Total Joint Replacements, By Dr. W. Kim Furman

Over the past ten years significant advances in total joint replacements (TJR) have occurred since the first hip replacement was performed in the United States in 1969. These improvements have opened up a whole new opportunity for treating young, active people with disabling arthritis. Currently, 75 million people in the United States suffer from arthritis. Three million of these are so severely affected that surgical intervention is required. Baby boomers make up a large proportion of this population because they have a tendency to work hard and play hard, resulting in early arthritis. The treatment for this age group has traditionally included conservative options including medications, injections, braces, and activity restrictions. Once reserved for patients greater then 60 years old, TJR has become more mainstream in the less then 60 year-old age group as a growing number of people with degenerative arthritis are turning towards TJR as a way of regaining their once active lives.
TJR, up until recently, has been delayed in the younger than 60 population, because it was felt that the implants would eventually wear out requiring revision surgery and each successive revision would not be as successful as the first operation. TJR has been done for well over 30 years. Approximately 300,000 TJR surgeries are done per year including hip and knee replacements. These replacements have been very successful with existing technologies in the older aging population, showing good to excellent results in over 90-95% of the cases at 10-15 years post-operatively. Unfortunately, in the younger age group, these prosthetic implants were not designed to last as long as the average life span of somebody in their 50's, and thus the big push to search for better materials and techniques to improve the longevity of the implants used.

The main problem with the implants has been mechanical failure over time. Failure is based on many factors including age at time of surgery, activity level, weight, and component design. Hip and knee replacements are composed of metal and plastic and it is plastic that has been the weak link. The most common later complication of TJR is an inflammatory reaction to tiny particles that gradually wear off of the artificial joint surfaces. These particles are absorbed by the surrounding tissues causing an inflammatory reaction. The inflammation triggers the action of special cells that eat away some of the bone, causing the implant to loosen

Over the past 5-10 years, improvements in materials, design, and surgical techniques have significantly increased the longevity of the implants to the point where we now feel comfortable implanting these in the young, active patients in their 40’s and 50’s. The ultimate goal is to develop implants that will last longer and provide function similar to what Mother Nature has designed for the normal hip and knee.

When discussing advances in joint replacements, we can break it down into material, design and surgical improvements.

Material Improvements

Three significant implant material improvements include the use of metal on metal prosthesis and new polyethylene, the plastic joints articulate on . Metal on metal is not new. It was used in hip replacements more than 30 years ago, but failed due to poor manufacturing technique. Current metallurgy has allowed us to come full circle in its use. The development of harder, smoother metal, allows it to be used as the articulating surface of a hip replacement instead of the standard plastic liner.

Another material reappearing in hip as well as knee replacements is ceramic. Ceramic was used years ago, with disappointing results. Better manufacturing technique has resulted in a more durable material making ceramic an excellent alternative bearing surface to reduce long term wear. Ceramic on ceramic and ceramic on plastic are used in hip replacements. Although still experimental, ceramic is being used as an articulating surface for knee replacement. Even though ceramic is a very strong material, its major drawback is its brittleness, making it subject to breakage.

Polyethylene, the gold standard for joint replacements has been the major weak link in TJR. A new technique in manufacturing the plastic liners has improved the long term strength and durability of the material reducing the wear particles to a minimum.

Design Improvements

Design advances have affected mainly the knee replacements over the hips. Mobile bearing knees have been done for over 25 years, but thanks to improved plastic and metallurgy, these will last longer. The mobile bearing system allows the plastic liner between the femur and the tibia bone to rotate, thus reducing further wear of the plastic. The 3-D knee (data driven design) is a new knee system developed with current state-of-the-art technology. Most knees presently in use have been designed based on the body’s normal knee mechanics. The 3-D knee has actually been designed based on how a total knee replacement will function once implanted. The ultimate goal is to allow for greater range of motion, less wear and tear on the plastic and improved longevity. Other material designs include coating implants with a roughened porous surface
made out of metal beads or fiber metal. This allows the body’s own bone to grow into the implant and stabilize it without the use of glue or bone cement. Cement has been considered a weak link in terms of longevity because over time, cement will eventually fail necessitating revision surgery. The use of cement-less implants will provide more durable, long lasting success. It is not new, having been around for over 20 years and is used more frequently in the younger population.

While some researchers are focused on implant improvements from the mechanical viewpoint, others are addressing the challenge from the biological perspective. Some surgeons have been using hydroxyapatite-coated implants in an attempt to promote rapid bone ingrowth. It is a material that is similar to the composition of normal bone. Hydroxyapatite can be applied to porous coated implants and is used without bone cement.

Surgical Improvements

Finally, newer surgical techniques have allowed both knee and hip replacements to be done through smaller incisions which ultimately will allow for shorter hospital stays, less blood loss, less pain, and a quicker return to function. Although these are relatively new and still requiring long-term study, they appear to be very promising surgical techniques.

If total joint replacement is an option for you, then it is imperative that you seek a board certified orthopedic surgeon who is fellowship trained in joint replacement surgery and performs at least 100 joints a year. Dr Furman is currently accepting new patients and is available for consultations and second opinions.