The Lachman Test

Written by Dr Sheila Strover on March 14, 2025

The Lachman Test is performed by the clinician to assess laxity of the anterior cruciate ligament when there is a suspected tear. Page updated July 2024 by Dr Sheila Strover (Clinical Editor)

Illustration showing the position of the examiner's hands for performing the Lachman test.

Illustration of surgeon performing the Lachman test on a patient.

What does the Lachman test measure?

The Lachman test assesses three things:

  • how far in millimetres the tibia moves forward in relation to the femur. This evaluates the restraint provided by the anterior cruciate ligament (ACL).
  • how this compares with the same test in the unaffected knee. Five mm or more is highly suggestive of a complete ACL tear.
  • how abrupt the endpoint feels, ie a hard endpoint (which is good) or a soft endpoint (which is not good) - the firmness of the endpoint is a measure of how well the ACL is performing in stabilising the knee.

How is the Lachman test performed?

With the patient lying on their back and the head supported, the knee is flexed to 20-30 degrees, and the patient encouraged to totally relax.

One hand grasps the femur, while the other grasps the upper tibia with the fingers at the back of the tibia and the thumb in front. Attempt is made to displace the tibia in relation to the femur, feeling both for the degree of displacement and the firmness of the end point.

Grading of the Lachman test

The surgeon will give the patient a Lachman grade to allow a record and compare changes over time.

Because people differ in their normal amount of joint laxity, the measurement is always compared to the other side, and the amount of forwards movement (anterior translation) recorded is the difference between the two sides.

"....Grading of ACL laxity is described as 1 through 3, which correlates to mild, moderate, and severe ACL injuries. Mild (grade I) is 0 to 5 mm, moderate is 6 to 10 mm (grade II), and severe is 11 to 15 mm (grade III) of anterior tibial translation compared to the uninjured side...."

Ryan Coffey et al

How accurate is the Lachman test?

The Lachman test is not the most accurate of the manual tests for an anterior cruciate ligament tear.

If there is blood in the knee, the test may be painful and trigger hamstrings spasm, which can make the measurement inaccurate.

Other common tests include the pivot shift test, anterior drawer test, Slocum test and evaluation with the KT2000 machine.

....diagnostic accuracy values for the Lachman test are lower than previously reported" and "...MRI and arthrometry...are recommended when the history is suggestive of an ACL tear, but tests are negative".

Pawel A Sokal et al

Anterior cruciate ligament, Anterior cruciate ligament injury, Instability, Tibiofemoral joint, Cruciate instability, Anterior translation, Sherman classification, Pivot shift test, Anterior drawer test, Slocum test, KT2000

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