What would you do? Acute extension block caused by anterior cruciate ligament tear: a case report.

Acute knee locking is usually attributed to a displaced meniscus tear. This case involved late diagnosis of mechanical extension block caused by anterior displacement of a torn anterior cruciate ligament (ACL) with impingement in extension. Definitive reconstruction was delayed after debridement of the ACL stump to improve preoperative range of motion. Despite this, the patient still had difficulty regaining extension after surgery. Early treatment of mechanical extension block may facilitate motion recovery after ACL reconstruction.