Is this a board certified ortho surgeon?? If not, I suggest you get a second opinion by one. Your vet's office may be resistant but I would insist. Normally LP is not painful and the symptoms you describe do not sound like any I have had with pups with LP.....maybe if they had torn a ligament but then they did not bear weight on the leg. If he is not showing issues with walking on that leg, I would insist on a second opinion for sure. This just does not sound right to me....there is a first time for everything and I suppose it is possible, but I would make absolutely certain!!
If you want to do this on your own without talking to your vet about your choice of surgeon, you can find one at:
American College of Veterinary Surgeons You will probably need a referral...just giving this to you so you can search.
Good luck!