Not too long ago, two significant orthopaedic implant suppliers, (Stryker Corp. and Zimmer Holdings Inc.) announced the availability of total knee replacement implants specifically developed for females. We all know that males and females are various, but how does this relate to knee implants?
The crucial difference is the relative size of the finish of the femur or thigh bone. For an offered 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 course compared to males. An implant which is proportioned based on male anatomy would, for that reason, be as well 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 trigger irritation of the surrounding soft-tissue. Faced with this scenario, orthopaedic surgeons are occasionally forced to downsize the femoral element in the course of total knee replacement surgical procedure. In downsizing the femoral component, the physician chooses a smaller implant, so that the implant does not overhang the sides of the bone.
There are, nonetheless, some possible disadvantages to downsizing based upon the variety of instrumentation system the surgeon is making use of throughout the knee replacement procedure. If the surgeon is employing an implant system where the femoral component is placed at a particular distance relative to the anterior surface of the femur (anterior referencing), excessive laxity in flexion can take place with downsizing. Alternatively, if the medical doctor 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 producing the implants more narrow in the ML direction. On a male knee, the implant could underhang leaving some distal femoral bone exposed, but this is normally not an issue.
In the organization announcements, each manufacturers noted that their new Female knee replacements are made 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 potential benefits are realized.
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