Lachman Test: Purpose, Procedure, and Clinical Interpretation

TL;DR

• The Lachman test assesses anterior tibial translation and ACL integrity with the patient supine and the knee flexed 20 to 30 degrees.
• The Lachman generally outperforms the anterior drawer because 90-degree knee flexion increases hamstring tension, which can restrict translation and mask ACL laxity.
• Reported diagnostic accuracy varies, but one clinical reference reports 87% sensitivity and 93% specificity.
• Failure to obtain hamstring relaxation is a common technique error that produces false-negative findings.

What the Lachman test measures

The Lachman test assesses one-plane anterior translation of the tibia relative to the femur. Because the ACL restrains anterior tibial movement, excessive translation or loss of its normal endpoint can indicate ACL disruption. Torg and colleagues popularized the test in 1976 from a technique attributed to orthopedic surgeon John Lachman, and it became the primary manual test for ACL integrity in clinical examination, according to a clinical overview of the Lachman test.

Clinicians often prefer the Lachman test during acute assessment because its mechanics limit the stabilizing effect of hamstring tension compared with the anterior drawer test. Pain, swelling, and guarding can still reduce diagnostic accuracy, so clinicians should interpret the finding alongside the injury history, broader knee examination, and imaging when indicated.

Performing the Lachman test step by step

1. Ask the patient to lie supine and relax the tested leg. Position the knee in approximately 20 to 30 degrees of flexion. Flexion below 20 degrees can increase posterior capsular restraint, while flexion beyond 30 degrees can recruit the hamstrings and reduce detectable anterior translation, as explained in a clinical guide to Lachman test positioning.

2. Stabilize the distal femur with one hand immediately above the joint line. Grasp the proximal tibia with the other hand immediately below the joint line, and place your thumb near the tibial tuberosity. Keep the tibia neutral or slightly externally rotated to reduce tension through the iliotibial band.

3. Apply a firm, smooth anterior force through the proximal tibia while holding the femur stationary. Avoid pulling through the ankle or distal tibia because distal hand placement reduces control and can make translation harder to judge.

4. Assess both the amount of anterior tibial movement and the endpoint when movement stops. Repeat the maneuver on the uninjured knee with similar positioning and force because normal laxity differs among patients.

5. Use a stabilized Lachman when hand size or thigh circumference prevents secure femoral control. Support the posterior thigh with your knee or thigh while maintaining the required knee flexion, then stabilize the femur and translate the proximal tibia anteriorly. The support provides a steadier anchor and helps you detect hamstring relaxation, as described in StatPearls’ Lachman test review.

6. Consider the prone Lachman when the supine position remains difficult. Place the patient prone with the knee flexed over the table edge, stabilize the femur, and direct force anteriorly through the posterior proximal tibia. Use the prone result as a confirmatory finding rather than the sole basis for excluding an ACL tear.

Interpreting findings: grading and end-feel

Interpret anterior translation against the contralateral knee, then pair the translation grade with endpoint quality. Baseline laxity varies between individuals, so millimeters alone can misrepresent ACL integrity.

A commonly used grading scale groups side-to-side translation as follows.

Published grading systems use different boundaries. For example, StatPearls describes grade I as 0 to 5 mm, grade II as 6 to 10 mm, and grade III as 11 to 15 mm. Documentation should identify the grading scheme or record the measured side-to-side difference rather than assume universal thresholds.

Endpoint quality often carries more diagnostic weight than the translation grade. A firm endpoint stops the tibia abruptly as the ACL restrains further anterior movement. A soft or absent endpoint lacks that abrupt restraint because secondary structures eventually limit translation instead.

Clinicians can record endpoint quality as A for firm or B for soft alongside the translation grade. A soft endpoint at any grade should raise suspicion for ACL disruption, even when the measured displacement appears modest. Conversely, a firm endpoint does not exclude a partial tear. Remaining intact fibers can create a deceptively normal stop despite increased translation or other findings that support ACL injury.

Sensitivity, specificity, and what a negative test really means

Reported accuracy varies enough that clinicians should avoid treating one estimate as definitive. A commonly cited reference reports 87% sensitivity and 93% specificity for the standard Lachman test, according to StatPearls’ Lachman test review. More recent pooled analyses reported sensitivity of 76% to 81% and specificity of 85% to 89%, suggesting that earlier estimates may have overstated performance. However, a prospective acute-injury study using a stabilized technique reported 91.7% sensitivity and 98.7% specificity, as reported in the prospective study of the stabilized Lachman test.

Likelihood ratios show how the result changes the probability of rupture. One meta-analysis estimated a positive likelihood ratio of 10.2 and a negative likelihood ratio of 0.14, as summarized in a clinical review of Lachman test accuracy. With a 50% pretest probability, those values would raise the probability to about 91% after a positive test or lower it to about 12% after a negative test. Lower pooled accuracy estimates would produce smaller shifts.

A correctly performed negative Lachman makes ACL rupture less likely, but it does not exclude one. Acute effusion, guarding, hamstring tension, poor stabilization, and partial tearing can reduce the test’s sensitivity. Clinicians should interpret a negative result alongside the injury history, the rest of the knee examination, and imaging when clinical suspicion remains high.

Why false negatives happen — and how to avoid them

Acute hemarthrosis can mask anterior translation by provoking pain, guarding, and restricted knee motion. In a 2024 prospective study of the stabilized Lachman test, all four false-negative Lachman tests occurred in patients with large effusions examined within seven days of injury. Three became positive after aspiration reduced the effusion. When guarding limits the examination, document the limitation and consider reassessment after symptoms permit better relaxation.

Hamstring co-contraction also resists anterior tibial movement and can produce an apparently firm endpoint. Before accepting a negative result, confirm that the posterior thigh and hamstrings feel relaxed. A stabilized Lachman can improve femoral control and help the examiner detect muscle tension, particularly when thigh size or examiner hand size makes the standard technique difficult.

Positioning errors reduce the test’s sensitivity. Recheck that the knee remains within 20 to 30 degrees of flexion and that the tibial hand contacts the proximal tibia rather than pulling distally. Excessive flexion increases hamstring restraint, while poor femoral stabilization allows unwanted movement instead of isolated tibial translation, as explained in StatPearls’ Lachman test review.

Timing and side-to-side comparison provide two quick checks. When feasible, examine the knee before substantial swelling develops. Always compare translation and end-feel with the uninjured limb because baseline laxity varies among patients. A negative result deserves less weight when effusion, guarding, or uncertain positioning compromised the examination.

Lachman vs. anterior drawer vs. pivot shift

The Lachman test is generally preferred for initial manual assessment because its 20 to 30 degrees of knee flexion limits hamstring tension and exposes anterior tibial translation. By comparison, the anterior drawer test places the knee at 90 degrees, where guarding and hamstring contraction can resist translation and mask ACL laxity, especially after an acute injury. Research reviews report lower diagnostic performance and reliability for the anterior drawer test.

The pivot shift assesses rotational instability rather than isolated anterior translation. A positive pivot shift can help confirm clinically significant ACL deficiency, but the maneuver requires patient relaxation and precise execution. Its lower sensitivity makes it unsuitable as a standalone test for excluding a tear, despite its generally higher specificity than the Lachman test.

Physical therapists should interpret these ACL special tests as complementary findings. The Lachman assesses anterior stability, while a well-executed pivot shift adds information about rotational instability. Combining test results with the injury history, effusion, range of motion, and side-to-side comparison provides a stronger clinical assessment than relying on any single maneuver.

Programming after a positive finding

A positive Lachman finding alone does not determine the rehabilitation plan. After diagnostic workup and surgical decision-making establish the care path, the physical therapist selects progression criteria based on the full clinical picture and any applicable surgical protocol.

Physitrack can serve as the delivery layer for phased ACL rehabilitation. Clinicians can build and adjust home exercise programs as patients meet defined criteria, then review reported completion between visits. Clinical decisions about exercise selection and progression remain with the treating clinician.

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How accurate is the Lachman test?

Reported accuracy varies by population, injury timing, and examiner technique. StatPearls reports 87% sensitivity and 93% specificity, while pooled estimates in other reviews are lower. Clinicians should interpret these figures alongside history and other ACL tests.

What does a positive Lachman test feel like?

A positive test produces increased anterior tibial translation compared with the opposite knee. The endpoint often feels soft, absent, or poorly defined rather than firm and abrupt. A soft endpoint raises concern even when translation appears modest.

Can the Lachman test miss an ACL tear?

The Lachman test can miss partial or complete tears. Acute effusion, guarding, and hamstring contraction can restrict translation and produce a false negative. In one acute study, every false-negative case involved a large effusion.

Why is Lachman preferred over anterior drawer?

The Lachman uses 20 to 30 degrees of knee flexion. The anterior drawer uses 90 degrees, where hamstring tension can oppose tibial translation. Lachman therefore tends to detect acute ACL laxity more reliably.

Does a negative Lachman rule out an ACL tear?

A negative Lachman lowers the probability of an ACL tear but does not exclude one. Technique errors, guarding, and partial tears can preserve a firm endpoint or limit translation. Persistent clinical suspicion warrants additional assessment and appropriate imaging.