I'm really no expert and I haven't really had experience with this (but my first dog is turning 8 soon, so I should begin to expect difficulties like these, I think) but I did some quick googling and just wanted to compile a list of similar situations. You've probably run into them already in your own research, but still.
"Have you heard of the Tellington T Touch? If you haven't, you can look it up.
One of the techniques is to use a towel to lift the dogs hind end. Wrap the towel under the dog & bring it back & as close as you can to the tuck just in front of the hind legs. Lift only high enough to get the weight off the back legs. Hold for a few seconds & repeat about 5 times. You can also walk her to her food & water & out side too, just by lifting her hind end with a towel.
This is to help lower back & hind legs."
"I have a 12 year old boxer with the same problems altho she could still walk with difficulty. The vet gave her a series of injections called PENTOSAN 100 i now take her on slow short walks. She had 4 shots over a 4 week period plus a booster 8 weeks later. Plus it was not too costly."
"(Lumbar instability) occurs when the ligaments, discs and joints that support the bones of the spine are damaged to the point they can no longer hold the bones together. This causes back pain. As the bones move out of place, they can pinch the nerves and cause leg pain and weakness and would have or should have been diagnoised by examination and x-ray. If she has been like this for a while, then it is likely that you have no continued gentle exercise (like swimming) which keeps the muscles strong and protects legs/back."
source for all three
"The last time I saw a dog that couldn't stand up (she just sat), the dog had pyometra, which is an infected uterus. This has to be removed surgically and costs about the same as a hysterectomy (essentially that is what it is).
If your dog has already had her hysterectomy (been spayed), then this can't be the reason."
source
Sorry I couldn't offer any advice of my own! I really hope your Samoyed heals up
