No abstract

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/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 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/extension 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.

Previous validations of biplane radiographic systems have estimated tracking accuracy by moving cadaveric knees through simulated motions. These validations were unable to replicate in vivo kinematics, including patella motion due to muscle activation, and failed to assess the imaging and tracking challenges related to contralateral limb obstruction. By replicating the muscle contraction, movement velocity, joint range of motion, and obstruction of the patella by the contralateral limb, the present study provides a realistic estimate of patellofemoral tracking accuracy for future in vivo studies.

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.

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 modelbased 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'' (>38 of flexion/extension residual motion) and ''solid fusion'' groups. Residual motion and PROs were compared between groups using Student t tests.