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Hello. My name is***** have been a veterinarian for 11 years.
Am I reading correctly that your question is what else can cause a back leg to not work and knuckle under?
Ok. I can help with that.
Any time there is knuckling over and the leg appears "dead," then there has been trauma to the brain or the spinal cord. If it is only a back leg, then the damage is in the cord behind the front legs (T2-L2 is the spinal column region). An embolus can cause that, as can a hematoma (bruise) or a disc problem. The disc can protrude and push on the spinal cord.
Really, the only way to know for sure is to do either an MRI or a myelogram (an x-ray taken after a special dye is injected around the spinal cord).
Yes, and embolism is one of the options, but you asked for many options, I had to include that one, even though you already have it on your radar. :)
Usually, they do fine, but in some cases, if it is a disc issue, it can cause more problems causing sudden paralysis of both back legs. This generally needs emergency treatment if you want to get function of the leg (or legs back).
Does that answer your questions?
What else can I help you with?