Introduction: Heterotopic ossification (HO) has been reported following hip, knee, cervical, and lumbar arthroplasties and posterolateral lumbar fusion with rhBMP-2. Data regarding HO following anterior cervical discectomy and fusion (ACDF) with rhBMP-2 is sparse. We evaluated grades and/or locations of HO and effects of HO on safety and efficacy in rhBMP-2 and allograft groups.
Methods: This was a sub-analysis of the prospective multicenter investigational device exemption trial comparing patients with symptomatic single-level cervical degenerative disc disease (DDD) who underwent ACDF with rhBMP-2 on an absorbable collagen sponge (rhBMP-2/ACS) or cortical allograft. Clinical outcomes were compared to previous disc replacement studies. Rate, location, grade, and size of HO were assessed preoperatively and at 24 months. Outcomes were radiographs (neutral AP/lateral; dynamic flexion-extension/lateral); Neck Disability Index (NDI); arm/neck pain scores; SF-36 PCS; gait assessment; Park classification; fusion success; and adverse events.
Results: At 24 months, the rate of any HO was significantly higher in rhBMP-2/ACS patients after adjusting for preoperative HO and by propensity score. In both groups, HO was primarily anterior; in the rhBMP-2/ACS group, no posterior HO was observed. Park Grade 3 HO at superior adjacent-level disc spaces significantly reduced ROM in both groups, more in the rhBMP-2/ACS group. At 24 months, anterior HO negatively affected NDI success (excluding neck/arm pain scores), neurological status, and overall success in rhBMP-2/ACS patients but not in allograft patients. No significant relationship was observed between HO and adverse events or additional surgeries in either group.
Conclusions: Implantation of rhBMP-2/ACS at 1.5 mg/mL with PEEK spacer and titanium plate is effective in inducing fusion and improving pain and function in patients undergoing ACDF for symptomatic single-level cervical DDD. HO rates were significantly higher in rhBMP-2/ACS patients compared to allograft patients, but fusion rates, NDI success, and neurological status were statistically superior in rhBMP-2/ACS patients.
Patient Care: Our research adds to the body of literature showing that implantation of rhBMP-2/ACS at 1.5 mg/mL with PEEK spacer and titanium plate is effective in inducing fusion and improving pain and function in patients undergoing ACDF for symptomatic single-level cervical DDD.
Learning Objectives: Identify the relationship between HO and adverse events in either treatment group.
Although HO rates were higher in rhBMP-2/ACS patients, describe why rhBMP-2/ACS is still considered safe and effective in inducing fusion and improving pain and function.