Thirty-five patients with documented absence of the anterior cruciate ligament were tested on the University of California, Los Angeles, instrumented clinical knee-testing apparatus and we measured the re sponse curves for the following testing modes: anterior posterior force versus displacement at full extension and at 20 and 90 degrees of flexion; varus-valgus moment versus angulation at full extension and 20 degrees of flexion; and tibial torque versus rotation at 20 degrees of tiexion. Absolute values of stiffness and laxity and right-left differences for these injured knees were com pared with identical quantities measured previously for a control population of forty-nine normal subjects with no history of treatment for injury to the knee. For both the uninjured knees and the knees without an anterior cruciate ligament, at 20 and 90 degrees of flexion the anterior-posterior laxity was greatest at ap proximately 15 degrees of external rotation of the foot. The injured knees demonstrated significantly increased total anterior-posterior laxity and decreased anterior stiffness when compared with the uninjured knees in all tested positions of the foot and knee. The mean increase in paired anterior-posterior laxity for the injured knees in this group of patients at Â±200 newtons of applied anterior-posterior force was 3. 1 millimeters ( + 39 per cent) at full extension, 5.5 millimeters ( + 57 per cent) at 20 degrees of fiexion, and 2.5 millimeters ( + 34 per cent) at 90 degrees of flexion. The mean reduction in anterior stiffness for injured knees was also greatest ( â€5”4¿ per cent) at 20 degrees of knee flexion. Only slight reduction in posterior stiffness ( â€”1¿6per cent) was mea sured at 20 degrees offiexion, and this probably reflected the presence of associated capsular and meniscal inju ries. In the group of anterior cruciate-deficient knees, the patients with an absent medial meniscus showed greater total anterior-posterior laxity in all three posi tions of knee flexion than did the patients @itsh an intact or torn meniscus. Varus-valgus laxity at full extension increased an average of 1.7 degrees ( + 36 per cent) for the injured knees, while varus and valgus stiffness decreased 21 per cent and 24 per cent. Absence of the medial meniscus (in a knee with absence of the anterior cruciate ligament) increased varus-valgus laxity at zero and 20 degrees of flexion. Torsional laxity increased by an average of 10 per cent in knees without an anterior cruciate ligament and internal rotation stiffness decreased 16 per cent. There was no difference in internal and external iso metric torque-generating capacity betweeen the injured and uninjured knees.
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