There is so much going on. It's a question of breaking it down into individual parts like the osteotomies, somewhat of amputations, radical resections, disarticulations, the soft tissue and other work, etc or using one unlisted code. There is no one code to describe this. It may be a matter of working with your provider(s) and payers individually to come to agreement on using unlisted codes and/or a combination of unlisted and existing CPT to bill for this. It has to be put into the contracts.
When I worked with an orthopedic oncology, hip preservation, complex joint reconstruction surgeon he would go to the individual payers and we would work out coding for the novel and other unlisted procedures he was performing to have it put in contracts on how this would be billed and the reimbursement.
It takes teamwork and partnership between the revenue cycle side and coding along with the providers if your practice is doing very specialized, complex cases with no codes. Otherwise, reimbursement will suffer and the providers will not be getting credit for their work. Someone who is not up to speed could code these type procedures incorrectly. I have seen where coders didn't understand and used incorrect codes for highly complex procedures and the reimbursement was totally off.
Whoever is in charge of coding, the revenue cycle director, surgeon and possibly the C-level team need to be involved in this, it shouldn't be left up to staff coders to try and figure it out with this type of case.