Lachman test: how to perform and interpret it
The Lachman test is the most accurate clinical test for an ACL tear. With the knee flexed to 20–30°, stabilise the femur and pull the tibia forward. It is positive when the tibia translates further forward than the other side, or the end feel is soft. It is both sensitive and specific, and more reliable acutely than the anterior drawer test.
Purpose
To assess anterior tibial translation and ACL integrity.
How to perform the Lachman test
- Position the patient supine and relaxed, with the knee flexed to 20–30°.
- Stabilise the distal femur with one hand.
- Grip the proximal tibia with the other hand, thumb on the joint line.
- Apply a brisk anterior force to the tibia and feel the amount of translation and the end feel.
- Compare with the uninjured knee.
Positive result and interpretation
Increased anterior translation compared with the other knee, and/or a soft or absent end feel.
Strongly suggests ACL rupture. A firm end feel with mild extra translation may indicate a partial tear. Hamstring guarding can produce a false negative.
Cluster it with
- Pivot shift test
- Anterior drawer test
- History of non-contact pivoting injury with a pop and rapid swelling
Common mistakes
- Testing with the knee too flexed or the patient not relaxed.
- Not comparing with the other side.
- Missing a posterior sag - a PCL-deficient knee can mimic extra anterior translation.
Frequently asked questions
What is the difference between the Lachman and anterior drawer tests?
Both assess the ACL. The Lachman is performed at 20–30° of flexion and is more reliable acutely; the anterior drawer is performed at 90°, where effusion and hamstring spasm reduce its sensitivity soon after injury.
How is the Lachman test graded?
Commonly by translation compared with the other side: grade 1 about 3–5 mm, grade 2 about 6–10 mm, grade 3 more than 10 mm, along with whether the end feel is firm or soft.