Changes in segmental intervertebral motion adjacent to cervical arthrodesis: A prospective study

Study Design. Prospective, observational. Objectives. Quantify the changes in intervertebral motion adjacent to cervical arthrodesis over time. Summary of Background Data. One of the frequently acknowledged sequelae following anterior cervical fusion is the development of adjacent segment disease. It has been argued that a spine fusion transfers stress to adjacent levels and results in increased compensatory motion. However, there are conflicting reports as to whether this actually occurs, and most of these are in vitro or retrospective clinical studies. Methods. Patients undergoing anterior cervical discectomy and fusion underwent a preoperative dynamic fluoroscopic study, followed by imaging at regular intervals after surgery. Imaging data were analyzed by a validated software system. Relative motion between adjacent vertebrae was then calculated, and changes in motion cephalad to the fusion followed over time. Results. Twenty-one patients were analyzed. Mean follow-up was 13 months (10-22 months). Intervertebral motion adjacent to the fusion changed by more than 4 in 4 of the 21 patients. However, on average, there was no difference between preoperative and postoperative motion for shear, flexion-extension, or vertical displacement at the anterior or posterior disc space. Conclusions. Although there was some individual variation, at a mean of 13 months following surgery, there was no significant change in the average junctional intervertebral motion. If fusion is going to affect adjacent motion, it appears that this does not consistently occur in the first 1 to 2 years following surgery. Additionally, there was no observable relationship between motion and development of degenerative changes during this time.