Regeneration process of severed rabbit common calcanean tendons influenced by external compression

Limited research has focused on the correlation between an external compression and the regeneration of ruptured Achilles tendons. The aim of this study was to evaluate the influence of a constricted paratenon with external compression on the regeneration process of separated rabbit common calcanean tendon stumps.

A transection, establishing a 4 mm gap, was created in the right common calcanean tendon of 24 young adult male New Zealand white rabbits. The animals were assigned to two groups: In the control group, only received cast immobilization. In the constricted paratenon (CP) group, the rabbits had a local 3-dimensional printed clasp applied to mimic external compression and same cast immobilization as the control group. Morphologic, histologic and immunohistochemistry examinations were performed at 2 and 4 weeks postoperative.

Separated tendon stumps were connected by novel granulated tendon fibrils in the control group. However, the regenerated tendon fibrils appeared insufficient in the CP group, the tendon length and the adhesion grade of the CP group was significantly larger than that of the control group at 4 weeks (P < 0.05, P = 0.030). Disorganized collagen and round-shaped fibroblasts were demonstrated in the CP group. A prolonged expression of proliferating cell nuclear antigen (PCNA) and lower intensity in clusters of differentiation 146 (CD146) were also shown in the CP group. A prolonged existence of the vascular endothelial growth factor (VEGF) and lesser intensity of the transforming growth factor-beta 1 (TGF-β1) were confirmed within this group. Furthermore, the CP group's expression had less collagen I than that of the control group at 4 weeks.

Sufficient regeneration can be obtained, even though there is an obvious gap between severed rabbit common calcanean tendon stumps. However, constricted paratenons with external compression can negatively influence the intrinsic regeneration process of the tendon fibrils and promotes the disorganization of regenerated collagen.