Instrumented measurement of anterior laxity of the knee.
We performed instrumented measurement of anterior-posterior laxity of the knee in thirty-three cadaver specimens, 338 normal subjects, and eighty-nine patients with unilateral disruption of the anterior cruciate ligament. The test instrument was the Medmetric knee arthrometer, model KT-2000. We measured total anterior-posterior laxity, produced by anterior and posterior loads of eighty-nine newtons (twenty pounds), and the anterior compliance index. The total anterior-posterior laxity is composed of an anterior displacement and a posterior displacement; these are measured from a testing reference position, defined as the resting position of the knee after applying and then releasing a posterior load of eighty-nine newtons. The anterior compliance index is defined as the anterior displacement between an anterior load of sixty-seven newtons and one of eighty-nine newtons. All tests were performed with the knee held on a thigh support that placed the knee in 20 +/- 5 degrees of flexion. The mean anterior displacement at eighty-nine newtons was 5.7 millimeters in a group of normal subjects and 13.0 millimeters in a group of patients with a disrupted anterior cruciate ligament. Ninety-two per cent of the normal subjects had a left knee-right knee difference in anterior displacement of no more than two millimeters, while 96 per cent of the patients with a unilateral disruption of the anterior cruciate ligament had an injured knee-normal knee difference in anterior displacement of more than two millimeters. Ninety-three per cent of the normal subjects had a difference in the left-right compliance index of no more than 0.5 millimeter, and 85 per cent of the patients with unilateral disruption of the anterior cruciate ligament had a difference in the compliance index of the injured and normal sides of more than 0.5 millimeter.
D000293:Adolescent; D000328:Adult; D002102:Cadaver; D002648:Child; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis*; D007718:Knee Injuries / Q000175:diagnosis; D007719:Knee Joint / Q000503:physiopathology*; D008023:Ligaments, Articular / Q000293:injuries*; D008297:Male; D008875:Middle Aged; D009983:Orthopedic Equipment; D011312:Pressure