Dr. James Andrews, a widely known sports medicine orthopedist in Gulf Breeze, Fla., wanted to test his suspicion that M.R.I.'s, the scans given to almost every injured athlete or casual exerciser, might be a bit misleading. So he scanned the shoulders of 31 perfectly healthy professional baseball pitchers. The pitchers were not injured and had no pain. But the M.R.I.'s found abnormal shoulder cartilage in 90 percent of them and abnormal rotator cuff tendons in 87 percent. "If you want an excuse to operate on a pitcher's throwing shoulder, just get an M.R.I.," Dr. Andrews says.