Superior patellar dislocation: the value of clinical examination and radiological investigation.

A 57-year-old obese woman with a history of osteoarthritis presented with an acutely painful left knee and an inability to bear weight following a twisting injury. The initial diagnosis in A&E was a ruptured patellar tendon. A more thorough clinical examination revealed a high-riding patellar with the knee hyper-extended and a patellar dimple, consistent with superior patellar dislocation. The diagnosis was confirmed with imaging and the patient successfully underwent closed reduction. She re-presented 2 months later with ipsilateral knee pain after climbing a step. The initial diagnosis was quadriceps tear and ultrasound confirmed a partial tear in proximal vastus medialis. She was discharged home with analgesia and splinting of the leg. Subsequent MRI demonstrated severe tricompartmental degenerative changes in the left knee, the tear in vastus medialis noted on ultrasound with disruption to the medial capsular structures in keeping with lateral subluxation of the knee.