Mike Napoli and Avascular Necrosis

It's official. Mike Napoli has signed with the Red Sox for one year and $5 million, with bonuses up to $8 million for staying on the field despite his hip problems.

According to Napoli's agent (via Boston.com's Extra Bases blog), Napoli has been diagnosed with avascular necrosis in both hips. From WebMD:

Avascular necrosis (AVN), also called osteonecrosis, aseptic necrosis, or ischemic bone necrosis, is a condition that occurs when there is loss of blood to the bone. Because bone is living tissue that requires blood, an interruption to the blood supply causes bone to die. If not stopped, this process eventually causes the bone to collapse...

In its early stages, AVN typically cause no symptoms; however, as the disease progresses it becomes painful. At first, you may experience pain when you put pressure on the affected bone. Then, pain may become more constant. If the disease progresses and the bone and surrounding joint collapse, you may experience severe pain that interferes with your ability to use your joint. The time between the first symptoms and collapse of the bone may range from several months to more than a year.

 According to Napoli's agent, he doesn't have any pain or symptoms yet, so it's very possible that he'll make it through the season without missing time, given the timeline of the disease. He's being treated by   "a metabolic bone disease specialist," and hopefully that will stave of symptoms for many years, because he's just 31 years old, and should have a long career ahead of him - playing more first base and less behind the plate should certainly help.