Is there a problem with my horse's spine?

Hi. My horse is a 13 y/o gelding QH. My friend gave him to me for free. He is well trained and rideable and never complains about a thing. But that is just the problem! He wouldn't buck a person off if he had a nail in his foot! So I'm uncertain if his back is actually causing him pain or not, after some long rides it twitches from the touch, but that was due to a saddle that didn't fit. But his spine sticks up all weird like, so I am wondering if maybe any sort of saddle would cause pressure or if maybe I shouldn't even be riding him :(. If anyone has any ideas they'd be very much appreciated. Here are some pictures.
http://i6.photobucket.com/albums/y24...u/DSCN0354.jpg
http://i6.photobucket.com/albums/y24...u/DSCN0355.jpg
http://i6.photobucket.com/albums/y24...u/DSCN0356.jpg
http://i6.photobucket.com/albums/y24...u/DSCN0357.jpg
http://i6.photobucket.com/albums/y24...u/DSCN0358.jpg

Have you asked your friend about it?? I would get a vet check since he is new to you, so you can make sure everything is up to date and find out what the deal is with his spine.

Your horse's back is slightly roached. In some horses it does not bother them and in others it does.

Many have to have a saddle specially fitted. In your case I surmise the saddle is bothering him and you may want to get a saddle fitter to take a closer look.

Oh... Can I ride him bareback or will he need special padding and a custom saddle?

He looks roach backed. it may or may not be a biggy. I'd show the pics to your vet. if necessary ave them come see the horse

Besides appearing roach-backed, your horse is also missing alot of muscle mass along his back and appears to be slightly underweight. You need to reassess his diet to ensure that he is getting enough to eat and an appropriate balance of nutrients. Then if his diet is appropriate you can begin working him to help build muscle along his topline---trotting and work over ground poles will help but be sure he's worked up to this gradually.