SYNOVIAL-MEMBRANE INVOLVEMENT IN OSTEOARTHRITIC TEMPOROMANDIBULAR JOINTS - A LIGHT-MICROSCOPIC STUDY

Objective. To study the light microscopic characteristics of the synov ial membrane of osteoarthritic temporomandibular joints to evaluate sy novial membrane involvement in the osteoarthritic process. Study desig n. Synovial membrane biopsies were obtained during unilateral arthrosc opy in 40 patients. Thirty-one temporomandibular joints were diagnosed with osteoarthritis. Osteoarthritis subgroups were defined on the bas is of the presence of symptoms related to disk displacement and perfor ation. The control group consisted of nine temporomandibular joints th at were not involved by osteoarthritis. During light microscopic exami nation of the synovial membranes, several light microscopic variables were recorded. Differences between groups and between subgroups were t ested with chi(2) Or Fisher's exact tests with Mann-Whitney U tests an d with Student's t tests. Results. In the osteoarthritis group, the nu mber of synovial intima cell layers was significantly higher, and fibr ous intima matrix and fibrous subintima were found significantly more frequently than in the control group. Moreover, in the osteoarthritis group, intima cell hypertrophy in combination with a closely packed ce ll composition was found significantly more often in the first year of clinical signs and symptoms, whereas intima hyperplasia, fibrous inti ma matrix, dense surface material, and subintima elastic fibers were f ound significantly more frequently in the first 2 years of clinical si gns and symptoms. Conclusions. The findings in this study suggest that osteoarthritis of the temporomandibular joint may initially result in synovial intima hyperplasia and cell hypertrophy, and subsequently in deposition of fibrous material in the intima matrix. Eventually, fibr osis of the subintimal tissue may occur in combination with degenerati on and subsequent normalization of the synovial intima cell layer. Ove rall, fibrosis was the most characteristic feature of synovial membran es of osteoarthritic temporomandibular joints. In conclusion, the invo lvement of the synovial membrane in osteoarthritis of the temporomandi bular joint is characterized by an early proliferative phase and a lat e fibrous phase. It appears that the intense and prolonged fibrous pha se may not be a normal appropriate response to an initial insult but r ather an aberrant counterproductive response.