Causes / typical injury mechanism: Basilar thumb arthritis, also known as thumb carpometacarpal (CMC) or trapeziometacarpal joint arthritis, arises as a result of degenerative attenuation of the anterior oblique ligament, which can lead to increased stress on the trapeziometacarpal joint. Increased stress on the joint can cause cartilage loss and pain.

Classic history and presentation: The condition presents as pain at the base of the thumb and difficulty with opening jars / bottle caps, writing, and turning keys.

Prevalence: Basilar thumb arthritis is the second most common type of arthritis in the hand. Prevalence increases with increasing age, and the disease is more common in women. Radiographic evidence of basilar thumb arthritis can be seen in as many as 40% of women aged 80 years and older.

Risk factors: Primary risk factors for the condition include female gender and older age.

Grade / classification system:
Eaton and Littler classification –

• Stage I: Widening of the CMC joint due to synovitis.
• Stage II: Joint space narrowing of the CMC joint with osteophytes less than 2 mm.
• Stage III: Joint space narrowing of the CMC joint with osteophytes greater than 2 mm, with or without radial subluxation of the thumb metacarpal on the trapezium.
• Stage IV: Scaphotrapeziotrapezoid (STT) joint involvement.