Sports medicine doctors have long noticed changes in elbow range of motion (ROM) for baseball pitchers. It's such a common thing, nothing much is thought about it. Several studies show that 50 to 80 percent of all baseball pitchers at the professional level have a fixed elbow flexion contracture. This means the elbow doesn't straighten all the way -- it is stuck in a slight amount of flexion all the time.
Should something be done about this? No study has been done to compare pitchers with and without elbow flexion contractures to help answer this question. A recent study of 33 professional pitchers was done. The players' records were reviewed and compared based on the amount of elbow motion present.
Age, number of years played, and number of innings pitched were all studied in relation to elbow motion. None of these factors seemed to make any difference in elbow motion. A mild loss of elbow extension doesn't seem to negatively affect players' performance.
You may want to keep a record for yourself. Keep track of your elbow motion each year. Compare any increases or decreases in motion with your pitching stats. Talk to your doctor if you see a decline in pitching ability as the elbow flexion contracture gets worse. A program of physical therapy and stretching may be helpful.