Swollen and deformed fingers can be caused by rheumatoid arthritis. Rheumatoid arthritis is caused by inflammation of the synovial membrane extending into the connective tissue and eroding the soft tissue and bone tissue of the joint, resulting in joint destruction and causing joint deformation. This in turn leads to localised lymphatic or venous return obstruction and increased permeability of the capillary wall, resulting in excessive fluid accumulation in the tissue spaces of the finger area, which causes tissue swelling due to the joint deformity.