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Knee ligament and meniscal injuries
Mechanism, findings, the test to do and the usual management for the five classic knee injuries.
| Injury | Mechanism | Findings | Key test | Management |
|---|---|---|---|---|
| ACL | Non-contact deceleration, cutting or pivoting, or landing near extension in valgus | A pop, can't continue, rapid hemarthrosis within hours; later giving way | Lachman (most sensitive); anterior drawer, pivot shift | Confirm with MRI; reconstruction for young active patients |
| PCL | Posterior force on the proximal tibia with the knee flexed — dashboard injury or a fall onto the flexed knee | Posterior sag of the tibia | Posterior drawer, sag sign | Often non-operative when isolated |
| MCL | Valgus blow to the lateral knee | Medial knee pain and tenderness along the ligament | Valgus stress at 30° of flexion | Hinged brace and rehab; look for ACL and medial meniscal tears |
| LCL and posterolateral corner | Varus blow to the medial knee, or hyperextension–varus | Lateral knee pain, varus laxity; often with cruciate injury | Varus stress at 30°; check the common fibular nerve (foot drop) | Often needs surgical repair |
| Meniscal tear | Twisting on a flexed, weight-bearing knee (young); minimal trauma such as squatting (older, degenerative) | Joint-line tenderness, swelling over a day, catching or locking | McMurray, Thessaly, Apley | Degenerative: physical therapy first. Locked knee (bucket-handle tear): arthroscopy |
Unhappy triad: ACL + MCL + medial meniscus, from a contact valgus blow.
The medial meniscus is torn more often because it is attached to the MCL. Rapid swelling suggests a vascular structure (ACL); swelling over a day suggests a meniscus.