Unil prim osteoarth of first carpometacarp joint, unsp hand

This code signifies a degenerative joint disease affecting the base of the thumb on one side, where the trapezium bone meets the first metacarpal. It indicates that the osteoarthritis is primary (not secondary to trauma or another condition) and the specific hand affected is not documented.

Apply this code when documentation confirms primary osteoarthritis of the first carpometacarpal joint, but the laterality (left or right hand) is not specified. This is appropriate for initial evaluations or when the physician's notes do not explicitly state which hand is affected.

• Ensure the documentation clearly states "primary" osteoarthritis; otherwise, consider codes for secondary osteoarthritis.
• If the laterality is known, use a more specific code (M18.11 for right, M18.12 for left).
• Avoid using this code if the osteoarthritis is bilateral; instead, use M18.13.