Sman,
Your son is sort in the proverbial position, between the rock and a hard place.
With positive ulnar variance, the ulna basically keeps banging in to the carpal bones of the wrist. This can cause ulnar impaction syndrome, which is essentially a bad bone bruise. It can also cause tears in the TFCC (triangular fibrocartilage complex). The TFCC is a disc of cartilage, sort of like the meniscus in the knee, which sits on the end of the ulna.
So, your son could be having pain from the impaction of the bones hitting each other and/or from a torn cartilage. But, he has basically done all of the nonoperative treatments: rest, splinting, NSAIDs, steroids.
He has had an MRI of the wrist; did it show any signs of the ulnar impaction syndrome? This can be manifested by edema in the marrow of the carpal bones, and later on, by deformity or damage to the bones.
A TFCC tear should also show up on an MRI, though sometimes an arthrogram has to be done to pick up a small tear.
I am assuming that his pain is in the region of the ulnar head, on the ulnar side of the wrist (small finger side). If he is having pain from the positive ulnar variance, the pain should be at its maximum in that soft spot, just distal to the ulnar head (the bone that sticks out of that side of the wrist). He should have a positive ulnar grind test.
If his pain is somewhere else in the wrist, then something else may be causing the problems. Just because something shows up on x-ray, doesn't always mean it is the root of the problem.
But, if it is ulnar sided wrist pain, and the usual nonoperative treatments don't work, the next step would usually be surgical. A wrist arthroscopy would be able to evaluate the TFCC, the intrinsic ligaments of the wrist, and the articular surfaces.
If the TFCC was torn, that can usually be fixed or debrided through the 'scope.
Ulnar impaction/positive ulnar variance can be treated with the "Wafer" procedure. This is where a small portion (a wafer) of the distal ulnar is shaved off. This corrects the variance, and usually resolves the impaction.
Sometimes, instead of the arthroscopic procedure, an open ulnar shortening is done in the shaft of the ulna. Here, a wafer of bone is removed from the shaft and then the bone ends are fixed with a plate/screws. This also corrects the variance.
The problem is that you son probably still has open growth plates and the surgeon does not want to take the chance of damaging the physis (growth plate) at the ulnar head.
The open procedure would not affect the physis, but it is a fairly good sized operation, that would put him out of commission for several months.
The pain with weather changes is due to the barometric pressure change that comes in with a weather front. Joints are enclosed spaces with pressure that is equal to the outside environment. When the pressure drops quickly outside, the body has to adjust the joint, and in traumatized joints, the pressure difference can cause pain. Some people can predict the weather better than the meteorologist, by the way their joints hurt.
So, since you, your son, and your surgeon are going to have to make some decisions, it is important to know exactly what is causing the pain. Is the long ulna bumping into the wrist bone, and does he, or does he not, have a torn TFCC.
If the MRI does not show impaction or a torn TFCC, then why is he having pain? What is the diagnosis?
From there, it is really hard, because you have basically tried all of the usual treatments. If you find something that looks promising, there usually isn't any harm in trying it, to see if it might help.
If he has a torn TFCC, a 'scope could be done to treat it, without the bony procedure until he reaches skeletal maturity. Other than that, if he is having significant pain when playing, he may have to give up playing, which is difficult to do.
I don't really have any magical treatment. Ice, heat, wrist support, NSAIDs, occasional steroid injection, and maybe surgery, are the usual treatments.
But, again, do make sure you have a firm diagnosis, so that the treatment plan can be tailored to the problem.
Hope you find a solution, so that you son can play.
Good luck.
PS: You state you saw a hand surgeon, who would normally be the one to manage a wrist problem, but, you might want to see if you could consult a sportsmedicine orthopedic surgeon. Sometimes, hand surgeons tend to follow the usual treatment plans, rather than look at the patient as an athlete. Just a thought, if playing is extremely important.
Again, good luck.