Artificial Hips
Once, arthritis or diseased hip bones condemned people to life in a wheelchair. Many young people choose to suffer rather than give up their mobility. Today, artificial hips eliminate that debilitating pain while enabling more than half a million people each year to return to active and even athletic lifestyles.
To understand how artificial hips have evolved, consider how they fail. This happens when the cartilage degrades between the hip socket and the ball-shaped end of the thigh bone (femur) that fits into it. This leads to painful bone-on-bone scraping. Physicians tried to solve this problem by replacing the end of the femur and, later, the hip cup, with combinations of metals, plastics, glass, and even ivory. The results were uneven at best.
It took until the 1960s for John Charnley to bring a true engineering perspective to artificial hips. A physician, Charnley learned engineering while managing a machine shop that made medical devices during WW II. When he met a patient whose hip prosthesis squeaked, he realized the implant had a friction problem.
Charnley's key innovation was to combine a small, smoothly polished femoral ball with a wear-resistant yet highly slippery plastic cup that he glued into place. This greatly increased the likelihood of successful surgeries.
Charnley's insights led to new generations of implants, but it was not easy. The hip, after all, supports two to three times the body's weight with every step and twice that when running. Biomedical engineers crafted their devices to distribute those loads without causing additional wear or pain.
Finding the right combination of materials also took time as researchers looked for durable combinations of metal and plastic that did not generate inflammation-causing wear particles. They also developed porous coatings that lock the femoral stem and hip cup into place without cement. This encourages bone growth, increasing hip stability and durability.
Today, hip implants last for decades while freeing patients from pain and immobility.