No, I am sorry, 29877 is not correct in my openion. It is a code for debridement of an ARTICULAR CARTILAGE . Ganglion is not cartilage.
GANGLION REMOVAL-BY EXCESION OR ENMASSREMOVAL OR DEBRIDEMENT, IS NOT THAT OF A CARTLAGE.
I would more closely give the code 29874- for removal of loose body or foreign body (eg)...... Ganglion near that joint can be considered as loose body .
Again removal enmass or in piece mils or as debridement of a ganglion cyst is going more towards "excision of the ganglion by arthroscopic procedure.
BUT,
If there was infection/- and he drained it (ASPIRATION), you could go for 29871- infection, lavage and drainage, AFTER enquiring him about whether he did lavage and drainage of the infected ganglion. I fthis is ruled out then , it has all the more merits for 29874.
Would this help you better.