EXPERIMENTAL AND MATHEMATICAL-METHODS FOR REPRESENTING RELATIVE SURFACE ELONGATION OF THE ACL

The common approach to assess the stabilizing role of the ACL in the k nee has been to measure the elongation of a few marked fibers in the l igament. A comparison of the relative elongation (RE) of these marked fibers between different specimens and studies is delicate due to the difficulty of marking the same fibers. More consistent comparisons wou ld be achieved if the RE of the whole ligament surface was presented. Hence, we developed a mathematical method leading to a continuous desc ription of the relative elongation of the ligament's surface based on experimental measurements of the RE of five fibers. The ligament fiber s of two knee specimens were marked by radiopaque markers and a Roentg en Stereophotogrammetric Analysis system was used to reconstruct the t hree-dimensional positions of these artificial landmarks. The mathemat ical procedure used isoparametric cubic splines to interpolate the con tours of the insertion sites. The results showed that the general patt ern of the RE for both specimens was similar, characterized by an undu lation near full flexion. In fact, close to full flexion all the RE of the fibers increased. Such a representation describes the changes in the RE for a given fiber during knee flexion and at the same time char acterizes the RE distribution at a given flexion angle.