Lachman Test for ACL Injury
The Lachman test diagnoses anterior cruciate ligament (ACL) tears and is the most sensitive clinical examination for detecting ACL rupture. 1
Test Characteristics and Diagnostic Performance
The Lachman test demonstrates superior diagnostic accuracy compared to other physical examination maneuvers for ACL injury:
- Sensitivity: 87.1% (95% CI 0.84-0.90), making it the most sensitive clinical test for ACL tears 2
- Negative likelihood ratio: 0.17 (95% CI 0.11-0.25), the lowest among ACL examination tests, meaning it is highly effective at ruling out ACL injury when negative 2
- Predictive value of a negative test: 70%, indicating reasonable confidence that the ACL is intact when the test is negative 3
Clinical Application
During the Lachman test, the examiner assesses anterior tibial translation relative to the femur with the knee flexed at 20-30 degrees. 1 A positive test reveals increased anterior translation and a soft or absent end-feel compared to the contralateral knee. 4
The test specifically evaluates ACL integrity by detecting pathologic anterior tibial displacement, with the lateral compartment contributing more to anterior translation than the medial compartment in ACL-deficient knees. 5
Comparison with Other ACL Tests
While the Lachman test has the highest sensitivity, the pivot shift test demonstrates higher specificity (97.5%) and positive likelihood ratio (16.00) for confirming ACL rupture. 2 The anterior drawer test is less reliable, particularly in acute settings with effusion and muscle guarding. 6
Technical Considerations
For examiners with small hands or when examining patients with large thigh circumference (>43 cm), the alternate Lachman test technique significantly outperforms the standard Lachman test, achieving 100% accuracy in patients with >2.5 mm bilateral laxity difference versus only 28% for the standard technique in large-thighed patients. 4
Intratester reliability ranges from moderate (Kappa 0.44-0.60), with intertester reliability varying from 0.42-0.69 depending on examiner experience. 3 These reliability limitations emphasize the importance of combining clinical examination with imaging confirmation when ACL injury is suspected. 1