Traditionally, anterior cruciate ligament (ACL) injuries have been difficult to diagnose in the Casualty Department. Studies have shown that the anterior drawer test has a poor sensitivity both in acute and chronic ACL deficient knees [4,6,9]; thus, more emphasis has been placed on the pivot shift and Lachman tests [3]. We report four cases of proven ACL rupture where clinical examination revealed an absent pivot shift and a near normal Lachman test following a displaced bucket handle tear of the medial meniscus. This finding has been reproduced in cadaver studies, and we conclude that if the history strongly suggests an ACL injury and examination reveals a stable knee, then the dual pathology of medial meniscus tear and ACL rupture should be suspected.
Case reports
Case 1
A 24-year-old man who injured his left knee playing rugby was referred to the Orthopaedic Clinic 3 months later. There were clinical signs of anterolateral instability in the left knee, and arthroscopy later confirmed a rupture of the ACL. The ACL was reconstructed using prosthetic scaffold. However, he sustained a fresh injury to the left knee 8 months postoperatively, and a further examination under anaesthesia (EUA) and arthroscopy revealed the presence of a rupture of the prosthetic ligament and a 2+ Lachman test and 2+ pivot shift. The patient subsequently presented 7 months later with acute locking of the left knee and was admitted for further surgery.
EUA revealed loss of full extension by 10 deg, with a 1+ Lachman test and absent pivot shift. At arthrotomy a displaced bucket handle tear of the medial meniscus was excised. A repeat examination following meniscal excision brought a return of the pivot shift and a 2+ Lachman test.