A rare case of isolated traumatic avulsion of the pes anserinus tendon

Complete rupture of the conjoint pes anserinus tendon is rare, and isolated rupture without injury to associated structures has not been previously reported in the literature. A case of complete isolated rupture of the pes anserinus tendon is described in a young, healthy male. The non-specific nature of the presentation and rarity of the condition makes diagnosis from history and examination alone challenging. Magnetic resonance imaging was critical in making the correct diagnosis and excluding other potential-associated injuries with the diagnosis confirmed intraoperatively. The patient underwent surgical repair and rehabilitation and made significant progress. The diagnosis may be overlooked on a routine knee MRI, particularly in the absence of other associated injuries. An untreated injury may result in a poor outcome for the patient, with chronic pain and reduced function. Hence it is important to consider it in traumatic injuries to the region, with a view for an extended scan to visualise the full extent of the pes tendons to their insertion, particularly when there is high fluid signal in the popliteal fossa along the semitendinosus.