A common cause of thumb arthritis is aging. Trauma or injury that was caused previously to the thumb joint can also lead to thumb arthritis.
The cartilage acts a cushion and covers the tip of the bones. This permits the bones to move smoothly against each other. The deterioration of the cartilage that covers the tip of the bones is called thumb arthritis. Eventually, the smooth surface gets rough. The bones then collide against each other, and this results in friction and damaging of the joints.
This damage may also lead to the growth of a new bone beside the existing ones. This is known as bone spurs, which can cause apparent lumps on your thumb.