Functional anatomy of the ACL fibers on the femoral attachment

Abstract

The fanlike extension fibers of the anterior cruciate ligament (ACL) adhere to the bone surface; regardless of the knee flexion angle, the fiber location and orientation do not change, in relation to the femoral surface. However, the ACL midsubstance fiber orientation related to the femur does change during knee motion. The ACL femoral attachment was divided into a central area of dense fibers, with direct insertion into the femur, and anterior and posterior fanlike extension areas. The central area resisted 82-90% of the anterior drawer force with the anterior and posterior fanlike areas at 2-3% and 11-15 %, respectively. Among the 4 central areas, most load was carried close to the roof of the intercondylar notch. An anatomic variation of the lateral intercondylar ridge (LIR) was identified in 94.0% of 318 femora and the distal half of LIR was not visible in 18.4% of these femora. The LIR was situated in the anteriormost part of the lateral condyle surface in 8.8% and in the posteriormost part in 8.5 %. The ACL attachment anterior margin was typically located anterior to the middle and distal part of LIR.