My Mastiff Tazzie was a front leg amputee (185 # post-amputation).  She did very well with a few stairs but I would not let her do a full flight since I was afraid she would tumble forward.  We were lucky enough to have our bedroom, den and outdoor access on the bottom floor so that is where she stayed.

It is true that spindle cell sarcoma rarely metastasizes so I would make your decision based on pain level.  I gave Tazzie meloxicam 7.5 mg once daily.  It is an NSAID like Rimadyl but pretty safe and you can get it pretty cheaply from a human pharmacy (your vet needs to write a script for it).  Always make sure your dog has baseline bloodwork to check liver and kidneys before starting a long-term NSAID.  Tramadol is also an option.

How fast is the tumor growing?  Some of these do not grow that fast so if pain is controlled you may still have quite some time before amputation is needed.  I am a veterinarian and I have had many patients with these joint tumors where we manage the pain and "debulk" the tumor as needed.  This means taking out the major part of it but leaving a small amount in the joint.  Did the biopsy report give a grade or level of malignancy?

If your dog is in otherwise good health then amputation is certainly an option and many giant dogs have done very well!

Pam

Rimadyl is generally a pretty safe NSAID but is seems to be harder on the liver than others.  My dog Tazzie had chronic hepatitis so I used meloxicam for her and her liver values stayed in the normal range the entire time she was on it.  Usually I would repeat bloodwork every 6-12 months to check organ function, although I checked Tazzie every 3 months due to her liver condition.  I have many dogs in our practice that stay on Rimadyl or other NSAIDS long-term without issues but some dogs do get vomiting or diarrhea with or without blood.  These side effects are reduced by giving the meds with food and by using the lowest effective dose.

Tramadol has a wide safety range and the main side effects seem to be sedation or nausea but most dogs take this long-term without any issues.  A good dose for your dog would be 100-200 mg orally 2-3 times daily.  My dog Kona has terrible arthritis and she is best managed with a small dose in the am and a larger dose at night to help her sleep.

As far as pain receptors I often add gabapentin and/or amantadine to prevent pain wind-up and to lower the NSAID dose and this seems to work best for nerve root pain. There are certainly nerves involved in the hock joint so these drugs may help if needed.

Usually I will debulk the tumor if it is larger than the whole joint or if the skin is getting too stretched out.  I am usually able to conserve enough skin to cover everything but sometimes a small area is left open to reduce tension and then heals with repeat bandaging.  I remember a shepherd mix who had 3 surgeries (about 1 per year) and never needed amputation but later passed away of other causes when she was 12 years old.

It sounds to me like you have some time to wait and see how your dog does with pain meds before you need to consider amputation. I'm sure that your vet can help guide you if and when that time may come.  Good luck!

Pam