Issue: April 2016
April 01, 2016
2 min read

Highly crosslinked polyethylene facilitated use of larger femoral heads in THA

A prospective evaluation showed larger femoral heads in THA prostheses did not increase wear, and no osteolysis was observed on CT scans.

Issue: April 2016
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A radiostereometric analysis showed low long-term wear and femoral head penetration that was similar for 28-mm and 36-mm femoral heads used total hip arthroplasty that articulated with highly crosslinked polyethylene acetabular cup liners.

The results of this prospective study are scheduled to be presented in a primary joint replacement session at the 17th EFORT Annual Congress in Geneva.

For these same sized femoral heads coupled with previous generation polyethylene liners, the wear rates were significantly different, according to Audrey Nebergall, PhD, who is scheduled to present the findings. The larger heads were associated with greater wear than what was seen with the smaller sizes. However, she told Orthopaedics Today Europe the larger head sizes in those articulations offered patients increased total hip arthroplasty (THA) stability and a decreased risk of THA dislocation, without an increased risk of wear-related osteolysis.

Next-generation polyethylene

“Larger head sizes are preferable, generally. With this highly crosslinked polyethylene (HXLPE), we are now able to use large head sizes to get the desired stability and range of motion that we would like without having to worry about increased wear, which is fantastic,” Nebergall said.

Nebergall and colleagues studied 12 patients who underwent THA with Longevity Highly Crosslinked Polyethylene (Zimmer Biomet) that articulated with either a 28-mm or 36-mm femoral head. Six patients in each head-size group agreed to return for a 13-year evaluation of their hip using radiostereometric analysis and CT scans.

The results showed the 13-year mean standard error steady state wear was 0.05 ± 0.02 mm, and there was no significant increase in wear over time between the groups. In addition, CT scans of each patient taken at final follow-up showed no evidence of osteolysis from wear particles, Nebergall said.

Decreased osteolysis observed

“We got CT scans because we wanted to have a closer look at what was happening with the bone around the implant because osteolysis was such a devastating problem that compromised the survival of THA in the past, with conventional polyethylene. We only had 12 patients in the study, but all of them showed no evidence of osteolysis, which is a major victory compared to previous generations of polyethylene,” she said.

One weakness of the study is it did not have a control group of patients who received femoral heads with conventional polyethylene liners for comparison. However, compared to results in the literature for osteolysis associated with the conventional polyethylene for THA, Nebergall said there is a significant improvement in osteolysis rates with the newer polyethylene liners.

“We are encouraged. This is a vast improvement over conventional polyethylene,” she said.

This study is in press, according to Nebergall, and highly crosslinked polyethylene has proven itself as a suitable alternative to conventional polyethylene, both due to decreased incidence of osteolysis and the ability to use larger head sizes without risking increased wear. – by Robert Linnehan

Disclosure: Nebergall reports no relevant financial disclosures.