Public Release:  Bones mend faster without marrow

New Scientist

COULD you strengthen bones and speed up recovery after fractures and breaks simply by removing some bone marrow with a syringe?

A new study in rats suggests that the technique could kick-start rapid self-healing in weakened or fractured bones, if followed up with injections of a bone growth hormone.

Agnes Vignery's team at Yale University anaesthetised a group of rats and drilled into the left thigh-bone of each animal before syringing out the bone marrow. Some of the rats received daily doses of parathyroid hormone (PTH), a clinically approved drug that encourages the growth of new bone.

After two weeks, X-rays of the rats showed that new bone had begun to form in the bone marrow cavity. In most rats, the new bone was short-lived - by the third week, marrow began to reappear and any new bone cells were reabsorbed to make room. But in the rats treated with PTH, new bone continued to grow in the cavity into the third week and the marrow did not return.

Vignery's team also discovered that the de-marrowed thighbones of the PTH-treated rats were stronger than their other legs, and the legs of rats not given PTH (Tissue Engineering, DOI: 10.1089/ten.2007.0261).

The study suggests that bone marrow usually inhibits the formation of new bone, says Vignery, and that simply removing the marrow and using drugs to encourage new bone growth could help treat weakened or broken bones.

"At first glance this appears counter-intuitive," says Brendon Noble at the University of Edinburgh, UK, since bone marrow generates the stem cells that would usually help repair bones. However, periosteum cells in the membrane that lines the outside of bones also have regenerative powers. "Perhaps they are sufficient to take on the role," Noble says.

Bone marrow is also needed to produce new blood cells, but Vignery says that removing it from damaged bones shouldn't affect a person's health, so long as marrow remains in other bones.

Warren Levy of Unigene Laboratories, in Fairfield, New Jersey, which provided Vignery's team with PTH for the study, believes the procedure could radically change the way patients are treated, particularly those with hip fractures. Such fractures often require major surgery, which is expensive and can be life-threatening in elderly patients. "Instead, if an X-ray reveals a fracture, you could go in with a needle right there in the doctor's suite and do without surgery," Levy says.

The patient would then be sent home with a prescription for PTH, and new bone would grow in the marrow cavity, repairing the fracture from the inside.

Peter Kay of the University of Manchester, UK, agrees that the technique sounds promising. "This sort of minimally invasive technique to replace surgery sounds controversial, but if you can strengthen rat's bones maybe there is potential." Levy says further animal tests are needed, but they hope to test the technique in humans before the end of the year.

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New Scientist reporter, Colin Barras

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