M Motohashi
Department of Orthopedic Surgery, Yokohama Kowan Hospital, Yokohama, Japan

PURPOSE. To assess the mechanism of injury of anterior cruciate ligaments, surgical results, and radiographic findings among patients with bilateral knee injuries, and to compare these features with those of patients sustaining unilateral injuries.
METHODS. From 1977 to 1988, among 458 patients with injury of anterior cruciate ligament operated in our hospital, 11 were of bilateral injury, in whom 10 could be followed up. A laxity score was calculated to evaluate laxity of 7 joints. A notch width index was measured to show the narrowing of femoral notch.

RESULTS. The mean follow-up duration was 3 years 3 months. All 10 patients with bilateral injury of anterior cruciate ligaments were female, and 90% had non-contact injuries. The mean (standard deviation) laxity score was significantly higher in the bilateral injury group than in the unilateral injury group (3.3 [1.4] versus 2.2 [1.4] points; p<0.05). The mean notch width index was significantly lower in the bilateral injury group than in the healthy group (0.278 [0.025] versus 0.294 [0.031]; p<0.05). The mean age at the time of the first injuries was significantly lower among the bilateral injury group than among the unilateral injury group (16.6 [2.1] years versus 19.8 [6.1]; p<0.05). The level of return to full sporting activities was low in the bilateral group.

CONCLUSION. These results suggest that several factors are involved in the occurrence of the anterior cruciate injuries. Besides being younger at the time of the first injury, patients in bilateral injury group had higher mean laxity score and lower mean notch width index than unilateral injury group. Most of the injuries in bilateral group were of non-contact type.