Chronic lymphoplasmacytic villonodular proliferative synovitis in the stifle of a 3‐year‐old dog without concomitant cranial cruciate ligament rupture

A 3‐year‐old, female, neutered border‐collie cross was referred for investigation and treatment of a suspected left cranial cruciate ligament rupture (CrCLR) following a 1‐month history of progressive pelvic limb lameness. Orthogonal radiographs and clinical examination findings were initially suggestive of a diagnosis of CrCLR. Surgical investigation via medial arthrotomy revealed both an intact CrCL and medial meniscus, and the presence of a small, soft tissue intraarticular mass. A histopathological diagnosis of chronic lymphoplasmacytic villonodular proliferative synovitis was made and revealed to be the underlying source of the progressive pelvic limb lameness. To the best of the authors’ knowledge, this is the youngest reported case of villonodular synovitis in a middle‐sized dog, with both successful surgical and rehabilitation management up to 6 months postoperatively.