Correlation between change in muscle excursion and collagen content after tendon rupture and delayed repair

BACKGROUND The objectives of the present study were to compare changes in muscle excursion, total collagen, and collagen subtypes after tenotomy over time and after delayed tendon repair. METHODS Tenotomy on the extensor digitorum tendon of the right second toes of 48 New Zealand White rabbits was performed; toes on the left leg were used as controls. Passive muscle excursion, total collagen content, and type I, III, and IV collagen contents were measured at 1, 2, 4, and 6 weeks after tenotomy. Next, passive muscle excursion and total collagen content were measured at 8 weeks after delayed tendon repair at 1, 2, 4, and 6 weeks after a tenotomy. RESULTS Passive muscle excursion decreased sequentially over time after tenotomy. Meanwhile, total collagen increased over time. These changes were significant after 4 weeks of injury. Type I collagen significantly increased, type III collagen significantly decreased, and type IV collagen had no significant change over time. Passive muscle excursion was negatively correlated with total collagen and type I collagen after tenotomy at each time point after tenotomy (p < 0.05). After tendon repair, increases in total collagen content after tenotomy were not reversed, despite early repairs at 1 and 2 weeks after tenotomy. CONCLUSIONS Increases in type I collagen were found to be associated with decreased excursion after tendon rupture. The increase in collagen that was observed after tenotomy was not reversed by repair within 8 weeks.