Introduction: Cervical disc arthroplasty (CDA) has been widely utilized for select patients with degenerative disc disease. However, ongoing challenges to CDA include the development of heterotopic ossification (HO). The aim of this study was to examine radiographic characteristics of CDA in relation to the development of HO.
Methods: A retrospective case series was performed on patients who underwent 1- to 2-level CDA at the University of Calgary. Radiological measurements such as global Cobb angle, global range-of-motion, and overhang of anterior endplate in relation to artificial disc were determined. Measurements were made on radiographs immediately after surgery and at follow-up of minimum of 1 years. HO was determined using the McAfee classification.
Results: Forty-five patients underwent CDA with a mean age of 46 years (SD: 9.5) and 26 (57.8%) were males. The median follow-up was 29 months (IQR: 45). Seventy-three percent and 27% of patient underwent 1-level and 2-level CDA respectively. Nineteen patients (33%) developed high grade HO (McAfee grade 3 and 4). The anterior endplate overhang diameter for patients with high-grade HO was 1.1mm ([95%CI 0.13-2.1], p=0.0027) larger compared to patients with low-grade HO. On univariate analysis, patients with >2mm endplate overhang had higher odds of developing high-grade HO (OR 4.0 [95%CI 1.1-14.9], p=0.02). On multivariable logistic regression, endplate diameter >2mm remained significant in predicting development of high-grade HO (OR 3.6 [95%CI 1.1-12.2], p=0.04) after adjusting for age, sex and level of operation. No significant relationship was observed between type of artificial disc and development of high grade HO (p=0.14).
Conclusions: Patients with >2mm of exposed endplate are at higher risk of developing HO. Ensuring adequate endplate coverage may be more important than specific artificial disc type in preventing high-grade HO.
Patient Care: The etiology of heterotopic ossification after cervical disc arthroplasty remains elusive. This study shows the amount of endplate coverage by the artificial disc is a predictor for development of high grade heterotopic ossification. Spine surgeons should consider maximizing endplate coverage to minimize the risk of development of heterotopic ossification.
Learning Objectives: By the conclusion of this session, participants should be able to 1) describe the natural history of the development of heterotopic ossification after cervical disc arthroplasty and 2) identify the importance of anterior endplate overhang coverage as a risk factor for developing heterotopic ossification.