Measurements of anterior laxity in normal and anterior cruciate absent knees with two instrumented test devices.

A new portable model of the University of California at Los Angeles (UCLA) instrumented clinical knee testing apparatus and the KT-1000 knee arthrometer were used to measure anterior laxity in normal and anterior cruciate absent knees. Normal ranges for both devices were established for a control group of 48 normal subjects. With the UCLA device at 200 N of applied tibial force, 95% of normal knees have an anterior laxity less than 8.0 mm and a side to side difference less than 2.0 mm; corresponding values for the KT-1000 at 89 N are 9.0 mm and 2.0 mm. Both devices showed that anterior laxity of 19 anterior cruciate absent knees was approximately double that for normal knees. Measurements taken with these two testing instruments do not have a one-to-one correlation, as the method of femoral constraint and the amount of applied tibial force will influence the magnitude of the recorded laxities. Proper interpretation of laxities measured with each device requires consideration of right-left scatter in a normal population tested with that particular device. Both devices were 90%-95% accurate in correctly classifying an anterior cruciate absent knee outside the normal range.