DEAR MAYO CLINIC:

If you have a broken bone, can bone marrow leak into your system? If so, how does it affect the rest of your body?

ANSWER:

When you break a bone, fat tissue from the bone marrow can leak into your blood. In many cases, this doesn't cause any problems. But in some situations, it may lead to a disorder known as fat embolism syndrome (FES). Although uncommon, FES can result in serious complications such as severe lung problems and seizures.

Bone marrow is the spongy tissue inside bones that makes blood cells. Fat tissue is one part of bone marrow, and some bones have more fat in the marrow than others. For example, in the body's long bones, such as those in the legs (femur, tibia and fibula), the bone marrow is made up mainly of fat cells. Smaller bones have much less fat tissue. With a broken bone, fat cells can enter the body's circulatory system and be carried by the bloodstream throughout the body. This is called fat embolism.

Fat embolism is quite common after major trauma in which one or more large bones are broken. But the body is usually able to clear the fat from circulation without any significant damage. Rarely, though, FES develops and people who have this condition can become quite ill as a result.

The exact cause of FES isn't well understood. Whether the condition occurs after a broken bone seems to depend, in part, on how much fat leaks into the circulation, as the risk of FES increases when larger bones break and when multiple bones are broken. Men develop FES more often than women, and younger people -- particularly those between the ages of 10 and 40 -- have a higher risk than older people.

In addition to broken bones, other causes of FES can include the trauma associated with total joint replacement of the hip and knee, and procedures that affect the central section of long bones that contain bone marrow (intramedullary canal), such as certain bone grafting procedures and some types of leg-length correction operations.

FES can affect many parts of the body, resulting in a wide variety of symptoms. Diagnosis, though, is based on the presence of one or more of the following major criteria within approximately 24 hours of an injury or orthopedic surgery: a rash of tiny round spots that appear on the skin due to bleeding under the skin (petechial rash); impaired lung function; and symptoms that indicate problems with the central nervous system (brain and spinal cord). Lung function damage from FES can cause conditions such as hypoxia (the tissues in the body don't get enough oxygen), and, in severe cases, acute respiratory distress syndrome (ARDS), a sudden failure of the respiratory system. Central nervous system symptoms from FES may range from drowsiness to seizures to coma.

There's no definitive treatment for FES. Once a person develops the disorder, treatment is geared toward minimizing the symptoms and providing supportive care that allows the body to eventually clear fat from the circulation. Common therapies for FES include stabilizing broken bones, managing blood pressure and, in severe cases, using a ventilator to assist with breathing.

Fortunately, most broken bones do not lead to FES. Also, when doctors can identify people who may be at risk for this condition, they can take steps, such as quickly immobilizing bones that are broken, to help prevent FES from developing.

Tad Mabry, M.D., Orthopedics, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

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