Histopathological Evaluation of Synovial Tissue in OA and RA

Synovial samples were obtained intra-operatively from 147 OA patients and 60 RA patients. As per the study protocol, orthopedic surgeons were requested to preferentially obtain a research sample from grossly abnormal-looking synovium. Tissue for histological examination was chosen by a pathologist on the basis of gross features including the smoothness and granularity of the synovial surface, red or brown discoloration, and the clarity, dullness, or opacity of the synovial layer, preferentially avoiding regions of electro-cautery effect.
Synovial samples were preferentially obtained from the most grossly inflamed (dull and opaque) area of the synovium. If there was no obviously inflamed synovium, samples were obtained from standard locations: the femoral aspects of the medial and lateral gutters and the central supratrochlear region of the suprapatellar pouch. OA synovial tissue samples were formalin-fixed and paraffin-embedded, and the RA tissues were fresh-frozen in optimal cutting temperature compound. Each tissue biopsy was sectioned at 5-μm thickness and stained with Harris-modified hematoxylin solution and eosin Y (H&E) manufactured by Epredia in Kalamazoo, MI. An expert musculoskeletal pathologist (ED) scored fourteen synovial histologic features in a single section for each patient: lymphocytic inflammation, mucoid change, fibrosis, fibrin, germinal centers, lining hyperplasia, neutrophils, detritus, plasma cells, binucleated plasma cells, Russell bodies, sub-lining giant cells, synovial lining giant cells, and mast cells. Detailed methods for scoring these features are included in the Appendix, some of which are described in prior studies [8 ] and available at www.hss.edu/pathology-synovitis.