Good question! Sometimes the patient's symptoms don't match the underlying pathology. So you can end up with pain, stiffness, loss of motion and function, and still only have a "mild case."
First, let's review heterotopic ossification. Literally, this is the growth of bone in the wrong place. Most often, islands of bone form inbetween the fibers of muscle. It's not a tumor, so it won't cause death. However, it can be painful enough to make you wish for death!
Grade zero means there's no heterotopic bone formation present. Grade one is the presence of islands of bone within the soft tissues. If bone spurs occur, but the joint space is
still good, then it's given a grade two. Grade three is with bone spurs and a narrow joint gap (
Fortunately, it can be treated even when it's a "mild grade." Ask your doctor what are your treatment options and what he or she recommends.