My dog is limping........help?

he has been limping for a while and we couldn't find a single clue why so we let it go as maybe a sprained ankle or just achy joints. he's 8...so it would be time fro age to be setting in. but then i just noticed his foot today and when he steps on his right foot one of his toes is straight out and not curved like the rest. it looks broken but when i pull on it there is no pain. i know this was not there before. it looks like when he steps down, the normal shape of his toe does not take place, instead it looks like the tendon underneath that curls the toe under properly just stopped working. like it's loose or ripped. is this a good guess or does somebody maybe have a better answer as to what is up with the toe?