What is wrong with my border collie's back legs?

My unusually large border collie(80 lbs)has had problems with his back legs since he started walking. He had a limp when he first started walking and I assumed his legs weren't fully developed. He was the smallest of the litter, so I expected him to be behind. AT 2 yrs old he is still having problems. He has muscle spasms every day. He often gets up and shakes his leg sort of like it has fallen asleep. It seems to be worse after he has been still for awhile. He stumbles at least once or twice a day, like his back legs are giving out. When he is walking around, his legs sometimes point inward or outward and he doesnt seem to notice it. He has hypothyroidism and has meds for that. He had his calcium checked and it was fine. I have asked my vet about it and she said we have to do an xray, but if it is a muscle problem, an xray wouldn't help. I have spent hundreds on my dog, trying to find out the problem and am running out of money. Could someone please point me in the right direction?

Asked by Member 898583 on Oct 8th 2009 Tagged legs, muscle, spasm, hypothyroidism, collie, disorder, limping, stumbling in Illness & Disease