Hormone May Cause Knee Injuries

The test-tube experiment found that tissue from the knee's anterior cruciate ligament grew less well when estrogen was added. The study was intended to help explain why women have four to six times the risk that men face. But the report is creating arguments among scientists.

``That study doesn't mean anything,' said Dr. Elizabeth A. Arendt of the University of Minnesota, who said the lab work was too limited. She also rejected the idea that estrogen can weaken the knee.

``Certainly, the hormone we believe is influential,' said Dr. Stephen Liu of UCLA Medical Center, who was one of the researchers.

Other factors also doubtless play a role, but this study and others argue that estrogen does weaken the ligament that helps to bind the upper and lower leg bones together, Liu said.

The findings are in the journal Clinical Orthopedics and Related Research; the abstract appeared on the National Library of Medicine's MEDLINE Web site.

In the study, 17 beta-estradiol, a form of estrogen, was added to fibroblasts, the cells that produce collagen, which makes up the tough tissue of the ligament. Researchers found fibroblasts grew at a lower rate in the first three days of the experiment and that growth was even slower in the presence of more estrogen. The effect eased as the 14-day experiment continued.

The cells have estrogen receptors, and estrogen apparently binded to the receptors, Liu said. ``When you find receptors on a tissue, they have to have some effect or they would not be present,' he said. ``Our study shows it decreased collagen buildup.'

The trouble comes in taking this test-tube finding to the next step - increased ACL damage in women at the time in their menstrual cycle when they have more estrogen.

``We have a fair amount of interesting information, but nothing that really explains in a convincing way why women are more at risk than men,' said Dr. Gerald A. Finerman, chairman of UCLA's orthopedic surgery department and senior author of the paper.

This may be because it would take a lot of work to get enough blood samples over enough time from enough women, Liu said.

Arendt doubts the data ever will come. Estrogen might well affect the ligament, but the hormone might well the ligament, she said. ``Estrogen is necessary for the good function of every other tissue,' she said. ``Why would the ligament be the poor sucker it is not good for?'

The joint-loosening effect of estrogen has a purpose, although not in the knee, Liu said. Especially in the pelvis, the looser joints in pregnant women make delivery easier. An effect of estrogen on the knee would be sort of a side effect, he said.

But other researchers have come up with other possible reasons for women's higher risk. These include women's weaker muscles, as well as male-female skeletal differences. Women can reduce their risk by developing greater muscle control and better balance, Arendt said. And researchers should spend more time looking into those strategies, she said.