Incidence and risk factors analysis of heterotopic ossification after cervical disc replacement

BACKGROUND: Cervical disc replacement (CDR) as a substitute for traditional fusion surgery has been widely used in treating degenerative cervical disc diseases. The objectives of this study were to assess the clinical and radiological findings for patients with heterotopic ossification (HO) following CDR and to detect the risk factors of HO after CDR. METHODS: A total of 125 patients with symptomatic cervical single- or double-level disc diseases, who underwent CDR procedure with Discover prosthesis in Department of Spine Surgery, Changzheng Orthopedics Hospital from March 2009 to March 2011, were enrolled in this retrospective study. Occurrence of HO was defined by the McAfee classification on cervical lateral X-rays in this study. Prosthesis vertebral ratio (PVR) was used to determine the matching degree between the cervical disc prosthesis and cervical vertebra. Logistic regression analyses were performed to determine the risk factors of HO. Variables evaluated for their association with HO occurrence included age, gender, high-intensity signal in spinal cord, preoperative range of motion (ROM), postoperative ROM, operation level number, and PVR. RESULTS: Mean follow-up time was (26.4±5.8) months. All the patients had significant symptoms and neurological function improvements during the follow-up period. The ROM of the operated segment from the preoperative period to the last follow-up was relatively well maintained. The rate of HO in this cohort of patients, who underwent Discover disc, was 27.92% per surgical level and 24.8% per patient by the last follow-up. There were 19 patients (19.79%) with HO in the single-level group while 12 patients (41.38%) in the double-level group. CONCLUSIONS: We identified preoperative high-intensity signal in spinal cord, postoperative ROM of surgical level, number of operation level, and PVR as significant risk factors for postoperative HO occurrence.