Segond tibial condyle fracture: lateral capsular ligament avulsion.

Avulsion fractures in the appendicular skeleton are a result of stress on a specific structure that is firmly attached to bone. A small avulsion fracture from the directly lateral surface of the lateral tibial condyle results from excessive tension on the lateral capsular ligament of the knee joint. Recognition of this fracture on an anteroposterior radiograph of a traumatized knee represents substantial evidence of major injury to the lateral joint capsule. This fracture also has a strong association with rupture of the anterior cruciate ligament. The avulsed tibial fragment is remarkably constant in site and appearance. The typical fragment is isolated by a longitudinal fracture line separating a small piece of bone from the lateral tibia. It is elliptical in outline (10 X 3 mm), with its proximal border lying 4 mm distal to the subarticular cortex of the lateral tibial condyle. A hemarthrosis of the knee joint is consistently visible.