The knee is considered to be one of the largest and heaviest joints in humans. It is very important in the normal functioning of the body, since it carries more than half of a person’s weight.

Approximately 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.

According to most experts, knees are the most complex type of orthopedic implant to manufacture. Artificial knees must accommodate a range of motion up to 120 degrees, allowing them to naturally bend and rotate.

Major knee components include the tibial, the femoral, and the kneecap or the patellar component. “The bearing component can be fixed or moving,” says Aarti Shetty, healthcare industry analyst at Frost & Sullivan Inc. (San Antonio). “The mobile bearing knee has been gaining momentum in recent years. Its design allows for less implant wear in comparison to the fixed bearing design, but it is more expensive.”

Knee implants are typically attached to leg bones, such as the femur or tibia, during surgery with screws. “Cementless implants are preferred whenever feasible, because they tend to last longer and are not prone to loosening under stress,” notes Bill Martineau, healthcare industry analyst at the Freedonia Group Inc. (Cleveland). “However, they require strong natural bones for successful ingrowth and placement. Older patients with fragile, brittle bones must usually be fitted with cemented implants to achieve successful results.”