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Causes
By Mayo Clinic staff
The exact cause of thumb arthritis, as with osteoarthritis in general, isn't known. Researchers suspect that it's a combination of factors, including being overweight, the aging process, joint injury or stress, heredity, muscle weakness and "cumulative load" to the joint. This is when you use your joint repetitively, such as in assembly line work.
Made up of the small bone at the base of your thumb (trapezium), the first bone of your thumb (first metacarpal), and the wrist's scaphotrapezio-trapezoidal joint, the basal joint allows your thumb its wide range of motion and allows your hand to pinch, grip and grasp objects.
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.
Your body goes to work repairing the damage, but the repairs may be inadequate, resulting instead in growth of new bone along the sides of the existing bone (bone spurs), which can produce noticeable lumps on your thumb joint.
