What is the sensitivity and specificity of the Lachmann test (Lachmann test) for diagnosing anterior cruciate ligament (ACL) injuries?

Sensitivity and Specificity of the Lachman Test for ACL Tears

The Lachman test demonstrates a sensitivity of 81-87% and specificity of 85-94% for detecting anterior cruciate ligament tears, making it the most sensitive clinical examination test available, though its diagnostic accuracy has been previously overestimated in older literature. 1, 2

Diagnostic Performance Metrics

Overall Accuracy

• Sensitivity: 81-87% across multiple meta-analyses, with the most recent bivariate analysis showing 81% (95% CI, 73-87%) 1, 2, 3
• Specificity: 85-94%, with pooled estimates of 85% (95% CI, 73-92%) 1, 2
• Diagnostic accuracy: 89.53% when compared directly to arthroscopy 4

Performance by Clinical Context

Complete ACL tears:

• Sensitivity drops to 68% (95% CI, 54-79%) 1
• Specificity: 79% (95% CI, 51-93%) 1

Post-acute presentations (>4-5 days after injury):

• Sensitivity: 70% (95% CI, 57-80%) 1
• Specificity: 77% (95% CI, 53-91%) 1
• The test performs optimally when delayed 4-5 days post-injury, achieving 84% sensitivity and 96% specificity for anterior talofibular ligament assessment 5

Acute presentations:

• Lower sensitivity than previously reported in older meta-analyses 1
• Historical data suggested 89% sensitivity, but recent bivariate modeling shows this was overestimated 2, 6

Comparison with Other Clinical Tests

The Lachman test is more sensitive but less specific than the pivot shift test:

• Pivot shift: 24-55% sensitivity but 94-98% specificity 1, 2, 3
• Anterior drawer: 83-92% sensitivity and 85-91% specificity (performs better in chronic vs. acute conditions) 1, 2, 4
• Lever sign: 83% sensitivity and 91% specificity 1

The pivot shift test has the highest positive likelihood ratio (LR+ = 16.00) for ruling in ACL tears, while the Lachman test has the lowest negative likelihood ratio (LR- = 0.17) for ruling out ACL tears. 3

Clinical Application Algorithm

For suspected ACL injury:

1. Perform the Lachman test first as the most sensitive screening examination 2, 3

   • If positive: proceed with pivot shift test for confirmation (high specificity) 2, 3
   • If negative: ACL tear is unlikely (best negative likelihood ratio) 3

2. Add the pivot shift test to increase diagnostic certainty when ruling in ACL injury 2, 3

   • Positive pivot shift with positive Lachman: very high probability of ACL tear 2

3. Consider delayed examination (4-5 days post-injury) to optimize test performance when initial acute examination is equivocal 5, 1

4. Obtain MRI for definitive diagnosis when clinical tests are discordant or surgical planning is needed 5, 4

   • MRI sensitivity: 93-98.57% and specificity: 87.5-100% 4, 6

Important Caveats

The Lachman test's diagnostic accuracy has been overestimated in previous literature because older meta-analyses used statistical methods that did not account for the non-independence of sensitivity and specificity, and included patients with concomitant ligament injuries that artificially inflated sensitivity 1

Test performance is significantly affected by:

• Timing of examination (acute vs. post-acute) 5, 1
• Presence of joint effusion or hemarthrosis limiting examination 5
• Examiner experience 4
• Patient guarding due to pain in acute settings 5
• Partial versus complete tears (lower sensitivity for complete tears) 1

When clinical examination is limited by pain or swelling, ultrasound can detect ACL injuries with 90% sensitivity and 97% specificity as an alternative to immediate MRI, though MRI remains superior for comprehensive evaluation 5