It's a tough area - how much a given condition impairs someone, and in what ways, is an inherently subjective area. I can see the argument that, whilst persistent pain is emotionally and psychologically debilitating it's not necessarily physically restrictive directly...
Wherever the line is drawn someone is going to be straddling it.
I'd like to think that there aren't health providers in the UK who'd comply with the operation for non-medical reason, but... there are private providers that probably would (I occasionally work in that sector, and profit is all for some of them), there are providers outside of the UK who have less-stringent regulatory regimes to comply with, and then there are undoubtedly psychiatric providers who'd argue that his mental quality of life is improved by his competing at elite level to the extent that the physical loss of a leg is the less impactful way forward... and as a non-expert it's difficult to be definitive that they'd be wrong, despite my instinct that it probably is.
O.