Insulin resistance is associated with belly fat, something men are more likely to tote. Leptin levels are related to what’s called subcutaneous fat — the fat that lies just under the skin, which women are more likely than men to have.

Researchers are also looking at whether joint shapes may make a difference in why women get more OA, says Jordan.  Women, for instance, have narrower thigh bones than men, and their bones are placed differently so that some researchers believe that women may experience more joint pressure. “But this has not been verified,” says Jordan.

Severity and Pain

Rakel’s 2011 study of 208 men and women with knee osteoarthritis found that women with knee OA had significantly more pain as they moved, and they couldn’t move as well as men.  At rest, their pain was similar.  “But when we [measured activity], women were moving around as much as men,” says Rakel.  Although researchers can’t explain why, Rakel speculates that women may just need to get around more.

Surprisingly, despite greater pain and disability, x-rays showed that women had less severe OA than men.  Men’s stronger muscles may explain why getting around is both easier and less painful for them than women, despite worse disease, says Rakel.  According to a 2004 study at the University of Pittsburgh, quadriceps (thigh muscle) strength makes function easier in those with knee OA.

Surprisingly, women with OA are far less likely to have knee replacements than men.  “In focus groups, women appear to have more concerns about recovery, are less willing to endure the pain of recovery, and hesitate to disrupt a caregiving role, “ says Kelli Allen, PhD, associate research professor at Duke Medical Center in Durham, N.C.

But gender bias may also play a role. A 2008 study at the Hospital for Sick Children in Toronto found that  physicians were 22 times more likely to recommend knee replacement to men than to women. “So maybe part of the reason women wait long is because they’re not encouraged or told that they should have surgery earlier because of an unconscious bias by the provider,” says O’Connor.

The difficulty is that when women wait, they go into surgery with more pain and dysfunction than men do, says O’Connor. “So, they never catch up with the men’s improvement, even those that get the same [degree] of benefit from surgery that men do.” 

The Difference From Childhood

Researchers are just beginning to examine if cartilage differences between men and women exist from childhood on. In a 2001 Tasmanian study of 92 children, 9 to 18 years old, the boys already had 16 to 31 percent more cartilage than the girls.

“Not all studies agree,” notes Jordan. “Still the potential is very exciting.  If we can see differences in boys and girl, then those may be a target for prevention.”