ULTRASTRUCTURAL CHARACTERISTICS OF THE SYNOVIAL-MEMBRANE IN OSTEOARTHRITIC TEMPOROMANDIBULAR JOINTS

Purpose: This study analyzed the ultrastructural characteristics of th e synovial membrane in various stages of osteoarthritis (OA) of the te mporomandibular joint (TMJ), and developed a classification of this in volvement based on these morphologic characteristics. Patients and Met hods: Synovial membrane biopsies were performed during unilateral arth roscopy in 40 patients. Thirty-one TMJs constituted the OA group; nine TMJs that were not involved by OA constituted the control group. Duri ng light microscopic (LM) examination, Various variables were recorded and related to the duration of clinical signs and symptoms. Ten synov ial membranes from osteoarthritic joints showing histologically visibl e pathologic changes in various stages and one control synovial membra ne were selected for electron microscopic examination. Results: The in itial, early, and intermediate stages of synovial membrane involvement in TMJ OA were characterized by intima hyperplasia. In the initial an d early stages, active and hypertrophic intimal cells are found. In th e intermediate stage, an increased number of both intracytoplasmic and extracellular filaments was predominant. Fibrosis of the subintimal t issue was initiated by an increased number of active fibroblasts. The late stage of synovial membrane involvement in TMJ OA was characterize d by a relatively normal synovial intima of normal thickness, whereas extensive fibrosis was seen in the subintimal tissues. Conclusions: Sy novial membrane involvement in TMJ OA is characterized by an early pro liferative phase with probable growth factor-mediated increases in the cellular activity of the synovial intima cells (resulting in hyperpla sia and hypertrophy), of fibroblasts (resulting in increased productio n of collagen fibrils and fibrosis), and of endothelial cells (resulti ng in blood vessel growth and hypervascularity). The late phase is cha racterized by extensive fibrosis of the subintimal tissue, whether cau sed by sustained production of growth factors or by chronic venous ins ufficiency, with normal or little cellular activity.