Mid-term follow-up of clinical and radiologic outcomes in cervical total disk replacement (Mobi-C): incidence of heterotopic ossification and risk factors.

Introduction: Cervical arthroplasty has been shown to have successful, short-term and long-term radiologic and clinical outcomes. The incidence of and predisposing factors for heterotopic ossification (HO) have not been determined. We retrospectively assessed the intermediate-term clinical and radiologic outcomes, especially the incidence of HO and its risk factors.
Methods: Our patient population consisted of 75 patients (85 levels) with cervical disk herniation. Mean follow-up was 40 months, with a minimum follow-up of 24 months. The numeric rating scale scores of neck and arm pain, the neck disability index, and Odom criteria were measured preoperatively and at 24 months postoperatively. Cervical overall lordosis, segmental lordosis, and range of motion at the operative level were evaluated immediately after surgery and at 1, 3, 6, 12, and 24 months postoperatively. The incidence and location of HO were evaluated at 12 and 24 months postoperatively. Univariate and multivariate logistic regression analyses were performed to determine the risk factors for HO.
Results: The mean numeric rating scale scores and neck disability index scores decreased significantly over 24 months. According to Odom criteria, this represented an overall success rate of 86.7%. Mean segmental lordosis and motion increased and then decreased until 24 months. HO occurred in 67 levels at 12 months postoperatively, increasing to 80 levels at 24 months. The multivariate logistic regression test showed a statistically significant difference when using a different surgical technique (P = 0.049).
Conclusions: Intermediate follow-up of cervical arthroplasty showed good clinical outcomes, although there was a trend toward reduction in alignment and motion at 24 months. The overall HO occurrence was 94.1% at 24 months. In our study, the most important factor affecting HO was the different surgical techniques.