Association of femoral intercondylar notch morphology, width index and the risk of anterior cruciate ligament injury

PURPOSE: To determine the relationship between femoral notch morphology, femoral notch width index and anterior cruciate ligament tears using magnetic resonance imaging of the knee. METHODS: This retrospective study was conducted on 560 patients who had magnetic resonance imaging (MRI) examinations of the knee between February 2010 and June 2011. Two morphological changes were investigated: the shape of the femoral notch and its width index. The femoral notch shape was classified into one of three types: Type A, which is a narrow (Stenotic) notch that appears narrowed from the base to the midsection as well as at the apex; Type U, in which the midsection does not taper, allowing for a wider contour to the notch than Type A; and Type W, which has the characteristics of Type U but with two apparent apices. The femoral notch width index was calculated as a ratio of central notch width and transcondylar or intercondylar width; values of 0.270 or more were considered as normal and values of 0.269 or less were considered as below normal. These measurements were correlated with the presence or absence of anterior cruciate ligament (ACL) tears. RESULTS: Of 560 patients, there were 280 cases of ACL tear. Of the 560 patients, 240 had a Type A femoral notch shape and 320 had a Type U or W femoral notch shape. Of those with Type A, 73 % (176 patients) had ACL tears, and of those with Type U or W, 32 % (104 patients) had ACL tears. Statistical analysis showed that the Type A notch correlated with ACL injury (p value < 0.0001). The femoral notch width index was low in 37 % (88 subjects) with Type A notch compared with 27.5 % (88 subjects) with Type U or W notches. Of the 280 subjects with ACL tear, only 17 % (48 patients) had a reduced femoral notch index. CONCLUSION: This study showed that the Type A femoral notch appears to be a risk factor for ACL injury, whereas a reduced notch index has no significant correlation to ACL injury. LEVEL OF EVIDENCE: III.