Lachman Maneuver for ACL Assessment
The Lachman test is the most sensitive and reliable clinical examination for detecting ACL rupture and should be performed with the patient supine, knee flexed to 20-30 degrees, while the examiner stabilizes the distal femur and applies anteriorly directed force to the proximal tibia, assessing for anterior tibial translation and end-feel quality compared to the contralateral knee. 1, 2
Test Procedure
The proper technique involves specific positioning and hand placement:
- Patient positioning: Supine with the affected knee flexed to 20-30 degrees 1, 2
- Examiner hand placement: One hand stabilizes the distal femur while the other applies anteriorly directed force to the proximal tibia 2
- Assessment parameters: Evaluate both the amount of anterior tibial translation AND the quality of the end-feel, comparing to the contralateral knee 2
Biomechanical Considerations
During the Lachman test, the lateral compartment of the knee contributes more than the medial compartment to anterior tibial translation in both normal and ACL-deficient knees, with ACL rupture causing increased laxity in both compartments but significantly greater contribution from the lateral side 3. This is coupled with tibial internal rotation 3.
Clinical Grading System
When the test is positive, grade the severity using the following criteria:
- Grade I: Proprioceptive appreciation of increased translation only 4, 5
- Grade II: Visible anterior translation of the tibia 4, 5
- Grade III: Passive subluxation of the tibia with patient supine 4, 5
- Grade IV: Patient can actively sublux the proximal tibia 4, 5
These grades correlate with statistically significant differences in measured anterior tibial displacement 4, 5.
Diagnostic Performance
The Lachman test demonstrates superior diagnostic characteristics compared to other ACL examination maneuvers:
- Sensitivity: 79% in acute settings 6
- Specificity: 91% 6
- Comparative advantage: More sensitive than the anterior drawer test 2
Important Caveat on Test Reliability
While the Lachman test is considered the gold standard, studies show moderate intratester reliability (Kappa 0.44-0.60) and intertester reliability (Kappa 0.42-0.69) 7. The predictive value of a negative test is 70%, making it more useful for ruling out ACL injury than confirming it (positive predictive value only 47%) 7. This means a negative Lachman test is more clinically valuable than a positive one in isolation.
Integration with Comprehensive ACL Assessment
The Lachman test should be combined with other clinical tests and patient-reported outcomes for optimal diagnostic accuracy:
- Clinical examination battery: Use Lachman test alongside pivot shift and anterior drawer tests 8
- Patient-reported measures: Incorporate IKDC subjective scores and KOOS 8
Comparative Test Performance in Acute Settings
In acute ACL injuries, the lever sign test shows slightly better sensitivity (82%) with lower likelihood ratio for negative results (0.21), while the pivot shift test has the highest positive likelihood ratio (11.60) but lowest sensitivity (55%) 6. However, the Lachman test remains the most widely recommended first-line examination 1, 2.