His brother had recurrent patellar instability.

His Beighton score was 7 out of 9. His overall lower limb alignment was normal. He had no effusion in his right knee. The VMO was present but weak. He had marked patellar apprehension ++. His mediolateral glide was at least ++++ with no firm end point. Clinically he suggested that he had a flat trochlea. His patellae tracked with a slight J-shape. He had no end point to his MPFL on the right knee. The knee flexed from −10° to 135°. There was no tibiofemoral joint line tenderness. He was Lachman’s ++, Anterior drawer ++, jerk test +, and MCL−.

A well-corticated bony fragment adjacent to the medial aspect of the patella, the bony fragment, measures 12 × 6 mm in size. This is located at the insertion of the medial patellar ligament/retinaculum. There is no associated bone oedema to suggest a recent injury. There is satisfactory articular cartilage of the patella and the adjacent trochlear groove. There is a relatively shallow trochlear groove [The boss height measures 3 mm]. The medial patellar retinaculum or ligament does not appear attenuated.

There is a complete tear of the anterior cruciate ligament. The posterior cruciate ligament is intact. Intact menisci with no features to suggest meniscal tears. The articular surfaces of the medial and lateral tibiofemoral compartments are intact. There is evidence of a previous injury of the medial collateral ligament which is thickened. Satisfactory appearances of the fibular collateral ligament. No significant joint effusion or synovitis.

No features to suggest a recent patellar dislocation. The well-corticated bony fragment on the medial border of the patella suggests a previous patellar dislocation with a small avulsed fragment at the insertion of the medial patellar retinaculum.

The anterior cruciate ligament is torn.