[Functional anatomy of the posterior cruciate ligament]

The human posterior cruciate ligament (7 unselected specimens) consists of 2 different bundles with a common tibial attachment: 1. a thin, flat and slightly twisted posterior bundle running to the posterior medial condyle taut in extension and lax in flexion of the knee, 2. a thick oval anterior bundle with parallel fibers running to the roof of the notch lax in extension and taut in flexion. This contra-tensile function explains the different posterior instability in extension or flexion of the knee in case of an isolated rupture of only 1 of these bundles.