Anterior-posterior stiffness and laxity of the knee after major ligament reconstruction.

We recorded anterior-posterior force-versus-displacement curves at 20 and 90 degrees of flexion preoperatively and three years after major ligament reconstruction in patients with documented absence of the anterior cruciate ligament. Patients who had an extracapsular stabilization procedure alone showed no significant changes in laxity or stiffness of the injured knee in either position of flexion. Those who underwent reconstruction of the absent anterior cruciate ligament utilizing the middle or medial one-third of the patellar ligament in addition to the extracapsular procedure showed a significant decrease in anterior laxity and increase in anterior stiffness of the injured knee at 20 degrees of flexion. These changes in stability were not observed at 90 degrees of flexion. Six patients with a cruciate substitution had improved laxity and stiffness values at one year postoperatively which were unchanged at three years. At three-year follow-up the increases in activity scores, decreased feelings of giving-way and pain, and elimination of the pivot shift were comparable in both groups of patients.

Measurement of knee stiffness and laxity in patients with documented absence of the anterior cruciate ligament.

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 response 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 flexion. Absolute values of stiffness and laxity and right-left differences for these injured knees were compared 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 approximately 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 +/- 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 flexion, and 2.5 millimeters (+34 per cent) at 90 degrees of flexion. The mean reduction in anterior stiffness for injured knees was also greatest (-54 per cent) at 20 degrees of knee flexion. Only slight reduction in posterior stiffness (-16 per cent) was measured at 20 degrees of flexion, and this probably reflected the presence of associated capsular and meniscal injuries. In the group of anterior cruciate-deficient knees, the patients with an absent medial meniscus showed greater total anterior-posterior laxity in all three positions of knee flexion than did the patients with 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.(ABSTRACT TRUNCATED AT 400 WORDS)