General Session: Cervical Motion Preservation

Presented by: P. Nunley - View Audio/Video Presentation (Members Only)


P. Nunley(1), D. Cavanaugh(1), E. Kerr(1), A. Utter(1), K. Frank(1), M. Stone(1)

(1) Spine Institute of Louisiana, Shreveport, LA, United States


Introduction: Heterotopic ossification (HO) can occur after treatment with cervical disc arthroplasty (CDA). This study´s purpose is to assess the prevalence and progression of HO in patients treated with CDA, and determine if HO is associated with diminished clinical outcomes seven-years after surgery.

Methods: A prospective, randomized, U.S. FDA clinical trial was conducted across 24 sites. Patients were followed annually to 5-years and at 7-years postoperatively. 389 patients were treated with 1- or 2-level CDA (Mobi-C Cervical Disc, Zimmer Biomet, Austin, TX). Preoperative patient characteristics included gender and BMI. Clinical and radiographic outcomes included HO, flexion/extension range of motion (ROM), NDI score, VAS neck pain score, SF-12 and patient satisfaction. Independent radiologists (MMI Inc., Houston, TX) conducted all radiographic evaluations. HO was classified using the system adapted from McAfee and Mehren. HO grades 3 and 4 were classified as clinically relevant due to restricted ROM. Fisher's exact test (P< 0.05) was used to test significant differences across groups.

Results: Clinically relevant HO was observed in 28.4% of 1-level patients. Grade 0/1 HO was present in 4.6% of patients, grade 2 in 66.7%, grade 3 in 17.6%, and grade 4 in 11.1%. From 5 to 7-years, 6.6% of patients showed HO progression of 1 or 2 grades, the remaining 93.4% of patients had no progression of HO. Obese patients (preop BMI≥30) had a higher prevalence of clinically relevant HO than non-obese patients (43.8% vs. 22.1%; p=0.035), and males had a higher prevalence than females (37.3% vs. 20.7%; p=0.09). Grades 0/1 and grade 2 HO had more ROM (14.4±6.7° and 12.3±5.9°, respectively), than patients with grade 3 or 4 (5.5±2.9° and 0.7±0.6°, respectively). For 2-level patients, 32.6% had clinically relevant HO. At the superior level, grade 0/1 was present in 4.5% of patients, grade 2 in 72.3%, grade 3 in 16.8%, and grade 4 in 6.5%. At the inferior level, grade 0/1 was present in 3.4% of patients, grade 2 in 64.9%, grade 3 in 27.0%, and grade 4 in 4.7%. From 5 to 7-years, 15.2% of patients showed HO progression of 1 or 2 grades, the remaining 84.8% of patients had no progression of HO. In 2-level CDA, clinically relevant HO was more prevalent in males vs. females (53.5% vs. 25.0%, p< 0.001), and a higher prevalence in obese patients (44.3% vs. 36.1%; p=0.38). Grades 0/1 and grade 2 HO had greater ROM (11.6±5.7° and 10.2±5.2°, respectively) than patients with grade 3 or 4 (3.8±2.1° and 0.7±0.5°, respectively). Patients with clinically relevant and non-clinically relevant HO had similar 7-year NDI, VAS neck pain scores, and SF-12 PCS. At 7-years, there were no cases of subsequent surgery because of HO, and patients with clinically relevant HO were equally satisfied with their procedure.

Conclusions: The majority of patients presented at 7-years without clinically relevant HO. Progression of HO was stable, 87.3% of all patients having no further development of HO from 5 to 7-years. Possible predictors for clinically relevant HO include preoperative obesity and male gender. Patients with Grade 3/4 HO had reduced range of motion, but maintained similar NDI, VAS neck pain scores, SF-12 and satisfaction compared to patients with less HO.