Alterations of rabbit craniomandibular joint tissues following experimental induction of anterior disk displacement : histochemical and immunohistochemical studiea

Abstract

The purpose of this study was to test the ·hypothesis · that surgical induction of anterior disk displacement (ADD) in the rabbit craniomandibular joint (CMJ) leads to cellular and extracellular alterations similar to those that occur in human ADD. The right joint of each of 35 rabbits was exposed surgically and the discal attachments of the CMJ were severed except for the posterior attachment (bilaminar zone). Then the disks were displaced anteriorly and sutured to the zygomatic arch. The left joint~ were treated as surgical controls. Twenty joints from ten additional rabbits were used as non-operated controls The rabbits were· anesthetized, perfused with fixative 24 hours (5 rabbits), 1 week (10 rabbits), 2 weeks (10 rabbits) and 6 weeks (10 rabbits) following induction of ADD. CMJ tissues were then removed after fixation, processed and stained for general histology using H&E stain, glycos.aminoglycans (GAGs) using alcian blue stain, elastic fibers using resorcin-fuchsin stain and nerve fibers. using. silver nitrate stain. In addition, immunohistochemical localization of . . type-I, type-II, type-III, type-VI, type-IX collagens and fibronectin (FN) as well as various GAGs, such as keratan sulfate (KS), chondroitin-4-sulfate (C4S), chondroitin-6-sulfate (C6S) and hyaluronic acid (HA). In addition to the link protein (LP) and neurofilaments (NF). The results showed a statistically significant enla.rgement of the condyles in the treated joints compared to controls (P < 0.01). The enlargement was characterized by statistically · significant increases in the cartilage thickness and the surface area of the condyle when compared to controls (P < 0.01). In addition, the results showed neovascularization, cell clustering and fibrillation of the displaced · disks, as -weli as, fibrosis of the bilaminar zone. The subchondral bone showed hemorrhage, fibrosi,s and cyst formation. The osteochondral junction showed _ splitting from . the subchondral bone. Condylar .cartllage in ADD joints showed neovas·cularization, cell clustering and hyperplasia. The· articular eminence showed. cell clustering along _ with hyperplasia of chondroid bone ·and synovial membrane. There was a loss of elastic fibers in the displaced disks and the loaded bilaminar zone, and there were fine elastic fibers among the chondrocytes in the condylar cartilage which were· not present in the cartilage of th~ control condyle. The results of the immunohistochemistry showed statistically significant depletion of KS, C4S, C6S, FN, HA (P < 0.05) at 2 weeks. Also, loss of LP, reduction. in type-II (P < 0.05), type-VI and type-IX collagens at 2 weeks compared to controls. Some areas even showed a switch in the type of collagen from type-II to type-I collagen. At 6 weeks there was statistically significant increases in the level of C4S, FN, HA and type-II collagen (P < 0.05). Also, there were increases in type-VI and type-IX collagens levels compared to controls. In addition, newly formed type-III collagen was seen in the osteoarthritic cartilage which was absent in control condyles. Link protein did not reappear for up to 6 weeks. In the bilaminar zone there were statistically significant increases in KS, C4S, C6S, FN (P < · 0.05). Also, type-III, type-VI and type-IX collagens were increased in the experimental groups compared to controls. In additio~, the appearance of newly formed type-11 collagen was seen which was absent in control bilaminar zone. Histological nerve fiber staining and immunostaining both showed that the control and. experimental bilaminar zones were heavily innervated. The bilaminar zone adhesions were also innervated. Some nerves were seen ~perieterating the condyle. It is concluded that surgical induction of ADD in the rabbit CMJ leads to cellular and extracellular alterations comparable to those found in human ADD, · osteoarthritis of the human knee joint and induced osteoarthritis of the knee joint in various animal models.