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November 2009: An Update on Hip and Knee Replacement

30 Oct 2009

Dr. Kris Alden is a fellowship-trained, board-eligible orthopedic surgeon who came to Weiss from the Mayo Clinic. His clinical specialty is orthopedic surgery and his areas of clinical interests include hip and knee replacement, minimally invasive hip and knee surgery, lower extremity surgery and hip resurfacing.

Kris John Alden, M.D., Ph.D.
Associate Clinical Professor of Surgery
University of Chicago Bone & Joint Replacement Center
Weiss Memorial Hospital
(773) 564-5870

A remarkable number of hip and knee replacements are completed each year, in excess of 500,000. In 2001, more than 300,000 knee replacements were performed, outpacing hip replacement. In the next 20 years, physicians expect that total number to increase to 750,000 annually. Hip and knee replacements have truly revolutionized the treatment of arthritis and are one of the greatest innovations in all of medicine in terms of quality of life and pain relief. With improved technology and updated surgical techniques, the durability of these implants has vastly improved.

Hip replacement
When do physicians recommend hip replacement? It is truly a matter of quality of life. For the most part, the timing for joint replacement is when you decide the time is right. The conventional treatment has been when you have symptoms that non-operative management fails to control. Surgeons have moved away from delaying the procedure as long as possible, in part because people today are much more active and are not willing to accept as much debility as they did 20 years ago. Surgeons and researchers have seen excellent, long-term results with modern technology. Also, a number of studies have shown the cost of waiting, in terms of functional debility and quality of life has increased. And there is an economic aspect in terms of missed days from work. All of this means that hospitals are performing hip replacements in younger people. There may be advantages to hip replacement surgery for people when they are less debilitated, since ultimately they will have better outcomes.

Many people typically think of total hip replacement, which involves a thigh component and a hip cavity component. Surgeons at Weiss replace both sides of the joint. Originally, physicians used cemented fixation, where cement acts as a grout and bonds the prosthesis to the bone. More recently, patients receive biologic fixation, where there are various coatings on the implants. Initially the stem is pressed into the bone tightly and eventually, the bone grows onto the prostheses.

Knee replacement
Total knee replacement

Similar to hip replacement, total knee replacement is a last resort to treat arthritis or other conditions affecting the knee, but again, patients are more active now and the indications are expanding. Total knee arthroplasty replaces both sides of the joint, at both the thigh and the shin side. The long-term results for total knee arthroplasty are excellent as well. Physicians have 15 to 20 years of data, and 90 percent survivorship, which indicates that the patient has not required further surgery. Some 25-year studies show 95 percent survivorship of total knee replacements. However, 25 years ago, surgeons were doing these replacements in less-active patients, so that should be taken into account. Modern knee replacement incorporates improved technology and surgical techniques, which will continue to improve upon this successful track record. Current design changes have been made to sustain the longevity of the prostheses.

Unicompartmental replacement
A unicompartmental knee replacement replaces one compartment: a medial or lateral compartment. Surgeons cut out the arthritic bone and resurface it. The benefit of this type of surgery is that it is done through a smaller incision, and the normal cartilage is maintained. It certainly is less invasive than a total knee replacement because there is no replacing at all.

Emerging techniques and technologies
In terms of return to function, quality of life, and pain relief, numerous studies support the improved outcomes of joint replacement surgery. The Mayo Clinic has reported an 80 to 86 percent survivorship rate for a study of 2,000 hip replacements over 30 years1. Thirty-year results from the University of Iowa2 show only 10 percent of femurs have been revised. The pelvis has a much higher revision rate, at 26 percent. However, these are 30-year results, which are excellent. For patients younger than 50, the results are not nearly as good as the older populations, but they have relatively good trends in survivorship. These outcomes are improving with newer prosthetic designs and techniques. With the introduction of cementless hip replacement, results demonstrate a 97 percent survivorship rate on both the thigh and the hip cavity side.

Technology is improving results in joint replacement. Certainly with computer assistance surgeons are getting better at molding anatomy to fit the patient, which enhances the longevity of prostheses. Bearing surfaces also are a critical component in survivorship. A major reason for failure of joint replacements is the loosening of the component. The femoral head can wear out, and the plastic becomes fatigued. This causes a reaction in the body, which over time loosens the component. To combat this problem, the plastic has been made stronger and more resistant to wear. Clinically, this new technology has been available for six years, and there has been a reduction in wear. In a patient, wear is measured by the femoral ball’s penetration into the plastic over time. There has been a 60- to 70-percent reduction in that penetration compared with the conventional polyethylene3. What will happen in 15 or 20 years is unknown, but the long-term results look favorable.

The other development has been the use of metal-on-metal bearings, which are harder and have a significantly lower wear rate. The metal particles generated by the rubbing of the two surfaces are much smaller than with the plastic particles, and therefore the bone-dissolving reaction in the body is not created. The major concern with metal bearings is the systemic concentration of metal ions, which appear in the blood and urine. Chromium, an element in metal ions, is known to cause gene mutations in various cells.

Another solution, one that has even less wear than metal, is ceramic bearing surfaces. The problem with ceramic is squeaking of the hip and more rarely, fracture of the joint head (approximately one in 10,000). Squeaking of the hip is a phenomenon which is not well understood, and the cause is controversial. Modern techniques and improved designs will reduce squeaking in the future, though it will likely not be eliminated. Recently, a researcher from the University of Chicago has joined the Bone and Joint Center team to help advance understanding of joint replacement dynamics and wear, including hip squeaking.

When people want these new bearings, surgeons must caution them. These developments are not tried and true, and the patient really has to be willing to take risks. The doctors at Weiss discuss bearing surface options with each patient at the time of the decision to do surgery. In general, what is tried and true is polyethylene. For patients younger than 50, metal-on-metal may be practical. However, metal-on-metal is not a good choice for women of childbearing age, as researchers do not know what impact these ions might have on a developing fetus. Metal-on-metal is not recommended for people with poor renal function. The ions are found in the urine, in the liver and the kidneys. They are cleared by the kidneys, so people with decreased renal function would not be good candidates.

Minimally invasive surgery
In general, all hip and knee replacements are performed using minimally invasive surgery. However, minimally invasive surgery is a misnomer. What is minimally invasive about cutting bones? The term “less invasive surgery” may be more accurate. Benefits include: less tissue damage, decreased blood loss, less pain and a quicker short-term recovery. With less invasive surgery, surgeons go through the same muscular plane and, importantly, it is the same hip replacement. Less invasive surgery customizes the surgery to the patient’s anatomy and needs at the time of the surgery.

Anesthesia and recovery
Improved anesthesia techniques have been beneficial for short-term recovery. Surgeons are performing hip and knee replacements with smaller incisions, and patients are more comfortable with improved anesthesia techniques. Patients are moving more quickly through surgery and postoperative rehabilitation. Our goal at Weiss is to get people walking in a pain-free manner with excellent long-term outcomes and survivorship of the implant.

For more information
If you would like more information about hip and knee replacement or would like an appointment, please call Dr. Alden’s office at (773) 564-5870.

1. Berry DJ, et al. J Bone Joint Surg Am. 2002 Feb; 84-A(2): 171-7.
2. Callaghan JJ, et al. The Journal of Bone and Joint Surgery. 2004; 86: 690-695.
3. D’Antonio JA, et al. Clin Orthop Relat Res. 2005; 441: 143-50.