There are two common mistakes made when coding an interpositional arthroplasty.
1. A partial or complete carpectomy is inclusive to the primary procedure and not additionally reported.
2. When a tendon is transferred during the suspension procedure a code is assigned based on recipient area or where the tendon is transferred to.
There are a couple of variations to this procedure. In a basic procedure the trapezium, which is the carpal bone that articulates with the first metacarpal is excised. An interpositional piece of material (can be an autograft, allograft, or prosthetic) is then positioned in the defect and may be pinned in place (internal fixation is inclusive). If an autograft is used only report 20924 if the graft is harvested through a separate incision.
A “suspension arthroplasty” is the procedure we commonly see in an ASC. The reason it’s called suspension is that the FCR tendon which is harvested for the tendon transfer has an insertion point on the base of the second metacarpal and after removing the trapezium a hole is drilled in the first metacarpal and then the FCR tendon is passed through the drill hole and tensioned to prevent the first metacarpal from migrating or moving out of position – so in principle one bone is “suspended” to the other. Since the work or transfer of the tendon is performed to the carpometacarpal area report CPT code 26480 carpometacarpal area, or dorsum of hand. Even though there are different variations of this procedure that does not change the coding, these services would be reported with CPT code 25447 - Arthroplasty, interposition, intercarpal or carpometacarpal joints.