The function of the anterior cruciate ligament during anterior drawer and Lachman's testing

In order to clarify the function of the anterior cruciate ligament (ACL) during clinical testing an in vivo arthroscopic method of assessing the tension of ACL was developed. Twenty young adult patients with normal knee ligaments and menisci were selected. A spring mechanism in the handle of the specially designed probe allowed the surgeon to apply a known perpendicularly directed force to the ligament while the amount of displacement was observed and recorded. Tension was determined in the anteromedial central and posterolateral portions of ACL before and during an anterior drawer test (knee flexed 90 degrees) and before and during a Lachman's test (knee flexed 15 degrees). The results were consistent in all 20 knees. Baseline tension was greater at 15 degrees of flexion than at 90 degrees. A Lachman's test produced maximal tension in the majority of the ligaments. The anterior drawer did not produce maximal tension in any portion of the ligament. Tension within the anteromedial and central portion of the ligament predominated during both uses. This analysis confirms the specificity of Lachman's test as an indicator of ACL integrity. The concept of two reciprocally functioning ACL "bands" by either anterior drawer or Lachman's test is not supported by our data.