Go and get your Class 1 certificate before you have been told that you do need a hip replacement. That way you will (probably) not have to stretch anything on the medical form and also, if the time ever does come for a replacement, it will fall within a Class 1 renewal, which will make things much easier than an initial.
As for the pathology of the thing, smashing up against a squash court wall in one's youth seems a good reason for arthritic hip degeneration. I played American squash, not that weedy substitute so beloved of the British. American squash smashes hips, the same way United smashes Guitars.