OBJECTIVE : The concept of accelerated degeneration of adjacent disc levels as a consequence of increased stress caused by interbody fusion of the cervical spine has been widely postulated. Therefore, reconstruction of a failed intervertebral disc with a functional disc prosthesis should offer the same benefits as fusion while simultaneously providing motion and thereby protecting the adjacent level discs from the abnormal stresses associated with fusion. This study was designed to determine whether a new, functional intervertebral cervical disc prosthesis can provide relief from objective neurological symptoms and signs, improve the patient's ability to perform activities of daily living, decrease pain, and provide stability and normal range of motion.
METHODS : We conducted a prospective, concurrently enrolled, multicenter trial of the Bryan Cervical Disc Prosthesis (Spinal Dynamics Corp., Mercer Island, WA) for the treatment of patients with single-level degenerative disc disease of the cervical spine. Patients with symptomatic cervical radiculopathy and/or myelopathy underwent implantation with the Bryan prosthesis after a standard anterior cervical discectomy. At scheduled follow-up periods, the effectiveness of the device was characterized by evaluating each patient's pain, neurological function, and range of motion at the implanted level.
RESULTS : Analysis included data regarding 60 patients at 6 months with 30 of those patients at 1 year. Clinical success at 6 months and 1 year after implantation was 86 and 90%, respectively, exceeding the study's acceptance criteria of 85%. These results compare favorably with the short-term clinical outcomes associated with anterior cervical discectomy and fusion reported in the literature. At 1 year, there was no measurable subsidence of the devices (based on a measurement detection threshold of 2 mm). Evidence of anterior and/or posterior device migration was detected in one patient and suspected in a second patient. There was no evidence of spondylotic bridging at the implanted disc space. The measured range of motion in flexion-extension, as determined by an independent radiologist, ranged from 1 to 21 degrees (mean range of motion, 9 ± 5 degrees). No devices have been explanted or surgically revised.
CONCLUSION : Discectomy and implantation of the device alleviates neurological symptoms and signs similar to anterior cervical discectomy and fusion. Radiographic evidence supports normal range of motion. The procedure is safe and the patients recover quickly. Restrictive postoperative management is not necessary. However, only after long-term follow-up of at least 5 years will it become clear whether the device remains functional, thus confirming these early favorable results. In addition, the influence on adjacent motion segments can be assessed after at least 5 years of follow-up.