Off-Label Bone Morphogenetic Protein 2 Use Results in Successful Posterolateral Lumbar Fusion in a Veteran Population.

INTRODUCTION: Patients within the US Veterans Health Administration (VA) system have higher rates of comorbidities and chronic pain, increasing risks of complications/poor outcomes following spine surgery. Although the use of bone morphogenetic protein 2 (BMP-2) is established for anterior lumbar interbody fusion, its indications for off-label use in posterolateral fusion are unclear. The objective of this study was to evaluate safety and utility of BMP-2 in posterolateral fusion through a 15-year experience at the VA. METHODS: Patients underwent posterolateral lumbosacral fusions with BMP-2 by a single VA surgeon from January 1, 2005, to January 1, 2020. The primary outcome was fusion assessed through postoperative radiographs. Secondary outcomes included adjacent segment disease (ASD) and postoperative pain clinic utilization. RESULTS: Sixty-eight patients underwent lumbosacral posterolateral fusion with BMP-2; 77.9% were discharged home and had no postoperative complications. All patients achieved bony fusion at a mean of 113.3 ± 59.9 days postoperatively. Five patients were diagnosed with cancer postoperatively, and eight patients required revision for ASD. No notable predictors of ASD exist. Preoperative opioid use predicted postoperative pain clinic utilization. DISCUSSION: Posterolateral lumbar fusion with BMP-2 in veterans yields high fusion rates and favorable complication profiles and should be considered in multimorbid hosts. STUDY DESIGN: Retrospective review of prospectively collected data.

Focused Perioperative Nutritional Supplementation Reduces Wound Complications in Patients Undergoing Spinal Fusion Surgery.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To evaluate intensive postoperative nutritional supplementation on wound healing complications and outcomes after spinal fusion surgery. BACKGROUND: Poor nutritional status leads to inferior postoperative outcomes by increasing mortality and predisposing patients to infection and wound healing complications. While perioperative nutritional supplementation has shown promise in mitigating these risks, there is a paucity of literature regarding specific nutritional routines in spinal fusion surgery. METHODS: A retrospective analysis was conducted on patients who underwent spinal fusion surgery between 2019 and 2022. Demographic and nutritional data, including preoperative prealbumin levels (PAB) and postoperative supplemental diet, were examined. Primary endpoints included wound complications, with secondary outcomes assessing Oswestry Disability Index (ODI) and Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Health (PH) scores. Statistical analyses included unpaired t-tests and Chi-squared/Fischer's exact tests with significance set at P<0.05. RESULTS: Patients receiving the supplemental diet (n=229) demonstrated fewer wound complications (7% vs. 21%, P=0.004) and reoperations (3% vs. 11%, P=0.016) compared to those without supplementation (n=56). No significant differences were observed in preoperative or postoperative PROMIS PH or ODI scores. Patients with normal preoperative PAB had more wound complications without the supplemental diet (5% vs. 18%, P=0.025). A similar trend was seen in the patients with low preoperative PAB (12% vs. 26%, P=0.12). CONCLUSION: Postoperative nutritional supplementation significantly reduces wound complications after spinal fusion surgery in a cost-effective manner. This study underscores the modifiability of certain perioperative risk factors and suggests that nutritional strategies can mitigate potential complications.

Formal Radiologist Interpretations of Intraoperative Spine Radiographs Have Low Clinical Value.

STUDY DESIGN: Retrospective cohort. OBJECTIVE: To evaluate the clinical relevance, usefulness, and financial implications of intraoperative radiograph interpretation by radiologists in spine surgery. SUMMARY OF BACKGROUND DATA: Due to rising health care costs, spine surgery is under scrutiny to maximize value-based care. Formal radiographic analysis remains a potential source of unnecessary health care costs, especially for intraoperative radiographs. MATERIALS AND METHODS: A retrospective cohort analysis was performed on all adult elective spine surgeries at a single institution between July 2020 and July 2021. Demographic and radiographic data were collected, including intraoperative localization and post-instrumentation radiographs. Financial data were obtained through the institution's price estimator. Radiographic characteristics included time from radiographic imaging to completion of radiologist interpretation report, completion of radiologist interpretation report before the conclusion of surgical procedure, clinical relevance, and clinical usefulness. Reports were considered clinically relevant if the spinal level of the procedure was described and clinically useful if completed before the conclusion of the procedure and deemed clinically relevant. RESULTS: Four hundred eighty-one intraoperative localization and post-instrumentation radiographs from 360 patients revealed a median delay of 128 minutes between imaging and completion of the interpretive report. Only 38.9% of reports were completed before the conclusion of surgery. There were 79.4% deemed clinically relevant and only 33.5% were clinically useful. Localization reports were completed more frequently before the conclusion of surgery (67.2% vs. 34.4%) but with lower clinical relevance (90.1% vs. 98.5%) and clinical usefulness (60.3% vs. 33.6%) than post-instrumentation reports. Each patient was charged $32 to $34 for the interpretation fee, cumulating a minimum total cost of $15,392. CONCLUSIONS: Formal radiographic interpretation of intraoperative spine radiographs was of low clinical utility for spine surgeons. Institutions should consider optimizing radiology workflows to improve timeliness and clinical relevance or evaluate the necessity of reflexive consultation to radiology for intraoperative imaging interpretation to ensure that value-based care is maximized during spine surgeries. LEVEL OF EVIDENCE: 3.

Modified Clavien-Dindo-Sink Classification System for operative complications in adult spine surgery.

OBJECTIVE: Currently there is no standardized mechanism to describe or compare complications in adult spine surgery. Thus, the purpose of the present study was to modify and validate the Clavien-Dindo-Sink complication classification system for applications in spine surgery. METHODS: The Clavien-Dindo-Sink complication classification system was evaluated and modified for spine surgery by four fellowship-trained spine surgeons using a consensus process. A distinct group of three fellowship-trained spine surgeons completed a randomized electronic survey grading 71 real-life clinical case scenarios. The survey was repeated 2 weeks after its initial completion. Fleiss' and Cohen's kappa (κ) statistics were used to evaluate interrater and intrarater reliabilities, respectively. RESULTS: Overall, interobserver reliability during the first and second rounds of grading was excellent with a κ of 0.847 (95% CI 0.785-0.908) and 0.852 (95% CI 0.791-0.913), respectively. In the first round, interrater reliability ranged from good to excellent with a κ of 0.778 for grade I (95% CI 0.644-0.912), 0.698 for grade II (95% CI 0.564-0.832), 0.861 for grade III (95% CI 0.727-0.996), 0.845 for grade IV-A (95% CI 0.711-0.979), 0.962 for grade IV-B (95% CI 0.828-1.097), and 0.960 for grade V (95% CI 0.826-1.094). Intraobserver reliability testing for all three independent observers was excellent with a κ of 0.971 (95% CI 0.944-0.999) for rater 1, 0.963 (95% CI 0.926-1.001) for rater 2, and 0.926 (95% CI 0.869-0.982) for rater 3. CONCLUSIONS: The Modified Clavien-Dindo-Sink Classification System demonstrates excellent interrater and intrarater reliability in adult spine surgery cases. This system provides a useful framework to better communicate the severity of spine-related complications.

MicroRNA-29a: a novel target for non-operative management of symptomatic lumbar spinal stenosis.

PURPOSE: Lumbar spinal stenosis (LSS) is the most common reason for spinal surgery in patients over the age of 65, and there are few effective non-surgical treatments. Therefore, the development of novel treatment or preventative modalities to decrease overall cost and morbidity associated with LSS is an urgent matter. The cause of LSS is multifactorial; however, a significant contributor is ligamentum flavum hypertrophy (LFH) which causes mechanical compression of the cauda equina or nerve roots. We assessed the role of a novel target, microRNA-29a (miR-29a), in LFH and investigated the potential for using miR-29a as a therapeutic means to combat LSS. METHODS: Ligamentum flavum (LF) tissue was collected from patients undergoing decompressive surgery for LSS and assessed for levels of miR-29a and pro-fibrotic protein expression. LF cell cultures were then transfected with either miR-29a over-expressor (agonist) or inhibitor (antagonist). The effects of over-expression and under-expression of miR-29a on expression of pro-fibrotic proteins was assessed. RESULTS: We demonstrated that LF at stenotic levels had a loss of miR-29a expression. This was associated with greater LF tissue thickness and higher mRNA levels of collagen I and III. We also demonstrated that miR29-a plays a direct role in the regulation of collagen gene expression in ligamentum flavum. Specifically, agents that increase miR-29a may attenuate LFH, while those that decrease miR-29a promote fibrosis and LFH. CONCLUSION: This study demonstrates that miR-29a may potentially be used to treat LFH and provides groundwork to initiate the development of a therapeutic product for LSS.

Transcranial Motor Evoked Potentials as a Predictive Modality for Postoperative Deficit in Cervical Spine Decompression Surgery - A Systematic Review and Meta-Analysis.

STUDY DESIGN: Systematic Review and Meta-analysis. OBJECTIVE: The purpose of this study was to evaluate whether transcranial motor evoked potential (TcMEP) alarms can predict postoperative neurologic complications in patients undergoing cervical spine decompression surgery. METHODS: A meta-analysis of the literature was performed using PubMed, Web of Science, and Embase to retrieve published reports on intraoperative TcMEP monitoring for patients undergoing cervical spine decompression surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR), of overall, reversible, and irreversible TcMEP changes for predicting postoperative neurological deficit were calculated. A subgroup analysis was performed to compare anterior vs posterior approaches. RESULTS: Nineteen studies consisting of 4608 patients were analyzed. The overall incidence of postoperative neurological deficits was 2.58% (119/4608). Overall TcMEP changes had a sensitivity of 56%, specificity of 94%, and DOR of 19.26 for predicting deficit. Reversible and irreversible changes had sensitivities of 16% and 49%, specificities of 95% and 98%, and DORs of 3.54 and 71.74, respectively. In anterior procedures, TcMEP changes had a DOR of 17.57, sensitivity of 49%, and specificity of 94%. In posterior procedures, TcMEP changes had a DOR of 21.01, sensitivity of 55%, and specificity of 94%. CONCLUSION: TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in cervical spine decompression surgery. Patients with new postoperative neurological deficits were 19 times more likely to have experienced intraoperative TcMEP changes than those without new deficits, with irreversible TcMEP changes indicating a much higher risk of deficit than reversible TcMEP changes.

Examining the safety profile of a standard dose tranexamic acid regimen in spine surgery.

OBJECTIVE: Perioperative blood loss during spinal surgery is associated with complications and in-hospital mortality. Weight-based administration of tranexamic acid (TXA) has the potential to reduce blood loss and related complications in spinal surgery; however, evidence for standardized dosing is lacking. The purpose of this study was to evaluate the impact of a standardized preoperative 2 g bolus TXA dosing regimen on perioperative transfusion, blood loss, thromboembolic events, and postoperative outcomes in spine surgery patients. METHODS: An institutional review board approved this retrospective review of prospectively enrolled adult spine patients (> 18 years of age). Patients were included who underwent elective and emergency spine surgery between September 2018 and July 2021. Patients who received a standardized 2 g dose of TXA were compared to patients who did not receive TXA. The primary outcome measure was perioperative transfusion. Secondary outcomes included estimated blood loss and thromboembolic or other perioperative complications. Descriptive statistics were calculated, and continuous variables were analyzed with the two-tailed independent t-test, while categorical variables were analyzed with the Fisher's exact test or chi-square test. Stepwise multivariate regression analysis was performed to examine independent risk factors for perioperative outcomes. RESULTS: TXA was administered to 353 of 453 (78%) patients, and there were no demographic differences between groups. Although the TXA group had more operative levels and a longer operative time, the transfusion rate was not different between the TXA and no-TXA groups (7.4% vs 8%, p = 0.83). Stepwise multivariate regression found that the number of operative levels was an independent predictor of perioperative transfusion and that both operative levels and operative time were correlated with estimated blood loss. TXA was not identified as an independent predictor of any postoperative complication. CONCLUSIONS: A standardized preoperative 2 g bolus TXA dosing regimen was associated with an excellent safety profile, and despite increased case complexity in terms of number of operative levels and operative time, patients treated with TXA did not require more blood transfusions than patients not treated with TXA.

Utility of transcranial motor-evoked potential changes in predicting postoperative deficit in lumbar decompression and fusion surgery: a systematic review and meta-analysis.

PURPOSE: The primary aim of this study was to evaluate whether TcMEP alarms can predict the occurrence of postoperative neurological deficit in patients undergoing lumbar spine surgery. The secondary aim was to determine whether the various types of TcMEP alarms including transient and persistent changes portend varying degrees of injury risk. METHODS: This was a systematic review and meta-analysis of the literature from PubMed, Web of Science, and Embase regarding outcomes of transcranial motor-evoked potential (TcMEP) monitoring during lumbar decompression and fusion surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR) of TcMEP alarms for predicting postoperative deficit were calculated and presented with forest plots and a summary receiver operating characteristic curve. RESULTS: Eight studies were included, consisting of 4923 patients. The incidence of postoperative neurological deficit was 0.73% (36/4923). The incidence of deficits in patients with significant TcMEP changes was 11.79% (27/229), while the incidence in those without changes was 0.19% (9/4694). All TcMEP alarms had a pooled sensitivity and specificity of 63 and 95% with a DOR of 34.92 (95% CI 7.95-153.42). Transient and persistent changes had sensitivities of 29% and 47%, specificities of 96% and 98%, and DORs of 8.04 and 66.06, respectively. CONCLUSION: TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in lumbar decompression and fusion surgery. Patients who awoke with new postoperative deficits were 35 times more likely to have experienced TcMEP changes intraoperatively, with persistent changes indicating higher risk of deficit than transient changes. LEVEL OF EVIDENCE II: Diagnostic Systematic Review.

Association Between Industry Sponsorship of Spine-Related Clinical Trials, Publication Status, and Research Outcomes.

STUDY DESIGN: Observational Database Study. OBJECTIVES: Prospective clinical trials in spinal surgery are expensive to conduct, especially when randomized, appropriately powered, and/or multicentered. Industry collaborations generate symbiotic relationships promoting technological advancement; however, they also allow for bias. To the authors' knowledge, there is no known analysis of correlations between industry sponsorship and publication rates of spine-related clinical trials. This observational work evaluates such potential associations. METHODS: The ClinicalTrials.gov database was queried with terms spine, spinal, spondylosis, spondylolysis, cervical, lumbar, and compression fracture over an 11-year period. Design characteristics and outcomes were recorded from 822 spine surgery-related trials. Trials were stratified based on funding source and intervention class. Groups were compared via two-tailed chi-square test of independence or Fisher's exact test (α = .05), based on completion status and publication rates of positive vs negative results. RESULTS: Industry-sponsored spine-related clinical trials were more likely to be terminated than their non-industry-sponsored counterparts (P < .001). Of the trials achieving publication, industry-sponsored trials reported positive results at a higher rate than did trials without industry funding (P = .037). Clinical trials examining devices were more likely to be terminated than those studying other intervention classes (P = .001). CONCLUSIONS: High termination rates and positive result publication rates among industry-sponsored clinical trials in spinal surgery likely reflect industry's influence on the research community. Such partnership alleviates financial burden and provides accessibility to cutting-edge innovation. It is essential that all parties remain mindful of the significant bias that funding source may impart on study outcome.

Dynamic Changes in Lumbar Spine Kinematics During Gait May Explain Improvement in Back Pain and Disability in Patients With Hip-Spine Syndrome.

STUDY DESIGN: Prospective cohort. OBJECTIVE: Determine if total hip arthroplasty (THA) changes lumbar spine kinematics during gait in a manner that explains the improvements in back pain seen in patients with hip-spine syndrome. SUMMARY OF BACKGROUND DATA: For patients with hip-spine syndrome, improvements in both hip and back pain have been demonstrated after THA; however, the exact mechanism of improvement in back pain remains unknown, as no corresponding changes in lumbar spine static radiographic parameters have been identified. METHODS: Thirteen patients with severe, unilateral hip osteoarthritis scheduled to undergo THA with concomitant back pain and disability were tested at baseline and 6 months after THA. Harris Hip Score (HHS) and Oswestry Disability Index questionnaires were completed; the static orientation of the spine and pelvis were measured on standing radiographs, and lumbar spine kinematics were measured during treadmill walking using a validated measurement system that matched subject-specific bone models created from CT scans to dynamic biplane radiographs. RESULTS: After THA, both the Oswestry Disability Index (36.3-11.3, P <0.001) and Harris Hip Score (55.7-77.9, P <0.001) improved; however, there were no changes in static intervertebral or pelvis orientation. During gait after THA, the overall lumbar spine (L1 to L5) was less lordotic from heel strike to contralateral toe off ( P <0.001), the L4 and L5 vertebra were less anteriorly tilted by 3.9° ( P =0.038) from midstance to contralateral heel strike and by 3.9° ( P =0.001) during stance, respectively. CONCLUSION: The decreased anterior tilt of the 2 lowest lumbar vertebrae and the corresponding loss of lumbar lordosis may reduce facet loading during the stance phase of gait after THA. This change in lumbar spine kinematics during gait is a potential mechanism to explain the observed improvements in back pain and disability after THA. LEVEL OF EVIDENCE: 4.

Should We Hire Our Current Fellow? Hiring Trends and Preferences in Spine Surgery.

OBJECTIVE: To provide insight into hiring trends/preferences in Academic Orthopaedic Spine Surgery after fellowship training. METHODS: Fellowship directors (FDs) listed by the North American Spine Society were surveyed regarding new faculty hiring preferences. Surveys were analyzed/stratified by response using the Kruskal-Wallis with Dunn multiple comparisons test, the Fisher exact test, and the Mann-Whitney U test for univariate comparisons. RESULTS: Thirty-two of 52 (61.5%) FDs responded. 32.3% of graduated fellows pursued academic medicine, which was preferred by FDs (3.59 ± 0.67; 1 to 5 scale). From 2015 to 2020, of the 2.25 ± 1.46 faculty members hired per program, 45.8% were former residents/fellows. Top listed hiring qualities were "strong recommendation from a trusted colleague" (84.4%), "prior personal experience, as a resident/fellow" (78.1%), and "amicable personality" (53.1%). Twelve (38%) answered "no", six (19%) "yes", and 14 (44%) "other", regarding if hiring former residents/fellows benefits the field of spine surgery. "Other" answers endorsing in-house hiring most commonly mentioned consistency/stability (28.6%) while those opposed most commonly mentioned lack of diversity of training/novel techniques (42.9%). When considering programmatic size, while the stated perception of FDs regarding in-house hiring at larger (>2 fellows) versus smaller (1 to 2 fellows) programs was equivalent, the mean percentage of in-house hires at larger programs (67.8% ± 35.8%) was significantly greater than that of smaller programs (33.3% ± 44.8%, P = 0.04). CONCLUSIONS: In-house hiring in spine surgery appears to occur more commonly than perceived by program leadership, particularly at larger fellowship programs. Further study of hiring preferences and their impact on the field of spine surgery is warranted. STUDY DESIGN: Prospective Survey Study.

Multilevel tandem spondylolisthesis associated with a reduced "safe zone" for a transpsoas lateral lumbar interbody fusion at L4-5.

OBJECTIVE: The aim of this study was to investigate the effect of degenerative spondylolisthesis (DS) on psoas anatomy and the L4-5 safe zone during lateral lumbar interbody fusion (LLIF). METHODS: In this retrospective, single-institution analysis, patients managed for low-back pain between 2016 and 2021 were identified. Inclusion criteria were adequate lumbar MR images and radiographs. Exclusion criteria were spine trauma, infection, metastases, transitional anatomy, or prior surgery. There were three age and sex propensity-matched cohorts: 1) controls without DS; 2) patients with single-level DS (SLDS); and 3) patients with multilevel, tandem DS (TDS). Axial T2-weighted MRI was used to measure the apical (ventral) and central positions of the psoas relative to the posterior tangent line at the L4-5 disc. Lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and PI-LL mismatch were measured on lumbar radiographs. The primary outcomes were apical and central psoas positions at L4-5, which were calculated using stepwise multivariate linear regression including demographics, spinopelvic parameters, and degree of DS. Secondary outcomes were associations between single- and multilevel DS and spinopelvic parameters, which were calculated using one-way ANOVA with Bonferroni correction for between-group comparisons. RESULTS: A total of 230 patients (92 without DS, 92 with SLDS, and 46 with TDS) were included. The mean age was 68.0 ± 8.9 years, and 185 patients (80.4%) were female. The mean BMI was 31.0 ± 7.1, and the mean age-adjusted Charlson Comorbidity Index (aCCI) was 4.2 ± 1.8. Age, BMI, sex, and aCCI were similar between the groups. Each increased grade of DS (no DS to SLDS to TDS) was associated with significantly increased PI (p < 0.05 for all relationships). PT, PI-LL mismatch, center psoas, and apical position were all significantly greater in the TDS group than in the no-DS and SLDS groups (p < 0.05). DS severity was independently associated with 2.4-mm (95% CI 1.1-3.8 mm) center and 2.6-mm (95% CI 1.2-3.9 mm) apical psoas anterior displacement per increased grade (increasing from no DS to SLDS to TDS). CONCLUSIONS: TDS represents more severe sagittal malalignment (PI-LL mismatch), pelvic compensation (PT), and changes in the psoas major muscle compared with no DS, and SLDS and is a risk factor for lumbar plexus injury during L4-5 LLIF due to a smaller safe zone.

To Cross the Cervicothoracic Junction? Terminating Posterior Cervical Fusion Constructs Proximal to the Cervicothoracic Junction Does Not Impart Increased Risk of Reoperation in Patients With Cervical Spondylotic Myelopathy.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: To evaluate the effect of caudal instrumentation level on revision rates following posterior cervical laminectomy and fusion. METHODS: A retrospective review of a prospectively collected database was performed. Minimum follow-up was one year. Patients were divided into two groups based on the caudal level of their index fusion construct (Group 1-cervical and Group 2- thoracic). Reoperation rates were compared between the two groups, and preoperative demographics and radiographic parameters were compared between patients who required revision and those who did not. Multivariate binomial regression analysis was performed to determine independent risk factors for revision surgery. RESULTS: One hundred thirty-seven (137/204) patients received fusion constructs that terminated at C7 (Group 1), while 67 (67/204) received fusion constructs that terminated at T1 or T2 (Group 2). The revision rate was 8.33% in the combined cohort, 7.3% in Group 1, and 10.4% in Group 2. There was no significant difference in revision rates between the 2 groups (P = .43). Multivariate regression analysis did not identify any independent risk factors for revision surgery. CONCLUSION: This study shows no evidence of increased risk of revision in patients with fusion constructs terminating in the cervical spine when compared to patients with constructs crossing the cervicothoracic junction. These findings support terminating the fusion construct proximal to the cervicothoracic junction when indicated. LEVEL OF EVIDENCE: III.

Pre-Operative Bariatric Surgery Imparts An Increased Risk of Infection, Re-Admission and Operative Intervention Following Elective Instrumented Lumbar Fusion.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: To evaluate the impact of bariatric surgery on patient outcomes following elective instrumented lumbar fusion. METHODS: A retrospective review of a prospectively collected database was performed. Patients who underwent a bariatric procedure prior to an elective instrumented lumbar fusion were evaluated. Lumbar procedures were performed at a large academic medical center from 1/1/2012 to 1/1/2018. The primary outcome was surgical site infection (SSI) requiring surgical debridement. Secondary outcomes were prolonged wound drainage requiring treatment, implant failure requiring revision, revision secondary to adjacent segment disease (ASD), and chronic pain states. A randomly selected, surgeon and comorbidity-matched group of 59 patients that underwent an elective lumbar fusion during that period was used as a control. Statistical analysis was performed using Student's two-way t-tests for continuous data, with significance defined as P < .05. RESULTS: Twenty-five patients were identified who underwent bariatric surgery prior to elective lumbar fusion. Mean follow-up was 2.4 ± 1.9 years in the bariatric group vs. 1.5 ± 1.3 years in the control group. Patients with a history of bariatric surgery had an increased incidence of SSI that required operative debridement, revision surgery due to ASD, and a higher incidence of chronic pain. Prolonged wound drainage and implant failure were equivalent between groups. CONCLUSION: In the present study, bariatric surgery prior to elective instrumented lumbar fusion was associated increased risk of surgical site infection, adjacent segment disease and chronic pain when compared to non-bariatric patients.

In Vivo Evidence of Early Instability and Late Stabilization in Motion Segments Immediately Superior to Anterior Cervical Arthrodesis.

STUDY DESIGN: Prospective cohort study. OBJECTIVE: The aim was to identify patient factors that affect adjacent segment kinematics after anterior cervical discectomy and fusion (ACDF) as measured by biplane radiography. SUMMARY OF BACKGROUND DATA: The etiology of adjacent segment disease (ASD) may be multifactorial. Previous studies have investigated associations between patient factors and ASD, although few attempted to link patient factors with mechanical changes in the spine that may explain ASD development. Previous studies manually measured intervertebral motion from static flexion/extension radiographs, however, manual measurements are unreliable, and those studies failed to measure intervertebral motion during rotation. METHODS: Patients had continuous cervical spine flexion/extension and axial rotation movements captured at 30 images per second in a dynamic biplane radiography system preoperatively and 1 year after ACDF. Digitally reconstructed radiographs generated from subject-specific computed tomography scans were matched to the biplane radiographs using a validated tracking process. Dynamic kinematics and preoperative disc height were calculated from this tracking process. Preoperative magnetic resonance imagings were evaluated for disc bulge. Patient age, sex, body mass index, smoking status, diabetes, psychiatric history, presence of an inciting event, and length of symptoms were collected. Multivariate linear regression was performed to identify patient factors associated with 1-year postoperative changes in adjacent segment kinematics. RESULTS: Sixty-three patients completed preoperative and postoperative testing. Superior adjacent segment disc height and disc bulge predicted the change in superior adjacent segment range of motion after surgery. Inferior adjacent segment disc bulge, smoking history, and the use of psychiatric medications predicted the change in inferior adjacent segment flexion/extension range of motion after surgery. CONCLUSIONS: Preexisting adjacent segment disc degeneration, as indicated by disc height and disc bulge, was associated with reduced adjacent segment motion after ACDF, while lack of preexisting adjacent disc degeneration was associated with increased adjacent segment motion after ACDF. These findings provide in vivo evidence supporting early instability and late stabilization in the pathophysiology of disc degeneration.

Ionizing Radiation Induces Disc Annulus Fibrosus Senescence and Matrix Catabolism via MMP-Mediated Pathways.

Previous research has identified an association between external radiation and disc degeneration, but the mechanism was poorly understood. This study explores the effects of ionizing radiation (IR) on inducing cellular senescence of annulus fibrosus (AF) in cell culture and in an in vivo mouse model. Exposure of AF cell culture to 10-15 Gy IR for 5 min followed by 5 days of culture incubation resulted in almost complete senescence induction as evidenced by SA-ßgal positive staining of cells and elevated mRNA expression of the p16 and p21 senescent markers. IR-induced senescent AF cells exhibited increased matrix catabolism, including elevated matrix metalloproteinase (MMP)-1 and -3 protein expression and aggrecanolysis. Analogous results were seen with whole body IR-exposed mice, demonstrating that genotoxic stress also drives disc cellular senescence and matrix catabolism in vivo. These results have important clinical implications in the potential adverse effects of ionizing radiation on spinal health.

The effects of pathology and one-level versus two-level arthrodesis on cervical spine intervertebral helical axis of motion.

The etiology of adjacent segment disease after anterior cervical discectomy and fusion (ACDF) remains controversial. Range of motion (ROM) is typically used to infer the effects of arthrodesis on adjacent segment motion following ACDF, however, ROM only measures the total amount of motion. In contrast, the helical axis of motion (HAM) quantifies how the motion occurs and may provide additional insight into the etiology of adjacent segment pathology. Synchronized biplane radiographs of the cervical spine were acquired at 30 images per second while 62 ACDF patients and 38 control participants performed dynamic neck flexion/extension. A validated tracking process matched digitally reconstructed radiographs created from subject-specific bone models to the radiographs with sub-millimeter accuracy. The intervertebral HAM was then calculated and compared between pre and 1 year post surgery in patients, and between patients and controls at corresponding motion segments using linear mixed-effects analysis. Small differences in the anterior/posterior location of the HAM were found between the symptomatic motion segments before surgery and corresponding motion segments in controls. No changes in the HAM of motion segments adjacent to the arthrodesis were observed from pre to 1-year post-surgery. No differences in adjacent segment HAM were found between patients with one- versus two-level arthrodesis. Neither symptomatic pathology nor arthrodesis appear to change the way motion occurs in the cervical spine during flexion/extension one year after one or two-level arthrodesis. These results suggest ACDF does not alter short-term adjacent segment kinematics in a way that would contribute to the development of adjacent segment disease.

Triggered Electromyography is a Useful Intraoperative Adjunct to Predict Postoperative Neurological Deficit Following Lumbar Pedicle Screw Instrumentation.

STUDY DESIGN: Systematic review and meta-analysis. OBJECTIVES: Malposition of pedicle screws during instrumentation in the lumbar spine is associated with complications secondary to spinal cord or nerve root injury. Intraoperative triggered electromyographic monitoring (t-EMG) may be used during instrumentation for early detection of malposition. The association between lumbar pedicle screws stimulated at low EMG thresholds and postoperative neurological deficits, however, remains unknown. The purpose of this study is to assess whether a low threshold t-EMG response to lumbar pedicle screw stimulation can serve as a predictive tool for postoperative neurological deficit. METHODS: The present study is a meta-analysis of the literature from PubMed, Web of Science, and Embase identifying prospective/retrospective studies with outcomes of patients who underwent lumbar spinal fusion with t-EMG testing. RESULTS: The total study cohort consisted of 2,236 patients and the total postoperative neurological deficit rate was 3.04%. 10.78% of the patients incurred at least 1 pedicle screw that was stimulated below the respective EMG alarm threshold intraoperatively. The incidence of postoperative neurological deficits in patients with a lumbar pedicle screw stimulated below EMG alarm threshold during placement was 13.28%, while only 1.80% in the patients without. The pooled DOR was 10.14. Sensitivity was 49% while specificity was 88%. CONCLUSIONS: Electrically activated lumbar pedicle screws resulting in low t-EMG alarm thresholds are highly specific but weakly sensitive for new postoperative neurological deficits. Patients with new postoperative neurological deficits after lumbar spine surgery were 10 times more likely to have had a lumbar pedicle screw stimulated at a low EMG threshold.

Residual Motion and Graft Type Do Not Influence Patient-reported Outcomes Following One- or Two-level Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Prospective cohort. OBJECTIVE: The aim of this study was to determine the effect of graft type on residual motion and the relationship among residual motion, smoking, and patient-reported outcome (PRO) scores following anterior cervical discectomy and fusion (ACDF). SUMMARY OF BACKGROUND DATA: Although most patients develop solid fusion based on static imaging following ACDF, dynamic imaging has revealed that many patients continue to have residual motion at the arthrodesis. METHODS: Forty-eight participants performed dynamic neck flexion/extension and axial rotation within a biplane radiography system 1 year following ACDF (21 one-level, 27 two-level). PRO scores included the Short Form-36, Neck Disability Index, and Cervical Spine Outcomes Questionnaire. An automated model-based tracking process matched subject-specific bone models to the biplane radiographs with sub-millimeter accuracy. Residual motion was measured across the entire arthrodesis site for both one- and two-level fusions in patients who received either allograft or autograft. Patients were divided into "pseudarthrosis" (>3° of flexion/extension residual motion) and "solid fusion" groups. Residual motion and PROs were compared between groups using Student t tests. RESULTS: Patients who received allograft showed more total flexion/extension residual motion (4.1° vs. 2.8°, P = 0.12), although this failed to reach significance. No differences were noted in PROs based on graft type (all P > 0.08) or the presence of pseudarthrosis (all P > 0.13). No differences were noted in residual motion between smokers and nonsmokers (all P > 0.15); however, smokers who received allograft reported worse outcomes than nonsmokers who received allograft and smokers who received autograft. CONCLUSION: Allograft may result in slightly more residual motion at the arthrodesis site 1 year after ACDF. However, there is minimal evidence that PROs are adversely affected by slightly increased residual motion, suggesting that the current definition of pseudarthrosis correlates poorly with clinically significant findings. Additionally, autograft appears to result in superior outcomes in patients who smoke.Level of Evidence: 2.

Surgery-related Factors Do Not Affect Short-term Adjacent Segment Kinematics After Anterior Cervical Arthrodesis.

STUDY DESIGN: Prospective cohort study. OBJECTIVE: The aim of this study was to identify surgical factors that affect adjacent segment kinematics after anterior cervical discectomy and fusion (ACDF) as measured by biplane radiography. SUMMARY OF BACKGROUND DATA: Previous studies investigated the effect of surgical factors on spine kinematics as a potential etiology for adjacent segment disease (ASD). Those studies used static flexion-extension radiographs to evaluate range of motion. However, measurements from static radiographs are known to be unreliable. Furthermore, those studies were unable to evaluate the effect of ACDF on adjacent segment axial rotation. METHODS: Patients had continuous cervical spine flexion/exten- sion and axial rotation movements captured at 30 images per second in a dynamic biplane radiography system preoperatively and 1 year after ACDF. Digitally reconstructed radiographs generated from subject-specific CT scans were matched to biplane radiographs using a previously validated tracking process. Dynamic kinematics, postoperative segmental kyphosis, and disc distraction were calculated from this tracking process. Plate-to-disc distance was measured on postoperative radiographs. Graft type was collected from the medical record. Multivariate linear regression was performed to identify surgical factors associated with 1-year post-surgery changes in adjacent segment kinematics. A secondary analysis was also performed to compare adjacent segment kinematics between each of the surgical factors and previously defined thresholds believed to be associated with adjacent segment degeneration. RESULTS: Fifty-nine patients completed preoperative and postoperative testing. No association was found between any of the surgical factors and change in adjacent segment flexion/exten- sion or axial rotation range of motion (all P > 0.09). The secondary analysis also did not identify differences between adjacent segment kinematics and surgical factors (all P > 0.07). CONCLUSION: Following ACDF for cervical spondylosis, factors related to surgical technique were not associated with short-term changes in adjacent segment kinematics that reflect the hypermobility hypothesized to lead to the development of ASD.Level of Evidence: 2.