Wow - that is a tough decision. The sports ortho should have the best information for you. When 2B was first diagnosed, the doc (team doctor for UF baseball) said that a loss of some range of motion was fairly common among baseball players - injury or not. I will be interested to know what your guy says.
Before 2B had his MRI, the doc told us that microfracture surgery had proven to be very successful at treating OCD, and that it would be our best option if surgery was necessary. It's supposed to get new cartilage to grow, and I did read one study where athletes (gymnasts) were back in serious competition in 5 months. The problem is that the new cartilage may not be as strong as the old cartilage. We were lucky, though. The MRI looked good, no unstable fragments, so no surgery. A month later, the follow up X-ray looked good and the lesion was < 1 cm. He has no pain, range of motion is now even better than his left arm (ice and Alieve every day seems to have really helped), and he is back out on the field - he's a MIF, not a pitcher. We have another X-ray in 2 months. He won't start lifting weights again until it's completely clean, but he is OK to play.
Please let us know how it goes next month. Tell your son to hang in there!