Rare Case of Subscapularis Myositis Ossificans with Intra-articular Extension.

Introduction: Many of the shoulder pathologies present with pain and stiffness; the principal diagnosis of this condition includes calcific tendonitis or rotator cuff tears. Among these, myositis ossificans is very rare.

Case report: A 22-year-old female presented to us with a complaint of pain in the shoulder for 6 months. On clinical examination, external rotation and internal rotation were restricted. On evaluation, X-ray was normal, while magnetic resonance imaging and computed tomography scan showed 1.5 cm × 1 cm lesion in the subscapularis extending in the shoulder joint. First an ultrasound-guided biopsy was performed, which was followed by open excision biopsy revealing myositis ossificans. Post-operative period was uneventful with the patient achieving full range of motion after 15 days of surgery. Shoulder functional score Constant-Murley score (0-100) increased from 66 to 95, and University of California score (0-35) improved from 17 to 34 from pre-operative to post-operative period, respectively.

Discussion: Myositis is usually a post-traumatic benign heterotopic ossificans that involves large muscles of extremities like the thigh, elbow, etc. So far, only 3 cases have been reported with involvement of rotator cuff tendons, but none with an intra-articular extension. Treatment of this condition is usually conservative; however, surgical treatment is indicated should be considered for those with impaired joint function, continued symptoms, or neurovascular problems. Thus, our case was successfully treated operatively because of impairment in her day-to-day activities.

Conclusion: Myositis ossificans is rare around the shoulder, but when present, it demonstrates differences with respect to appearance and location as compared to other commonly reported heterotopic ossification. Its management should be according to the degree of symptoms and patient-specific complaints.