Back legs shake

Question
My older dog's back legs shake constantly.  He drags his back legs if he tries to move quickly or if he walks for an extended period of time.  He also has trouble standing from a sitting or lying position as well as trouble with stairs.  Why does he shake? How come he can't work his back legs?

Answer
Most likely because he cannot actually feel them very well. There are so many reasons Eric that a dog loses control of his back legs.
The most common ones are spinal stenosis, which is a narrowing of the spinal column and it becomes pinched so that the signals are slowed down or erratic.

Spondolytis which is like a stenosis but involves the spinal column breaking down.
Central nervous system issues due to age or lesions on the brain.
Here is an article on the many causes and symptoms:
http://www.petplace.com/article-printer-friendly.aspx?id=35

I would have your vet do an exam and evaluation on your dog Eric. He may be too old to do a lot for but at least you will know.

If their hearts are bad they can also have back leg issues due to bad circulation.

I don't think he is in pain, but he could be if he is suffering from a ruptured disc or a tumor of the spine.

That is why it is so important to have your vet look him over.