Microscopic observation of a rat spontaneous anterior cruciate ligament healing

Introduction/Background Controlling abnormal joint movement immediately after anterior cruciate ligament (ACL) injury could prevent destruction of intra-articular tissues and lead to spontaneous ACL healing. In a previous study, healing tissue was observed between the remnant gaps in the process of spontaneous ACL healing. The purpose of this study was to evaluate the healing tissue as observed in the process of spontaneous ACL healing by histological analysis. Material and method A total of 30 adult male Wistar rats were randomly assigned to three groups: Sham, ACL transection (ACLT), and Controlled abnormal movement (CAM). The ACLT group and the CAM group underwent an ACL transection procedure, and the CAM group underwent extra-articular braking to control for abnormal tibial translation. Samples of the knee joints were harvested at 1 and 2 weeks postoperatively, and stained by Hematoxylin-Eosin (HE), Aldehyde Fuchsin-Masson Goldner (AF-MG), and anti-CD68 antibody. Results HE staining showed that ACL healing was not observed in the ACLT group, while spontaneous ACL healing was observed at 2 weeks postoperatively in the CAM group. AF-MG stains showed that the healing area consists of collagen. CD68 positive cells were mainly located at the superficial layer and the fibrous layer in all groups. Furthermore, in the CAM group, CD68 positive cells were located at the remnant at 1 week postoperatively and at the healing area at 2 weeks postoperatively. Conclusion This study indicates that correcting abnormal kinetics during the early stages of ACL injury is critical for spontaneous ACL healing, and the healing tissue observed in the healing area contains collagen and type A synoviocytes.