Bony Encasement of the Ulnar Nerve Secondary to Heterotopic Ossification of the Elbow: An Evaluation of Long-Term Outcomes.

BACKGROUND: Ulnar neuropathy at the elbow caused by heterotopic ossification (HO) is a rare condition. This retrospective study aims to report on 32 consecutive cases of ulnar nerve encasement caused by elbow HO and evaluate long-term outcomes of operative management and a standardized postoperative rehabilitation regimen.

METHODS: A retrospective case series was conducted on 32 elbows (27 patients) that underwent operative management of bony ulnar nerve encasement. All procedures were performed in the inpatient setting at an Academic Level 1 Trauma Center from September 1999 to July 2021 by one of three fellowship-trained shoulder and elbow. Postoperatively, all patients received formal physical therapy, heterotopic ossification prophylaxis (30 received indomethacin, 2 received radiation), and a structured continuous passive motion machine regimen. Patient demographics, age, gender, type of injury, history of tobacco use, and medical comorbidities were obtained to include in the analysis. Long-term follow-up examinations were performed to evaluate elbow flexion-extension arc of motion, Mayo Elbow Performance Scores (MEPS), and visual analog scale (VAS) pain scores.

RESULTS: Thirty-two elbows with complete bony ulnar nerve encasement secondary to HO were identified (14 from burns, 15 from trauma, 3 closed head injuries). Following surgery, the mean flexion-extension arc of motion improved significantly, increasing from 21° to 100° at long-term follow-up (average 8.7 years, range 2-17 years), with statistically significant improvements in preoperative versus long-term postoperative elbow extension (p < 0.001), flexion (p < 0.001), and total arc of motion (p < 0.001). There was a statistically significant improvement in pre- vs. post-procedure ulnar nerve function, as demonstrated by a decrease in average McGowan grade (1.2 to 0.7; p = 0.002). Additionally, 63% of patients with preoperative ulnar neuropathy symptoms (20/32) had either complete resolution or subjective improvement after surgery. The mean time from injury to surgery was 518 days (range 65-943 days). Age, gender, time to surgery, and medical co-morbidities were not associated with outcomes. The complication rate was 9% (3/32). Patients had an average flexion-extension arc of motion of 97 degrees and average MEPS of 80 ("good") at long-term follow-up.

CONCLUSIONS: The combination of operative management, postoperative heterotopic ossification prophylaxis, and a regimented rehabilitation program has proven to be a durable solution for treating and ensuring good long-term functional outcomes for patients with elbow HO and bony ulnar nerve encasement. This treatment approach leads to superior range of motion, improved or resolved ulnar neuropathy, and good to excellent long-term functional outcomes.