Influence of gradual elongation to the patella tendon insertion in rabbits.

Hirotaka Mutsuzaki,Masataka Sakane,Shintarou Watanabe,Yasuyoshi Wadano,Hiromi Nakajima

doi:10.3390/ijms150814835

Abstract

The purpose of this study was to examine the histological changes at the patella tendon (PT) insertion site under gradual elongation in rabbits. Gradual elongation of the PT was performed using external fixation for 4 weeks, with a lengthening speed of 0.5 mm/day (elongation group; n = 24). Rabbits in the sham group underwent the same surgical procedure without gradual elongation (sham group; n = 24). Eight animals were sacrificed 1, 2 and 4 weeks after surgery in each group, respectively. Average thicknesses of stained glycosaminoglycan (GAGs) areas by Safranin-O staining in the total cartilage layer and the uncalcified fibrocartilage layer in the elongation group were significantly higher than that in the sham group at 4 weeks (p < 0.05) and that in the intact PT group (n = 6, p < 0.05). In the elongation group, the peak in the average thicknesses of the stained GAGs areas in the total cartilage layer and the uncalcified fibrocartilage layer were observed at 4 weeks. Gradual elongation of PT insertion significantly affected the increase in the average thicknesses of the stained GAGs areas in the cartilage layer especially in the uncalcified fibrocartilage layer at 4 weeks in rabbits. Clinically, insertions of tendon and ligament can extend during gradual elongation using external fixation more than 4 weeks after the operation.

Highlights

A tendon/ligament insertion site, such as that of the patella tendon (PT) or the anterior cruciate ligament (ACL), represents a functionally graded material system that exhibits a gradual transition in the tissue from an unmineralized tissue, to an unmineralized fibrocartilage, to a mineralized fibrocartilage, and to a mineralized tissue [1,2,3]
ACL tibial insertions after rupture result in an increase in the chondrocyte apoptosis rate and a decrease in average thicknesses of the stained GAG areas; this is well replicated in ACL
No significant differences were found in the average percentages of proliferating cell nuclear antigen (PCNA)-positive chondrocytes between any pair of the

Summary

Introduction

A tendon/ligament insertion site, such as that of the patella tendon (PT) or the anterior cruciate ligament (ACL), represents a functionally graded material system that exhibits a gradual transition in the tissue from an unmineralized tissue (i.e., tendon or ligament), to an unmineralized fibrocartilage, to a mineralized fibrocartilage, and to a mineralized tissue (i.e., bone) [1,2,3]. The glycosaminoglycans (GAGs) and cartilage layer are presumed to resist tensile, compressive and shear stresses at the insertion site [3] and provide the ability for the tissue to absorb water and maintain flexibility in the ligaments [4]. ACL tibial insertions after rupture result in an increase in the chondrocyte apoptosis rate and a decrease in average thicknesses of the stained GAG areas; this is well replicated in ACL tibial insertions after ACL resection in rabbit models of repair in our previous studies [5,6,7,8]. In the ACL partial resection animal model, the average thicknesses of the stained GAGs areas in the remaining ligament area increased up until 4 weeks, and gradually decreased until

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