The Effects of Cervical Orthoses on Head and Intervertebral Range of Motion.

STUDY DESIGN: Prospective Cohort. OBJECTIVE: Quantify and compare the effectiveness of cervical orthoses in restricting intervertebral kinematics during multiplanar motions. SUMMARY OF BACKGROUND DATA: Previous studies evaluating the efficacy of cervical orthoses measured global head motion and did not evaluate individual cervical motion segment mobility. Prior studies focused only on the flexion/extension motion. METHODS: Twenty adults without neck pain participated. Vertebral motion from the occiput through T1 was imaged using dynamic biplane radiography. Intervertebral motion was measured using an automated registration process with validated accuracy better than 1 degree. Participants performed independent trials of maximal flexion/extension, axial rotation, and lateral bending in a randomized order of unbraced, soft collar (foam), hard collar (Aspen), and cervical thoracic orthosis (CTO) (Aspen) conditions. Repeated-measures ANOVA was used to identify differences in the range of motion (ROM) among brace conditions for each motion. RESULTS: Compared with no collar, the soft collar reduced flexion/extension ROM from occiput/C1 through C4/C5, and reduced axial rotation ROM at C1/C2 and from C3/C4 through C5/C6. The soft collar did not reduce motion at any motion segment during lateral bending. Compared with the soft collar, the hard collar reduced intervertebral motion at every motion segment during all motions, except for occiput/C1 during axial rotation and C1/C2 during lateral bending. The CTO reduced motion compared with the hard collar only at C6/C7 during flexion/extension and lateral bending. CONCLUSIONS: The soft collar was ineffective as a restraint to intervertebral motion during lateral bending, but it did reduce intervertebral motion during flexion/extension and axial rotation. The hard collar reduced intervertebral motion compared with the soft collar across all motion directions. The CTO provided a minimal reduction in intervertebral motion compared with the hard collar. The utility in using a CTO rather than a hard collar is questionable, given the cost and little or no additional motion restriction.

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.

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.

Cervical Spine Fractures: Who Really Needs CT Angiography?

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: Compare a novel two-step algorithm for indicating a computed tomography angiography (CTA) in the setting of a cervical spine fracture with established gold standard criteria. SUMMARY OF BACKGROUND DATA: As CTA permits the rapid detection of blunt cerebrovascular injuries (BCVI), screening criteria for its use have broadened. However, more recent work warns of the potential for the overdiagnosis of BCVI, which must be considered with the adoption of broad criteria. METHODS: A novel two-step metric for indicating CTA screening was compared with the American College of Surgeons guidelines and the expanded Denver Criteria using patients who presented with cervical spine fractures to a tertiary-level 1 trauma center from January 1, 2012 to January 1, 2016. The ability for each metric to identify BCVI and posterior circulation strokes that occurred during this period was assessed. RESULTS: A total of 721 patients with cervical fractures were included, of whom 417 underwent CTAs (57.8%). Sixty-eight BCVIs and seven strokes were diagnosed in this cohort. All algorithms detected an equivalent number of BCVIs (52 with the novel metric, 54 with the ACS and Denver Criteria, P = 0.84) and strokes (7/7, 100% with the novel metric, 6/7, 85.7% with the ACS and Denver Criteria, P = 1.0). However, 63% fewer scans would have been needed with the proposed screening algorithm compared with the ACS or Denver Criteria (261/721, 36.2% of all patients with our criteria vs. 413/721, 57.3% with the ACS standard and 417/721, 57.8%) with the Denver Criteria, P < 0.0002 for each). CONCLUSION: A two-step criterion based on mechanism of injury and patient factors is a potentially useful guide for identifying patients at risk of BCVI and stroke after cervical spine fractures. Further prospective analyses are required prior to widespread clinical adoption. LEVEL OF EVIDENCE: 4.

Longitudinal Study of the Six Degrees of Freedom Cervical Spine Range of Motion During Dynamic Flexion, Extension, and Rotation After Single-level Anterior Arthrodesis.

STUDY DESIGN: A longitudinal study using biplane radiography to measure in vivo intervertebral range of motion (ROM) during dynamic flexion/extension, and rotation. OBJECTIVE: To longitudinally compare intervertebral maximal ROM and midrange motion in asymptomatic control subjects and single-level arthrodesis patients. SUMMARY OF BACKGROUND DATA: In vitro studies consistently report that adjacent segment maximal ROM increases superior and inferior to cervical arthrodesis. Previous in vivo results have been conflicting, indicating that maximal ROM may or may not increase superior and/or inferior to the arthrodesis. There are no previous reports of midrange motion in arthrodesis patients and similar-aged controls. METHODS: Eight single-level (C5/C6) anterior arthrodesis patients (tested 7 ±â€Š1 months and 28 ±â€Š6 months postsurgery) and six asymptomatic control subjects (tested twice, 58 ±â€Š6 months apart) performed dynamic full ROM flexion/extension and axial rotation whereas biplane radiographs were collected at 30 images per second. A previously validated tracking process determined three-dimensional vertebral position from each pair of radiographs with submillimeter accuracy. The intervertebral maximal ROM and midrange motion in flexion/extension, rotation, lateral bending, and anterior-posterior translation were compared between test dates and between groups. RESULTS: Adjacent segment maximal ROM did not increase over time during flexion/extension, or rotation movements. Adjacent segment maximal rotational ROM was not significantly greater in arthrodesis patients than in corresponding motion segments of similar-aged controls. C4/C5 adjacent segment rotation during the midrange of head motion and maximal anterior-posterior translation were significantly greater in arthrodesis patients than in the corresponding motion segment in controls on the second test date. CONCLUSION: C5/C6 arthrodesis appears to significantly affect midrange, but not end-range, adjacent segment motions. The effects of arthrodesis on adjacent segment motion may be best evaluated by longitudinal studies that compare maximal and midrange adjacent segment motion to corresponding motion segments of similar-aged controls to determine if the adjacent segment motion is truly excessive. LEVEL OF EVIDENCE: 3.

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.

In vivo cervical facet joint capsule deformation during flexion-extension.

STUDY DESIGN: Nonrandomized controlled cohort. OBJECTIVE: To characterize subaxial cervical facet joint kinematics and facet joint capsule (FJC) deformation during in vivo, dynamic flexion-extension. To assess the effect of single-level anterior arthrodesis on adjacent segment FJC deformation. SUMMARY OF BACKGROUND DATA: The cervical facet joint has been identified as the most common source of neck pain, and it is thought to play a role in chronic neck pain related to whiplash injury. Our current knowledge of cervical facet joint kinematics is based on cadaveric mechanical testing. METHODS: Fourteen asymptomatic controls and 9 C5-C6 arthrodesis patients performed full range of motion flexion-extension while biplane radiographs were collected at 30 Hz. A volumetric model-based tracking process determined 3-dimensional vertebral position with submillimeter accuracy. FJC fibers were modeled and grouped into anterior, lateral, posterior-lateral, posterior, and posterior-medial regions. FJC fiber deformations (total, shear, and compression-distraction) relative to the static position were determined for each cervical motion segment (C2-C3 through C6-C7) during flexion-extension. RESULTS: No significant differences in the rate of fiber deformation in flexion were identified among motion segments (P = 0.159); however, significant differences were observed among fiber regions (P < 0.001). Significant differences in the rate of fiber deformation in extension were identified among motion segments (P < 0.001) and among fiber regions (P = 0.001). The rate of FJC deformation in extension adjacent to the arthrodesis was 45% less than that in corresponding motion segments in control subjects (P = 0.001). CONCLUSION: In control subjects, FJC deformations are significantly different among vertebral levels and capsule regions when vertebrae are in an extended orientation. In a flexed orientation, FJC deformations are different only among capsule regions. Single-level anterior arthrodesis is associated with significantly less FJC deformation adjacent to the arthrodesis when the spine is in an extended orientation. LEVEL OF EVIDENCE: 4.

Cervical motion segment percent contributions to flexion-extension during continuous functional movement in control subjects and arthrodesis patients.

STUDY DESIGN: Case control study. OBJECTIVE: To quantify precisely and compare intervertebral segmental contributions to cervical spine flexion-extension during continuous, functional flexion-extension in asymptomatic subjects with patients who underwent single-level anterior arthrodesis. SUMMARY OF BACKGROUND DATA: Segmental contributions to cervical flexion-extension have traditionally been determined using single images collected at full flexion and full extension. These calculations neglect midrange motion and assume that percent contributions to motion remain constant throughout the entire flexion-extension range of motion (ROM). METHODS: Six patients with single-level (C5-C6) anterior arthrodesis and 18 asymptomatic control subjects performed flexion-extension while biplane radiographs were collected at 30 images per second. A previously validated tracking process determined 3-dimensional vertebral position with submillimeter accuracy during continuous flexion-extension. Mixed-effects models of segmental percent contribution to C2-C7 flexion-extension were developed to identify differences in percent contribution within each motion segment, among motion segments, and between controls and patients who underwent arthrodesis over the full ROM. RESULTS: The C2-C3, C3-C4, and C4-C5 motion segments made their maximum contributions during the midrange of motion. The C5-C6 and C6-C7 motion segments, in contrast, made their maximum contributions near the start and end of the ROM. Arthrodesis patients' contribution from the C4-C5 motion segment increased significantly over the range of motion from 30% to 95% of the total flexion-extension ROM (average increased contribution of 5.1%) and arthrodesis patients' contribution from the C6-C7 motion segment increased significantly over the entire flexion-extension ROM (average increased percentage contribution of 8.9%) in comparison to controls. CONCLUSION: Cervical motion segment contributions to flexion-extension change significantly during the flexion-extension motion. The largest change in percent contribution to motion, relative to controls, occurs at the C6-C7 motion segment, over the entire ROM, suggesting a potential mechanical mechanism for the clinical observation of increased incidence of adjacent segment degeneration at C6-C7 rather than at C4-C5 after C5-C6 arthrodesis.