Objective: Movement in an artificial disc would be assumed to be a necessary function of the disc. The purpose of this study was to establish whether, if any, relationship existed between movement in the artificial disc and outcome.

Subjects: 25 patients who had received an artificial disc prosthesis were assessed using radiological methods. Despite many vagaries in the measurement of X-rays, fluoroscopy was used to assess gross movement and end of flexion/extension views used to measure degrees of motion.

Outcome measures: Oswestry disability score.

Results: A very clear relationship has been established between motion in the artificial disc and outcome.

Conclusions: It is likely that spinal fusion will ultimately give way to disc replacement. Although spinal fusion has been shown in the Swedish spine series to produce good outcomes for significant numbers of patients, it remains to be seen whether the retention of motion will enhance outcome in low back pain patients. This series suggests that the retention of motion is an important component in the outcome of surgery in back pain sufferers.