Science Fiction
Gender differences are addressed by offering a wide range of sizing options.
Science Fact
The issue is not sizing. The issue is aspect ratio.
Of course, the
female knee is generally smaller than the male knee. But the important
distinctions are not limited to sizing alone. A typical female knee also has
a different M/L-to-A/P aspect ratio.1,4,5
When female data alone is used to create an optimal sizing scheme, the implant geometries differ significantly from an optimal sizing scheme derived from male data alone. When male and female data are combined to determine an average, the sizing scheme is compromised. It is not optimal for either female or male knees. Even knee systems that provide narrower M/L widths in the smaller sizes do not address the need for narrower M/L widths in the larger sizes, where the potential overhang is greater.1
The M/L dimension of femoral implants from some gender-neutral knee systems may not fit some female anatomies.4 A femoral implant that overhangs the bone at the distal, anterior, and posterior M/L interfaces is more likely to impinge on soft tissues.4 This may lead to soft-tissue irritation and affect soft-tissue balancing.1
Comparing the Facts
The Zimmer Gender Solutions™ NexGen® High-Flex Implants are the only knee implants that address the aspect ratio differences between female and male knees throughout the entire range of available sizes.
1. Hitt K, Shurman II J, Greene K, et al.
Anthropometric measurements of the human knee: correlation to the sizing of
current knee arthroplasty systems. J Bone Joint Surg.
2003;85:115-122.
4. Chin KR, Dalury DF, Zurakowski D, Scott RD. Intraoperative measurements of male and female distal femurs during primary total knee arthroplasty. J Knee Surg. 2002;15(4):213-217.
5. Mahfouz M, Booth R Jr, Argenson, J, Merkl, BC, Abdel Fatah EE, Kuhn MJ. Analysis of variation of adult femora using sex specific statistical atlases . Presented at: Computer Methods in Biomechanics and Biomedical Engineering Conference; 2006.
