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.

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.

Spine Fractures of Patients with Ankylosing Spondylitis and Diffuse Idiopathic Skeletal Hyperostosis: Fracture Severity and Injury-Related Mortality at a Level I Trauma Center.

STUDY DESIGN: Retrospective review of prospectively collected cohort. PURPOSE: To identify differences in treatment and mortality of spine fractures in patients with ankylosing conditions of the spine. OVERVIEW OF LITERATURE: Ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH) are the two most common etiologies of ankylosing spinal disorder (ASD). However, studies on the treatment and outcomes of spine fractures in AS and DISH patients remain few. METHODS: Patients presenting with a spine fracture were diagnosed with AS or DISH at a single tertiary care center between 2010 and 2019. We excluded those who lacked cross-sectional imaging or fractures occurring at spinal segments affected by ankylosis, as well as polytraumatized patients. Patient demographics, injury mechanism, fracture level, neurologic status, treatment, and 1-year mortality were recorded. Computed tomography imaging was reviewed by two independent readers and graded according to the indicated AO Spine Injury Classification System. Differences in fracture severity, treatment method, and mortality were examined using Student t -tests, chi-square tests, and two-proportion Z-tests with significance set to p <0.05. RESULTS: We identified 167 patients with spine fracture diagnosed with AS or DISH. Patients with AS had more severe fractures and more commonly had surgery than patients with DISH (p <0.001). Despite these differences, 1-year mortality did not significantly differ between AS and DISH patients (p =0.14). CONCLUSIONS: Although patients with AS suffered more severe fractures compared to DISH and more frequently underwent surgery for these injuries, outcomes and 1-year mortality did not differ significantly between the two groups. For patients with ASDs and fractures, outcomes appear similar regardless of treatment modality. Consequently, there may be an opportunity for critical reappraisal of operative indications in ASD and a larger role for nonoperative management in these challenging patients.

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.

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.

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.

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.

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.

The effects of age, pathology, and fusion on cervical neural foramen area.

Cervical radiculopathy is a relatively common neurological disorder, often resulting from mechanical compression of the nerve root within the neural foramen. Anterior cervical discectomy and fusion (ACDF) is a common treatment for radicular symptoms that do not resolve after conservative treatment. One mechanism by which ACDF is believed to resolve symptoms is by replacing degenerated disc tissue with bone graft to increase the neural foramen area, however in vivo evidence demonstrating this is lacking. The aim of this study was to evaluate the effects of age, pathology, and fusion on bony neural foramen area. Participants included 30 young adult controls (<35 years old), 23 middle-aged controls (36 to 60 years old), and 36 cervical arthrodesis patients tested before and after ACDF surgery. Participants' cervical spines were imaged in the neutral, full flexion, and full extension positions while seated within a biplane radiography system. A validated model-based tracking technique determined three-dimensional vertebral position and orientation and automated software identified the neural foramen area in each head position. The neural foramen area decreased throughout the entire sub-axial cervical spine with age and pathology, however, no changes in neural foramen area were observed due solely to replacing degenerated disc tissue with bone graft. The neural foramen area was not associated with disc height in young adult controls, but moderate to strong associations were observed in middle-aged controls. The results provide evidence to inform the debate regarding localized versus systemic spinal degeneration and provide novel insight into the mechanism of pain relief after ACDF.

Severe pulmonary injury leading to death during thoracic rod removal: a case report.

PURPOSE: Removal of hardware procedures following posterior spinal fusion is most commonly performed for hardware irritation without overt infection. It is imperative that surgeons realize that serious complications may arise from this procedure. The purpose of this report is to report a case of a pneumothorax that developed in a thoracolumbar removal of hardware case that resulted in a patient death. METHODS: Retrospective review of a patient's medical record and imaging. RESULTS: A 74-year-old patient with a history of T4-10 anterior discectomy and fusion with rib autograft and T4-L2 posterior fusion underwent a removal of hardware procedure for delayed surgical site infection. During the procedure, the tip of the bolt cutter jaw broke and entered the pulmonary cavity leading to a pneumothorax. The patient developed pneumonia 1 month postoperatively and passed away. CONCLUSIONS: This case report highlights one of the rare but potential complications of spinal removal of hardware surgery. It is essential that surgeons are aware of the possibility of pulmonary complications during thoracolumbar removal of hardware cases so that they may fully counsel their patients on the potential risks.

Undisclosed Conflict of Interest Is Prevalent in Spine Literature.

STUDY DESIGN: Cohort study. OBJECTIVE: The aim of this study was to determine the rate of accurate conflict of interest (COI) disclosure within three prominent subspecialty Spine journals during a 4-year period. SUMMARY OF BACKGROUND DATA: Industry-physician relationships are crucial for technological advancement in spine surgery but serve as a source of bias in biomedical research. The Open Payments Database (OPD) was established after 2010 to increase financial transparency. METHODS: All research articles published from 2014 to 2017 in Spine, The Spine Journal (TSJ), and the Journal of Neurosurgery: Spine (JNS) were reviewed in this study. In these articles, all author's COI statements were recorded. The OPD was queried for all author entries within the disclose period of the journal. Discrepancies between the author's self-reported COIs and the documented COIs from OPD were recorded. RESULTS: A total of 6816 articles meeting inclusion criteria between 2014 and 2017 in Spine, TSJ, and JNS with 39,869 contributing authors. Overall, 15.8% of all authors were found to have an OPD financial relationship. Of 2633 authors in Spine with financial disclosures, 77.1% had accurate financial disclosures; 42.5% and 41.0% of authors with financial relationships in the OPD had accurate financial disclosures in TSJ and JNS, respectively. The total value of undisclosed conflicts of interest between 2014 and 2017 was $421 million with $1.48 billion in accurate disclosures. Of undisclosed payments, 68.7% were <$1000 and only 7.2% were >$10,000. Undisclosed payments included $180 million in research funding and $188 million in royalties. CONCLUSION: This study demonstrates that undisclosed COI is highly prevalent for authors in major Spine journals. This study indicates that there remains a need to standardize definitions and financial thresholds for significant COI as well as to shift the reporting burden for COI to journals who actively review potential COIs instead of relying on self-reporting. LEVEL OF EVIDENCE: 3.

Does Resection of the Posterior Longitudinal Ligament Impact the Incidence of C5 Palsy After Cervical Corpectomy Procedures?: A Review of 459 Consecutive Cases.

STUDY DESIGN: Retrospective review. OBJECTIVE: To evaluate key risk factors for the development of C5 palsy after cervical corpectomy, including resection of the posterior longitudinal ligament (PLL). SUMMARY OF BACKGROUND DATA: Postoperative C5 palsy is a well-known complication after cervical spine surgery. It is unknown whether resection of the PLL affects the incidence of C5 palsy. METHODS: We performed a retrospective review of 459 consecutive patients undergoing anterior cervical corpectomies over a 15-year period. Medical records were reviewed to gather demographic data, operative details, and the incidence of C5 palsy. We performed regression analyses to identify variables that predicted the development of C5 palsy. RESULTS: Our final analysis included 397 patients (females 51.4%, mean age 55.6 ±â€Š11.6 yrs). Anterior corpectomy alone was performed in 255 (64.2%) patients, and combined anterior and posterior fusion was performed in 142 (35.8%) patients. Twenty-four patients (6.0%) developed C5 nerve palsy. Univariable regression demonstrated age greater than 65 (odds ratio, OR 2.7, 95% confidence interval, CI 1.2 to 6.3), corpectomy of three or more levels (OR 6.3, 95% CI 2.1 to 18.9), presence of ossification of the PLL (OR 4.3, 95% CI 1.6 to 11.7), and complete or partial resection of the PLL (OR 2.6, 95% CI 1.0 to 6.7) predicted development of C5 palsy. Multivariable regression demonstrated that the odds of getting C5 palsy with complete or partial resection of the PLL is 4.0 times (95% CI 1.5 to 10.5) higher compared with patients with an intact PLL. There were no significant differences in C5 palsy rates based on surgical approach (anterior vs. anterior plus posterior), sex, smoking status, or diabetes. CONCLUSION: Age greater than 65 years, corpectomy of three or more levels, presence of ossification of the PLL, and complete or partial resection of the PLL significantly predicted the development of C5 palsy. LEVEL OF EVIDENCE: 4.

Prevalence of venous thromboembolic events after elective major thoracolumbar degenerative spine surgery.

STUDY DESIGN: A case-control study. OBJECTIVE: The purposes of this study were to establish the prevalence of venous thromboembolic disease in patients undergoing elective major thoracolumbar degenerative spine surgery and identify risk factors. SUMMARY OF BACKGROUND DATA: Venous thromboembolic events (VTE) are a serious complication of orthopedic surgery, but the prevalence of VTE after elective thoracolumbar degenerative spine surgery is not well known. METHODS: This was a case-control study of 5766 consecutive elective thoracolumbar degenerative spine surgeries. Symptomatic pulmonary emboli (PE) were diagnosed by spiral chest CT scans, nuclear scintigraphic ventilation-perfusion, and angiography. Deep vein thromboses (DVT) were diagnosed by venous duplex scans. The prevalence of VTE was analyzed according to patient demographic variables and type of surgery performed. RESULTS: The prevalence of developing a VTE was 1.5% (89/5766), with a prevalence of symptomatic PE of 0.88% (51/5766) and DVT of 0.66% (38/5766). There were 47% males and 53% females with a mean age of 60.3 years. In patients undergoing 5-segment fusions the prevalence of PE was 3.1% (P=0.022). Patients who had ≥4 segments fused had a prevalence of PE of 1.7% (P=0.014). The odds of having a PE in those above 65 years at the time of surgery were 2.196 times as large as for those below 65 years. Noncontributory factors included sex, instrumentation, and revision surgery. CONCLUSIONS: This case-control study of 5766 patients who underwent elective thoracolumbar degenerative spine surgery revealed a prevalence of VTE of 1.5%, with a prevalence of PE of 0.88% and DVT of 0.66%. Patients with increasingly extensive surgery had a higher risk of PE, specifically those undergoing fusion of ≥5 segments.

The revision rate and occurrence of adjacent segment disease after anterior cervical discectomy and fusion: a study of 672 consecutive patients.

LEVEL III: retrospective cohort study. OBJECTIVE: The aim of this study was to determine the rate of revision surgery and the occurrence of adjacent segment disease of patients undergoing ACDF for cervical radiculopathy and myelopathy using more modern-day instrumentation techniques. SUMMARY OF BACKGROUND DATA: Anterior cervical discectomy and fusion (ACDF) has long been the preferred treatment for cervical radiculopathy and myelopathy. METHODS: All patients undergoing ACDF between January of 2000 and December of 2010 were included. Age, sex, height, weight, body mass index, symptoms at presentation, number of levels fused, graft type, and smoking status were recorded. Outcomes included revision rate, reason for revision surgery, time to revision surgery, presence and grade of adjacent segment disease, distance from the instrumentation to the cranial and caudal endplate (plate-to-disc distance), and reporting of symptoms of adjacent segment disease at the final follow-up. RESULTS: A total of 672 patients were included in this study. The average duration of follow-up was 31 months. One hundred one (15%) patients underwent revision surgery. The reason for revision surgery was adjacent segment disease in 47 (47.5%), pseudarthrosis in 45 (45.5%) and a new problem at a nonadjacent level in 7 (7.1%) of those patients. The need for revision surgery was not affected by patient age, sex, body mass index, smoking status, symptoms at presentation, number of levels fused, plate-to-disc distance or graft type. CONCLUSION: The revision rate after ACDF is 15%. Most revisions were done for either adjacent segment disease or pseudarthrosis. No specific risk factors for revision surgery were identified in this study. LEVEL OF EVIDENCE: 3.

Vertebral artery injuries in cervical spine surgery.

BACKGROUND CONTEXT: Vertebral artery injuries (VAIs) are rare but serious complications of cervical spine surgery, with the potential to cause catastrophic bleeding, permanent neurologic impairment, and even death. The present literature regarding incidence of this complication largely comprises a single surgeon or small multicenter case series. PURPOSE: We sought to gather a large sample of high-volume surgeons to adequately characterize the incidence and risk factors for VAI, management strategies used, and patient outcomes after VAI. STUDY DESIGN: The study was constructed as a cross-sectional study comprising all cervical spine patients operated on by the members of the international Cervical Spine Research Society (CSRS). PATIENT SAMPLE: All patients who have undergone cervical spine surgery by a current member of CSRS as of the spring of 2012. OUTCOME MEASURES: For each surgeon surveyed, we collected self-reported measures to include the number of cervical cases performed in the surgeon's career, the number of VAIs encountered, the stage of the case during which the injury occurred, the management strategies used, and the overall patient outcome after injury. METHODS: An anonymous 10-question web-based survey was distributed to the members of the CSRS. Statistical analysis was performed using Student t tests for numerical outcomes and chi-squared analysis for categorical variables. RESULTS: One hundred forty-one CSRS members (of 195 total, 72%) responded to the survey, accounting for a total of 163,324 cervical spine surgeries performed. The overall incidence of VAI was 0.07% (111/163,324). Posterior instrumentation of the upper cervical spine (32.4%), anterior corpectomy (23.4%), and posterior exposure of the cervical spine (11.7%) were the most common stages of the case to result in an injury to the vertebral artery. Discectomy (9%) and anterior exposure of the spine (7.2%) were also common time points for an arterial injury. One-fifth (22/111) of all VAI involved an anomalous course of the vertebral artery. The most common management of VAI was by direct tamponade. The outcomes of VAIs included no permanent sequelae in 90% of patients, permanent neurologic sequelae in 5.5%, and death in 4.5%. Surgeons at academic and private centers had nearly identical rates of VAIs. However, surgeons who had performed 300 or fewer cervical spine surgeries in their career had a VAI incidence of 0.33% compared with 0.06% in those with greater than 300 lifetime cases (p=.028). CONCLUSIONS: The overall incidence of VAI during cervical spine surgery reported from this survey was 0.07%. Less experienced surgeons had a higher rate of VAI compared with their more experienced peers. The results of VAI are highly variable, resulting in no permanent harm most of the time; however, permanent neurologic injury or death occur in 10% of cases.

Subject-specific inverse dynamics of the head and cervical spine during in vivo dynamic flexion-extension.

The effects of degeneration and surgery on cervical spine mechanics are commonly evaluated through in vitro testing and finite element models derived from these tests. The objectives of the current study were to estimate the load applied to the C2 vertebra during in vivo functional flexion-extension and to evaluate the effects of anterior cervical arthrodesis on spine kinetics. Spine and head kinematics from 16 subjects (six arthrodesis patients and ten asymptomatic controls) were determined during functional flexion-extension using dynamic stereo X-ray and conventional reflective markers. Subject-specific inverse dynamics models, including three flexor muscles and four extensor muscles attached to the skull, estimated the force applied to C2. Total force applied to C2 was not significantly different between arthrodesis and control groups at any 10 deg increment of head flexion-extension (all p values ≥ 0.937). Forces applied to C2 were smallest in the neutral position, increased slowly with flexion, and increased rapidly with extension. Muscle moment arms changed significantly during flexion-extension, and were dependent upon the direction of head motion. The results suggest that in vitro protocols and finite element models that apply constant loads to C2 do not accurately represent in vivo cervical spine kinetics.

Six-degrees-of-freedom cervical spine range of motion during dynamic flexion-extension after single-level anterior arthrodesis: comparison with asymptomatic control subjects.

BACKGROUND: The etiology of adjacent-segment disease following cervical spine arthrodesis remains controversial. The objective of the current study was to evaluate cervical intervertebral range of motion during dynamic flexion-extension in patients who had undergone a single-level arthrodesis and in asymptomatic control subjects. METHODS: Ten patients who had undergone a single-level (C5/C6) anterior arthrodesis and twenty asymptomatic control subjects performed continuous full range-of-motion flexion-extension while biplane radiographs were collected at thirty images per second. A previously validated tracking process determined three-dimensional vertebral position on each pair of radiographs with submillimeter accuracy. Six-degrees-of-freedom kinematics between adjacent vertebrae were calculated throughout the entire flexion-extension movement cycle over multiple trials for each participant. Cervical kinematics were also calculated from images collected during static full flexion and static full extension. RESULTS: The C4/C5 motion segment moved through a larger extension range of motion and a smaller flexion range of motion in the subjects with the arthrodesis than in the controls. The extension difference between the arthrodesis and control groups was 3.8° (95% CI [confidence interval], 0.9° to 6.6°; p = 0.011) and the flexion difference was -2.9° (95% CI, -5.3° to -0.5°; p = 0.019). Adjacent-segment posterior translation was greater in the arthrodesis group than in the controls, with a C4/C5 difference of 0.8 mm (95% CI, 0.0 to 1.6 mm) and a C6/C7 difference of 0.4 mm (95% CI, 0.0 to 0.8 mm; p = 0.016). Translation range of motion and rotation range of motion were consistently larger when measured on images collected during dynamic functional movement as opposed to images collected at static full flexion or full extension. The upper 95% CI limit for anterior-posterior translation range of motion was 3.45 mm at C3/C4 and C4/C5, but only 2.3 mm at C6/C7. CONCLUSIONS: C5/C6 arthrodesis does not affect the total range of motion in adjacent vertebral segments, but it does alter the distribution of adjacent-segment motion toward more extension and less flexion superior to the arthrodesis and more posterior translation superior and inferior to the arthrodesis during in vivo functional loading. Range of motion measured from static full-flexion and full-extension images underestimates dynamic range of motion. Clinical evaluation of excessive anterior-posterior translation should take into account the cervical vertebral level.

Prediction of blood loss during surgery on the lumbar spine with the patient supported prone on the Jackson table.

BACKGROUND CONTEXT: To date, many studies have examined the effects of one or several factors on blood loss during lumbar spine surgery. The nature and extent of the operation, patient position, blood pressure, and a variety of factors related to patient size have been touted as predictors of blood loss. PURPOSE: To measure multiple factors implicated as determinants of blood loss and develop a multivariable statistical model capable of predicting blood loss. STUDY DESIGN: An observational study of patients undergoing lumbar spine surgery in the prone position on the Jackson table. PATIENT SAMPLE: A total of 71 healthy adult men and women undergoing lumbar spine surgery in a university hospital setting. OUTCOME MEASURE: Blood loss during surgery. METHODS: We observed 35 surgeries and recorded demographic and body habitus data on each patient as well as surgical variables, blood pressure, and peripheral venous pressure. We measured bladder pressure intermittently as a surrogate for intra-abdominal pressure. We constructed a statistical model with the results and validated that model in a separate set of 36 subjects. RESULTS: The Jackson table supported all our patients regardless of body dimensions without causing an increase in bladder pressure. Blood loss during surgery averaged 1,167±998 mL (mean±1 standard deviation, range 32-3,745). The statistical model was able to account for about 75% of the variability in blood loss using four variables: the number of laminectomies, whether bone was harvested from the iliac crest, experience of the surgeon doing the initial exposure and closure, and distension of the epidural veins. Data on these variables that were collected in the validation study found a multiple correlation coefficient (R(2)) of 0.66 between predicted and observed blood loss. CONCLUSIONS: This is the first study to build a successful multivariable predictive model of blood loss during spine surgery. The Jackson table was effective in supporting patients with different body sizes and shapes, thus removing raised intra-abdominal pressure as an important factor.

The incidence of C5 palsy after multilevel cervical decompression procedures: a review of 750 consecutive cases.

STUDY DESIGN: Retrospective review of 750 consecutive multilevel cervical spine decompression surgeries performed by a single spine surgeon. OBJECTIVE: To determine the incidence of C5 palsy in a large consecutive series of multilevel cervical spine decompression procedures. SUMMARY OF BACKGROUND DATA: Palsy of the C5 nerve is a well-known potential complication of cervical spine surgery with reported rates ranging from 0% to 30%. The etiology remains uncertain but has been attributed to iatrogenic injury during surgery, tethering from shifting of the spinal cord, spinal cord ischemia, and reperfusion injury of the spinal cord. METHODS: We included patients undergoing multilevel cervical corpectomy, corpectomy with posterior fusion, posterior laminectomy and fusion, and laminoplasty. Exclusion criteria included lack of follow-up data, spinal cord injury preventing preoperative or postoperative motor testing, or surgery not involving the C5 level. Incidence of C5 palsy was determined and compared to determine whether significant differences existed among the various procedures, patient age, sex, revision surgery, preoperative weakness, diabetes, smoking, number of levels decompressed, and history of previous upper extremity surgery. RESULTS: Of the 750 patients, 120 were eliminated on the basis of the exclusion criteria. The 630 patients included in the analysis consisted of 292 females and 338 males. The mean age was 58 years (range, 19-87). The incidence of C5 nerve palsy for the entire group was 42 of 630 (6.7%). The incidence was highest for the laminectomy and fusion group (9.5%), followed by the corpectomy with posterior fusion group (8.4%), the corpectomy group (5.1%), and finally the laminoplasty group (4.8%), although these differences did not reach statistical significance. There was a significantly higher incidence in males (8.6% vs. 4.5%, P = 0.05). CONCLUSION: Incidence of C5 nerve palsy after cervical spine decompression was 6.7%. This is consistent with previously published studies and represents the largest series of North American patients to date. There is no statistically significant difference in incidence of C5 palsy based on surgical procedure, although there was a trend toward higher rates with laminectomy and fusion.