The diagnosis of knee motion limits, subluxations, and ligament injury

Abstract

The clinical diagnosis of knee ligament injuries requires the clinician to: 1) estimate the abnormal motion limits that occur in one or more of the six degrees of freedom that comprise three-dimensional motion; 2) determine the abnormal position (subluxation) of the medial and lateral tibiofemoral compartments; and 3) precisely de fine the anatomical structures injured and degree of that injury. To determine the clinician's ability to perform these tasks, we evaluated 11 knee surgeons' clinical examination for knee instability. The positions and mo tions induced were measured in right-left cadaveric knees by a three-dimensional instrumented spacial link age. We compared the clinicians' estimate of knee motion limits and subluxations with the actual meas ured values. Before and after the clinicians' examina tion, the three-dimensional limits of knee motion were measured in the knees in the laboratory under defined loading conditions. Also, in one knee, the ACL and superficial medial collateral ligament were cut and the examiners, none of whom were informed of the sec tioning, were asked to arrive at a diagnosis. The results for all of the clinical instability tests were similar. There was wide variability between examiners in the starting position of knee flexion and tibial rotation and in the amount of tibial translation and rotation induced. Although some examiners displaced the knee to the maximal displacement limits obtained in the laboratory, others did not, by a substantial margin. This suggests a wide variation in the loads applied by ex aminers to the knee joint during the tests. For the overall series of clinical tests, only 6 of 11 examiners estimated the amount of AP displacement, tibial rota tion, and medial-lateral joint space opening within the acceptable limits defined in the study. Nine of the 11 examiners correctly diagnosed the instability in the sectioned ligaments; there were numerous errors in diagnosis of injury to other ligament structures. The most frequent misdiagnosis (7 of 11 examiners) was the interpretation of the increased external tibial rotation in the ligament-sectioned knee as representing an injury to the posterolateral ligament structures where, in fact, the injury was to the ACL and medial ligament struc tures. We concluded that 1) examination test techniques must be standardized as to test conditions so that clinicians conduct similar tests; 2) comparisons among clinicians in quantitating knee motion limits may be invalid because of the wide variations that occur; 3) instrumented teaching models should be developed to increase interexaminer clinical test reproducibility; 4) given the variability of examiners' estimates, reliable joint arthrometer or stress radiography test methods should be developed and considered a requirement for reporting clinical results; and 5) the diagnosis of rotatory subluxations is highly subject to diagnostic error and requires a careful assessment of the anterior-posterior position of the medial and lateral tibial plateaus relative to the femur.