I would code 26210 Excision or curettage of bone cyst or benign tumor of proximal, middle, or distal phalanx of finger;. since the op report describes the mass being at the bone level: "the mass was mobilized at its base at the distal phalanx level and then excised... The base of the mass was debrided with the rongeur" (a rongeur is an instrument used for removing bone)." Since we don't have anything in the ICD-10 index under mass, bone or mass, finger, and it is not a tumor, I would go to "disorder, bone" and find M89.8X4 Other specified disorders of bone, hand for a mass of the finger.