Object. The authors report the preservation of motion at surgically treated and adjacent spinal segments after placing an artificial cervical joint (ACJ) and they describe the influence of interbody fusion on changes in angulation occurring in the sagittal plane at adjacent levels in the treatment of cervical spondylosis. Methods. The authors conducted a prospective nonrandomized study of patients in whom an ACJ was placed or autologous bone graft interbody fusion was performed. Angular measurements at levels adjacent to that surgically treated were calculated using plain flexion—extension radiographs obtained at 6-month intervals. Analyses of qualitative data, such as increase or decrease in adjacent-level motion, and the degree of disc degeneration were performed. Quantitative data were also analyzed. In the fusion group a significant increase in adjacent-level movement was demonstrated at the 12-month follow-up visit compared with the group of patients in whom ACJs were placed (p < 0.001). The increase in movement occurred predominantly at intervertebral discs that were preoperatively regarded as normal (p < 0.02). An overall reduction in adjacent-level movement was observed in patients who underwent joint replacement, although this was compensated for by the movement provided by the ACJ itself. Conclusions. Fusion results in increased motion at adjacent levels. The increase in adjacent-level motion derives from those discs that appear radiologically normal prior to surgery. It remains unknown whether ACJs have a protective influence on adjacent intervertebral discs.

We found that patients in both the arthroplasty and arthrodesis groups had improvement following surgery; furthermore, improvement was similar between the groups, with no worsening of myelopathy in the arthroplasty group. While the findings at two years postoperatively suggest that arthroplasty is equivalent to arthrodesis for the treatment of cervical myelopathy for a single-level abnormality localized to the disc space, the present study did not evaluate the treatment of retrovertebral compression as occurs in association with ossification of the posterior longitudinal ligament, and we cannot comment upon the treatment of this condition.

Object A prospective, randomized clinical trial was conducted to compare the Prestige II Cervical Disc with anterior decompression and fusion for the treatment of single-level degenerative disease. Standardized clinical outcome measures and radiographic examinations were used at prescribed postoperative intervals to compare the treatment groups. Methods Patients with symptomatic single-level cervical disc disease who met the inclusion/exclusion criteria defined in the protocol were randomized to receive the Prestige II disc or iliac crest autograft fusion. All patients underwent a standardized neurological and radiographic examination and completed outcomes questionnaires (Neck Disability Index and Short Form–36) preoperatively and at each postoperative interval (6 weeks and 3, 6, 12, and 24 months). Two independent radiologists reviewed all x-ray films and assessed motion at the treated level and adjacent segments. Standard statistical methods were used to compare all outcome measures. Preliminary results in 55 patients enrolled in the study are presented. Several patients have reached the final (24-month) follow-up interval. Clinical and radiographic results are encouraging, with significant improvement seen in both treatment groups. Radiographic results show that the Prestige II disc maintains motion at the treated level without adjacent-segment compromise. Conclusions Cervical spine arthroplasty is an exciting and rapidly developing surgical treatment option. An objective comparison with fusion is important to advance this option. This is the first prospective randomized trial in which cervical arthroplasty is compared with fusion. The preliminary results from this limited number of patients indicate that the Prestige II disc is potentially a viable alternative to fusion for primary cervical disc disease; however, further clinical studies with larger sample sizes will be required to show statistical equivalence.

An in vitro biomechanical study was conducted to determine the effects of fusion and nonfusion anterior cervical instrumentation on cervical spine biomechanics in a multilevel human cadaveric model. Three spine conditions were studied: harvested, single-level artificial cervical joint, and single-level graft with anterior cervical plate. A programmable testing apparatus was used that replicated physiologic flexion/extension and lateral bending. Measurements included vertebral motion, applied load, and bending moments. Relative rotations at the superior, implanted, and inferior motion segment units (MSUs) were normalized with respect to the overall rotation of those three MSUs and compared using a one-way analysis of variance (P < 0.05). Application of an anterior cervical plate decreased motion across the fusion site relative to the harvested and artificial joint spine conditions. The reduced motion was compensated for by an increase in motion at the adjacent segments. Use of an artificial cervical joint did not alter the motion patterns at either the instrumented level or the adjacent segments compared with the harvested condition for all modes of testing.