Bilaterality in anterior cruciate ligament injuries

Nonsimultaneous, bilateral ACL injuries are not uncom mon. We studied a group of patients with these injuries to determine possible predisposing factors that could aid in early detection and prevention of contralateral ACL injury. Retrospective analysis of 1,120 patients with ACL ruptures who were treated between 1983 and 1987 revealed 45 patients with bilateral ruptures. Complete follow-up data were available for 41 of these patients. We examined age at initial injury, sex, interval between initial and contralateral ACL injury, mechanism of injury, activity at injury, medical and family histories, treatment of initial injury, and radiographic measurement of inter condylar notch width. The overall incidence of bilaterality was 4.01 % in the 28 male and 13 female patients. Their average age was 19 years and 10 months. The average interval between initial and contralateral injury was 47 months. A non contact cutting maneuver was the most common mech anism of injury. We devised a method to measure and compare in tercondylar notch widths on plain radiographs. We com pared the mean notch width index (NWI) of the bilateral group to the mean NWI of a group of 50 consecutive patients with "normal" knees and to the mean NWI of 50 consecutive patients with acute ACL ruptures. The mean NWI for the normal group was .2338, for the acute ACL group, .2248, and for the bilateral group, .1961. We noted a statistically significant difference when we compared the bilateral group to the normal and acute groups (P < 0.0001, respectively). There was no statistically significant difference between the NWI of the normal and acute ACL groups. None of the other variables studied were found to be significant. We identified a large subgroup of patients (59%) in the bilateral group who had sustained their initial injury at a relatively young age (average, 16 years) through noncontact mechanisms and who had a low NWI. These patients sustained their contralateral injury within 2 years of their initial ACL injury (average interval, 15 months) regardless of their initial treatment. We believe that young individuals who sustain an ACL tear by noncontact mechanisms and have a low NWI, carry a significant risk for contralateral ACL rup ture and should be strongly counseled regarding that possibility.