Characterization of a Novel Model of Overuse-Induced Calcific Achilles Tendinopathy in Mice: Contralateral Tendinopathy Following Unilateral Tenotomy

Objective: To develop a simple but reproducible overuse induced animal model of Achilles tendinopathy in mice for better understanding the underlying mechanism and prevention of calcific Achilles tendinopathy. Methods: 80 C57/B6 mice (8-9 weeks old) were employed and randomly divided into control group and experimental group. Unilateral Achilles tenotomy was performed on the right hindlimb of experiment group. After 12 weeks, the onset of Achilles tedinopathy in the contralateral Achilles tendon was determined by radiological assessment, histological analysis, electron microscopy observation and biomechanical test. Results: The onset of calcific Achilles tendinopathy in contralateral Achilles tendon was confirmed after 12 weeks unilateral tenotomy. The contralateral Achilles tendon of experimental group was characterized as hypercelluarity, neovascularization and fused collagen fiber disarrangement, compared to the control group. Importantly, intratendon endochondral ossification and calcaneus deformity was featured in contralateral Achilles tendon. Additionally, poor biomechanical properties in the contralateral Achilles tendon revealed the incidence of Achilles tedinopathy. Conclusion: We hereby introduce a novel simple but reproducible spontaneous contralateral calcific Achilles tendinopathy model in mice, which represents the overuse conditions during the tendinopathy development in human-beings. It should be a useful tool to further study the underlying pathogenesis of calcific Achilles tendinopathy.