Date Published: July 01, 2017
Author(s): Chavaunne T. Thorpe, Graham P. Riley, Helen L. Birch, Peter D. Clegg, Hazel R.C. Screen.
Tendon is composed of rope-like fascicles bound together by interfascicular matrix (IFM). The IFM is critical for the function of energy storing tendons, facilitating sliding between fascicles to allow these tendons to cyclically stretch and recoil. This capacity is required to a lesser degree in positional tendons. We have previously demonstrated that both fascicles and IFM in energy storing tendons have superior fatigue resistance compared with positional tendons, but the effect of ageing on the fatigue properties of these different tendon subunits has not been determined. Energy storing tendons become more injury-prone with ageing, indicating reduced fatigue resistance, hence we tested the hypothesis that the decline in fatigue life with ageing in energy storing tendons would be more pronounced in the IFM than in fascicles. We further hypothesised that tendon subunit fatigue resistance would not alter with ageing in positional tendons. Fascicles and IFM from young and old energy storing and positional tendons were subjected to cyclic fatigue testing until failure, and mechanical properties were calculated. The results show that both IFM and fascicles from the SDFT exhibit a similar magnitude of reduced fatigue life with ageing. By contrast, the fatigue life of positional tendon subunits was unaffected by ageing. The age-related decline in fatigue life of tendon subunits in energy storing tendons is likely to contribute to the increased risk of injury in aged tendons. Full understanding of the mechanisms resulting in this reduced fatigue life will aid in the development of treatments and interventions to prevent age-related tendinopathy.
Understanding the effect of ageing on tendon-structure function relationships is crucial for the development of effective preventative measures and treatments for age-related tendon injury. In this study, we demonstrate for the first time that the fatigue resistance of the interfascicular matrix decreases with ageing in energy storing tendons. This is likely to contribute to the increased risk of injury in aged tendons. Full understanding of the mechanisms that result in this reduced fatigue resistance will aid in the development of treatments and interventions to prevent age-related tendinopathy.
Tendons attach muscle to bone and transfer force generated by muscle contraction to the skeleton, facilitating movement. The ability to withstand large unidirectional forces is provided by their structure; tendons are hierarchical fibre-composite materials, in which type I collagen molecules group together to form subunits of increasing diameter, the largest of which is the fascicle . Adjacent fascicles are bound together by a looser matrix, termed the interfascicular matrix (IFM; sometimes referred to as the endotenon).
This is the first study to investigate age-related alterations in the fatigue behaviour of the tendon IFM, and also provide a comprehensive analysis of age-related alterations in fascicle fatigue resistance. The results support the hypothesis, demonstrating an age-related decline in fatigue life of subunits from energy storing tendons. However, there was no significant difference in the degree of reduction in fatigue life between the fascicles and IFM of the energy storing SDFT. In further support of the hypothesis, both fascicle and IFM fatigue resistance remained unchanged with ageing in the positional CDET.
We observed an age-related decline in fatigue life of subunits from energy storing tendons. By contrast, fatigue resistance of the subunits of positional tendons were unaffected by ageing. These findings indicate that IFM and fascicle fatigue life are equally important for the fatigue resistance of the whole tendon, and the age-related decline in the fatigue life of tendon subunits is likely to contribute to the increased risk of injury, and likely reduced fatigue resistance, in aged tendons. Full understanding of the mechanisms resulting in this reduced fatigue life will aid in the development of treatments and interventions to prevent age-related tendinopathy.