Anterior cruciate ligament femoral footprint is oblong-ovate, triangular, or two-tears shaped in healthy young adults: three-dimensional MRI analysis

Purpose This study aimed to evaluate the morphology of the anterior cruciate ligament (ACL) femoral footprint with three-dimensional magnetic resonance imaging (3D MRI) in healthy knees.Methods Fifty subjects with healthy knees were recruited, utilising 3D-SPACE sequences for ACL evaluation. The ACL was manually segmented, and the shape, size and location of the ACL femoral footprint were evaluated on a reformatted oblique-sagittal plane, which aligned closely with the ACL attachment. Statistical analysis included one-way ANOVA for continuous variables and Fisher's exact test for categorical variables, with a P value < 0.05 considered significant.Results Three types of ACL femoral footprint shape were identified, namely, oblong-ovate (OO) in 33 knees (66%), triangular (Tr) in 12 knees (24%) and two-tears (TT) in 5 knees (10%), with the mean areas being 58, 47 and 68 mm(2), respectively. Within group TT, regions with similar sizes but different locations were identified: high tear (TT-H) and low tear (TT-L). Notably, group OO demonstrated a larger notch height index, whilst group TT was characterised by a larger alpha angle and lateral femoral condyle index. A noticeable variation was observed in the location of the femoral footprint centre across groups, with group TT-L and group Tr showing a more distal position relative to the apex of the deep cartilage. According to the Bernard and Hertel (BH) grid, the ACL femoral footprint centres in group TT-L exhibited a shallower and higher position than other groups. Furthermore, compared to group OO and TT-H, group Tr showed a significantly higher position according to the BH grid.Conclusion In this study, the morphology of the ACL femoral footprint in healthy young adults was accurately evaluated using 3D MRI, revealing three distinct shapes: OO, Tr and TT. The different ACL femoral footprint types showed similar areas but markedly different locations. These findings emphasise the necessity of considering both the shape and precise location of the ACL femoral footprint during clinical assessments, which might help surgeons enhance patient-specific surgical plans before ACL reconstruction.