Knee replacement designed for women

Men’s and women’s knees are not anatomically the same. For the most part, women’s knees are shaped like a trapezoid.

By: Harvey E. Smires, M.D.
   Every year, some 300,000 Americans undergo knee replacement surgery. In fact, according to the American Academy of Orthopedic Surgeons, it’s the most frequently replaced joint in the body. Until recently, the fact that about two-thirds of the patients undergoing this procedure each year were women, made little or no difference. But that is about to change.
   The knee is the largest joint in the body, and is used almost constantly to perform routine everyday activities. The knee is made up of the lower end of the thighbone (or femur), which rotates on the upper end of the tibia (or shinbone), and the kneecap (also known as the patella), which slides in a groove on the end of the femur. Large ligaments attach to the femur and tibia to provide stability. The long thigh muscles give the knee strength.
   The joint surfaces, where these three bones touch, are covered with cartilage that serves as a cushion for the bones and enables them to move easily.
   The remaining surfaces of the knee are covered by the synovial membrane, a thin, smooth tissue liner. This membrane releases a special fluid that lubricates the knee, reducing friction almost completely in a healthy, normally functioning knee.
   Unfortunately, diseases such as rheumatoid arthritis or osteoarthritis, injuries or trauma to the knee, and sometimes even normal wear and tear as we age, can damage the cartilage and wear away the synovial membrane. The result is pain, muscle weakness and a loss of function.
   For some patients, knee pain can be temporary; for them, over-the-counter or prescription medications can help to alleviate the discomfort. For many people, however, severe and constant knee pain and its resulting disability can indicate the need to pursue surgery as a solution. Knee replacement surgery has been highly successful in relieving pain and restoring the function and use of the knee for millions of Americans.
   During the procedure, surfaces of the damaged knee joint are replaced with prosthetic components. Knee prostheses come in various dimensions so they can be fitted to match each patient’s size as closely as possible. These prosthetic knees were originally developed by mapping out men’s and women’s knees, averaging the sizes and then developing a range of implants to be used for the procedure.
   In recent years, however, research has shown that men’s and women’s knees are not anatomically the same. For the most part, women’s knees are shaped like a trapezoid. They are slightly deeper in length and narrower from side to side than men’s knees, which are more rectangular in shape.
   In the past, women undergoing knee replacement surgery typically received smaller implants than men, but the overall proportions of the implant still didn’t take into consideration the anatomical differences in the female knee. While the majority of knee replacements are successful, in some instances, women have been disappointed, citing residual pain and decreased range of motion.
   A new replacement knee, specifically designed for women, promises to change all that. Approved by the FDA in May, the Gender Solutions High-Flex Knee is the first gender-specific prosthesis that addresses the distinct and scientifically documented anatomical differences in men’s and women’s knees. Designed using digital MRI and CT images to specifically map out the female knee anatomy, the new prosthetic joint more than ever before, closely mimics the mechanics of a woman’s knee.
   In general, knee implants are sized by measuring the end of the femur from front to back (anterior-posterior) and from side to side (medio-lateral).
   Because of the anatomical difference between women’s knees and men’s knees, a gender-neutral implant that fits from anterior to posterior — or front to back — can sometimes be too wide for women, causing it to overhang the bone. The new gender-specific knee implant has been reshaped, taking those anatomical differences into consideration — most notably offering relatively deeper anterior-posterior dimensions to somewhat narrower medio-lateral or side to side dimension, offering women a new range of options for a more tailored fit.
   Furthermore, the front of the new implant is thinner, more closely mimicking the female knee, which is typically less prominent than a man’s knee. In the past, gender-neutral knees have left some women complaining of a "bulky" feeling in their prosthetic knee, although that typically didn’t impact its functionality.
   Finally, the new replacement knee also takes into account the different angle between the pelvis and knee joint in a woman’s body so that the kneecap tracks more smoothly over the end of the femur, enhancing functionality and improving range of motion.
   If you’re a woman experiencing chronic knee pain, find out whether you might be a candidate for knee replacement surgery and whether you might benefit from the new gender specific knee implant now available. To find a Princeton HealthCare System orthopedic surgeon, call (888) 742-7496 or visit www.princetonhcs.org.