Mechanical properties of a rat patellar tendon stress-shielded in situ

The effects of stress deprivation on the mechanical properties of the patel lar tendon (PT) were studied using 14 albino rats. The PT was stress-shield ed with cerclages on one side, while the contralateral patellar tendon serv ed as a sham-operated control. After 10 weeks, paired load-strain as well a s load-relaxation experiments were performed (11 and 3 specimen pairs, resp ectively). Mechanical tests showed, irrespective of the cerclage material u sed, that strain was increased significantly after stress-shielding (P < 0. 02). The time constant significantly decreased in the stress-shielded speci mens under 5 N loads, which may be considered 'physiological'. Tissue remod eling might explain the observed changes in the viscoelastic behaviour of t he stress-shielded tendons. Loading, even in the physiological range of nor mal daily activity, may lead to an elongation of previously stress-shielded tendons or ligaments and consequently alter the behaviour of a joint.