Many dogs can suffer from weakness in their back legs. A visit with your veterinarian can help you rule out possibilities. There are several different reasons why your dog may suffer from hind leg weakness.
Lumbosacral Stenosis Syndrome
Lumbosacral stenosis syndrome also known as cauda equine is arthritis of the joints between the lumbar vertebra and the sacrum. Dogs suffering from this disease experience weakness and pain in their hind legs. This disease is mostly seen in large breed dogs, particularly German Shepherds. Dogs who are excessively overweight are at risk for this disease.
Degenerative Myelopathy is a nerve disorder that causes weakening of the hind legs.
Most dogs, when first diagnosed with diabetes experience hind leg weakness. This is found to be more common with cats than dogs.
Avoid feeding your dog people food, such as macadamia nuts. The American Society for the Prevention of Cruelty to Animals notes, "Affected dogs develop weakness in their rear legs, appear to be in pain, may have tremors and may develop a low grade fever."
As dogs grow older they tend to slow down. Age can also bring on diseases such as Cushing's disease, which causes leg weakness.