To me it almost looks like a dislocation on the one side. I know with hip displasia the joints can slip but the one side almost looks dislocated (which could be from the ball popping out because of the dysplasia). I don't have any vet training and am only basing what I say on xrays Ive seen over the years in texts or from bring a dog into the vet. I know with dogs this problem is usually fixed with surgery which Im not sure could be an option since a hedgie is so small, when an older dog we had had issues from arthritis which can set in with long term hip displasia I know we were giving a dosage of aspirin for him. Not sure if this would be safe for a hedgie though and the dose would have to be so small and theres no saying that they can even have it. The aspirin was only symptomatic treatment because the dog was older and it wasn't recommended to do a surgery. One thing I can think of though basing purely on the situation with dogs is that they are recommended not to climb, jump, run and was told to just take them for leisurely walks for excerise, since this is a hedgie that can't be walked you might have to take the wheel out if he uses it (running can aggrivate a bad joint) and work on another excerise like swimming (if he likes it because it puts little stress on the joint) or letting him roam around in a play area .
I'm very interested to hear the replies on this thread since I have never heard of this in hedgehogs and could help with future situations that may occur with other owners. I hope your hedgie feels better