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.