PetMD explains that one of the most common reasons that dogs experience rear-leg paralysis is due to trauma at some point along the nerve path. Moving the rear legs requires the use of the dog’s brain, spinal cord and peripheral nerves, which transmit information to and from the brain. Often, the problem is that the linkage between the spinal cord and the brain has been disrupted.
A dog's spinal cord travels through 24 different protective vertebrae, according to PetMD. Intervertebral discs between the vertebrae act as cushions. While the vertebrae and intervertebral discs usually protect the nerves well, portions of the nerve can become pinched, which results in impaired nerve impulse transmission.
WebMD states that traumatic injuries are not the only causes of hind-limb paralysis. For example, some breeds are genetically predisposed to a disease that damages the spinal nerves, called degenerative myelopathy. This is a progressive disease of older dogs, and it is most prevalent in Welsh corgis, boxers, German shepherds, Chesapeake Bay retrievers and Irish setters.
Other potential causes of rear leg paralysis in dogs include distemper, Rocky Mountain spotted fever, emboli and tumors. Additionally, slipped or herniated discs can also lead to rear leg paralysis, according to WebMD.