This paper introduces the Lachman test for diagnosing ACL instability, performed with the knee between full extension and 15 degrees of flexion. It reviews 250 athlete knees at surgery to define how often the ACL is injured and how it correlates with clinical tests. The authors explain why the classic 90-degree anterior drawer test frequently fails.
When you examine an acutely injured, swollen knee, flexing to 90 degrees for the anterior drawer often fails. The authors identify three reasons: hemarthrosis blocks flexion, hamstring spasm resists tibial translation, and the posterior horn of the medial meniscus buttresses against the convex femoral condyle like a doorstop.
The Lachman test at 0 to 15 degrees solves all three problems. The flat weight-bearing femoral surface no longer blocks the tibia, and extending the knee neutralizes hamstring pull. This is why Lachman is more sensitive in the acute setting.
The practical rule: when you find a medial meniscus tear, look hard for an ACL injury, because 79% coexist. Also examine the knee again after meniscectomy, since removing the meniscus can unmask rotatory instability that was previously masked. Remember the caveat: an incarcerated bucket-handle tear can mechanically block translation and produce a false negative Lachman.
This paper introduces the Lachman test for diagnosing ACL instability, performed with the knee between full extension and 15 degrees of flexion. It reviews 250 athlete knees at surgery to define how often the ACL is injured and how it correlates with clinical tests. The authors explain why the classic 90-degree anterior drawer test frequently fails.
When you examine an acutely injured, swollen knee, flexing to 90 degrees for the anterior drawer often fails. The authors identify three reasons: hemarthrosis blocks flexion, hamstring spasm resists tibial translation, and the posterior horn of the medial meniscus buttresses against the convex femoral condyle like a doorstop.
The Lachman test at 0 to 15 degrees solves all three problems. The flat weight-bearing femoral surface no longer blocks the tibia, and extending the knee neutralizes hamstring pull. This is why Lachman is more sensitive in the acute setting.
The practical rule: when you find a medial meniscus tear, look hard for an ACL injury, because 79% coexist. Also examine the knee again after meniscectomy, since removing the meniscus can unmask rotatory instability that was previously masked. Remember the caveat: an incarcerated bucket-handle tear can mechanically block translation and produce a false negative Lachman.