How is the Lachman test (Anterior Cruciate Ligament injury assessment) performed?

How to Perform the Lachman Test

The Lachman test is performed with the patient supine, the knee flexed to 20-30 degrees, the examiner stabilizing the distal femur with one hand while applying an anteriorly directed force to the proximal tibia with the other hand, assessing for anterior tibial translation and end-feel quality compared to the contralateral knee. 1

Patient Positioning

• Patient lies supine on the examination table 2
• Knee flexed to approximately 20-30 degrees (some sources specify 25 degrees) 2, 3
• The leg should be relaxed to minimize muscle guarding 4

Examiner Hand Placement

• One hand stabilizes the distal femur (typically placed on the lateral aspect of the distal thigh) 2, 4
• The other hand grasps the proximal tibia (typically placed on the medial aspect of the proximal tibia just below the joint line) 2, 4
• The examiner's thumb of the tibial hand should rest on the tibial plateau to better appreciate translation 4

Test Execution

• Apply a firm anteriorly directed force to the proximal tibia while the femur remains stabilized 2, 4
• The force should be steady and controlled, not jerky 4
• Assess both the amount of anterior tibial translation AND the quality of the end-feel 4, 5
• Always compare to the contralateral (uninjured) knee for reference 4, 5

Interpretation

Grading System 4, 5

• Grade I: Proprioceptive appreciation only (subtle increased translation)
• Grade II: Visible anterior translation of the tibia
• Grade III: Passive subluxation of the tibia with patient supine
• Grade IV: Patient can actively sublux the proximal tibia

Key Findings

• Positive test: Increased anterior tibial translation (typically >3mm difference compared to contralateral side) with a soft or absent end-feel 4, 6
• Negative test: Minimal translation with a firm end-feel 6
• The lateral compartment contributes more to anterior translation than the medial compartment in ACL-deficient knees 3

Clinical Pearls and Pitfalls

• The Lachman test is the most reliable clinical test for ACL rupture, more sensitive than the anterior drawer test 1, 3
• Muscle guarding can produce false-negative results, particularly in acute injuries with pain and effusion 6
• The test has moderate intratester reliability (Kappa 0.44-0.60) and intertester reliability (Kappa 0.42-0.69) 6
• Predictive value of a negative test (70%) is better than a positive test (47%), meaning the test is more useful for ruling out ACL injury than confirming it 6
• Testing under anesthesia increases sensitivity by eliminating muscle guarding (average 2.4mm more translation detected) 2

Alternative Technique: Drop Leg Lachman Test 2

• Patient supine with the leg abducted off the side of the table and flexed 25 degrees
• Thigh stabilized to the table with one hand
• Patient's foot held between examiner's legs
• Free hand applies anteriorly directed force
• This modification produces 1.8-2.4mm greater average excursion than standard Lachman and is physically easier to perform 2