The ACL is the most clinically significant knee ligament, the primary restraint against the anterior tibial translation that would allow the knee to buckle during cutting and pivoting movements. Approximately 200,000 ACL reconstructions are performed annually in the USA alone. The ACL has two functional bundles — the anteromedial bundle (tight in flexion, resists anterior translation) and the posterolateral bundle (tight in extension, resists rotational forces and hyperextension).
| Origin | Posteromedial surface of the lateral femoral condyle in the intercondylar notch |
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| Insertion | Anterior intercondylar area of the tibia between the anterior horns of the medial and lateral menisci |
| Actions | Primary restraint against anterior tibial translation and internal tibial rotation; secondary restraint against varus and valgus stress |
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ACL tears produce an audible or felt pop with immediate swelling from haemarthrosis (from the middle geniculate artery within the ACL substance). The Lachman test (anterior tibial translation at 30 degrees of knee flexion) is the most sensitive clinical test (85 percent). MRI confirms the tear and associated injuries — medial meniscal tears in 50 percent, lateral meniscal tears in 25 percent, and bone bruises in virtually all acute ACL tears. ACL reconstruction using bone-patellar tendon-bone, hamstring, or quadriceps tendon graft is performed for active patients wishing to return to pivoting sports.
Anterior tibial translation injury from non-contact pivoting or contact knee hyperextension producing immediate haemarthrosis and positive Lachman test, managed with ACL reconstruction for active patients.
