Biochemical analysis of collagen in adhesive tissues formed after digital flexor tendon injuries

Restrictive adhesion is a major problem following flexor tendon surgery. We investigated crosslinks and types of collagen in two adhesive tissue models in chickens, characterized by loose adhesion and dense adhesion. The flexor digitorum profundus tendon was cut and sutured in two ways: (1) the severed tendon was sutured outside the tendon sheath (loose adhesion model), and (2) the tendon sheath was excised and the severed tendon was sutured on the damaged bony floor (dense adhesion model). Biochemical analysis of collagen was done for each group after tenorrhaphy. In the outside-sheath group, the ratio of the collagen crosslinks, dihydroxylysinonorleucine/hydroxylysinonorleucine, was lower than that in the sheath-excised group at 12 weeks, while the collagen crosslinks ratio remained considerably high in the sheath-excised group. The ratio of type III collagen to type I collagen in the outside-sheath group was higher than that in the sheath-excised group at 12 weeks and approached an almost normal value at 24 weeks. The collagen type III/I ratio remained low in the sheath-excised group. The current study shows that biochemical properties are different between loose and dense adhesions. In dense adhesive scars, pathological collagen turnover occurs even at 24 weeks after tenorrhaphy.