Longer needles needed for fatter buttocks

The growing epidemic of obesity means that many women and some men aren't getting the full benefit of vaccines and other intramuscular injections, researchers here said today.

The solution may be longer needles, said Victoria Chan, M.B., of the Adelaide and Meath Hospital in Dublin colleagues reported at the Radiological Society of North America meeting here.

Many medications designed to be delivered by injection into a major muscle group, such as the buttocks, don't make it into muscle when the buttocks are overly fat, said Dr. Chan. Indeed, in a prospective imaging study, Dr. Chan and colleagues found that more than two-thirds of injections failed to reach muscle tissue.

"Our study has demonstrated that a majority of people -- especially women -- are not getting the proper dosage from injections to the buttocks," Dr. Chan said. "There's no question that obesity is the underlying cause."

The implication of the study is that -- as the epidemic expands -- more and more patients may not get the full benefit from intramuscular injections, she said. Because fat tissue has fewer blood vessels than muscle, it is less effective in distributing medications, reports MedPage Today.

Before the examinations the patients had a small air bubble injected into their buttocks using a standard-sized needle. The researchers analysed the CT images to determine the location of the air bubble. They found that the success rate of the jabs was only 8% in women - meaning that 23 out of 25 women did not receive an injection into the muscle. In men, the success rate was 56%.

Just 32% of the total group of patients had injections that delivered the air bubble correctly.

"Our study has shown that 68% of intramuscular injections do not reach the muscles of the buttock. The amount of fat tissue overlying the muscles exceeds the length of the needles commonly used for these injections," said Dr Chan.