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Design of Joint Replacement Improved for Women

More and more studies are bringing to our attention the differences in knee anatomy between men and women. This is important when considering having a total knee replacement (TKR).

In the past, joint replacements for the knee were designed to fit both men and women. This concept was called a down the middle design. The average size and shape of both male and female knees were combined to come up with a one-design-fits-all kind of approach.

Then a wider range of implant systems was designed. There were still problems with this method. For example, in the average adult female, the smaller sizes were too small. And the larger sizes were too large. The new joint would hang over the edge of the femur (thighbone).

But with modern technology, three-dimensional (3-D) CT scans and computer analysis have started to change things. With new information about the differences in the size and shape of women's anatomic knees compared to men's, new implant designs can be made.

Three of those anatomic variations are reported in this article. These differences include a less prominent anterior condyle, an increased Q (quadriceps) angle, and a decreased side-to-side and front-to-back ratio.

The condyle is the bottom part of the femur that forms the top half of the knee joint. The female femur and condyles are not as wide as the male's. The femoral side of the joint tends to be more of a trapezoid shape in women and a rectangular shape in men.

Without the proper size, shape, and dimensions, the implant can't reproduce the correct knee motion and biomechanics. The surrounding soft tissues become irritated and off-balance. Because of the differences in anatomy, surgeons often have to make adjustments for women during the operation.

With newer, better implant designs fewer adjustments will be needed. Researchers hope that by making a femoral implant just for women, the knee will work better. There will be fewer problems with patellar (knee cap) tracking. And the joint won't be overstuffed with an implant that's too large and doesn't fit well.

References: Sheryl Conley et al. The Female Knee: Anatomic Variations. In Journal of the American Academy of Orthopaedic Surgeons. Vol. 15. Supplement 1. Pp. S31-S36.

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