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Lately, two major orthopaedic implant suppliers, (Stryker Corp. and Zimmer Holdings Inc.) announced the availability of total knee replacement implants particularly created for women. We all know that guys and ladies are various, but how does this relate to knee implants?

The key distinction is the relative size of the end of the femur or thigh bone. For a provided front-to-back or anterior-posterior (AP) width, the femurs of females have a tendency to be narrower in the medial-lateral (ML) or side-to-side direction compared to males. An implant which is proportioned based on male anatomy would, therefore, be also wide on a similarly sized female. The outcome is that when a surgeon sizes the implant based on the AP width of the femur, the implant could overhang the narrower female bone and cause irritation of the surrounding soft-tissue. Faced with this situation, orthopaedic surgeons are at times forced to downsize the femoral component during total knee replacement surgical procedure. In downsizing the femoral element, the medical professional chooses a smaller sized implant, so that the implant does not overhang the sides of the bone.

There are, nevertheless, some potential disadvantages to downsizing depending upon the type of instrumentation system the surgeon is making use of in the course of the knee replacement procedure. If the surgeon is employing an implant method exactly where the femoral component is placed at a distinct distance relative to the anterior surface of the femur (anterior referencing), excessive laxity in flexion can take place with downsizing. Alternatively, if the medical professional is employing a method which references the posterior aspect of the femur, the resulting femoral preparation could notch or undercut the anterior aspect of the femur. This could, in turn, lead to fracture of the femur.

Recognizing that neither of the above scenarios is desirable, the makers of implants particularly created for females have sought to remedy this by generating the implants far more narrow in the ML course. On a male knee, the implant could underhang leaving some distal femoral bone exposed, but this is normally not a problem.

In the company announcements, both manufacturers noted that their new Female knee replacements are designed to address the far more narrow female femur. Zimmer also noted that differences extend beyond femur width to items such as the angle of the femur in relation to the tibia. It will be exciting to see how these new implants fair clinically and no matter whether the possible benefits are realized. achillotrain

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