Arthritis in the thumb typically develops as a result of an injury or trauma to the joint, according to the Mayo Clinic. People with osteoarthritis in larger joints may also develop arthritis within the thumb.
Arthritis in the thumb causes cartilage that covers the ends of the bones to deteriorate as the smooth surface of the thumb roughens, according to the Mayo Clinic. When arthritis in the thumb is present, bones rub against each other, causing joint damage and friction. As a result of damage to the joint, new bone may grow alongside the existing bone, which can produce lumps on the thumb joints.
Certain factors may increase risk for thumb arthritis, such as age, gender and hereditary conditions, according to the Mayo Clinic. Females and individuals 40 or older are more at risk for thumb arthritis as well as individuals with hereditary conditions such as malformed joints or joint ligament laxity. Individuals who experience sprains, fractures or injuries to the basal joint are also more at risk for thumb arthritis.
Activities that put consistent stress on the thumb joints may put people at risk for thumb arthritis, according to the Mayo Clinic. In addition, rheumatoid arthritis or illnesses affecting the function or structure of cartilage present risk factors.