OrthoVirginia Blog

A World of Choices: Innovative Bearing Surfaces and Design Boost Total Joint Replacement Options

Dr. McMahon practices in our Fair Oaks office.
Dr. Martinelli practices in our Alexandria and Springfield offices.

As aging baby boomers create an ever-growing demand for joint replacement services, groundbreaking advances in the biomedical engineering industry are rapidly changing the way joint replacement is performed, opening up a host of options. Commonwealth is at the forefront of these developments, offering patients the very latest in total joint replacement technology, with a growing emphasis on durability and customization.

Longer-lasting implants make surgery an increasingly viable and successful choice for younger, active adults. Cutting-edge materials such as titanium, ceramics, and polyethelene (plastic), as well as improved fabrication technology, have strengthened weight-bearing surfaces, minimizing wear and increasing implant longevity. Larger prosthetic head size also improves hip stability. These advancements are especially beneficial for patients in their 40s, 50s, and 60s who lead active lives, have physically challenging jobs, or want to continue to play sports.

A Brief History

When British surgeon Sir John Charnley first perfected modern total hip replacement in the 1960s, his material of choice was low-friction Teflon. But Teflon implants didn’t last long and most surgeries had to be repeated within a few years. Dr. Charnley went on to try various combinations of materials and fixation techniques, all the while advancing the science to where it is today.

Historically, the weak link has been the premature wear of the bearing surface of the hip prosthesis, especially the standard metal-on-plastic bearing surface that can result in pain and loosening of the implant — and possibly require revision surgery. In recent years, engineers have produced some promising alternatives, including highly cross-linked polyethylene, ceramic bearings, and metal-on-metal bearings.

As with any new technology, however, there are potential pitfalls, and manufacturers continue to refine the options. The goal has always been to attempt to solve two coexistent problems, the first is that wear will lead to instability and a need to revise the components, and the second is that wear generates particles that can be toxic to the local tissue or to the bone in-growth process, leading to bone loss, failure, and, in some very rare cases, local fracture.

Science Marches On

The most recent innovations have been in the area of the hip cup liner. A promising new design is special plastics with built in anti-oxidant chemicals to help fight the toxic environment present inside the body joint cavities. Combined with better fabrication technologies, the promise of a longer lasting prosthesis is on the horizon.

Ceramic heads, with either a ceramic or highly cross-linked polyethelene cup, have shown significant wear reduction in the lab. But persistent worries about the potential for cracking of the ceramic ball or squeaking of the ceramic-on-ceramic replacements have led to cautious patient selection for these implants.

Metal-on-metal implants were another design advancement with promising early results, and as of 2009 accounted for almost 25% of implants done in the United States. However, recent highly publicized problems have resulted in a re-thinking of their place in the hip replacement world.

Design Advancements

Another big step forward for hip and knee replacement patients: implants are now modular, with multiple pieces. If a part wears out, the surgeon can swap it with relative ease. This offers physicians and patients greater opportunities down the line to be more easily revised.

Manufacturers are also moving toward custom implants, as doctors and patients push for more options and more precise fits that will last longer with better wear characteristics. Designers are focusing on the anatomic differences that can lead to potential problems in implant sizing, especially among knee replacement patients. Mobile bearing and high flexibility implants promise better and more natural motion for athletic and daily activities, but because they are still in early use, there is no long-term scientific proof that they make a significant difference.

Ultimately, patient age, activity level, overall health, and the condition of the bone are the main factors considered when choosing the optimum type of joint replacement implant. Patients will often come to us with information about new products or promising design elements, and we certainly want to be abreast of the current research that is out there. But in the end, it comes down to one-on-one evaluation – first in the surgeon’s office, then in the operating room, if necessary. It’s not unusual to re-evaluate the preoperative assessment at the point of surgery because of new information that cannot be obtained without seeing the condition of the joint. At Commonwealth, we pride ourselves on our ability to provide this level of personalized care for each of our patients.

Read more about Dr. Martinelli and Dr. McMahon