The histological analysis of the anterior cruciate ligament of canine after radiofrequency shrinkage.

ABSTRACT

OBJECTIVE: Radiofrequency (RF) shrinkage has been widely conducted in clinical practice and the anterior cruciate ligament (ACL) laxity is regarded as one of the indications. However, basic researches regarding the postoperative histological changes were still insufficient. The study aimed to investigate postoperative histological changes of different areas of ACL for further identifying the optimal area for RF shrinkage. MATERIALS AND METHODS: A total of 29 healthy canine (16.5 ± 2.2 kg, 4.1 ± 0.7 years) were recruited, 24 of which were randomly divided into group A and group B. The epiphyseal arrest was confirmed by X-ray examination in all animals. On one canine, an ACL's vascular perfusion model was established by the ink-perfusion method to observe the blood supply of the ACL. The mid-portion of ACL was conducted by RF in group A while the amph-portions of ACL were conducted in group B. Two legs of each canine were sub-divided into fixation group (group A1 and B1) and non-fixation group (group A2 and B2). 8 ACLs were separated from the rest 4 canine. 2 ACLs were sent for the histological examination after RF shrinkage and the rest 6 ACLs were served as blank controls. Masson staining and hematoxylin-eosin (H-E) staining were applied to observe the features of inner fibrous changes of ACL, cell count and vascular density. RESULTS: According to the Masson staining, collagenous tissues were observed in area after RF shrinkage, which was more evident among group B1 than the others. The cellar density in both group A and B was found lower at 12 weeks postoperatively than that at 6 weeks postoperatively (p < 0.05). In addition, the cellar density in B1 group was found higher than that in A1 group at both 6 and 12 weeks postoperatively (p < 0.05). The density of subsynovial vessel in B1 group was found higher than that in A1 group at 6 weeks postoperatively (p < 0.05) and the density of subsynovial vessel in both A1 and B1 groups was found lower at 12 postoperatively weeks than that at 6 weeks postoperatively (p < 0.05). In both A2 and B2 groups, all ACLs were found ruptured at 12 weeks postoperatively. CONCLUSIONS: The postoperative revascularization pattern of RF-treated ACL was permeating from the synovium to the RF-treated areas, and the best area for the RF shrinkage treatment was the amph-portions of the ACL. Moreover, the application of postoperative external fixation to restrict the movement of injured limb was necessary.