Uncovertebral hypertrophy is a significant risk factor for the occurrence of heterotopic ossification after cervical disc replacement: survivorship analysis of Bryan disc for single-level cervical arthroplasty

The purpose of this study is to investigate the incidence of heterotopic ossification (HO) in the Bryan cervical arthroplasty group and to identify associations between preoperative factors and the development of HO. We performed a retrospective review of clinical and radiological data on patients who underwent single-level cervical arthroplasty with Bryan prosthesis between January 2005 and September 2007. Patients were postoperatively followed-up at 1, 3, 6, 12 months and every year thereafter. The clinical assessment was conducted using Odom's criteria. The presence of HO was evaluated on the basis of X-ray at each time-point according to the McAfee classification. In this study, we focused on survivorship of Bryan prosthesis for single-level arthroplasty. The occurrence of ROM-affecting HO was defined as a functional failure and was used as an endpoint for determining survivorship. Through the analysis of 19 cases of Bryan disc arthroplasty for cervical radiculopathy and/or myelopathy, we revealed that ROM-affecting HO occurs in as many as 36.8% of cases and found that 37% of patients had ROM-affecting HO within 24 months following surgery. The overall survival time to the occurrence of ROM-affecting HO was 36.4 +/- 4.4 months. Survival time of the prosthesis in the patient group without preoperative uncovertebral hypertrophy was significantly longer than that in the patient group with preoperative uncovertebral hypertrophy (47.2 months vs 25.5 months, = 0.02). Cox regression proportional hazard analysis illustrated that preoperative uncovertebral hypertrophy was determined as a significant risk factor for the occurrence of ROM-affecting HO (hazard ratio = 12.30; 95% confidential interval = 1.10-137.03; = 0.04). These findings suggest that the condition of the uncovertebral joint must be evaluated in preoperative planning for Bryan cervical arthroplasty.