Type V collagen is increased during rabbit medial collateral ligament healing

To understand the reparative process of medial collateral ligament (MCL), fibrillar collagen and their relative ratios in healing MCL with anterior cruciate ligament (ACL) reconstruction were analyzed. Skeletally mature New Zealand white rabbits were subjected to a mop-end tear of MCL without repair with ACL reconstruction. Rabbits were killed 6 and 52 weeks after injury. Ligamentous tissues from the injury site and sham controls were soaked in 0.5 M acetic acid for 24 h, minced, and treated with pepsin to solubilize collagen. Pepsin solubilized about 80% of the total collagen as determined by hydroxyproline analysis of the pepsin residues. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the solubilized collagen revealed presence of fibrillar collagen types I, III, and V. Densitometric scanning of the protein bands corresponding to types I, III, and V collagen indicated that in sham controls types III and V collagen represented about 8% and 12%, respectively, of the type I collagen whereas the healed MCL ligaments at 6 weeks showed significant increase in type III and V collagen to about 19% and 24%, respectively. By 52 weeks type III collagen in the healed MCL had returned to that of sham controls while type V collagen remained elevated at approximately 18%. These data suggest that presence of type V collagen in high concentration in healing ligaments may have an influence on collagen fibril diameters seen in healed ligament and should be included in the analysis when evaluating ligament healing.