what causes legs to be weak
An infection with the bacteria that causes botulism can also cause a dogâs hind legs to suddenly go weak, though this is rare, says Dr. Benson. Accompanying symptoms of this would be excessive drooling, slack jaw and dilated pupils.
The cause of your dog's back leg weakness may be pain from arthritis. As dogs age, especially large dogs, the hip and knee joints begin to deteriorate and the cushioning in the joints disintegrates. An X-ray can generally confirm the presence of arthritis.