Lachman Test: the most reliable test for detecting an ACL tear

If you had to pick just one manual test to suspect an anterior cruciate ligament (ACL) tear, the literature is fairly unanimous: the Lachman test. It's more sensitive than the classic anterior drawer and is better tolerated in the acute phase, which makes it one of the first maneuvers to master in knee assessment.

What does this test measure?

The Lachman test evaluates the anterior translation of the tibia relative to the femur with the knee in slight flexion (20-30°), the position where the ACL is the main stabilizer against that translation. Besides the amount of displacement, it's essential to assess the "end-feel" (the sensation at the end of the movement): firm and crisp if the ligament is intact, or soft and "mushy" if it's torn.

Equipment needed

• Treatment table
• No additional tools required (instrumented versions with an arthrometer exist, but aren't essential)

Step-by-step protocol

1. The patient lies supine, with the knee to be tested flexed about 20-30° (you can rest the patient's thigh on your own leg or a cushion to maintain that flexion without effort from the patient)
2. With one hand, stabilize the femur just above the knee
3. With the other hand, grasp the proximal tibia (just below the joint line) and apply a quick but controlled anterior translation force
4. Assess two things: the amount of displacement (always compare with the healthy contralateral knee) and the end-feel at the end of the movement
5. Repeat 2-3 times to confirm the sensation

Common mistakes

• Not comparing with the contralateral knee ("normal" varies a lot between people)
• Performing the test with too much or too little flexion (outside the 20-30° range loses specificity)
• Not paying attention to the end-feel and focusing only on the amount of displacement

How to interpret the result

Result	Interpretation
Displacement similar to the healthy side, firm end-feel	Negative — ACL likely intact
Greater displacement than the healthy side, soft/mushy end-feel	Positive — suggests an ACL tear
Slightly increased displacement with firm end-feel	Possible partial or constitutional laxity; interpret with caution

The Lachman test has high sensitivity for detecting ACL tears, but with a positive (or inconclusive with compatible clinical history: a "pop" episode, immediate swelling, sense of instability) result, confirmation with MRI and specialized medical assessment is recommended.

Relationship with other tests

The Lachman is often combined with:

• Pivot Shift Test — to assess the rotational instability associated with an ACL tear
• Anterior Drawer Test — a classic complementary maneuver, though less sensitive in the acute phase

Track stability over time

Whether an ACL tear is managed conservatively or surgically, it's useful to document the evolution of laxity and, above all, the functional tests that determine return to sport. With Movalytics you can log the Lachman test result alongside jump and strength tests at each phase of the process, and see at a glance how the athlete is progressing.

Frequently asked questions

What's the difference between the Lachman test and the anterior drawer? Both assess anterior tibial translation, but the Lachman is done with less knee flexion (20-30° vs 90°) and is more sensitive, especially in the acute phase when swelling or muscle spasm limits flexion. Can it be negative even if there's an ACL tear? Yes, especially if there's significant protective muscle spasm in the acute phase, or if there's an associated injury (for example, a meniscus tear) that blocks the movement. That's why clinical suspicion should always be considered in context. How soon after the injury can this test be done? It can be attempted from the very first moment, but in the very acute phase (first 24-48h) pain and spasm can make it harder to interpret; it's sometimes repeated a few days later once the initial inflammation subsides.