For what it is worth, the extensor tendons to the fingers enter the hand from the dorsal forearm, cross the dorsal wrist, then proceed over the hand/metacarpals to the fingers. The Extensor Digitorum Communis (EDC) tendons and Extensor Indicis Proprius (EIP) cross the dorsal wrist together through a single/common "compartment." The Extensor Digiti Quinti (EDQ) to the small finger may have its own "compartment," but not necessarily always and may enter with the other extensors. When an Extensor Tenosynovectomy is done, it is usually done at the dorsal wrist level then extended distally into the dorsal hand or proximally into the dorsal forearm as necessary, and rarely all the way out to and including the finger(s). The other thing to take into consideration is the underlying diagnosis as this affects the coding. If there is chronic florid hypertrophic tenosynovitis such as Rheumatoid Arthritis or chronic infectious tenosynovitis, the 25116 for "Radical" Extensor Tenosynovectomy would apply, particularly if multiple extensor compartments were opened/treated. For less severe tenosynovitis and when only one compartment is opened/treated, then 25118 would apply. For the case mentioned in this query, I think 25118 would be most correct.
I hope this helps.
Respectfully submitted, Alan Pechacek, M.D.