The classic, some might say stereotypical, image of a hip replacement patient used to be an elderly person, hunched over in pain (picture a cane for added effect here), the new hip not working anywhere near that of the “original” equipment.

But one company, Active Implants (AIC; Memphis, Tennessee), says it is developing a new material that may be used to create longer-lasting implants, more resistant to deterioration and better able to fight off infection.

Researchers in the Campbell Clinic Department of Orthopaedic Surgery at the University of Tennessee Health Science Center (Memphis) presented a paper, sponsored by AIC, on use of a medial grade form of polyurethane polymer, used in other medical applications, at the recent combined meeting of the world’s Orthopaedic Research Societies in Honolulu. Their report touts the use of this polymer material for applications in joint reconstruction, with data indicating that it can reduce by seven times the harmful chemicals formed as a result of the presence of wear particle debris in the body.

One avenue of research on this problem has been related to the reaction of implant materials to otherwise innocuous infectious agents.

And Richard Treharne, PhD, VP of orthopedic research for AIC, said that an “Ah-ha” moment put him on to this approach for reducing wear and infection, and a better pathway for understanding why artificial joints can react so differently in different individuals.

He said that researchers have long known that one of the first places that infections migrate to in the body is the joints. And he said that previous research at the Campbell Clinic found that even minute infections that do not cause any clinical symptoms — such as, for instance, those that enter the body during tooth brushing — can become attached to the wear particles of the traditional plastic material used in joint replacement, a type of polyethylene called UHMWPE, a plastic that articulates or rubs against an artificial hip implant.

What has been observed is that infectious agents such as these, once attached to wear particles, can create chemicals that destroy the bone around the hip joint by a process called “osteolysis.” This bone destruction can lead to implant loosening, which often leads to pain and an implant failure requiring major revision surgery.

“It’s a theory — not everyone believes it,” Treharne told MDD. But he thinks it’s more than speculation.

“I first heard about it a year and a half ago, and it was one of those ‘Ah-ha’ moments,” he said. “I started thinking about why could a replacement in one patient be fine 30 years later, and another replacement in a patient with similar demographics have bone loss and deterioration after just a few years.”

He said the next question was, “What were the variables?” An obvious variable, he said, is “an external element coming into the body. Our doctors on staff describe it as a ‘Trojan horse.’ A doctor can have complete sanitary conditions, and a sanitary implant. Then the patient gets this Trojan horse coming into the body through exposure to everyday, common infections.

“Our bodies handle these subclinical infections, but they end up going through the heart and to the joints — that’s why one becomes so sore when they have the flu or flu-like symptoms.”

He further explains: “These bugs (endotoxins) migrate to the joints of people who have hip replacements. If these endotoxins attach to those, they create compounds called cytokines which are known to cause osteolysis. So the ‘Ah-ha’ theory is that one can have total sanitary conditions and still the hip material can be compromised with bacteria.”

This debris is well-known to cause loosening of the hip implants, thereby limiting the useful life of these artificial joints.

AIC says is search for longer-lasting artificial hips is driven by the desire to be able to implant artificial joints in a pool of patients that seems to be getting younger – one of the emerging trends in orthopedics due to high-impact injuries among this group and the ability of new technologies to enable an early joint implant followed by a later revision, with greatly lessened risk of reduced mobility or adverse events.

Then there is the longer life expectancy for hip implant patients, and an increase in demand by patients for greater activity at all ages.

Treharne sasid that the name of the company reflects its true mission.

“Active Implants — we try to find something that will work in younger, more active patients. One of the main reasons surgeries are postponed or canceled is because there is a pretty high chance that they will get a revision — depending on who you ask or which part of the body” the implant is made.

“This family of products is already being used in some products in the cardiovascular and spinal area and are already on the market in various applications,” Treharne noted. “We’re hoping for an orthopedic total hip application. That may be the best place to work of all the products.

“There is about a 20-25% revision rate in the hips, so people postpone the surgery as long as possible. Unfortunately, these people stop doing what they want to do in life. When they finally take action — by then it’s kind of a race – you either die or you might be too late to retain any previous activities you are used to.”

UT’s Smith said, “Our laboratory has been studying the wear particles of the polyethylene material used in artificial joints for many years. This alternative material has produced results that warrant further research to confirm its superiority as a plastic implant material.”

“From an orthopedic surgeon’s perspective, I believe these findings are significant, and a signal that we may have entered a new era of joint replacement materials,” said Michael Lewis, MD, executive VP for medical development of AIC.

And Stephen Bradshaw, president/CEO of AIC, said that the research out of UT, “combined with other studies, confirms this family of polyurethane materials, used for years in cardiovascular applications, has properties equal to and now better than the traditional polyethylene used for joint replacement.”