The Stabilized Lachman’s Test: A Highly Sensitive, Specific and Accurate Test to Diagnose Acute ACL Tears

Abstract

Background The Lachman’s Test (LT) is the one of the most relied tests for the clinical diagnosis of a torn Anterior Cruciate Ligament (ACL). The accuracy of the traditional LT is largely dependent on the skill and experience of the observer as well as the timing of the knee was examined in respect to the injury. Wroble & Linderfeld first described the stabilized Lachman’s Test (SLT) in 1988. The examiner’s thigh is placed underneath and supports the thigh while the examiner’s hand (the opposite one to the extremity being examined) is used to stabilize the thigh. Purpose The purpose of this study was to prospectively analyze the sensitivity, specificity, and accuracy of the SLT to diagnose acute ACL tears. The hypothesis is that the SLT is a very sensitive, specific, and accurate test to diagnose ACL deficiency in acutely injured knees. Methods Two hundred patients with acute knee injuries were prospectively studied. All were examined within 30 days of injury (average – 8.3 days). Any patients with a previous ipsilateral or contralateral ligament knee injury were excluded from this study. All knees were examined prior to examining or interviewing the patient. There were 83 (41.5%) females and 117 (58.5%) males with an average age of 27.3 years. The SLT results were not graded but recorded as a positive or negative result. ACL tears were definitively diagnosed with MRI. Results On the initial examination there were 46 (23%) patients that had SLT that was recorded as positive and 154 (77%) that were considered negative. Forty-eight patients (24%) had a torn ACL and in 152 (76%) knees, the ACL was found to be intact by MRI. The SLT produced 44 (22%) true positives and 150 (75%) true negatives as well as 4 (2%) false negatives and 2 (1%) false positives. The resulting sensitivity was 91.7%, specificity was 98.7% and accuracy was 97%. The positive predictive value was 95.7% with the negative predictive value of 97.0%. The positive likelihood ratio was 69.9 and the negative likelihood ration was 0.085 Discussion The SLT is a highly sensitive, specific and accurate test for diagnosing ACL tears in the knee. The advantage of the SLT is that it allows the patient to relax the leg easily because the thigh is resting on a stable object. The examiner will feel the lower extremity relax by increased pressure on their own thigh and as soon as they feel this the SLT is performed. The examiner’s hand can now easily stabilize the thigh and control the leg’s rotation even in patients with large thighs or with clinicians with smaller hands, thus increasing the reliability and reproducibility of the SLT. Conclusion The SLT is highly sensitive, specific and accurate and has advantages over the standard LT. The SLT is a valuable tool in the armament of the clinician’s physical exam and diagnostic testing. It is beneficial for clinicians to at least try and compare it to the standard LT, especially those with less clinical experience.