MEDICINE

Replacing the skeleton bone by bone

Patricia Hluchy November 14 1983
MEDICINE

Replacing the skeleton bone by bone

Patricia Hluchy November 14 1983

Replacing the skeleton bone by bone

Patricia Hluchy

MEDICINE

Until a few decades ago, parts of the human skeleton were irreplaceable. But now, due to an as-

tonishing array of surgical techniques and implant devices, orthopedic and plastic surgeons are replacing and rebuilding many skeletal parts. Each year North American doctors implant more than 150,000 artificial joints, from the shoulders to the toes, although hips are by far the most common and successful implants. What is more, surgeons are developing more sophisticated techniques for grafting bone. The technology is advancing at such a rate that some surgeons predict the recovery prospects for future implant recipients will increase by 100 per cent in as little as two years. Said Dr. Jo Miller, orthopedic surgeon-in-chief at The Montreal General Hospital and head of orthopedic surgery at McGill University: “Advances in technique have been so dramatic that, by comparison, the techniques used five years ago are completely unacceptable.”

In addition to advances in the design and implantation techniques of artificial joints, some of which are now manufactured with a porous surface so that the patient’s bone actually grows into them, scientists continue to work on an alternative to human bone for reconstructive surgery. The Mitsubishi Mining and Cement Co. in Tokyo announced in September that it had developed an artificial bone almost identical in composition to human bone. Mitsubishi scientists have implanted the bonelike substance, apatite ceramic, in more than 100 animals and they believe that they will use the material on humans within two years.

Until then, another recent discovery—a porous coating for joints— may fill the gap. Up to 10 per cent of patients with artificial hips have experienced a loosening of the joints, a condition which sometimes requires a second, more risky and complex implant operation. As a result, surgeons have been reluctant to use implants for patients who would put a particularly great strain on them, such as obese people and active patients under 50. But the new artificial joints with a porous coating may be the solution for those patients, said University of Toronto biomaterial scientist Robert Pilliar, who developed the concept. Pilliar’s design involves coating the surfaces of implants where they are fastened to bone

with a multiple layer of thousands of tiny metal balls. The porous surface allows the patient’s bone, which has been cut to size for the implant, to grow into the device, forming such a strong bond that cement is unnecessary. Until porous-coated implants are a proven alternative, surgeons such as Miller are con-

vinced that they should strive to improve adhesion with cement. But so far the new method looks very promising. Ann McKenna, 39, a Kingston, Ont., merchant who suffers from rheumatoid arthritis, was the second Canadian to have a porous-coated knee installed,

last January. “I am able to walk,” said McKenna, who needed a cane for walking before her surgery. “Had it been glue, I would have had to count every step.”

There have been numerous other advances in implants in the past decade. Dr. Charles Sorbie, an orthopedic surgeon and acting head of the department of surgery at Queen’s University in Kingston, said that computer analysis of joint X-rays has led to a better understanding of dimensions and geometry, and, as a result, to better designs for implants. Sorbie, who is part of a team including engineers and design technologists, said his group has used computer analyses to develop an elbow replacement “that is superior to any on the market today.”

Other surgeons are optimistic that the future lies in bone grafts, especially for younger, more active patients who may outlive a joint implant. “We feel we are on the frontier,” said Dr. Norman Schachar, director of orthopedic research at the University of Calgary and one of the few Canadians doing pioneering work in bone and cartilage grafts. “There is nothing better biologically than biologic tissues,” he declared. Such grafts can come from ribs or other “expendable” bones in the patient himself, from other patients whose bones are removed or from cadavers, in which case they are called allografts. Surgeons perform allografts on young patients who have had tumors or accidents that have destroyed their joints. The transplanted bone becomes a sort of scaffold over which the patient’s own bone grows. Often those grafts spare the patient stiffening of the joint or even amputation. Dr. Allan Gross, chief of the combined orthopedic units at Toronto General and Mount Sinai hospitals, performs about 20 allografts a year—more than anyone else in Canada. Gross’s work is unique because he uses fresh rather than frozen bone tissue, and 70 per cent of his operations have been successful. Said Gross: “The results are providing a viable alternative to implants.”

As surgeons continue to refine bone graft techniques, progress in the development of a bonelike substance may one day make their job easier. To Gross and other researchers, an artificial bone that was biologically acceptable and worked well as a natural bone scaffold would be invaluable. Added Gross: “With artificial bone, you could have it ready on the shelf.