The onset of rheumatoid arthritis is an inflammatory process. With joint inflammation, the synovium thickens. Synovial cells increase in number during the thickening stage. The synovium becomes edematous (fluid-filled) and enriched with new blood vessel formation. Synovial fluid production increases and the joint capsule swells along with these changes. Circulating inflammatory cells infiltrate the joint tissue. The cellular processes that occur during inflammation and the resulting changes are referred to as active synovitis. With active synovitis, irritation and swelling of the joint lining, degradation of cartilage, and bone erosions can occur.
Rheumatoid Arthritis: Early Diagnosis and Treatment. Pathology of RA. PP.16-19. By John J. Cush MD, Michael E. Weinblatt, MD, and Arthur Kavanaugh, MD. Third Edition. Copyright 2010.
The Normal Joint. WorldOrtho. Joints Part 1. By Sarah Saw and Magdalena Mironowicz. Accessed 6/25/2012.
The joint capsule: structure, composition, ageing and disease. Journal of Anatomy. Ralphs JR et al. June 1994.
The Normal Synovium. Malcolm D. Smith. The Open Rheumatology Journal, 2011, 5, (Suppl 1:M2) 100-106
Joints. Merck Manual Home Health Handbook. Pekka Mooar, M.D. July 2007.