To me it fits low spine problems with the discs.
There can be a highly variable pain presentation, even if there is not overt nerve compression.
In fact, piriformus muscle strain can contribute to the overall picture.
If it is the outside of the thigh, Ilieotibial band strain or contraction can also be involved.
It is impossible to say exactly without a full structural exam, which is what he should have and this should be done by a physiatrist [PM&R] given the situation.
In a situation like this, it is often a combination of deficits that is producing the picture.
I think he needs that exam, an x ray of the prosthesis on that side, and an MRI of the lower spine, as long as his prostheses are compatible with MRI.
OK, so you might have more questions or want to give me more information: Please use reply to expert if you have further questions. Also, please click a positive rating [hopefully excellent—that’s how we are paid, per rating]. If you forgot something, come back. I am here http://www.justanswer.com/medical/expert-dr-thomas/