Study Design: Prospective, randomized, multicenter clinical trial.
Objective: Kinematic analysis of target level and adjacent motion segments after Bryan artificial cervical disc replacement versus anterior cervical fusion.
Summary of Background Data: Disc arthroplasty has been shown to provide short-term clinical results that are comparable or better than those attained with traditional anterior cervical discectomy and fusion. One purported benefit of arthroplasty is the ability to prevent or delay adjacent level operations.
Methods: All patients received either a single-level anterior cervical discectomy and fusion with an anterior cervical plate (Atlantis anterior cervical plate, n=221) or a single-level artificial cervical disc replacement (Bryan cervical disc prosthesis, n=242) at C3 to C7. Flexion, extension, and neutral lateral radiographs were obtained preoperatively, and at regular intervals of 24 months. Cervical vertebral bodies were tracked to calculate the functional spinal unit motion parameters, including flexion/extension range of motion and translation. If visible, the functional spinal unit parameters were obtained at the operative level as well as the level above and below.
Results: Significantly more motion was retained in the disc replacement group than the plated group at the index level. The disc replacement group retained an average of 7.95 degrees at 24 months. The preoperative motion was 6.43 degrees and there was no evidence of degradation of motion over 24 months. In contrast, the average range of motion in the fusion group was 1.11 degrees at 3-month follow-up and gradually decreased to 0.87 degrees at 24 months. The preoperative motion was 8.39 degrees. The Bryan disc did not migrate. At 24-month follow-up, there was no case of subsidence of the Bryan disc. There was no evidence of bridging bone across any of the Bryan implant disc spaces.
Conclusions: The Bryan disc treatment, on average, maintained flexion/extension range of motion without degradation over 24 months. No ectopic bridging ossification was seen in any of the Bryan discs and no subsidence or displacement of the Bryan disc occurred.