Anatomy Msk · Year 1 · from Anatomy Msk
Case 1: Anterior Cruciate Ligament (ACL) Tear
Clinical Image
Source: Wikimedia Commons - ACL Tear MRI - CC BY-SA 3.0
Case Presentation
A 22-year-old female soccer player presents to the emergency department after injuring her left knee during a game. She was planting her left foot to change direction when she felt her knee "give way." She heard and felt a "pop" at the time of injury and fell to the ground unable to continue playing. She reports immediate swelling of the knee within 2 hours. Physical examination reveals a tense effusion of the left knee. Range of motion is limited by pain and swelling (10-90 degrees vs. full on the right). Lachman test is positive with increased anterior tibial translation and soft endpoint compared to the right knee. Anterior drawer test is also positive. Pivot shift test reproduces her sensation of instability. There is no varus or valgus instability. McMurray test is equivocal. Radiographs show no fracture but a joint effusion. MRI confirms a complete midsubstance ACL tear with bone bruising in the lateral femoral condyle and posterolateral tibial plateau (typical pivot shift pattern). There is also a lateral meniscus posterior horn tear. After discussion of treatment options, she elects for ACL reconstruction with patellar tendon autograft to return to competitive sports.
Key Learning Points
- The ACL prevents anterior translation of the tibia and provides rotational stability
- ACL injuries commonly occur with non-contact pivoting, cutting, or landing with knee near extension
- Females have 2-8 times higher ACL injury rates due to anatomic, hormonal, and neuromuscular factors
- Acute hemarthrosis after knee injury is ACL tear until proven otherwise (70% have ACL injury)
- Lachman test is more sensitive than anterior drawer; pivot shift indicates functional instability