Thumb arthritis is the most common form of osteoarthritis affecting the hand. Also called basal joint arthritis, thumb arthritis occurs when the cushioning cartilage wears away from the adjoining ends of the bones that form your thumb joint (carpometacarpal joint). Thumb arthritis can cause severe hand pain, swelling, and decreased strength and range of motion, making it difficult to do simple household tasks, such as turning doorknobs and opening jars. Treatment for thumb arthritis may include self-care measures, splints, medication or corticosteroid injections. If you have severe thumb arthritis, you may need surgery.