The implant addresses three distinct and scientifically documented shape differences in women's and men's knees. Designed using three-dimensional computed tomography imaging, the Gender Solutions High-Flex Knee more closely mimics the joints and inner workings of women's knees.
"We'll be the first in Dallas to use the new design," said Dr. Robert Bucholz, chairman of orthopaedic surgery at UT Southwestern. "This is one in a series of technical improvements in the design of knee implants that is long overdue."
During total knee replacement surgery, or arthroplasty, surfaces of the thighbone (femur), the shinbone (tibia) and the kneecap (patella) are replaced with a metal-and-plastic implant.
Traditionally, the implants have been designed based on men's knees. For women, smaller implants were used, but size did not resolve the anatomical differences, which sometimes accounted for pain and discomfort and an "awkward" feeling.
Researchers have found numerous shape differences between the average male and female knee. The new replacement, created by Zimmer, Inc., of Warsaw, Ind., and approved in May by the Food and Drug Administration, addresses three gender-specific issues:
- Narrower shape: Knee implants are typically sized by measuring the end of the femur from front to back and from side to side. Most women's knees are shaped like a trapezoid and narrower from side to side; men's knees are more rectangular. Implant size is typically based on the front-to-back measurement to allow the knee to move and flex properly. In women, however, an implant that fits from front to back can be too wide from side to side, sometimes causing it to overhang the bone.
- Thinner density: Typically, the bone in the front of a woman's knee is less prominent than in a man's. After traditional implantations, some women describe a "bulky" feeling in the joint despite better function. The front of the new implant is thinner so the replacement more closely matches the female anatomy.
- Tracking: A woman's femur attaches to the tibia at a slightly different angle than a man's because most women have wider hips. The angle difference between the pelvis and the knee joint — taken into account with the new implant — affects how the kneecap tracks over the end of the femur as the knee moves through a range of motion.
Dr. Bucholz said about 80 percent of knees are replaced because patients suffer from osteoarthritis. The condition causes the cartilage that cushions the bones of the knee to soften and wear away. The bones then rub against one another, causing knee pain.
The number of joint and knee replacement procedures performed by orthopaedic surgeons is increasing due, in part, to aging baby boomers and an increasingly overweight population. In the 1950s, the first artificial knees were little more than crude hinges; now there are a variety of knee-replacement designs that take into account age, weight, activity level and overall health.According to the National Institutes of Health's consensus statement on total knee replacement released in February 2004, the surgery is highly successful and is supported by more than two decades of follow-up data.
"It is one of the most successful elective procedures that we perform," said Dr. Bucholz.
Each year, more than 400,000 patients undergo total knee replacement surgery in the United States and nearly two-thirds are women, according to the latest National Hospital Discharge Survey, which is compiled by the U.S. Department of Health and Human Services.
At UT Southwestern University Hospitals, orthopaedic surgeons annually perform about 450 knee replacements. Surgeons use time-tested protocols for surgical technique, pain management and rehabilitation. They also provide an array of other reconstructive procedures for the hip and knee.
For more information on knee-replacement surgery at UT Southwestern University Hospitals, please call 214-648-3065.
Connie Piloto | EurekAlert!
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