Lay him on his side and check his flexibility in all joints one at a time. Compare with the other front leg. Stretch the leg completely out, and then bend completely back in. They won't always whine, but might show a little wince, so watch his face. If he gives you any resistance (trying to pull the leg back away from you, ect.) let him be for a little while.

Feel the shoulders extensively. When he's sitting, extend the leg by the paw foward and then tuck the leg back. Check inbetween his toes for anything that could have gotten lodged in there.

If he or his family has a history of arthritis, it might not be a bad idea to start him on glucosomine.

If he seems too painful, or winces it wouldn't hurt to just go for an x-ray. I've seen dogs that completely dislocated their shoulders and hips and run on them, but seldom walk.