938 - First Reported Case of Piriformis Heterotopic Ossification in a Postmenopausal Woman with Osteoporosis, Prior Aromatase Inhibitor Therapy, and Prolonged Immobility

Case Diagnosis: Piriformis heterotopic ossification (HO) in a 74-year-old postmenopausal woman with osteoporosis, prior aromatase inhibitor (AI) therapy, and prolonged immobility. To our knowledge, this represents the first reported case in this unique risk profile.

Case Description: A 74-year-old woman with a history of osteoporosis and prior AI therapy for breast cancer presented with progressive left hip and leg pain following hospitalization and reduced mobility. She denied recent trauma or surgery. Exam showed limited left hip extension (0° vs 10° contralateral). Pelvic radiographs demonstrated HO localized to the left piriformis. Conservative rehabilitation was initiated with gentle, pain-free range of motion, gradual weight-bearing, and functional retraining. Within three weeks, she demonstrated measurable gains in hip extension and mobility. Follow-up imaging revealed decreased size and density of the ossification.

Discussions: HO most commonly follows trauma, surgery, or neurologic injury; piriformis involvement is exceedingly rare. This case highlights a unique confluence of risk factors—postmenopausal bone loss, prior AI therapy (associated with musculoskeletal syndromes), osteoporosis, and immobility. Symptoms mimicked other etiologies of hip pain, underscoring the importance of imaging for accurate diagnosis. Notably, conservative rehabilitation alone yielded both symptomatic and radiographic improvement, suggesting early physical therapy may play a role in modifying disease course in select HO presentations.

Conclusions: This case represents the first report of piriformis HO in a postmenopausal woman with osteoporosis, prior AI therapy, and immobility. Successful management with non-operative rehabilitation emphasizes the value of clinical vigilance, timely imaging, and targeted therapy. Larger studies are needed to clarify risk factors, optimal treatment, and long-term outcomes in this rare condition.