What is the casting supposed to accomplish? I'd be VERY hesitant. Rehab from even two weeks in a cast can be significant (and DON'T let them tell you it isn't. I wound up with a truly awful case of elbow tendinitis because they told me to "resume normal activities" as soon as the cast on my hand came off).
If it was me I'd start with the PT (make sure you find a good one who knows about cycling) and go from there. But what do I know.
No two skeletons are alike, and there are a whole lot of variations - common and less common ones - that doctors like to label as "abnormalities."
Speed comes from what you put behind you. - Judi Ketteler