I don’t think I have the description reversed in Sutter’s case. He had arm surgery after being signed by the Cubs and his old pitches stopped working. He learned his signature new pitch from an instructor in the minor leagues, to whom he’d return for years whenever he was off. Early in his major league career the Cubs made a big deal about how the pitch had saved his career. He had shoulder problems late in his career, after the Cards were smart enough to trade to the Braves. Perhaps they were from all the splitters.
We may both be right on this. Sutter may have developed the pitch to cope with shoulder issues. I seem to remember that the splitter was a suspected culprit in elbow trouble for guys like Mike Scott.