Mine too had a back injury. A stress fracture in the Pars area of the L5 vertebra that he suffered at the end of his sophomore year of high school.
It took awhile to diagnosis and even longer to treat. He, also, was "pitching in pain" and it only hurt when he pitched.
It was nearly impossible to see on an MRI and only showed on a bone scan. Great advice here. The Neuro guys are much better equipped to handle this kind of injury.
Two things ... 1) We found out that its a common injury to pitchers, tennis players and football linemen. 2) We also found out that, when the calcification is complete, along with the healing, that area is now stronger than the surrounding bone.
It took 18 months for complete recovery but it WAS a complete recovery. Knowing what you are up against is the most important thing.