Semimembranosus Calcific Tendinopathy

Calcific tendinopathy is a condition marked by the deposition of hydroxyapatite crystals within tendons. Although it most frequently affects the rotator cuff tendons, cases involving the lower extremities are exceedingly rare, with no documented cases involving the semimembranosus in the literature. A 41-year-old man presented with 2 years of nontraumatic, medial knee pain, catching, and tightness. Clinical examination revealed localized tenderness over the posterior medial knee with no laxity or reproduced pain with provocative maneuvers. Radiographs and magnetic resonance imaging confirmed a calcific deposit at the semimembranosus tendon. The patient had attempted over-the-counter anti-inflammatories and stretches. Corticosteroid injection was performed under ultrasound guidance with resolution of symptoms at 2 and 6 weeks follow-ups. Based on review of literature, this is the first reported case of semimembranosus calcific tendinopathy and thus should be considered in the differential diagnosis of posteromedial knee pain. Ultrasound-guided corticosteroid injections can be effective in confirming the diagnosis and treatment of semimembranosus calcific tendinopathy.