ACL Anatomy

The anterior cruciate ligament (ACL) is currently described as an hour-glass shaped structure of dense connective tissue thought to be composed of an anteromedial (AMB) and posterolateral bundle (PLB). The two bundles work reciprocally to restrain anterior tibial translation and internal tibial rotation. In foetal stages, the anteromedial and posterolateral bundle are separated by a septum which embeds the supplying vasculature. The foetal two-bundle entity of the ACL is not necessarily reflected in its adult microarchitecture. In the adult ACL, several non-parallel fibre-bundles compose a flat and rectangular core structure with a four-layered insertional anchor architecture. Diverging fibres form a membranous fan-like extension, completing broad, bipartite insertional areas. The interface between core fibres and diverging fibres is characterised by a fold which deepens in knee flexion. It has been hypothesised that the two-bundle appearance of the ACL might represent an impression rather than an entity. Even though newer approaches describe the ACL to be a continuum of fibres with a gradient across the ligament, it is of interest to distinguish an anteromedial from a posterolateral portion, as these portions inherit different biomechanical properties. In synergy with the dynamic anatomic understanding of the knee, ACL reconstruction techniques have constantly been refined.