Implications of muscular defense in testing for the anterior drawer sign in the knee. A stress radiographic investigation.

This study was performed with the aim of shedding some light on the effect of muscular guarding during clinical testing of the knee for anteroposterior laxity. Twenty physicians were tested on a knee phantom, for force used during testing for the anterior drawer sign. The force used averaged 109 N (range, 70 to 180 N). Fifteen patients were examined by stress radiography. Radiographs were taken with the knee flexed to 90 degrees (the drawer test position) and with the knee flexed to 15 degrees (the Lachman position). A comparison was made between the laxity measured on forward traction in the relaxed knee, and during traction while the patient was instructed to counteract the forward displacement of the tibia by tensing the hamstrings, thus simulating muscular defense. The test procedure was executed first with 80 N and then with 160 N applied. The opposing effect of tensing the hamstrings on the anterior shift of the tibia was significantly less at 15 degrees of knee flexion (with 80 N, P less than 0.02; with 160 N, P less than 0.05) than at 90 degrees. With the hamstrings tensed and the knee flexed to 90 degrees, no statistically significant gain in drawer sign was achieved by increasing the force from 80 to 160 N. With the knee in the Lachman position, increasing the force produced a significantly greater anterior drawer sign (P less than 0.01).