To better understand the mechanics of this test and why it is effective, you may want to review basic knee anatomy.
What is the Lachman Test of the Knee?
The Lachman Test is commonly used in orthopedic examinations to test for anterior cruciate ligament (ACL) integrity. The test primarily targets the posterolateral bundle of the ligament. It tests one-plane anterior stability and is one of the most well known and most used special tests.
- anterior cruciate ligament (ACL)
- posterior cruciate ligament (PCL)
- arcuate-popliteus complex
The test is performed with the patient in a relaxed supine position. The knee to be tested should be flexed to about 20 degrees. One of the examiners hands holds and stabilizes the distal femur of the leg to be tested. The examiners other hand firmly grasps the proximal tibia of the same leg.
From the starting position the examiner pulls anteriorly on the proximal tibia.
Positive Lachman Test
This test is considered positive if there is a soft or mushy end feel to the translation of the tibia. A soft end feel / endpoint is indicative of secondary structures stopping the continued anterior translation of the tibia. Excessive anterior translation may also be noted. A hard/firm end feel will be felt when the ACL is intact and abruptly halts continued anterior translation.
Accuracy of Test
The Lachman Test is quite accurate but should not be used as the only criterion for ruling in or out ACL integrity. Of the ACL integrity tests, it is widely considered to be the most sensitive.
video source: University of Wisconsin – Department of Family Medicine