What is the Lachman Test (LT) for assessing anterior cruciate ligament (ACL) integrity?

The Lachman Test: A Gold Standard for ACL Injury Assessment

The Lachman test is the most reliable and accurate clinical examination test for diagnosing anterior cruciate ligament (ACL) injuries, with a sensitivity of 79% and specificity of 91%.

Technique and Proper Execution

The Lachman test is performed as follows:

1. Patient positioning: The patient lies supine with the knee flexed at 20-30 degrees
2. Hand placement:
   • One hand stabilizes the femur
   • The other hand grasps the proximal tibia
3. Movement: The examiner applies an anterior force to the proximal tibia
4. Assessment: The examiner evaluates:
   • The amount of anterior tibial translation
   • The quality of the endpoint (firm vs. soft)

Grading System

The Lachman test can be graded using a standardized system 1:

• Grade I: Proprioceptive appreciation of a positive test
• Grade II: Visible anterior translation of the tibia
• Grade III: Passive subluxation of the tibia with the patient supine
• Grade IV: Ability of the patient with an ACL-deficient knee to actively sublux the proximal tibia

Biomechanical Basis

Dynamic MRI analysis has revealed what actually happens during the Lachman test 2:

• The lateral compartment contributes more than the medial compartment to anterior tibial translation
• ACL rupture leads to increased laxity in both compartments, with significantly greater contribution from the lateral side
• ACL rupture results in anterior tibial translation coupled with tibial internal rotation

Diagnostic Accuracy and Clinical Significance

The Lachman test has superior diagnostic value compared to other clinical tests for ACL injury:

• It is recognized as the most reliable non-invasive clinical method for determining ACL integrity 1
• It can be performed accurately even in acute injuries when pain and swelling might limit other tests
• A positive Lachman test is highly indicative of ACL damage and should prompt further evaluation

Role in Clinical Decision Making

The Lachman test plays a critical role in the diagnostic algorithm for knee injuries:

• It should be performed in all patients with suspected ACL injury
• A positive test should lead to consideration of MRI for definitive diagnosis 3
• The test is part of a comprehensive functional assessment battery used to determine return-to-play readiness after ACL reconstruction 3

Limitations and Considerations

Despite its high reliability, there are some limitations to consider:

• The test may be difficult to perform in patients with large thighs or significant muscle guarding
• Partial ACL tears may produce equivocal results
• The predictive value of a positive test (47%) is lower than the predictive value of a negative test (70%) 4

Integration with Other Assessment Tools

The Lachman test is often used in conjunction with other clinical tests and imaging:

• MRI remains the gold standard for definitive diagnosis of ACL tears 3
• The combination of clinical tests (Lachman, pivot shift, and anterior drawer) with patient-reported outcome measures should be used for comprehensive assessment 3
• For return-to-play decisions, the Lachman test should be part of a test battery that includes strength tests and hop tests 3

The Lachman test remains a cornerstone of knee examination and should be mastered by all clinicians who evaluate patients with knee injuries.