CausesBy Mayo Clinic staff
Thumb arthritis usually occurs as a result of trauma or injury to the joint. Some people also develop thumb arthritis in association with osteoarthritis in larger joints.
The basal joint gives the thumb a wide range of motion, allowing you to pinch, grip and grasp objects. The bones in the thumb's basal joint are the first metacarpal bone, which runs through the heel of your hand, and the trapezium (truh-PEE-zee-um), a small bone at the base of your thumb.
In a normal basal joint, cartilage covers the ends of the bones — acting as a cushion and allowing bones to glide smoothly against each other. With thumb arthritis, the cartilage that covers the ends of the bones deteriorates and its smooth surface roughens. The bones then rub against each other, resulting in friction and joint damage.
The damage to the joint may result in growth of new bone along the sides of the existing bone (bone spurs), which can produce noticeable lumps on your thumb joint.
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