Reliability and diagnostic accuracy of the lachman test performed in a prone position

Study Design: Prospective, blinded, diagnostic accuracy study. Objective: To investigate the reliability and diagnostic accuracy of the Lachman test, performed in a prone position, to detect the presence of an anterior cruciate ligament (ACL) tear. Direct arthroscopic visualization and a consensus of clinical findings, including joint arthrometry and magnetic resonance imaging, were used as the reference standards. Background: An alternative position for evaluating the integrity of the ACL has been proposed as a means for examiners with smaller hands to adequately stabilize the thigh of a larger individual; however, the diagnostic accuracy of this method has not been established. Methods: Fifty-two consecutive patients with a complaint of knee pain were independently evaluated in a prone position for the status of their ACL by 2 physical therapists, before any other diagnostic assessment. The 31 men and 21 women ranged in age from 16 to 57 (mean ± SD, 34.3 ± 4.2) years and in acuity of knee injury from 21 to 365 (mean ± SD, 195 ±130) days. Results: Twenty-three of 52 (44%) of the patients had a torn ACL. The agreement between examiners was 90%, with a kappa coefficient of 0.81. The sensitivity of the prone Lachman test was 70% and the specificity was 97%, resulting in a positive likelihood ratio of 20.17 and a negative likelihood ratio of 0.32. The positive predictive value was 94% and the negative predictive value was 80%. The diagnostic odds ratio was 64.0, with a number needed to diagnose of 1.5. Conclusion: The prone Lachman test is a reliable evaluation technique that can be used to confirm the presence of an ACL tear; however, the test should not be used as the sole criterion to rule out the presence of the injury. Level Of Evidence: Diagnosis, level 2b.