Last month, my mother fell down the stairs and broke her sternum. The doctor gave her morphine for it. Now she's complaining about terrible pain in her right leg, the thigh area. She describes it as being sharp, like someone is stabbing her with a knife that's on fire. Heat seems to make it worse, and she has trouble walking on it. What could be wrong?

If heat makes it worse it is nerve, not muscle. Cold for nerves, heat for muscles.

Thing about nerve damage is that you can injure a nerve and it doesn't become a painful problem for a long period of time (this can happen to muscles as well sometimes) especially if you injure the tissue around a nerve, the process of healing of that tissue starts off with the tissue being rebuilt thicker than before to prevent future injury to the same area. This in turn could lead to a minor torn muscle which doesn't cause pain (or other soft tissue) becoming thicker thus pressing against a nerve which can be extremely painful.

Since she fell not too long ago I would strongly urge seeing the doctor again and having him/her take a few pictures.

Another thing that comes to mind is a blood clot which is cutting off blood which can lead to swelling tissues which again press hard against a nerve. Now days they have portable sonogram machines which allows for a quick peek to see what is going on with soft tissues.

Now if it is a blood clot, applying heat runs the risk of losing the clot and that can lead to heart attack, stroke if it travels to the brain or the heart.

In either case pain is a symptom of a problem, severe pain needs immediate professional attention. If you can't get her in to a doctor tomorrow by appointment then I strongly urge you to visit Emergency Room. Yes it that serious.

David

I agree that if there's any chance of it being a clot, she needs to go to the doctor, already.

just for the record, the only way a blood clot in the leg can cause a heart attack or stroke is if there's a congenital hole in the heart, which is unlikely to have been occult for a lifetime, and is comparatively rare. Blood clots in the leg, when they travel, go to the lung, which, depending on size and location, can cause death from acute heart failure -- which is not a heart attack. Most blood clots of the sort that can travel begin in the calf area, not the thigh; but it's still a possibility. The only way to get a reliable diagnosis is for her to be seen by a physician. This is just guessing.