Purpose and hypothesis: The principal purpose of this paper was to identify whether femoral notch morphology was different in females without anterior cruciate ligament (ACL) injury from those with ACL injury. Magnetic resonance imaging (MRI) was used to assess the femoral notch type, notch width index and 'α angle' in female patients and measure these differences.
Methods: This is a retrospective case control study of 119 female patients, 58 with ACL injury and 61 patients without ACL injury who underwent knee MRI between March 2014 and April 2016. The morphometric measurements were taken by two independent observers. The femoral notch width index was calculated as the ratio between the central notch width and transcondylar or intercondylar width; values >0.27 were considered normal. The femoral notch shape was classified as Type A, Type U or Type W, with Type A describing a stenotic notch, Type U a notch with a wider contour and Type W a wider Type U with two apices apparent. The angle between the longitudinal femoral axis and the Blumensaat line was identified as the 'α angle'. The statistical analysis was performed with t tests, simple and multivariable logistic regression analysis to evaluate the strength of these specific femoral notch morphometric values as predictive factors to ACL rupture.
Results: Stenotic femoral notch Type A was identified as a high risk factor to ACL injury (odds ratio [OR] = 2.8; p = 0.03). There was no significant difference between the two groups for the notch width index (OR = 0.7; p = n.s.) and the 'α angle' (OR 1.02; p = n.s.). Significant association between NWI and stenotic notch was found (p < 0.01).
Conclusions: This study showed that Type A stenotic femoral notch can be considered as a valuable predictive factor for ACL injury. Notch width index and 'α angle' are weak indicators in ACL injury prognosis. Ligament impingement may be inferred as an important mechanism in female ACL rupture. Injury prevention strategies, such as prehabilitation programmes, could be introduced in the benefit of young females with stenotic notch.
Level of evidence: III.
Keywords: Anterior cruciate ligament injury; Female; Femoral notch; Magnetic resonance imaging.