Arthroscopic and synovial correlates of pain in osteoarthritis

Abstract

PATIENTS AND METHODS D EFINITION OF DISEASE complicates the correlation of pain with other features of knee joint osteoarthritis (OA). Patient selection for clinical trials is limited by the fact that joint pain is often present before joint destruction is demonstrated by radiographs.“* Direct inspection of the joint by knee arthroscopy can detect cartilage degeneration and hence confirm the diagnosis of OA before radiographic changes occur.3 Thus, patients presumed to have an early stage of OA also may be selected for screening of disease. Recently, the American College of Rheumatology (ACR; formerly the American Rheumatism Association) published criteria for classification of OA of the knee.’ These criteria can be tested by arthroscopy. Abnormal cartilage per se may not explain pain in OA because cartilage lacks innervation. However, joint pain in OA could be caused by a pathological process in the synovial membrane. There is controversy regarding the presence or absence of synovitis in OA4*’ based on diverging results in previous studies.“‘* The question has been addressed by a recent arthroscopic study using immunohistologic stains of the synovium.” An intense inflammation was demonstrated in synovium areas near OA cartilage, whereas the remainder of the joint interior remained without inflammation. Biopsies of involved synovium guided by direct visualization microscopically displayed highly inflammatory changes comparable to the synovial changes in rheumatoid arthritis. In contrast, tissues sampled from apparently noninflamed areas lacked immunohistopathologic signs of synovitis. Thus, microscopic examination verified the arthroscopic findings of local synovitis.13 Among the patients referred to the Department of Rheumatology, Huddinge University Hospital, for investigation of knee joint pain, five patients were studied who fulfilled the ACR clinical criteria for classification of OA’ and lacked other signs of a specific form of arthritis. They had given informed consent for the study. Patients were evaluated for the six sets of ACR criteria. Synovial fluid was not available in one of the five patients. No signs of disease in joints other than the knee were apparent at clinical examination. Arthroscopy of the knee joints was performed under local anesthesia. The pressure of irrigating solution was kept below the capillary blood pressure to avoid interference with the synovial circulation. The optics and biopsy forceps were introduced through the joint capsule at different points to enable biopsy sampling under direct vision, as previously described.“.‘4 The synovial biopsy specimens were snapfrozen at 70°C, and frozen sections were examined ,by immunohistochemical single and double stainings with monoclonal antibodies to T lymphocytes, macrophages, HLA-DR antigens, and immunoglobulins, as in earlier studies.‘3,‘4