Really sorry to hear about your brother and his difficulty with HO. My husband is a high level quad and also developed HO about 3 months after his injury. He was in SCI rehab at the time at one of the model SCI Hospitals (Craig Hospital). He was immediately put on Didronel. Is your brother on Didronel?
Didronel will do nothing to remove calcium that has already been deposited. It is a preventative drug, and has no effect on existing ossification. It also has no effect on the underlying process which produces the bony matrix. But it sure can prevent things from getting worse. Many physicians recommend prophylactic use of Didronel in all acute spinal cord injuries,
It seems like my husband was on Didronel for maybe 6 months initially. After we came home, the HO flared up again, and he was back on the Didronel for another several months. And you are correct, surgery should not be considered until the HO is mature.
I would certainly seek the advice of a physiatrist (physical medicine and rehabilitation doctor) who specializes in SCI. Or if you can get him to one of the model SCI facilities for an outpatient evaluation, that might also be helpful.
That is one thing that I have learned through the 10 years we have been doing this, some of these complications are so specific and unique to SCI that the average medical professional has little experience or knowledge with the appropriate treatment as it relates to a patient with a SCI. I would definitely get a second opinion from someone knowledgeable in treating SCI before I considered amputation.
Just my 2 cents. Good luck.