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Study: Crosslinked polyethylene may last a lifetime in patients older than 50 years
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SAN FRANCISCO — The results of an award-winning study indicate a low risk of wear-through and clinically significant osteolysis during the lives of patients older than 50 years who undergo total hip arthroplasty with crosslinked polyethylene bearings.
“Over 10 years, gait speed decreased an average of about 9% and gait cycles decreased an average of about 16%,” Andrew K. Battenberg, BS, of the David Geffen School of Medicine, University of California, Los Angeles, said. “Concurrently, wear rate decreased by about 40%. Patients greater than 50 years old at the time of surgery with 28-mm or 32-mm bearings are unlikely to experience wear-through or clinically significant osteolysis during their lifetime with crosslinked polyethylene and longer-term experience is needed to assess the risk of osteolysis with larger heads.”
Andrew K. Battenberg
He noted that gait speed is the number of cycles per minute while the patient is active. Gait cycles are the total number of cycles per day or cycles per year. Battenberg presented the Frank Stinchfield Award-winning study at the 2012 Specialty Day Meeting of The Hip Society, here.
Battenberg and colleagues studied 14 patients with a mean age of 55 years who underwent total hip arthroplasty (THA) using 28-mm or 32-mm bearings made of 5 mRad re-melted crosslinked polyethylene (Marathon; DePuy). They assessed activity using a microprocessor placed on the patients’ ankles at two time periods — once within 4 years of THA or the early postoperative period, and again at a minimum of 10 years after THA or in the late postoperative period. The investigators also studied wear at both time points using 2-D edge detection-based software.
Activity in the early postoperative period (1.5 years mean) was 2.04 million cycles per year and 1.71 million cycles per year during the late postoperative period (11.1 years mean), indicating activity declined 16%. Battenberg’s team found the mean gait speed was 15.4 cycles per minute in the early period and 14 cycles per minute in the late period, signaling an 8.8% decrease.
Patients who were younger than 65 years at the time of surgery, had a greater decrease in gait speed from the early to the late period (9.7% vs. 5.5%), while patients who were older than 65 years at surgery had a significantly slower gait speed at both time points. Looking at activity, they discovered that patients who were older than 65 years at the time of surgery were significantly less active at both time points and had a greater decrease between the two time periods (28% vs. 14%) than those younger than 65 years.
Polyethylene linear wear and volumetric wear rates decreased from the early to late periods by 42% and 48%, respectively. Maximum linear penetration was 0.87 mm and maximum volumetric wear was 435 mm3, but investigators saw no evidence of osteolysis in any hip.
In a study of 32 mm hips, no osteolysis was observed at a minimum of 10 years when the linear wear rate was less than 0.1 mm per year, according to the researchers. This corresponded to roughly 650 mm3 of volumetric wear.
According to the study, the annual mean volumetric wear rate was 15 mm3 in the first 5 years and there was a 40% mean decrease in wear from the first 5 years to the following 8 years, culminating in a 3% compounded decrease in the annual polyethylene wear rate. Battenberg also cited U.S. data that estimated most 50 year olds live an additional 31 years.
“Using this as a wear model, total volumetric wear over 31 years would be predicted to be 305 mm3 and a low risk of osteolysis during one’s lifetime,” he said. “[The] maximum linear penetration was 0.87 mm. At this rate, it would take nearly 40 years to penetrate a 3-mm liner with a constant wear rate, but wear decreases over time.” – by Gina Brockenbrough, MA
Reference:
- Battenberg AK, Hopkins JS, Kupiec AD, Schmalzried TP. Decreasing patient activity with aging: Implications for crosslinked polyethylene wear. Presented at The Hip Society 2012 Specialty Day. Feb. 11. San Francisco.
For more information:
- Andrew K. Battenberg, MS, can be reached at Orthopaedic Hospital, 2400 South Flower St., Los Angeles, CA 90007; email: akbatten@ucla.edu.
- Disclosure: Battenberg has no relevant financial disclosures.