Joint replacement: what’s a nice joint like you doing in a dame like this?

“Gentlemen, we can rebuild him. We have the technology.” So began each episode of The Six Million Dollar Man.

Twenty-some years after that TV series aired, we still don’t have bionic people capable of superhuman feats of strength and speed, but we do have lots of people walking around with artificial parts: especially, artificial joints. My own “bionic Mom” is among them; she has two artificial knees and, as of last week, an artificial shoulder. A joint is formed by the ends of two or more bones connected by thick tissues. Some are basically hinges, like the knee; others have a ball-and-socket construction, like the hip. In a normal joint, the bone ends are covered with a smooth layer of cartilage, which allows nearly frictionless, pain-free movement. But when disease or injury damages the cartilage, joints become stiff and painful. In 1925, Dr. M. N. Smith-Petersen, a Boston surgeon, tried to address this problem by molding a piece of glass into the shape of a hollow hemisphere and fitting it over the ball of a patient’s hip joint. Glass proved to be too fragile, so he tried other materials, including plastic and stainless steel, and eventually, and successfully, a cobalt-chromium alloy. By the 1940s, Smith-Petersen’s “mold arthroplasty” was state-of-the-art–but the resurfacing technique used to coat the ball of the hip joint was unreliable, and many patients continued to have pain and limited movement.

In the 1950s, surgeons began replacing the entire ball of the hip joint, a process called hemiarthroplasty. The artificial ball was connected to the femur by a metal stem, but there was no truly effective method of fastening the ball to the femur, and many patients suffered pain when the implant loosened. Fast-setting dental acrylic eventually eased that problem.

Neither mold arthroplasty nor hemiarthroplasty did anything about the socket. But in 1958 English surgeon John Charnley replaced the eroded arthritic socket in a patient undergoing hemiarthroplasty with a Teflon implant. When that didn’t work, he tried polyethylene–which worked wonderfully. By 1961, Charnley was performing total hip replacement regularly and getting good results. Today hundreds of thousands of hip replacements are performed annually.

Knee replacement surgery followed a parallel line of development, with a number of less-than-satisfactory experiments eventually leading to the first modern knee replacement in 1968, a metal-and-plastic prothesis secured to the bone with cement developed by Frank Gunston (a Canadian!). Further refinements gave us what is used today: a prothesis made of three components, fixed to the bone with cement, which cover all three surfaces of the knee, the femur, the tibia, and the patella (kneecap).

Shoulder replacement surgery is performed less often, because people can usually manage with shoulder problems better than they can with knee or hip problems, but it uses the same basic technology.

One big recent innovation has been the replacement of cement in some cases with specially designed implants that have a textured, porous surface. This allows the bone to grow into the implant, holding it in place more securely.

Of course, like any surgery, joint replacement surgery has risks, small but real. They include infection, blood clots, loosening of the prosthesis in the bone, dislocation of the new joint, excessive wear in the new joint, breakage of parts of the prosthesis, and nerve damage. Nor are replacement joints permanent; they may wear out in as little as 10 years. But the benefits include reduced pain and often increased joint mobility.

And surgeons continue to experiment. For example, Dr. Ruth Chaytor, an orthopedic surgeon at Sir Mortimer B. David Jewish General Hospital in Montreal, has been testing ankle replacement surgery.

Until now, the only surgical treatment for arthritis in the ankle has been fusing the ankle bones together. But that leaves patients limping and puts extra strain on other joints, such as the hips and knees.

The replacement ankle, like other replacement joints, is made of a mixture of metal and plastic parts. Dr. Chaytor has installed it in five patients, all of whom are doing well, and she has a long waiting list of other patients anxious to have the surgery.

Besides hips, knees, shoulders and ankles, elbows, wrists, and joints in the fingers and toes can also be replaced.

My semi-bionic mother may not be able to run 100 kilometres an hour or lift a truck, but if she can use her shoulder again without so much pain, that will be good enough for her–and me.

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