Consistency of Subcortical Osseous Structures in Femoral Cruciate Ligament Attachment Sites: A Combined 3D-CT and Histological Anatomical Study

Background/Objectives: Accurate identification of the functional femoral attachment of the anterior (ACL) and posterior cruciate ligament (PCL) is essential for anatomic reconstruction and for patient-specific femoral tunnel planning, yet correct intraoperative localization remains inconsistent. This anatomical study investigated whether subcortical bone features provide evidence of functional cruciate ligament attachment and whether surrounding osseous ridges are reliable landmarks. Methods: Computed tomography (CT) scans of 20 paired, fresh-frozen distal femora (10 body donors) were processed using 3D volume rendering to visualize the intercondylar fossa walls and to assess the presence of four characteristic ridges: lateral intercondylar ridge (LIR), lateral bifurcate ridge (LBR), medial intercondylar ridge (MIR) and medial bifurcate ridge (MBR). In addition, thin-ground section histology of the femoral insertion sites was performed to characterize insertion morphology. Results: Histology demonstrated distinct direct and indirect insertions for both ligaments; the direct insertion exhibited a characteristic four-layer transition (ligament, non-calcified fibrocartilage, calcified fibrocartilage, bone), whereas the indirect insertion showed collagen fibers attaching directly to bone. The LIR and MIR were present in 85% and 80% of specimens, respectively, while the LBR and MBR were less frequent (LBR 25%, MBR 10%). No significant associations were found between ridge presence and age, sex or laterality. Conclusions: These findings support the direct insertion as the functional cruciate attachment and suggest that the LIR and MIR—due to their consistent occurrence and location at the rim of the direct insertion—are the most useful bony landmarks for individualized femoral tunnel orientation, whereas bifurcate ridges should be considered adjunctive when present. The observed variability provides a rationale to stratify cases requiring adjunct imaging or navigation.