Knees for Women, or, How Not to Do Gendered Innovations

Today, a quick case study to illustrate potential pitfalls on the road to gendered innovations.

Two weeks ago, I highlighted important gendered innovations in medicine that resulted from paying more attention to sex/gender differences. But sex differences can also be exaggerated. Take the knee.

Knee replacement (or, more officially, Total Knee Arthoplasty, TKA) is a common procedure, and women make up the majority of patients (about 66%). The knees used in TKA are unisex, developed based on the anatomy of female and male patients. Importantly, though the implants aren’t designated “female” or “male,” surgeons do have different size and shape options.

Enter Zimmer Biomet. In 2006, the company analyzed data on sex differences in knee anatomy and concluded that women and men differed on several anatomical measurements (these are fairly technical, but you can read more about them here). They went on to design a “female” knee (The Zimmer Gender Solutions Knee) based on the female-typical measurements.

Yay, gendered innovations, right? Not really.

While, on average, female and male knees differ, sex is less important in this case than other intersecting variables. Two of the sex differences Zimmer identified disappeared when height was taken into account. Since women are on average shorter than men on average, there is an apparent sex difference in these two measurements, but height is clearly the more important variable to pay attention to when selecting knee replacements. The third main anatomical difference doesn’t seem to be clinically significant.

The “female” knee replacement is a solution without a problem.

Unfortunately, design for women is often just a marketing strategy to sell us things we don’t need (remember pens for women?). This “pink it and shrink it” strategy not only fails to fix a real problem but also perpetuates stereotypes of the Venus and Mars variety.

There are two problems in the knee case: ignoring within-group variation and between-group overlap. Both come from the fact that when we talk about sex/gender differences, we’re really talking about statistical averages.

Within-group variation means simply that not all women are alike and not all men are alike. This variation can result from any number of factors. Some of those are described as intersecting identities (and oppressions). All too often, people say “women” when they really mean “White, Euro-American, cishet, able-bodied, adult-but-not-old women.” Other variation is just chance: some people happen to be taller than others.

The second, between-group overlap, is a reminder that many people who are classified in one group might have bodies, traits, or experiences more typical of another. In the knee case, men are on average taller than women, but some men are going to be shorter than some women. In the public transit case, women took more trips as part of care work than men, and building transit systems that recognize that work will, on average, aid women more than men. But overlooking the men and gender diverse people who also do care work would only result in the hardening of stereotypes and gender roles.

So, we didn’t need “female” knee replacements.  The problem here wasn’t too much sex analysis, but an oversimplified one. 

Read more here, and stay tuned for turtles!