Rheumatoid arthritis may cause pain, swelling, stiffness, and tenderness in foot joints. If the disease progresses, joints may become distorted and disabled. Pain and tenderness is common under the ball of the foot. The joints between the foot and the toes (metatarsophalangeal joints) swell and move, causing the toes to curl and overlap. The big toe may bend inward (hallux valgus). The middle toes may bend into a clawlike curl (hammer toe).