My dog is limping and I'm scared

My dog (actually my fiance's) is about 10 years old. He adopted him from the humane society when he was a puppy.
We have just started noticing that his back legs are looking weak and it seems as though the muscle mass is deteriorating. He has also started whimpering when he is laying down and sometimes while he is sleeping. We started giving him glucosamine/chondrointin supplements a few months ago to try to slow the cartilage deterioration but we haven't noticed any change.
Today, I noticed that he is now limping and holding up his front paw like he stepped on something sharp but I inspected it intensly and found nothing.
We are taking him to the vet this week but I am scared. This is the first dog I have ever been around and I love him.
Has anyone ever had their dog go through something like this? My fiance isn't home today and I am debating on whether or not to take him to an emergency clinic.

the hind end problems sound chronic and IMO, unless there is a severe change in his mobility or comfort shouldn't need an emergency vet.

as for the supplements, you might try a different one, as i have found that what works for one dog doesn't work for all dogs. i have had good results with glyco flex.

the only time i took a dog to the emergency clinic for limping was when ares stood up, took two steps and fell down. the e-vet was useless. misdiagnosed it and sent us home with meds that i would never give.

i probably wouldn't take him to the emergency clinic, but i would get him seen by your regular vet as soon as you can. do you live in an area where lyme disease is prevalent? limping on a front leg can be a symptom of lyme.

have you considered trying pain medication for him for the hind end issues? there are risks and he'd need to have bloodwork checked (they can, in some cases, affect the liver), but they might help him be a lot more comfortable in his golden years.