Abstract des Autors

In order to evaluate the contribution of the knee ligaments to restrain joint motions, knowledge about their structural properties is required. Due to the variable relative insertion orientation of the ligaments during knee motion, however, different fiber bundles are recruited, each with their specific mechanical properties. Hence, the structural properties vary as a function of knee motion. For this reason, a relationship between the structural tensile properties and the relative insertion orientation is required in order to define the role of the ligaments in knee mechanics. In the present study, this relationship is determined by performing a series of tensile tests in which the relative orientations of the sites of human knee bone-ligament-bone preparations were varied systematically. The experimentally obtained stiffness was significantly affected by the relative orientation of the insertion sites, but more profoundly for the anterior and posterior cruciate ligaments (ACL and PCL) as compared to the medial and lateral collateral ligaments (MCL and LCVL). The average decreases in stiffness per 5ø tilt of the insertion sites were estimated at -11.6+/-3.5 N/mm (ACL), -20.9+/-2.7 N/mm (PCL), -2.6+/-0.9 N/mm (MCL) and -3.7+/-0.3 N/mm (LCL). For the PCL and the MCL these changes in stiffness with tilt were rather insensitive to the side of the femoral insertion site which was lifted. The ACL and the LCL, conversely, displayed significant differences in stiffness changes between the different tilt directions. It is shown that the results of ligament tensile tests, particularly of the cruciate ligaments, are extremely sensitive to the orientation of the specimens in the loading apparatus. Since there is bound to be a variation in ligament orientations in earlier tensile studies, the variation in properties reported can be explained. It is concluded that the functional roles of the ligaments, particularly the cruciate ligaments, vary considerably during knee motions. Hence, functionally speaking, there is no such thing as 'the ligament stiffness'. Verf.-Referat