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New Total Knee Replacements Specially Designed for Female Anatomy
By Lou Serpe
Recently, two major orthopaedic implant manufacturers, (Stryker Corp. and Zimmer
Holdings Inc.) announced the availability of total knee replacement implants specifically
designed for women. We all know that men and women are different, but how does
this relate to knee implants?
The key difference is the relative size of the end of the femur or thigh bone.
For a given front-to-back or anterior-posterior (AP) width, the femurs of females
tend 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 too wide on a similarly sized female. The result 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 sometimes forced to downsize
the femoral component during total knee replacement surgery. In downsizing the
femoral component, the doctor chooses a smaller implant, so that the implant
does not overhang the sides of the bone.
There are, however, some potential disadvantages to downsizing depending upon
the type of instrumentation system the surgeon is using during the knee replacement
procedure. If the surgeon is using 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 occur with downsizing.
Alternatively, if the doctor is using a system 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 specifically designed for females have sought to remedy this by making
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
generally not a problem.
In the company announcements, both manufacturers noted that their new Female
knee replacements are designed to address the more narrow female femur. Zimmer
also noted that differences extend beyond femur width to things such as the
angle of the femur in relation to the tibia. It will be interesting to see how
these new implants fair clinically and whether the potential advantages are
realized. About the Author For more great information on total
knee replacement, please visit : http://www.totalkneeinfo.comtoday!
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