Symmetry of the femoral notch width index

A small femoral notch width index has been reported as a predictive factor for anterior cruciate ligament injury and implicated in the higher incidence of anterior cruciate ligament injuries in female athletes. Notch-plasty has been recommended for the unaffected knees of patients who have torn one anterior cruciate ligament and whose notch width index falls one standard deviation below "normal". However, the symmetry of the notch width index has not been specifically studied. We compared the notch width index in both knees of 40 male and 40 female patients. Half of the patients in each group had anterior cruciate ligament injuries, all from a noncontact mechanism. We found that the notch width indexes of the right and left knees of the same patient are essentially symmetrical, regardless of sex or anterior cruciate ligament status. Although the female patients tended to have smaller notch width indexes than the male patients, the difference was not statistically significant. Moreover, the ranges of notch width indexes in male and female patients overlapped considerably. Finally, there was no difference in notch width index between patients with and without anterior cruciate ligament tears. These findings suggest that the notch width index alone is not the critical etiologic factor in the patient with a unilateral anterior cruciate ligament tear. Furthermore, the increased incidence of anterior cruciate ligament tears in female patients compared with male patients in the same sports cannot be attributed to notch width index alone.