Body Parts: Femur is bone with the most ---- in a lot of categories

By: BRADLEY J. FIKES - Staff Writer | Saturday, February 24, 2007 11:53 PM PST ∞

The femur, or thigh bone, claims a lot of superlatives. It's the longest bone in the human body, and has the most volume. The upper end is part of the hip joint, the largest joint in the body. The lower end is part of the knee joint, one of the most complex in the body. And the most abundant source of bone marrow is ---- you guessed it.

Another claim for the femur is that of strongest bone in the body. But it's not unbreakable, as Gov. Arnold Schwarzenegger found out in a skiing accident. The December accident fractured his right femur, and he literally hobbled into his Jan. 5 second-term inaugural ceremony on crutches.

Such injuries usually heal without permanent damage. The femur has a plentiful supply of bone stem cells, which turn into bone tissue and repair fractures. Bone is not static: its mineral component, mainly calcium phosphate, is constantly being removed and replenished.

Usually, these forces of mineral deposition and removal remain in balance, but they can be altered by exercise or the lack of it. When people exercise, bone mineral density increases, in keeping with the heavier demands of greater activity. When someone doesn't exercise, bone mineral density decreases.

If the decrease is severe, it is known as osteoporosis, with the bone becoming porous and prone to breakage. Too much density, and calcium can deposit where it's not supposed to go, leading to such conditions as calcium "spurs," painful growths on the bone.

Calcification is regulated by a molecule called inorganic pyrophospate. Researcher Jose Luis Millan of the Burnham Institute for Medical Research helped make that discovery as part of a team funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

This bone density balance gets harder to keep as we age. Bone density decreases, sometimes resulting in osteoporosis. The National Osteoporosis foundation suggests taking five steps to prevent the disease:

- Get your daily recommended amounts of calcium and vitamin D

- Engage in regular weight-bearing exercise

- Avoid smoking and excessive alcohol

- Talk to your health-care provider about bone health

- When appropriate, have a bone-density test and take medication

More information is available at www.nof.org/prevention.

Because of the femur's size and juncture with the hip joint, fractures in that location occur more frequently in the elderly. The "neck" of the femur, the narrowing just below the ball of the femur that fits into the joint, is especially vulnerable. Such a fracture will interrupt the flow of blood to the ball or head of the femur, which contains marrow and other bone tissue. The tissue then dies, causing osteonecrosis.

Because bone is living tissue, osteonecrosis weakens it. When bone tissue dies, replenishment stops. So a necrotic bone can collapse. It also causes pain and is vulnerable to infection. Osteonecrosis is most likely to occur in the femoral head.

If femoral head osteonecrosis is not treated in time, the only alternative may be an artificial joint. While artificial joints restore mobility, they often wear out. Natural joints are still medicine's state of the art.

Contact staff writer Bradley J. Fikes at (760) 739-6641 or bfikes@nctimes.com.

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