The Right Fit
Hip-replacement surgery has dramatically altered the future for thousands of people crippled by arthritic hip joints. I know one man who reveled in adventures such as jumping from helicopters and skiing down virgin slopes -- until arthritis in his right hip made even walking difficult for him. Today, thanks to hip replacement, although he no longer leaps from helicopters, he is once again skiing advanced slopes. The problem has been, though, that artificial hips could not survive long-term wear and tear, and often had to be replaced. Consequently, doctors usually recommended that patients wait as long as possible for surgery to maximize the possibility that the hip joint would outlive the person. Now, English researchers are evaluating another approach to material for replacement parts -- a ceramic socket with a metal head for the thighbone (the femur). The team is taking the ceramic-on-metal model into clinical trials shortly. If tests prove successful, the researchers say the new model will likely be available for use within five years. To discuss this potential advancement in the hip-joint-replacement world, I called orthopedic surgeon Thomas P. Schmalzried, MD, associate medical director of the Joint Replacement Institute at Orthopaedic Hospital in Los Angeles. Dr. Schmalzried told me that metal-on-metal was actually used as far back as the 1960s, but design problems flawed the original prostheses. The next improvement was the evolution of using metal for the femur head and a cup made of polyethylene (a type of plastic) for the socket. However, this conventional polyethylene turned out to be a major problem in the so-called "wearing out" of the prosthesis -- the process in which normal use of the joint causes small particles of the prosthesis material to break off. Eventually, so many particles can accumulate around the joint that they cause inflammation and bone loss, thereby necessitating a new prosthesis and another surgery to position it. With conventional polyethylene, the particles were bigger and sooner created the need for another replacement. When metal-on-metal bearings became available in the last decade, they created considerably less debris around the joint, says Dr. Schmalzried. They also have had remarkable success in providing patients with greater mobility, allowing them to partake in virtually all activities. These prostheses have not been in use long enough for doctors to have data on their durability, but Dr. Schmalzried says they have found that the metal-on-metal models from 30 years ago -- even with their design flaws -- have proved to be durable in patients all these years later. Not everyone can tolerate metal-on-metal prosthesis, though. Although Dr. Schmalzried emphasizes that it is extremely rare, some people are sensitive to the nickel alloy used in the metal and cannot tolerate the ions released by the rubbing of the bearings. When released, these ions can cause inflammation around the joint, and in turn pain and degeneration. He says this is the primary problem with the metal-on-metal, and he doesn't see that the ceramic-on-metal model would improve the situation in any meaningful way. Consequently, he remains satisfied with the number of choices now available to patients. These include the improved polyethylene material (called cross-linked) for the joint socket that can be used with a metal or ceramic head, ceramic on ceramic and metal on metal, including titanium alloys that do not contain nickel. Dr. Schmalzried advises potential hip-replacement patients to discuss their goals, lifestyle and expectations with the surgeon, and work together to determine which choice of material is appropriate. He says the salient criteria for a patient's decision should not be age, but rather the person's level of activity. polyethylene may be fine for older or less active people, whereas those who are more active want to consider the more durable metal-based options. One other piece of good news: Surgery now requires only three days in the hospital and surprisingly little follow-up therapy. Unlike knee replacement with its grueling regimen of physical therapy, hip-replacement patients recover rapidly -- with a few weeks of rehabilitation -- and need to perform only simple exercises, including stationary bike riding, walking and some gentle stretching, says Dr. Schmalzried.