2009 Volume 4 Issue 4 Pages 539-549
Incomplete or subfailure injuries of tendons occur more frequently than their complete ruptures. However, the mechanical behavior of the incompletely injured tissues is poorly understood. In the present study, we quantified the mechanical properties, microstructure, and ultrastructure of rabbit patellar tendons subjected to non-destructive overloading. No significant changes in the mechanical properties were observed in the tendon specimens which were applied a subfailure stretch equivalent to 80% of the failure stress of the control tendons at a low strain rate (1.67 %/sec). There was a significant decrease not in the tensile strength but in the tangent modulus of the specimens when they were subjected to 90% of the control failure stress at the low rate. For the same level of overloading at a high strain rate (16.7 %/sec), both the modulus and strength of the overloaded specimens were significantly lower than those of the control ones. Microstructually, irrespective of the strain rate, crimped collagen fibers in the overloaded tendons were straightened by the 90% overloading. In contrast, adverse alterations in the ultrastructure were induced by the 90% overloading only at the high rate. These results indicate that tendinous tissues have potential capacities to maintain the original strength if a relatively high overload is monotonically applied at lower strain rates. However, it is possible that subfailure overloads delivered at higher strain rates produce more severe changes in the properties and structures of the tissues.
