Semimembranosus Tendinopathy

Chronic posteromedial knee pain in a runner, with tenderness localised over the semimembranosus insertion and pain on resisted knee flexion, suggests semimembranosus tendinopathy, which is an overuse tendinopathy of the distal semimembranosus at its insertion on the posteromedial tibia and a recognised cause of posteromedial-corner knee pain. However, posteromedial knee pain has several possible sources, so I would not assume the tendon is the cause until I have confirmed it. The main differentials are a posterior-horn medial meniscus tear, which can present very similarly, pes anserine bursitis, which is usually a little more anteromedial, a popliteal or Baker's cyst, posteromedial-corner or medial collateral pathology, and referred medial-compartment osteoarthritis. So I would precisely localise the tenderness to the semimembranosus insertion, provoke the pain with resisted knee flexion, and use imaging - ultrasound is a useful adjunct or alternative to MRI for the posteromedial corner, and MRI characterises the tendon and excludes a meniscal tear. Management is non-operative first: relative rest and activity modification, eccentric and progressive loading rehabilitation, NSAIDs, and an image-guided corticosteroid injection for refractory cases, together with correcting the overuse cause through training-load and biomechanical adjustment. Surgery - debridement or reattachment - is rarely required and is reserved for genuinely refractory cases once the diagnosis is secure.