Lachman Test for an ACL Tear

The Lachman test is used to diagnose an anterior cruciate ligament (ACL) tear. The ACL is one of four major knee ligaments that contribute to the stability of the knee joint. An ACL tear often occurs as a sport-related injury and may require surgical reconstruction for treatment.

Physical therapist using a Lachman's test on a patient for an ACL tear
Jan-Otto / Getty Images

How the Test Is Performed

With the patient lying flat and relaxed, the examiner bends the knee slightly (about 20 to 30 degrees). The examiner then stabilizes the thigh while pulling the shin forward. Holding the leg in slight external rotation (outwards) will help relax the IT band.

The test places stress on the ACL. Both the amount of movement (shifting) of the shin bone, as well as the feel of the endpoint of movement (how solid the ligament feels), offer information about the ACL.

Knees with a damaged ACL may demonstrate more movement and a less firm endpoint during a Lachman test.


Most examiners grade the results of the Lachman test on two criteria. First, the endpoint, and second, the amount of laxity. When assessing the endpoint, the examiner is feeling for the ACL limiting the amount of shifting of the shin bone.

Typically an examiner will describe the endpoint as either "firm" or "soft." A firm endpoint implies the ACL is doing its job to limit the amount of movement in the knee joint. A soft endpoint is indicative of the ACL not functioning well and other structures (the secondary stabilizers) limiting the amount of movement in the joint.

The second criteria to assess the Lachman test is the amount of laxity (movement) of the joint. The grading is based on a comparison to the non-injured extremity. Therefore, it is common for your healthcare provider to examine both knees to determine the grade of the Lachman test.

Grading of Lachman Test

  • Normal: No side-to-side difference.
  • Grade 1 (mild): 3-5 mm more translation of the tibia on the femur.
  • Grade 2 (moderate): 5-10 mm more translation of the tibia on the femur.
  • Grade 3 (severe): >10 mm more translation of the tibia on the femur.

These measurements can be difficult to quantify, and oftentimes different examiners may come up with different results. Some healthcare providers use a tool, called a KT-1000, to perform this test. The KT-1000 has been shown to be a reliable measure that can more precisely measure the grade of the Lachman test.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Makhmalbaf H, Moradi A, Ganji S, Omidi-kashani F. Accuracy of lachman and anterior drawer tests for anterior cruciate ligament injuries. Arch Bone Jt Surg. 2013;1(2):94-7.

  2. Abulhasan J, Snow M, Anley C, Bakhsh M, Grey M. An extensive evaluation of different knee stability assessment measures: a systematic reviewJournal of Functional Morphology and Kinesiology. 2016;1(2):209-229. doi:10.3390/jfmk1020209

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.