| The Other Bone Disease People with older hip implants face risk of progressive bone loss to osteolysis By DAVID RUMBACH Tribune Staff Writer Surgeon Anthony McPherron found what he expected when he opened up Kenn Workman's left hip. The bone around the metal and plastic parts of Workman's artificial joint was badly decayed. A cavity had formed in his pelvis, above the plastic-lined metal cup that serves as the socket of the prosthetic joint. What should have been dense pelvic bone was a mushy mess. Workman's long leg bone also had deteriorated. The outer layers of bone at the top of his femur had become thin and weak. It might be too weak, McPherron feared, to hold the metal stem that had been inserted into it nine years before. That stem has to be strong to hold the metal ball that fits into the socket. Like a master carpenter, the orthopedic surgeon set to work making needed repairs. Using specially designed surgical tools, he "slap-hammered'' both components to make sure they were still solidly attached. He pressure-packed the cave above the metal socket with $7,000 worth of surgical putty. He placed bone grafts on the weakened sides of the femur and tied them down with cables that cost $5,000. A year and five months later, McPherron's orthopedic handiwork is holding up pretty well. Workman can walk short distances and make it up and down the steps of his second-floor apartment in Plymouth. But he frequently has pain in his hip and worries what will happen if the new components should fail. At age 50, he already has had three hip replacement or revision surgeries. Could it all be cobbled together again? Progressive bone disease linked to artificial joints Workman's bone condition is an extreme example of a progressive disease called osteolysis. Although largely unknown to the public, it is expected to develop in thousands of people with artificial joints in the coming decade. It is the most common cause of failure in artificial hip joints. Ironically, osteolysis is actually caused by the artificial joints themselves, McPherron said: joints that contain, as it were, the seeds of their own destruction. It occurs very gradually as microscopic particles are rubbed off the surface of the polyethylene components and migrate to nearby bone. The body reacts to these foreign bodies as it does to a splinter in your finger, sending immune cells to attack and destroy. But the polyethylene won't dissolve, and the cellular changes gradually destroy the bone tissue instead. Fortunately, there is reason to believe that manufacturers have solved the problem by improving the plastic and other materials used in newer implants. But that won't make a difference to the hundreds of thousands of people who already have the older components, more wear-prone inside their hips, he said. "We're going to be seeing this problem for the next 20 years,'' McPherron said. "It's (the incidence of osteolysis) going to get worse before it gets better.'' As osteolysis weakens the bone around the components, the socket and femoral stem may lose their solid anchorage. The person begins to feel pain while walking, and a surgery to either repair or replace the artificial joint becomes necessary. More than one in 10 hip replacement surgeries are "revisions'' of a previous implant. A revision surgery can be simple, McPherron said. Replacing the thick plastic liner in the socket, for example, might take no more than 35 to 40 minutes. But if the bone has been weakened by osteolysis, the surgery can become complex. Because the ball fits snugly in the socket, surgeons must use a jolting force to pull it out. For example, if the person's pelvis has osteolysis, the force applied to dislocate the ball might fracture the pelvis, McPherron said. Then the surgeon has to delve into his bag of human-carpentry techniques to make things right. "Osteolysis can make revision a nightmare,'' McPherron said. Risk varies among patients Not everyone with an artificial hip is at the same risk of developing osteolysis. Physically active people or those who have had their artificial hip for a long time are more likely to develop the condition. The microscopic debris particles that cause osteolysis come from the "bearing surfaces'' of the joints -- the surfaces where parts rub together. "Young healthy guys tend to do more and have the fast wear,'' McPherron said. McPherron said he tries to keep a close eye on patients to monitor for the emergence of osteolysis, which can be seen on X-rays. He said he sees his patient one, then three, then five years after surgery to make sure things are going well, and then once a year after that. If X-rays show emerging osteolysis, but the patient still is not having any pain, he checks them every six months. "If things get worse, we punt and do surgery,'' he said. "If we catch it early, we can operate when it's a lot less likely to have problems.'' The American Academy of Orthopedic Surgeons has no official position on how often artificial hips should be X-rayed to look for osteolysis. But a 2001 article in the academy's journal says most researchers recommend screening every year or two and then more frequently if bone loss is detected. Dr. William Robb, an assistant professor of orthopedic surgery at Northwestern University, said yearly monitoring with exams and X-rays has been the standard ever since total hip replacement surgeries first became widespread in the 1960s. But the standard often is not followed because many insurance plans, including Medicare, do not pay for X-rays unless the person is having pain. Also, patients themselves often do so well with their new hips that they don't see the need for a visit to the doctor. "It's hard for them to realize that there's a little time bomb in there that might go off,'' Robb said. "We need to reinforce the need for monitoring.'' Robb estimated that as many as 2.5 million implant patients in the United States should be monitored yearly for osteolysis. Solving osteolysis Dr. Frederick Ferlic, an orthopedic surgeon in South Bend, said people who received their implants after 2000 are at a lower risk of osteolysis. "A good analogy would be a tire,'' he said. "It used to be they'd wear out after 10,000 miles. Now we have tires that go 50,000 miles.'' Ferlic cautions that it will take many years of actual experience by patients to show for sure whether the osteolysis problem has been solved. Medical innovations that work in laboratories often fail to pan out in the human body, he said. Even with the older components, Ferlic said the risk of osteolysis is relatively low. He estimates a person with an older implant has only about 5 percent to 10 percent chance of developing the disease after 15 to 20 years of use. "You can't prevent it,'' he said. "The first warning sign will be pain, because it will be loose.'' Harry A. McKellop, a researcher at Los Angeles Orthopedic Hospital, said the overall risk of artificial hip failure from all causes, including infections and cracking of the femoral stem, is 1 percent per year. That's an annual, cumulative risk, so that after 15 years, the chance that a prosthetic hip is still working is 85 percent, and 15 percent that it had to be replaced. Even though the percentage is small, many thousands of people are affected because the number of hip replacement surgeries has grown so large. In 2000 alone, about 295,000 total and partial hip implants were performed in the United States, including 31,000 revisions. McKellop said researchers also are looking for medicines that will slow down the progression of osteolysis. One experiment in dogs found that a medication used for treatment of osteoporosis was effective in slowing down the progression of osteolysis, he said. Since many people with artificial hips take medicines for osteoporosis, they may already be receiving the added benefit of slowing down the other bone disease, osteolysis. |