Effect of Anterior Cervical Discectomy and Fusion Compared to Cervical Arthroplasty on Dynamics of Adjacent Segment Disease

Background Data: After anterior cervical discectomy; the effect of cervical fusion or cervical arthroplasty on the dynamics of adjacent segments and the overall cervical spine has a direct impact on the final clinical outcome Purpose: To compare the effect of the cervical fusion (ACDF) versus arthroplasty after anterior cervical discectomy on the cervical dynamics, this can predispose to adjacent segment diseases at those levels. Study Design: A comparative retrospective study between two groups; cervical arthroplasty group, and the cervical fusion group. Patients and Methods: A total of 36 consecutive patients underwent anterior cervical discectomy with a mean follow-up of 24 months. Patients were classified into two groups; Group I (20 patients) were operated for (ACDF), Group II (16 patients) were operated for anterior cervical discectomy and prosthesis (arthroplasty). Preoperative and postoperative clinical assessments were done by using the Neck Disability Index (NDI) and the Japanese Orthopedic Association (JOA) score for myelopathy patients. In all patients, at final follow-up, a neuro-radiographic assessment (cervical spine static and dynamic x-ray and MRI) was done. The angle of the operated disc level, the angle of above and below adjacent segments and their range of motion (ROM), and global cervical curve Cobb angle (C2-7) were measured. Results: In group I; the mean angle of the global cervical curve improved from 3.4° preoperative (kyphosis) to 14.5°postoperative (P<0.001), where in group II, angle improved from 4.6° to 16.5° (P=0.6). The mean segmental ROM of adjacent segments didn’t show significant instability. The mean ROM at upper adjacent levels was 11.1°, and at the lower adjacent levels was 10.2° (normally up to 10 degrees). In group II, however, the mean angle of ROM was 7.8° at upper adjacent levels and 9.6° at lower adjacent levels. Postoperative improvement of JOA and NDI scores was statistically significant (P<0.001) in group-I (JOA improved from14.3±1.25 to 16.6±0.9, and NDI improved from 21.1±5.8 to 7.63±4.9), where in group-II JOA improved from 15.7±1.2 to 16.2±1.1 and NDI improved from 19±2.1 to 16±8.7. Symptomatic ASD was observed in 5 patients (20%) in group I and in none of group II patients Conclusion: Compensatory increase in ROM of the contiguous adjacent segments in patients subjected to ACDF may lead to ASD especially in those with asymptomatic