HEALTH & MEDICINE :: APRIL/MAY 2007
The Gender-Specific (Female) Total Knee Replacement: Fact or Fiction?
Total knee replacement (TKR) has been a very successful treatment for osteoarthritis of the knee when nonoperative treatment fails. The procedure involves replacing the degenerative cartilage in the knee with metal and plastic components. This typically results in relief of pain and restoration of knee function. Several knee replacement designs are currently available from different manufacturers and all have some design elements in common. These include a femoral component that fits onto the end of the thigh bone, or femur, and a tibial component that is placed on the upper surface of the leg bone, or tibia. A plastic tray is placed between these two metal components to allow low-friction movement and a plastic button is placed on the undersurface of the knee cap, or patella. These implants are available in different sizes based on the measured size of the patient’s knee, however, no distinction between male and female knees has been made until now.
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Figure 3
A woman’s knee is anatomically different from a man’s knee, particularly around the femur. There are essentially three main differences that have been identified in studies using computed imaging to compare the knees of men and women. The first difference involves the thickness of the bone in the anterior, or front portion of the femur. This area is thinner in the female knee compared to the male knee. Secondly, the ratio of height to width at the end of the femur is higher in women, meaning that for any given height, the width of a female knee is smaller (Figure 1). Finally, the angle at which the thigh muscle (quadriceps) pulls on the knee cap is higher in women than in men. Implant designs that do not take these differences into consideration can theoretically lead to increased pressure between the patella and femur contributing to patellar pain, overhang of the femoral implant on the bone leading to soft tissue irritation, and abnormal tracking of the patella on the femur, resulting in possible patellar pain and instability.
The gender-specific (female) TKR was designed to account for these differences between men and women. Unlike the traditional components, the femoral component of the female TKR has a thinner flange along the anterior, or front portion, of the femur to reduce the pressure between this area and the patella. Also, the width of the female TKR femoral component is smaller for any given height to avoid overhang on the bone (Figure 2). Thirdly, the tracking angle of the patella on the femoral component is 3 degrees greater in the female TKR compared to traditional components in order to replicate the patellar movement seen in female knees (Figure 3). These design modifications will hopefully translate into improved longevity and function of the components and a more normal “feel” of the knee in females undergoing TKR.
Traditional TKR implants that preceded this design certainly provided, and continue to provide excellent pain relief and function to many women. The gender-specific TKR represents an attempt to more accurately reproduce the normal anatomy in the female knee and to improve upon an already successful procedure. Long-term studies will determine whether this is a fundamental improvement or merely a detour in the design of TKR implants. In the mean time, the theory behind the implants is sound and women facing TKR surgery may wish to consider this design.
Dr Manifold is a board certified Orthopaedic surgeon in Dover, Delaware, specializing in knee and shoulder disorders. He completed his fellowship training in knee replacement and reconstruction at The Insall Scott Kelly Institute/Beth Israel Medical Center, New York, and completed an Orthopaedic residency at New York Orthopaedic Hospital/ Columbia-Presbyterian Medical Center, New York. He graduated medical school from Temple University School of Medicine, Philadelphia. Dr. Manifold’s office practice is at Tooze, Easter & Manifold, MD, PA 720 S. Queen St. Dover, DE. To schedule an appointment, call 302-735-8700.
