). The mean follow-up was 100.4 months (24.6-207.7 mo). Clinical data, self-assessment of patient satisfaction, and Oswestry Disability Index collected at each clinical control or by phone call for the older files and radiologic assessments were reviewed. The surgical revision strategy included posterior fusion in 41 patients (group A) and TDR removal and anterior fusion in 7 patients (group B), of which 6 patients had an additional posterior fixation.

RESULTS

Facet joint osteoarthritis was associated with TDR failure in 85%. In 68% the position of the prosthesis was suboptimal. Range of motion was preserved in 25%, limited in extension in 65%, and limited in flexion in 40%. Limited range of motion and facet joint osteoarthritis were significantly related (P=0.0008). The complication rate in group B was 43% including iliac vein laceration. Preoperative and 2-year follow-up Oswestry Disability Index were 25.5 and 22.0, respectively, in group A versus 27.9 and 21.3 in group B.

CONCLUSIONS

Posterior osteoarthritis was the principal cause of recurrent LBP in failed TDR. The anterior approach for revision carried a major vascular risk, whereas a simple posterior instrumented fusion leads to the same clinical results.

LEVEL OF EVIDENCE

Level IV.

Mean 5-Year Follow-Up Results of a Facet Replacement Device in the Treatment of Lumbar Spinal Stenosis and Degenerative Spondylolisthesis

OBJECTIVE

Flexible stabilization has been utilized to maintain spinal mobility in patients with early-stage lumbar spinal stenosis (LSS). Previous literature has not yet established any nonfusion solution as a viable treatment option for patients with severe posterior degeneration of the lumbar spine. This feasibility study evaluates the mean 5-year outcomes of patients treated with the Total Posterior Spine System (TOPS) facet replacement system in the surgical management of lumbar spinal stenosis and degenerative spondylolisthesis.

METHODS

Ten patients (2 men, 8 women, mean age: 59.6 years) were enrolled into a non-randomized prospective clinical study. Patients were evaluated with standing anteroposterior, lateral, flexion and extension radiographs and magnetic resonance imaging scans, back and leg pain visual analog scale scores, Oswestry Disability Index, Zurich Claudication Questionnaire and the SF-36 questionnaires, preoperatively, 6 months, 1 year, 2 years, and latest follow-up at a mean of 5 years postoperatively (range: 55-74 months). Flexion and extension standing lumbar spine radiographs were obtained at 2 years to assess range of motion at the stabilized segment.

RESULTS

The clinical outcome scores for the cohort improved significantly across all scoring systems. Radiographs at 2 years did not reveal any loss of position or loosening of metal work. There were 2 incidental durotomies and no failures at 5 years, with no patient requiring revision surgery.

CONCLUSIONS

The TOPS implant maintains clinical improvement and motion in the surgical management of LSS and spondylolisthesis, suggesting that it can be considered an option for these indications.

Allogeneic mesenchymal precursor cells treatment for chronic low back pain associated with degenerative disc disease: a prospective randomized, placebo-controlled 36-month study of safety and efficacy

BACKGROUND CONTEXT PURPOSE

Evaluate the safety and efficacy of a single intradiscal injection of STRO-3+ adult allogeneic mesenchymal precursor cells (MPCs) combined with hyaluronic acid (HA) in subjects with chronic low back pain (CLBP) associated with degenerative disc disease (DDD) through 36-month follow-up.

STUDY DESIGN/SETTING

A multicenter, randomized, controlled study conducted at 13 clinical sites (12 in the United States and 1 in Australia).

SUBJECT SAMPLE

A total of 100 subjects with chronic low back pain associated with moderate DDD (modified Pfirrmann score of 3-6) at one level from L1 to S1 for at least 6 months and failing 3 months of conservative treatment, including physical therapy were randomized in a 3:3:2:2 ratio to receive 6 million MPCs with HA, 18 million MPCs with HA, HA vehicle control, or saline control (placebo) treatment.

OUTCOME MEASURES

Subjects were clinically and radiographically evaluated at 1, 3, 6, 12, 24, and 36 months postinjection. Subject-reported outcomes including adverse events, LBP on a Visual Analog Scale (VAS), Oswestry Disability Index (ODI), SF-36 and Work Productivity and Activity Index were collected.

METHODS

Clinical and radiographic measures were collected at each visit. All randomized subjects were included in the safety assessments and analyzed based on the treatment received. Safety assessments included assessments of AEs, physical and radiographic examinations and laboratory testing. Efficacy assessments evaluated changes in VAS, ODI, and modified Pfirrmann (MP) scores between all active and control groups, respectively. Assessments included least squares mean (Mean), LS mean change from baseline (Mean Change) and responder analyses in order to assess the clinical significance of observed changes from baseline. The population for efficacy assessments was adjusted for the confounding effects of post-treatment interventions (PTIs). This study was conducted under an FDA Investigational New Drug application sponsored and funded by Mesoblast.

RESULTS

There were significant differences between the control and MPC groups for improvement in VAS and ODI. The PTI-corrected VAS and ODI Means and Mean Change analyses; the proportion of subjects with VAS ≥30% and ≥50% improvement from baseline; absolute VAS score ≤20; and ODI reduction ≥10 and ≥15 points from baseline showed MPC therapy superior to controls at various time points through 36 months. Additionally, the proportion of subjects achieving the minimally important change and clinically significant change composite endpoints for the MPC groups was also superior compared with controls at various time points from baseline to 36 months. There were no significant differences in change in MP score from baseline across the groups. There were also no statistically significant differences in change in modified MP score at the level above or below the level treated between study arms. Both the procedure and treatment were well tolerated and there were no clinical symptoms of immune reaction to allogeneic MPCs. There was a low rate of Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Events, and the rates of these events in the MPC groups were not significantly different from the control groups. One TEAE of severe back pain was possibly related to study agent and one TEAE of implantation site infection was considered to be related to the study procedure.

CONCLUSIONS

Results provide evidence that intradiscal injection of MPCs could be a safe, effective, durable, and minimally invasive therapy for subjects who have CLBP associated with moderate DDD.

In vivo intervertebral kinematics and disc deformations of the human cervical spine during walking

The kinematics of the cervical spine during various functional neck motions has been widely reported. However, no data has been reported on the cervical intervertebral kinematics during walking, the most frequently performed daily functional activity. In this study, we evaluated cervical kinematics and disc deformation of asymptomatic subjects during a gait cycle using a dual fluoroscopic imaging system. Our measurements showed that the vertical translation of the cervical spine (1.6 ± 0.1 Hz) occurred at twice the frequency of the gait cycle (0.8 ± 0.1 Hz). The overall ranges of motion (ROMs) of the entire (C2-T1) cervical spine were 5.0 ± 3.1° in the flexion-extension rotation, 3.4 ± 1.0° in the lateral-bending rotation, and 5.8 ± 2.1° in the axial-twisting rotation during walking. Each intervertebral disc (measured at the disc centre location) dynamically deformed in its axial direction in a range of 16.2 ± 5.7% ~ 23.7 ± 8.7% (without significant differences among different segment levels, p > 0.05), similar to the ranges of shear deformations of the same disc (p > 0.05, except for the C7-T1 disc, where p = 0.010). These data could be useful for improvements of diagnosis and treatment methods of cervical pathologies.

Prognostic Factors for Adjacent Segment Disease After L4-L5 Lumbar Fusion

BACKGROUND

Adjacent segment disease (ASD) is an important consideration during decision making for lumbar spinal fusion.

OBJECTIVE

To identify risk factors for development of ASD after L4-L5 fusion and differences in incidence between rostral and caudal ASD.

METHODS

We retrospectively reviewed all consecutive patients at a single institution who underwent first-time spinal fusion at the L4-L5 level for degenerative spinal disease over a 10-yr period, using posterolateral pedicular screw fixation with or without posterior interbody fusion. ASD was defined as clinical and radiographic evidence of degenerative spinal disease requiring reoperation at the level rostral (L3-L4) or caudal (L5-S1) to the index fusion.

RESULTS

Among 131 identified patients, the incidence of ASD requiring reoperation was 25.2% (n = 33). Twenty-four cases (18.3% of the entire cohort) developed rostral ASD (segment L3-L4), 3 cases (2.3%) developed caudal (L5-S1), and 6 cases (4.6%) developed bilateral ASD (both rostral and caudal). Cumulatively, the incidence of caudal ASD was significantly lower than rostral ASD (P < .001). Following multivariate logistic regression for factors associated with ASD reoperation, decompression of segments outside the fusion construct was associated with higher ASD rates (odds ratio [OR] = 2.68, P = .039), as was female gender (OR = 3.55, P = .011), whereas older age was associated with lower ASD incidence (OR = 0.95, P = .011).

CONCLUSION

When considering posterior L4-L5 fusion, surgeons should refrain from prophylactic procedures in the L5-S1 level, without clinical indications, because ASD incidence on that segment is reassuringly low.

Efficacy of interspinous device on adjacent segment degeneration after single level posterior lumbar interbody fusion: a minimum 2-year follow-up

OBJECTIVE

Adjacent segment degeneration (ASD) is a well-known problem of posterior lumbar interbody fusion (PLIF). A device for interspinous assisted motion (DIAM) has been recently applied at the adjacent segment to pedicle screw instrumentation to create a dynamic transition zone. The aim of this study was to determine whether DIAM implantation at the adjacent segment could reduce the occurrence of radiologic and symptomatic ASD.

METHODS

This retrospective study reviewed 51 patients who underwent PLIF with or without DIAM between 2005 and 2016. They were followed up for more than 24 months. The mean follow-up was over 5 years. Fourteen patients underwent PLIF with DIAM implantation at the cephalad level (Group A) and 37 patients received PLIF only (Group B). In radiologic ASD, several parameters were measured using pre- and post-operative radiographs and magnetic resonance image for lumbar degenerative disease and paraspinal muscle. Visual analogue scale (VAS) and Roland-Morris Disability Questionnaire (RMDQ) scores of back and leg were used to investigate symptomatic ASD.

RESULTS

In postoperative radiographic changes, disc height narrowing and progression of spondylolisthesis at adjacent segment were significantly less in group A than those in group B (0.58 mm versus 1.17 mm, p = 0.038 and 0.30 mm versus 1.69 mm, p = 0.041, respectively). In clinical assessments, back VAS and RMDQ scores improved significantly more in group A (-4.07 versus -2.54, p = 0.029 and -7.57 versus -5.43, p = 0.016, respectively).

CONCLUSION

DIAM implantation with single-level PLIF could prevent disc height narrowing and progression of spondylolisthesis at adjacent segment. Clinically, DIAM implantation reduced back pain and disability. Therefore, DIAM implantation could help slow the progression of both radiologic and symptomatic ASD.

A Case of Thoracic Spondylosis Deformans and Multilevel Instrumented Spinal Fusion in an 84-Year-Old Male

Spondylosis deformans is a type of spinal claw osteophytosis which can be found on the anterolateral vertebral bodies of any region, and which consists of protrusions of intervertebral disc tissue covered by a bony shell. We report here a case of thoracic spondylosis deformans and multilevel instrumented fusion found during routine dissection of a cadaver. Theories of the etiology of this condition are reviewed in general, and with respect to this specific case and the potential interaction of the presenting comorbidities. The clinical implications of these osteophytes, including musculoskeletal and visceral sequelae, are also discussed.

Percutaneous transforaminal endoscopic decompression for lumbar spinal stenosis with degenerative spondylolisthesis in the elderly

OBJECTIVES

Percutaneous transforaminal endoscopic decompression (PTED) under local anesthesia is rarely performed for lumbar spinal stenosis (LSS) with degenerative lumbar spondylolisthesis (DLS) because of the limited field of vision, inherent instability, etc. The objective of this study was to describe the procedure of the PTED technique and to demonstrate the early clinical outcomes.

PATIENTS AND METHODS

From January 2017 to January 2019, 40 consecutive patients aged 60 and older were diagnosed with LSS with DLS in our institution and underwent PTED. All patient were followed up to 1 year postoperatively. The clinical outcomes were evaluated using the visual analogue scale (VAS), Oswestry Disability Index (ODI) and modified MacNab criteria.

RESULTS

The mean age was 70.2 ± 7.1 years. Follow-up ranged from 12 to 24 months. The mean ± SD values of the preoperative VAS leg pain and ODI scores were 7.5 ± 1.1 and 67.3 ± 9.3, respectively. The scores improved to 2.2 ± 1.1 and 20.7 ± 8.1 at 12 months postoperatively. The outcomes of the modified MacNab criteria showed that 87.5 % of patients obtained a good-to-excellent rate. The percent slippage of spondylolisthesis before surgery (10.8 ± 2.6 %) and at the end of follow-up (11.0 ± 2.4 %) was not significantly different. One patient had a dural tear and intracranial hypertension, and one patient had tibialis anterior weakness.

CONCLUSION

PTED under local anesthesia could be an effective treatment method for LSS with DLS in elderly patients. However, potential complications still require further evaluation.

Subsidence after total lumbar disc replacement is predictable and related to clinical outcome

Purpose

As yet, there are no studies describing a relationship between radiographic subsidence after lumbar total disc replacement (TDR) and patient symptoms. To investigate if subsidence, in terms of penetrated bone volume or angular rotation over time (ΔPBV and ΔAR), is related to clinical outcome. To assess if subsidence can be predicted by position implant asymmetry (IA) or relative size of the TDR, areal undersizing index (AUI) on direct post-operative radiographs.

Methods

Retrospective cohort study consists of 209 consecutive patients with lumbar TDR for degenerative disc disease. A three-dimensional graphical representation of the implant in relation to the bony endplates was created on conventional radiographs. Consequently, the PBV, AR, IA and AUI were calculated, direct post-operative (DPO) and at last follow-up (LFU). For clinical evaluation, patients with substantial pain (VAS ≥ 50) and malfunction (ODI ≥ 40) were considered failures.

Results

At a mean follow-up of 16.7 years, 152 patients (73%) were available for analysis. In 32 patients, revision by spinal fusion had been performed. Both ΔAR (4.33° vs. 1.83°, p = 0.019) and ΔPBV (1448.4 mm3 vs. 747.3 mm3, p = 0.003) were significantly higher in the failure-compared to the success-group. Using ROC curves, thresholds for symptomatic subsidence were defined as ΔPBV ≥ 829 mm3 or PBV-LFU ≥ 1223 mm3 [area under the curve (AUC) 0.723, p = 0.003 and 0.724, p = 0.005, respectively]. Associations between symptomatic subsidence and AUI-DPO ≥ 0.50 (AUC 0.750, p = 0.002) and AR-DPO ≥ 3.95° (AUC 0.690, p = 0.022) were found.

Conclusion

Subsidence of a TDR is associated with a worse clinical outcome. The occurrence of subsidence is higher in case of incorrect placement or shape mismatch.

A novel dynamic fixation system with biodegradable components on lumbar fusion between articular processes in a canine model

The objective of this study was to design a novel dynamic fixation system with biodegradable components, apply it for lumbar fusion between articular processes and compare the fusion results and biomechanical changes to those of conventional rigid fixation. The novel dynamic fixation system was designed using a finite element model, stress distributions were compared and 24 mongrel dogs were randomly assigned to two groups and subjected to either posterior lumbar fusion surgery with a novel dynamic fixation system or titanium rods at the L5-L6 segments. Lumbar spines were assessed in both groups to detect radiographic, manual palpation and biomechanical changes. Histological examination was performed on organs and surrounding tissues. In the novel dynamic fixation system, stress was mainly distributed on the meshing teeth of the magnesium alloy spacer. The magnesium alloy components maintained their initial shape 8 weeks after the operation, but the meshing teeth were almost completely degraded at 16 weeks. The novel dynamic fixation system revealed an increased lateral bending range of motion at 8 weeks; however, both groups showed similar radiographic grades, fusion stiffness, manual palpation and histological results. The novel dynamic fixation system design is suitable, and its degradation in vivo is safe. The novel dynamic fixation system can be applied for posterior lumbar fusion between articular processes and complete the fusion like titanium rods.

Load-transfer in the human vertebral body following lumbar total disc arthroplasty: Effects of implant size and stiffness in axial compression and forward flexion

Adverse clinical outcomes for total disc arthroplasty (TDA), including subsidence, heterotopic ossification, and adjacent-level vertebral fracture, suggest problems with the underlying biomechanics. To gain insight, we investigated the role of size and stiffness of TDA implants on load-transfer within a vertebral body. Uniquely, we accounted for the realistic multi-scale geometric features of the trabecular micro-architecture and cortical shell. Using voxel-based finite element analysis derived from a micro-computed tomography scan of one human L1 vertebral body (74-μm-sized elements), a series of generic elliptically shaped implants were analyzed. We parametrically modeled three implant sizes (small, medium [a typical clinical size], and large) and three implant materials (metallic, E = 100 GPa; polymeric, E = 1 GPa; and tissue-engineered, E = 0.01 GPa). Analyses were run for two load cases: 800 N in uniform compression and flexion-induced anterior impingement. Results were compared to those of an intact model without an implant and loaded instead via a disc-like material. We found that TDA implantation increased stress in the bone tissue by over 50% in large portions of the vertebra. These changes depended more on implant size than material, and there was an interaction between implant size and loading condition. For the small implant, flexion increased the 98th-percentile of stress by 32 ± 24% relative to compression, but the overall stress distribution and trabecular-cortical load-sharing were relatively insensitive to loading mode. In contrast, for the medium and large implants, flexion increased the 98th-percentile of stress by 42 ± 9% and 87 ± 29%, respectively, and substantially re-distributed stress within the vertebra; in particular overloading the anterior trabecular centrum and cortex. We conclude that TDA implants can substantially alter stress deep within the lumbar vertebra, depending primarily on implant size. For implants of typical clinical size, bending-induced impingement can substantially increase stress in local regions and may therefore be one factor driving subsidence in vivo.

Pathomechanism of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the main contributor to low back pain, which is a leading cause of disability worldwide. Although substantial progress has been made in elucidating the molecular mechanisms of IDD, fundamental and long-lasting treatments for IDD are still lacking. With increased understanding of the complex pathomechanism of IDD, alternative strategies for treating IDD can be discovered. A brief overview of the prevalence and epidemiologic risk factors of IDD is provided in this review, followed by the descriptions of anatomic, cellular, and molecular structure of the intervertebral disc as well as the molecular pathophysiology of IDD. Finally, the recent findings of intervertebral disc progenitors are reviewed and the future perspectives are discussed.

Biomechanical analysis of single-level interbody fusion with different internal fixation rod materials: a finite element analysis

Background

Lumbar spinal fusion with rigid spinal fixators as one of the high risk factors related to adjacent-segment failure. The purpose of this study is to investigate how the material properties of spinal fixation rods influence the biomechanical behavior at the instrumented and adjacent levels through the use of the finite element method.

Methods

Five finite element models were constructed in our study to simulate the human spine pre- and post-surgery. For the four post-surgical models, the spines were implanted with rods made of three different materials: (i) titanium rod, (ii) PEEK rod with interbody PEEK cage, (iii) Biodegradable rod with interbody PEEK cage, and (iv) PEEK cage without pedicle screw fixation (no rods).

Results

Fusion of the lumbar spine using PEEK or biodegradable rods allowed a similar ROM at both the fusion and adjacent levels under all conditions. The models with PEEK and biodegradable rods also showed a similar increase in contact forces at adjacent facet joints, but both were less than the model with a titanium rod.

Conclusions

Flexible rods or cages with non-instrumented fusion can mitigate the increased contact forces on adjacent facet joints typically found following spinal fixation, and could also reduce the level of stress shielding at the bone graft.

Long-term clinical outcome of the Charité III total lumbar disc replacement

Purpose

To compare the long-term clinical results and complications of two revision strategies for patients with failed total disc replacements (TDRs).

Methods

In 19 patients, the TDR was removed and the intervertebral defect was filled with a femoral head bone strut graft. In addition, instrumented posterolateral fusion was performed (removal group). In 36 patients, only a posterolateral instrumented fusion was performed (fusion group). Visual analogue scale (VAS) for pain and Oswestry Disability Index (ODI) were completed pre- and post-revision surgery. Intra- and post-operative complications of both revision strategies were assessed.

Results

The median follow-up was 12.3 years (range 5.3–24.3). In both the removal and fusion group, a similar (p = 0.515 and p = 0419, respectively) but significant decrease in VAS- (p = 0.001 and p = 0.001, respectively) and ODI-score (p = 0.033 and p = 0.013, respectively) at post-revision surgery compared to pre-revision surgery was seen. A clinically relevant improvement in VAS- and ODI-score was found in 62.5% and 43.8% in the removal group and in 43.5% and 39.1% in the fusion group (p = 0.242 and p = 0.773, respectively). Removal of the TDR was associated with substantial intra-operative complications such as major vessel bleeding and ureter lesion. The percentage of late reoperations for complications such as pseudarthrosis was comparable for both revision strategies.

Conclusions

Revision of a failed TDR is clinically beneficial in about half of the patients. No clear benefits for additional TDR removal as compared to posterolateral instrumented fusion alone could be identified. Particularly, when considering the substantial risks and complications, great caution is warranted with removal of the TDR.

Graphic abstract

These slides can be retrieved under Electronic Supplementary Material.

Analysis of clinical effect and radiographic outcomes of Isobar TTL system for two-segment lumbar degenerative disease: a retrospective study

Background

Nonfusion fixation is an effective way to treat lumbar degeneration. In the present study, we analyzed the clinical effects and radiographic outcomes of the Isobar TTL system used to treat two-segment lumbar degenerative disease.

Method

Forty-one patients diagnosed with two-segment lumbar degenerative disease underwent surgical implantation of the Isobar TTL dynamic stabilization system (n = 20) or a rigid system (n = 21) from January 2013 to June 2017. The mean follow-up time was 23.6 (range 15–37) months. Clinical results were evaluated with the Oswestry Disability Index (ODI), modified Macnab criteria, and the visual analog score (VAS). Radiographic evaluations included the height of the intervertebral space and the range of motion (ROM) of the treated and adjacent segments. The intervertebral disc signal was classified using the modified Pfirrmann grading system and the University of California at Los Angeles (UCLA) system.

Results

The clinical results, including the ODI and VAS, showed that there was significant improvement in the two groups after implantation and that the difference between the two groups was not significant. In addition, the clinical efficacy indicated by the modified Macnab criteria for the two groups was similar. Radiological outcomes included the height of the intervertebral space, lumbar mobility, and intervertebral disc signal. The height of the intervertebral space of the upper adjacent segment L2/3 in the rigid group was significantly lower than that in the Isobar TTL group at the last follow-up. Furthermore, the number of ROMs of the fixed-segment L3/4 in the Isobar TTL group was significantly less than that before implantation, suggesting that the fixed-segment ROMs in the Isobar TTL group were limited. In addition, the ROM of the upper adjacent segment L2/3 in the last follow-up of the rigid group increased significantly, while that of the Isobar TTL group did not change after implantation. Finally, the incidence of adjacent-segment degeneration (ASD) was significantly greater in the rigid group than in the Isobar TTL group according to the UCLA system.

Conclusion

The Isobar TTL system can be clinically effective for treating two-segment lumbar degenerative disease. Compared with rigid fixation, the Isobar TTL system yielded better radiographic outcomes and maintained the mobility of the treated segments with less impact on the proximal adjacent segment.

Multiscale and multimodal structure-function analysis of intervertebral disc degeneration in a rabbit model

OBJECTIVES

The objective of this study was to perform a quantitative analysis of the structural and functional alterations in the intervertebral disc during in vivo degeneration, using emerging tools that enable rigorous assessment from the microscale to the macroscale, as well as to correlate these outcomes with noninvasive, clinically relevant imaging parameters.

DESIGN

Degeneration was induced in a rabbit model by puncturing the annulus fibrosus (AF) with a 16-gauge needle. 2, 4, 8, and 12 weeks following puncture, degenerative changes in the discs were evaluated via magnetic resonance imaging (MRI), whole motion segment biomechanics, atomic force microscopy, histology and polarized light microscopy, immunohistochemistry, biochemical content, and second harmonic generation imaging.

RESULTS

Following puncture, degeneration was evident through marked changes in whole disc structure and mechanics. Puncture acutely compromised disc macro and microscale mechanics, followed by progressive stiffening and remodeling. Histological analysis showed substantial anterior fibrotic remodeling and osteophyte formation, as well as an overall reduction in disc height, and disorganization and infolding of the AF lamellae into the NP space. Increases in NP collagen content and aggrecan breakdown products were also noted within 4 weeks. On MRI, NP T2 was reduced at all post-puncture time points and correlated significantly with microscale indentation modulus.

CONCLUSION

This study defined the time dependent changes in disc structure-function relationships during IVD degeneration in a rabbit annular injury model and correlated degeneration severity with clinical imaging parameters. Our findings identified AF infolding and occupancy of the space as a principle mechanism of disc degeneration in response to needle puncture, and provide new insights to direct the development of novel therapeutics.

Long-term clinical outcome of two revision strategies for failed total disc replacements

PURPOSE

To compare the long-term clinical results and complications of two revision strategies for patients with failed total disc replacements (TDRs).

METHODS

In 19 patients, the TDR was removed and the intervertebral defect was filled with a femoral head bone strut graft. In addition, instrumented posterolateral fusion was performed (removal group). In 36 patients, only a posterolateral instrumented fusion was performed (fusion group). Visual Analogue Scale (VAS) for pain and Oswestry Disability Index (ODI) were completed pre- and post-revision surgery. Intra- and post-operative complications of both revision strategies were assessed.

RESULTS

The median follow-up was 12.3 years (range 5.3-24.3). In both the removal and fusion groups, a similar (p = 0.515 and p = 0419, respectively) but significant decrease in VAS (p = 0.001 and p = 0.001, respectively) and ODI score (p = 0.033 and p = 0.013, respectively) at post-revision surgery compared to pre-revision surgery was seen. A clinically relevant improvement in VAS and ODI score was found in 62.5% and 43.8% in the removal group and in 43.5% and 39.1% in the fusion group (p = 0.242 and p = 0.773, respectively). Removal of the TDR was associated with substantial intra-operative complications such as major vessel bleeding and ureter lesion. The percentage of late re-operations for complications such as pseudarthrosis were comparable for both revision strategies.

CONCLUSIONS

Revision of a failed TDR is clinically beneficial in about half of the patients. No clear benefits for additional TDR removal as compared to posterolateral instrumented fusion alone could be identified. In particular, when considering the substantial risks and complications, great caution is warranted with removal of the TDR. These slides can be retrieved under Electronic Supplementary Material.

Trans-foraminal endoscopic uniportal decompression in degenerative lumbar spondylolisthesis: a technical and case report

Background

Degenerative spondylolisthesis is a common spinal pathology. Traditionally, spinal fusion is an accepted standard surgical treatment for listhesis. But fusion is a major intervention with its known pitfalls. With technological progression, minimally invasive spinal fusion (MISF) procedures are becoming mainstream. Percutaneous trans-foraminal endoscopic lumbar discectomy/decompressions (PTELD) without stabilization has many advantages over even a MISF for select group of patients.

Case presentation

In this case report, we describe using a uniportal unilateral trans-foraminal approach (TFA) for stable listhesis with lumbar disc herniation (LDH) causing chronic bilateral radicular symptoms and back pain with acute exacerbation. Under local anesthesia, we used a flat entry for PTELD, which facilitates an approach to both disc sides ventrally and even dorsal aspect lateral recess decompression on the dominant ipsilateral side. No fixation was done. An excellent outcome is obtained immediately at 6 weeks and maintained at 39 months of follow-up.

Conclusion

PTELD is worth considering as an intermediate procedure before fusion is offered in lateral recess stenosis in stable listhesis patients who have consented and understand the progressive cascade of spinal degeneration.

An upper bound computational model for investigation of fusion effects on adjacent segment biomechanics of the lumbar spine

Prediction of the biomechanical effects of fusion surgery on adjacent segments is a challenge in computational biomechanics of the spine. In this study, a two-segment L3-L4-L5 computational model was developed to simulate the effects of spinal fusion on adjacent segment biomechanical responses under a follower load condition. The interaction between the degenerative segment (L4-5) and the adjacent segment (L3-4) was simulated using an equivalent follower spring. The spring stiffness was calibrated using a rigid fusion of a completely degenerated disc model at the L4-5 level, resulting in an upper bound response at the adjacent (L3-4) segment. The obtained upper bound equivalent follower spring was used to simulate the upper bound biomechanical responses of fusion of the disc with different degeneration grades. It was predicted that as the disc degeneration grade at the degenerative segment decreased, the effect on the adjacent segment responses decreased accordingly after fusion. The data indicated that the upper bound computational model can be a useful computational tool for evaluation of the interaction between segments and for investigation of the biomechanical mechanisms of adjacent segment degeneration after fusion.

Bicortical Screw Purchase at Upper Instrumented Vertebra (UIV) Can Cause UIV Fracture After Adult Spinal Deformity Surgery: A Finite Element Analysis Study

OBJECTIVE

To examine the biomechanical stress distribution at the upper instrumented vertebra (UIV) according to unicortical- and bicortical purchase model by finite element analysis (FEA).

METHODS

A T8 to Sacrum with implant finite element model was developed and validated. The pedicle screws were unicortically or bicortically inserted from T10 to L5, and each model was compared and the von Mises (VM) yield stress of T10 was calculated. According to the motion (flexion, extension, lateral bending, and axial rotation) of spine, boundary condition values were set as 15°, 15°, 10°, 4°.

RESULTS

Although the 2 stress values did not show a significant difference between the unicortical- and bicortical purchase models in the flexion and extension, bicortical purchase model showed a larger stress distribution. However, the asymmetric behavior was significantly greater in the case of lateral bending (0.802 MPa vs. 0.489 MPa) and the rotation (5.545 MPa vs. 4.905 MPa). The greater stress was observed on the spinal body surface abutting the implanted screw. Although the maximum stress was observed around the implanted screw in the bicortical purchase model under axial loading, the VM stress of both models was not significantly different.

CONCLUSION

Bicortical purchase model showed a larger stress distribution than the unicortical model, especially in the case of lateral bending and the rotation behavior. Our biomechanical simulation by FEA indicates that bicortical fixation at UIV can be a risk factor for early UIV compression fracture after adult spinal deformity surgery.