Biomechanical and Histological Study of the Naturally Healed Anterior Cruciate Ligament after Partial Transection in the Rabbit

Bae, Dae Kyung; Yoon, Kyoung Ho; Chun, Young Soo

Abstract

INTRODUCTION
The natural healing of ligaments has been the subject of various experimental investigations. This study was designed to clarify the natural process of healing of the anterior cruciate ligament injury in the rabbits using histological and biomechanical methods.
MATERIALS AND METHODS
Healing of the anterior cruciate ligament was studied in 54 rabbits. In one side of the knee of each animal, the anterior cruciate ligament was transected partially, and in the contralateral knee, a sham operation was performed. Mechanical testings and histological studies of the ligaments were done at one week, six weeks, and twelve weeks postoperatively.
RESULTS
At one week, the partial transected ligaments exhibited 41.66% of the strength of the ligaments on the side of the sham operation. At six weeks, the strength of partially transected ligaments had been regained to 57.29%. At twelve weeks, the ligaments were 60.39% as strong as on the contralateral side. At one week, the ultimate tensile strength of the ligaments with their cutting side at 2 mm away from ligamentous insertion to femur or tibia was stronger than cases at midsubstance. Strain of ligament was similar with the control group on each period. Modulus of elasticity was 46.23% of normal ligaments at twelve week. Histologically, the defect was filled with young repair tissue and collagen laydown that was still somewhat different from normal ligamentous tissue.
CONCLUSION
Although the mechanical properties of the regenerated ligaments were poor, this study demonstrates that the anterior cruciate ligament of the rabbits has healing potential. Also injured ligaments heal with fibroblasts and collagen fibers, histologically and biomechanically different from a normal ligament.