Serial changes of tendon histomorphology and strain elastography after induced achilles tendinopathy in rabbits: An in vivo study

Objectives - The purpose of this study was to investigate and compare the serial changes of morphology and strain in the early process of Achilles tendinopathy in a rabbit model. Methods - A total of 10 New Zealand white rabbits underwent ligation of one of their Achilles tendons to induce ischemic injury. Both inflamed and contralateral Achilles tendons were serially evaluated with 3 follow-ups: the first on days 3 to 5, the second on days 9 to 13, and the third and last follow-up on days 15 to 20 after surgery. During each examination, tendon thickness was measured and red, green, and blue pixel intensities of the elastogram were analyzed using color histogram analysis software. Differences between the inflamed and control group were compared. Results - The mean thickness of the inflamed tendons increased during consecutive follow-ups and was significantly larger than that of control tendons (P<.01). The mean red pixel intensity ratio of the inflamed tendons was also serially increased and was higher than that in the control tendons, indicating softening. However, the difference was significant only in the second and third follow-ups (P<.01). Conclusions - Tendon thickening and softening developed during the early process of Achilles tendinopathy in a rabbit model. Tendon softening may present later than thickening.