Anterior Cruciate Ligament Tear
A ligamentous disruption most often sustained during pivoting or deceleration in sport, producing rotational instability of the knee.
Overview
The anterior cruciate ligament is the primary restraint to anterior translation of the tibia on the femur and a secondary restraint to internal rotation. Disruption typically occurs through a non-contact pivoting mechanism with the foot planted and the knee near extension, although contact injuries are also common in collision sport. A haemarthrosis develops within hours in the majority of cases, reflecting bleeding from the torn ligament and frequently associated chondral or meniscal injury.
Epidemiology
Estimated incidence in the general population is 30 to 78 per 100,000 person-years, with young athletes in pivoting sports carrying several-fold higher risk. Female athletes have a two- to eight-fold higher rate than males in comparable sports, attributed to differences in neuromuscular control, limb alignment, hormonal environment, and notch geometry. Peak age is between 15 and 25 years.
Symptoms
Patients typically report a sudden pop or shift, rapid swelling, and inability to continue activity. On examination the Lachman test, anterior drawer, and pivot shift are the principal clinical tests, of which the Lachman is the most sensitive for acute injury. Persistent rotational instability, episodes of giving way on cutting, and apprehension with pivoting characterise the chronic phase.