Gender-Specific Knee Replacement
Knee replacement surgery offers excellent surgical treatment for end-stage arthritis. Patients are able to get back to their day-to-day activities without the fear of knee pain. Technological advances have been made in the designs of knee replacement implants so they mimic the natural knee motion closely.
Gender-specific implants involve the use of implants designed specifically for females. Gender-specific implants are relatively new and there is no long-term data to suggest if they are better than traditional implants.
The male and the female knee
The human knee is formed by the thigh bone, the shinbone, and the kneecap. There is a slight variation in the anatomy of the human male and the female knee joint. In males, the lower end of the thigh bone forming the knee joint is wider than the female joint (medial to lateral distance).
Similarly, the height of the bony knobs of the lower thigh bone (femoral condyles) is more in males. The kneecap (patella) sits in a groove formed by the femoral condyles. The groove is deeper in males as compared to females.
The thigh muscles in front of the knee (quadriceps) that are responsible for straightening the leg are attached to the kneecap via the quadriceps tendon. The kneecap is attached to the upper end of the shin bone (tibia) via the patellar tendon. The angle formed by the thigh muscles’ attachment with the kneecap is different in males and females.
Knee replacement biomechanics
Knee replacement surgery is most commonly done to treat end-stage osteoarthritis. During the surgery, the bony ends forming the knee joint are replaced with metal alloy prosthetic parts. The lower end of the femur is replaced with a femoral component and the upper part of the tibia is replaced with a tibial component.
The size of the prosthetic metal implants is determined by the size of the bone removed during the surgery. The surgeon cuts the bone to remove the arthritic bone and as well as to correct any deformity caused by arthritis. The implants are capped at the bony ends using special bone cement.
The undersurface of the kneecap (patella) is usually covered by a prosthetic plastic part. A polyethylene plastic spacer is introduced in between the metal parts to smooth the movement and provide stability.
Balancing the knee joint is an important part of knee replacement surgery. The surgeon tries to equalize and balance the forces acting in front, back, and the sides of the knee. The balancing ensures that the prosthetic knee joint is stable and allows movement in the natural range of motion.
A balanced prosthetic knee joint allows movements that closely resemble the natural knee. A balanced and stable knee joint also ensures the implants would last for many years or even a lifetime.
Traditionally, the size of implants used during the surgery is “off the shelf” implants. The off the shelf implants come in different sizes. Traditional implants are made to resemble an average knee and with sizes small and large.
The surgeon measures the amount of bone removed during the surgery and depending upon the size choose the best fitting off-the-shelf implants. Gender-specific implants are made keeping in mind the anatomy of the female knee.
While the traditional implant sizes used in females have been extremely successful, gender-specific implants were recently introduced to potentially make the implants resemble the natural knee as close as possible.
The gender-specific implants for female knees have a smaller medial to lateral distance so they resemble the natural knee. The front-to-back distance of the implant also closely matched the natural knee.
The modification in gender-specific implants prevents overhang or underhanging of the implant which may be encountered in traditional off-the-shelf implants. The patellar tracking is also optimized for the female anatomy in gender-specific implants.
Gender-specific implants are fairly recent advancements in the field of tried and tested traditional knee replacement implants. While studies have shown their benefits compared to traditional implants, there are no long-term studies to conclude if they offer any functional benefit from the traditional implants.
Knee replacement surgeries are highly successful and on average, the traditional knee implants may last 20 years or longer. While technological advancements like gender-specific knees may offer additional benefits, they may not be best suited for all patients. Speak with your orthopedic surgeon regarding the implants that may be best suited for your case. Additionally, surgeons may not be comfortable using implants that may not have been tried and tested for a long time.