Usually they don't try to get a cat's temperature down, they're thermostats work differently than ours. The fact that they're doing this is a bit worrisome. It's not bad, mind you, but it means they can't find the cause of the elevated temp (which...you already know). I would think it may be caused by an arthritic inflammation (how old is your cat?) which is possibly what the vet is guessing at if he's giving him cortisone.
Otherwise...there are certain genetic conditions that can cause a temperature elevation, but hopefully you won't have to go there. I wouldn't want to guess about what it could be as I;d preferably be wrong (although many of them are harmless enough and treatable).
One thing you can do is track back the past week before kitty got sick and try to find ANY small change in lifestyle, be it diet, weather, etc... something is causing kitty to run hot, the question is if it's environmental, infectious (looks like this was ruled out if white blood cell count is normal) or genetic.
Thanks! During the op they found that this was an historic fracture (pre current ownership - she was adopted from the SPCA) of about 4/5 yrs and the femur head has fused with the hip socket. The femur head can therefore not be removed in any event. They took some scrapings of cartilage to check for abnormalities. So on the face of it the fracture isn't the reason for her being listless and her discomfort. The other problem is her temperature won't go down - stays around 40,4C (now 3rd day). They've done blood tests, urine tests, extensive lab work - no parasites, white blood count normal, no renal problems, stool fine. X-rays of the chest shows nothing abnormal and first X-rays only picked the old fracture. They've given her pain medication and anti-inflammatories and will now give some cortisone to try and het the temp down. No bite marks of any kind, no broken skin, no abscesses. Stumped. The fracture isn't the reason for her condition, yet her lower back area near the tail base and hip is sensitive. What is the cause of the high temp? They are now going to scan the abdominal cavity to make sure there are no growths, etc which there probably won't be since all tests are normal. Please, any thoughts on this?
Yes, usually cats adjust very well to these types of injuries and still have a happy quality of life.
Otherwise...this is one of those cases where I hesitate to say if he's right or wrong. Your best choice would be to get a second/third opinion (make sure on is a legitimate animal hospital, not just a vet) as to which is the wisest course.
I know the work you're talking about and one of the biggest problems is length of recovery. Animals aren't people and you can't force them to do physical therapy. I believe the femur removal is more practical because of quicker recovery time, but I'm not as familiar with the details on that.