Enforced downhill running has been reported to induce tendinosis in the rat supraspinatus tendon but similar exercise failed to induce Achilles tendinosis in this animal. Due to the presence of acromial arch in the shoulder, accessing the supraspinatus tendon with physical modalities is difficult; thus this model may not be suitable for studying the treatment for tendinosis. To develop a rat model for Achilles tendinosis, we tested 14 mature Sprague–Dawley rats by dividing them into 2 groups of 7 each. The experimental group was subjected to a daily enforced downhill bipedal running program by suspending their upper bodies so that they ran with their hind limbs on a treadmill for 1 hr/day for 8 weeks. The downward inclination was 20° and the speed was 17 m/min. The animals in the control group did not undergo any exercise. After 8 weeks, the Achilles tendons were harvested and subjected to histological and biomechanical analysis. Histological examination revealed tenocyte proliferation, change in tenocytes appearance, and collagen bundle disintegration in the running group. The biomechanical testing revealed significant decrease in stiffness (p = 0.002) and ultimate tensile strength (p = 0.016) in the running group than in the control group. Both the histological and biomechanical findings are suggestive of changes in the tendon of the running group that resembled the pathological changes of tendinosis in human. This new model of Achilles tendinosis in rat will be useful for studying the etiology and subsequent management strategies of this condition.
Objective: This study investigated the effects of a therapeutic laser, passive stretching, and their combined treatment on the strength of Achilles tendons with overuse pathologies. Background data: Tendinopathy involving overuse is usually treated with exercise and stretching, but there has been no report on the treatment effect of a therapeutic laser combined with passive stretching on managing this condition. Despite the beneficial effect of a therapeutic laser on healing tendons that have had traumatic injury, its effect on degenerative tendons is not known. Methods: Twenty-five mature Sprague-Dawley (SD) rats were used, with 20 subjected to daily bipedal downhill running for 8 weeks, to induce Achilles overuse, and 5 as normal controls. The exercised rats were divided into four groups: 1, laser treatment; 2, passive stretching; 3, combined laser and stretching; and 4, no treatment, running controls. GaAlAs laser with 660 nm wavelength was applied to both Achilles tendons for 50 sec for Groups 1 and 3. Passive stretching of 20 times/10 sec of maximum ankle plantar flexion was applied to Groups 2 and 3. Treatments were applied after each running session for a a total of 56 treatment sessions. On week 9, the tendons were tested for load-relaxation, stiffness, and ultimate strength. Results: Stiffness was different (p=0.01), difference in ultimate strength was marginally insignificant (p=0.07), and load-relaxation difference was not significant among groups. Post-hoc analyses revealed that the mean stiffness of all the four exercise groups was lower than the normal control, whereas the ultimate strength from the laser and combined laser and stretching was not different from that of the normal control group, but was higher than that of the passive stretching and no treatment groups. Conclusions: We conclude that a therapeutic laser and combined laser with passive stretching might slow down the decrease in Achilles tendon strength but would not be able to stop the pathological changes of overuse from developing.
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