Reliability and Diagnostic Accuracy of the Lachman Test Performed in a Prone Position
Mulligan EP, Harwell JL, Robertson WJ. J Orthop Sports Phys Ther. 2011;41(10):749-57. Epub 2011 Sep 4.
The Lachman test has been defined as the clinical gold standard for assessing anterior cruciate ligament (ACL) tears (see video by the study authors). Unfortunately, the test can be challenging for clinicians with smaller hands or patients with larger thighs. In these challenging situations, it has been proposed that the Lachman test can be performed in the prone position (see video by the study authors) but the diagnostic accuracy of this test has not been well established. Therefore, Mulligan et al. evaluated the reliability and diagnostic accuracy of the prone Lachman test for detecting ACL tears. The study evaluated 52 consecutive patients that were referred from an emergency room to an orthopedic surgery/sports medicine service with a complaint of knee pain. Patients were excluded if they could not lay prone, or had a suspected fracture, total joint replacement, suspected posterior cruciate ligament injury, knee surgery in the past 6 months, or the presence of serious nonmechanical pathology. Two licensed physical therapists (with different amounts of experience) independently performed the prone Lachman test without knowledge of other clinical findings. Both physical therapists participated in a one-hour training session to enhance consistency. The clinicians conducted the screening for exclusion criteria first, followed by the prone Lachman test, then the traditional Lachman test, and finally a KT1000 arthrometer was used to quantify anterior tibial translation. Fifteen patients had the status of their ACL confirmed with arthroscopy and 37 patients were confirmed clinically (2 of 3 findings: positive magnetic resonance imaging, >3 mm of laxity on KT1000 at 30 lbs of force, or positive exam by a third independent clinician). Twenty-three of the 52 patients had an ACL tear. The 2 physical therapists had 90% agreement with their interpretation of the prone Lachman test and agreed 79% of the time with the regular Lachman test. Sixteen of the 23 patients with an ACL tear were identified by the prone Lachman test (sensitivity = 0.70). Twenty-eight off the 29 patients without an ACL tear were correctly defined with the prone Lachman test (specificity = 0.97). Based on the number needed to diagnose = 1.5 it can be inferred that the prone Lachman test “would be accurate for every 2 of 3 patients on whom the test would be performed.”
This study is important because it provides insight into the accuracy and reliability of the prone Lachman test. Compared to the performance of the traditional Lachman test, (specificity = 0.91 to 0.94, sensitivity = 0.85 to 0.87; from recent meta-analyses) the prone Lachman test showed slightly better specificity but slightly lower sensitivity (slightly better at ruling out intact ACLs but slightly worse at detecting ACL tears). The authors suggest “the prone Lachman test should be considered a valuable complement in the evaluation of knee laxity when it may be difficult for the examiner to manually stabilize the femur.” It will be interesting to see further research exploring how the prone Lachman test performs among patients that the traditional Lachman test might be a challenge. To implement this in the clinical setting it important to practice the test (remember the clinicians did a training session together) and recognize when the traditional Lachman test might not be optimal.  What are your experiences with the prone Lachman test?
Written by: Jeffrey Driban
Reviewed by: Kyle Harris
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