Wear analysis of the Bryan Cervical Disc prosthesis.

STUDY DESIGN: In vitro wear testing of the Bryan Cervical Disc prosthesis was performed in a cervical spine simulator. The biologic response was assessed in chimpanzee and goat animal models. OBJECTIVE: Determine the wear characteristics of the Bryan disc. SUMMARY OF BACKGROUND DATA: Large joint arthroplasties fail most commonly by wear and consequent formation of particulate material, which induces an inflammatory response. Therefore, measuring the wear characteristics of the new spinal disc replacements is important. METHODS: Six prosthetic assembles were tested to 10 or 40 million cycles by load and motion and 3 additional assemblies were tested by load only in a cervical spine simulator. Any debris was examined using ASTM standards. The local biologic response to the prosthesis was examined in two chimpanzees. Nine goats were used to assess the biologic response in both local and distant tissues. Arthrodesis was performed on three additional control goats that received an allograft and an anterior cervical plate. RESULTS: Wear results: cervical spine simulators that applied the loads and motions associated with activities of daily living produced wear particulate at a rate of 1.2 mg per million cycles. Device height decreased 0.02 mm per million cycles with approximately 77% of this decrease due to gradual creep of the nucleus under the constant compressive load. Particles generated were granular in shape with a mean feret diameter of 3.9 microm. All animals tolerated placement of the Bryan disc. Wear debris was present in the periprosthetic and epidural spaces in some animals. However, no significant inflammatory response was observed. No wear material was found distant from the implant in draining lymph tissue, the liver, or the spleen. CONCLUSIONS: The Bryan disc has satisfactory wear characteristics and does not produce a significant inflammatory response.

Cervical motion segment replacement.

When symptoms bring to light a cervical spine degenerative disc process that requires surgical intervention, a symptom relieving procedure such as decompression, followed by functional restoration, arthroplasty, offers the benefit of prophylaxis of accelerated spondylosis at the operated level. In addition, by altering the biomechanical stress factors at adjacent levels, theoretically it should offer prophylactic benefit at these levels as well. The design requirements for a cervical disc prosthesis, the importance of precision instrumentation, and technique are described. Mechanical testing, animal testing, the study design for the EU clinical study, and the operative technique are discussed. The clinical 1- and 2-year data to date are presented.