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

Abstract

Understanding the excursion change after tendon rupture is important in selection of optimal treatment time and options. The objectives of the present study were, first, to learn whether the change in collagen content, thought to determine passive stiffness of muscle, is related to change in muscle excursion after tendon rupture with delayed repair. The second objective was to determine the contribution of the collagen subtypes to passive stiffness after tenotomy. Tenotomy on the extensor digitorum muscle of the second toe of New Zealand White rabbits was performed with or without subsequent repair. Muscle excursion, total collagen, and collagen subtype were assessed at various times after tenotomy. Total collagen and type I collagen significantly increased with time after tenotomy (p < 0.05), excursion and type III collagen decreased significantly (p < 0.05), and there was no significant change in type IV collagen (p = 0.106). Muscle excursion ratio was significantly negatively correlated (p < 0.05) with total collagen and type I collagen after tenotomy. Perimysium and endomysium thickening and a greater number of connections between thickened endomysia were noted 6 weeks after tenotomy compared to the control. The total collagen 8 weeks after tendon repair increased significantly and muscle excursion decreased significantly with delay in repair (p < 0.05), so that the excursion was significantly negatively correlated with total collagen (p < 0.05). The increase in collagen that was observed after tenotomy was not reversed by repair. Improvement in excursion was noted when repair was delayed by 1 or 2 weeks, but when it was delayed by 4 or 6 weeks, excursion decreased. Type I collagen has been associated with decreased excursion after tendon rupture. It may be that the decreased excursion observed after tendon rupture could be avoided if type I collagen accumulation could be prevented. Also, since muscle excursion was not improved when repair was performed more than 4 weeks after rupture, tendon transfer might be the best treatment option for tendon ruptures that have been neglected for more than 4 weeks.