Movement and joints: effects of overuse on anuran knee tissues.

Movement plays a main role in the correct development of joint tissues. In tetrapods, changes in normal movements produce alterations of such tissues during the ontogeny and in adult stages. The knee-joint is ideal for observing the influence of movement disorders, due to biomechanical properties of its components, which are involved in load transmission. We analyze the reaction of knee tissues under extreme exercise in juveniles and adults of five species of anurans with different locomotor modes. We use anurans as the case study because they undergo great mechanical stress during locomotion. We predicted that (a) knee tissues subjected to overuse will suffer a structural disorganization process; (b) adults will experience deeper morphological changes than juveniles; and (c) morphological changes will be higher in jumpers compared to walkers. To address these questions, we stimulated specimens on a treadmill belt during 2 months. We performed histological analyses of the knee of both treated and control specimens. As we expected, overuse caused structural changes in knee tissues. These alterations were gradual and higher in adults, and similar between jumpers and walkers species. This study represents a first approach to the understanding of the dynamics of anuran knee tissues during the ontogeny, and in relation to locomotion. Interestingly, the alterations found were similar to those observed in anurans subjected to reduced mobility and also to those described in joint diseases (i.e., osteoarthritis and tendinosis) in mammals, suggesting that among tetrapods, changes in movement generate similar responses in the tissues involved.