To study the light microscopic characteristics of the synovial membrane of osteoarthritic temporomandibular joints to evaluate synovial membrane involvement in the osteoarthritic process.
Synovial membrane biopsies were obtained during unilateral arthroscopy in 40 patients. Thirty-one temporomandibular joints were diagnosed with osteoarthritis. Osteoarthritis subgroups were defined on the basis of the presence of symptoms related to disk displacement and perforation. The control group consisted of nine temporomandibular joints that were not involved by osteoarthritis. During light microscopic examination of the synovial membranes, several light microscopic variables were recorded. Differences between groups and between subgroups were tested with chi 2 or Fisher's exact tests with Mann-Whitney U tests and with Student's t tests.
In the osteoarthritis group, the number of synovial intima cell layers was significantly higher, and fibrous 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 cell composition was found significantly more often in the first year of clinical signs and symptoms, whereas intima hyperplasia, fibrous intima matrix, dense surface material, and subintima elastic fibers were found significantly more frequently in the first 2 years of clinical signs and symptoms.
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, fibrosis of the subintimal tissue may occur in combination with degeneration and subsequent normalization of the synovial intima cell layer. Overall, fibrosis was the most characteristic feature of synovial membranes of osteoarthritic temporomandibular joints. In conclusion, the involvement of the synovial membrane in osteoarthritis of the temporomandibular joint is characterized by an early proliferative phase and a late fibrous phase. It appears that the intense and prolonged fibrous phase may not be a normal appropriate response to an initial insult but rather an aberrant counterproductive response.