The fibre bundle anatomy of human cruciate ligaments

The cruciate ligaments of the knee consist of numerous fascicles, groups of which comprise fibre bundles. The stabilising function of these ligaments is established by changes in the lengths and orientations of the fascicles. Understanding the function of knee ligaments thus requires an understanding of their 3-dimensional fascicle architecture. Hitherto, the cruciate ligaments have been considered functionally as single-dimensional 'ropes' or, at the most, as consisting of anterior and posterior parts. It is evident from the appearance of these ligamentous structures, however, that fascicles in more than 2 directions are present. This study investigated how many and which fibre bundles are minimally needed to preserve the main fascicle directions in the ligaments. An anatomical analysis of the cruciate ligaments was performed using a 3-dimensional measuring device. Three anterior and 3 posterior cruciate ligaments were isolated and their fascicles measures. Based on the courses of the fascicles, fibre bundles were defined, dissected bluntly, and their corresponding insertion sites measured. Finally, the insertion sites of the bundles were connected into straight-line representations by a computer and transformed to the anatomical position of the knee, so as to be useful for functional analyses of the ligaments. It was found that 6-10 bundles are sufficient to represent the main fascicle directions of the ligaments. Although the number of fibre bundles is not identical for all ligaments, the femur and the tibia are connected in a consistent way by these bundles. Even the ways in which the fibre bundles change their interrelationship from the femoral to the tibial insertion sites are comparable. The results serve as a detailed anatomical basis for functional analyses of the cruciate ligaments.