Gender-friendly Knee Implantation Makes Giant Leap for Womankind

by Frank Garcia, MD

Total knee replacement is a highly successful surgery, strongly supported by more than 20 years of follow-up data, according to the National Institute of Health. The NIH consensus panel concluded that the total knee replacement provides substantial improvement in patients’ pain, functional status, and overall health-related quality of life in about nine out of every 10 patients.

Interestingly, women are more susceptible to knee pain and disability than men. More patients are having knee replacements than ever before, and of the 500,000 knee replacements performed each year, two-thirds of them are for women. Certainly, orthopaedics is not the only specialty within which patients are showing gender differentiators.

Recently, medical literature has reported significant differences in the epidemiology, accuracy of diagnostic tests, and outcomes to treatment for different diseases between males and females, meaning that certain considerations must be made for the female patient.

Take heart disease, for example. The Women’s Ischemia Syndrome Evaluation, or WISE, study found that the gold standard test for assessing coronary artery disease, the coronary angiogram, may not spot the more diffuse buildup of plaque that often forms in the smaller coronary arteries of the female heart. Additionally, certain risk factors play a bigger role in the development of heart disease in women, who often experience more subtle symptoms at the time of presentation. These differences may account for the fact that women are less likely than men to undergo procedures such as angioplasty or bypass surgery. Other diseases with known gender differences include autoimmune disorders, mental health problems, and certain types of cancer, to name a few.

Knee implants for both men and women have functioned very well for many years. However, even though most women are content with the results after total knee replacements, some still have residual pain, particularly toward the anterior of the knee, which is primarily caused by the implant rather than the technique. Ongoing research indicates that the female knee is not simply a smaller version of the male knee.

The original knee replacements were based on models that averaged sizes between the male and female anatomy. This method creates a significant size difference between the female knee and the implants available.

Computational bioengineers obtained three-dimensional CT data of more than 800 knees and used this data to create highly detailed virtual blueprints of the knee. The study measured multiple dimensional parameters and found that 19 of 23 parameters were statistically different between males and females. The results confirmed that the shape of female bones typically falls into different ranges than males, and that these differences are statistically significant.

The new gender-specific knee implants address three subtle, identifiable, and distinct differences between the male and female knee. First, the female knee is typically narrower from medial to lateral and more trapezoidal in shape. Surgeons typically choose an implant based on the anterior to posterior measurements, which is the key to allowing the knee to move in flexion properly. However, an implant that fits the female knee from anterior to posterior will often be too wide from medial to lateral, causing overhanging of the implant and potentially impinging on the surrounding ligaments and tendons.

Second, the condyles in the anterior portion of the female knee are typically less prominent than in the male knee. A standard implant may cause the joint to feel “bulky,” which may result in anterior pain and decreased function.

Third, the angle between the pelvis and the knee affects how the patella tracks over the end of the femur. Women tend to have a different Q-angle than men because of the specific differences in shape and contour. Traditional artificial knees may produce a feeling of unnatural tracking in the female patient because of these specific differences.

Although these anatomical differences are subtle, the variance between male and female knees is noticeable. The new model of implants takes these distinctions into account by altering shapes based on the female knee anatomy. These implants actually should not be considered gender-specific, but rather “gender-friendly.”

The implants are innovative; however, they require long-term follow-up to determine clinical outcomes. The new implant has ramifications beyond just a better fit for women. It also will aid in treating those with rheumatoid arthritis because people with the disease tend to have female-shaped knees. Reportedly, around 10% to 15% of the men and 65% of the women suffering from RA have knees for which this new product will create a better fit.

While this new implant is one of the first steps toward gender-specific orthopaedic care, it is certainly not the last. The number of medical implants and procedures that account for our population’s diverse anatomy continues to increase.

Dr. Garcia is an orthopaedic surgeon with the San Antonio Orthopaedic Group, specializing in arthro-scopic surgery and total joint reconstruction. He is chairman of orthopaedics at CHRISTUS Santa Rosa Hospital, where he performed the inaugural gender-specific knee replacement surgery in July 2006.