Is it used when a bone graft is placed subcutaneously in the abdomen then retrieved later for repair, or
Is it when a bone graft is placed to repair a skull defect or wound?

CPT reads: incision and subcutaneous placement of cranial bone graft (list separately in addition to code for primary procedure)

CDR reads: A cranial bone graft is placed onto a part of the skull for repair following craniectomy, craniotomy or other intracranial surgery.