VARIATIONS IN RUPTURE SITE AND SURFACE STRAINS AT FAILURE IN THE MATURING RABBIT MEDIAL COLLATERAL LIGAMENT

The relationship between the pattern of surface strain and the site of failure in maturing rabbit ligaments was studied in vitro. Bone-media l collateral ligament (MCL)-bone complexes of 24 female New Zealand Wh ite rabbits at 3, 6, 9 and 12 months of age (n = 6 rabbits, 12 MCLs pe r group) were tested in tension to failure. A video dimension analysis (VDA) system was used to map the surface strain at failure across the width and along the length of the menial side of each MCL during test ing. Results showed that the highest strains were consistently located at the femoral insertion decreasing towards the midsubstance, with th e highest strain occurring in the anterior portion of the MCL immediat ely adjacent to the femoral insertion. Strains of the complex at failu re increased with rabbit maturation. The strain distribution however, did not change dramatically, even though the locations of MCL failure changed from exclusively tibial avulsion in the three month old rabbit s to predominantly midsubstance failures in the 12 month old rabbits. In the six month old rabbits, there was a particular dissociation with all MCLs failing near the tibial insertion while femoral strains were apparently the highest. These results suggest two possibilities beyon d that of some unknown artifacts of optical strain measurement. First, since failure sites rarely correlated with areas of maximum surface s train in this study, it seems possible that higher strains could exist deeper in the tissue, particularly at the bone-ligament interface of the tibial insertion in immature animals and somewhere within the mids ubstance of the MCL in the adult. Secondly it is possible that the lig ament material may be heterogeneous.