We report the five-year outcome of a randomised controlled trial which used radiostereometric analysis (RSA) to assess the influence of surface oxidised zirconium (OxZr, Oxinium) on polyethylene wear in vivo.

A total of 120 patients, 85 women and 35 men with a mean age of 70 years (59 to 80) who were scheduled for primary cemented total hip arthroplasty were randomly allocated to four study groups. Patients were blinded to their group assignment and received either a conventional polyethylene (CPE) or a highly cross-linked (HXL) acetabular component of identical design. On the femoral side patients received a 28 mm head made of either cobalt-chromium (CoCr) or OxZr.

The proximal head penetration (wear) was measured with repeated RSA examinations over five years. Clinical outcome was measured using the Harris hip score.

There was no difference in polyethylene wear between the two head materials when used with either of the two types of acetabular component (p = 0.3 to 0.6). When comparing the two types of polyethylene there was a significant difference in favour of HXLPE, regardless of the head material used (p < 0.001).

In conclusion, we found no advantage of OxZr over CoCr in terms of polyethylene wear after five years of follow-up. Our findings do not support laboratory results which have shown a reduced rate of wear with OxZr. They do however add to the evidence on the better resistance to wear of HXLPE over CPE.

Cite this article: Bone Joint J 2015;97-B:1463–9.

Background

Improving quality and efficiency is a priority in health policy. Several studies have shown a correlation between high hospital volume and improved results of surgery. In Norway, orthopaedic surgeons operate a relatively low number of total knee replacements compared with other countries. The number of total knee replacements has, however, increased significantly over the past 10 years.

Some studies have also shown an association between surgeon volume and outcomes after total knee arthroplasty (TKA).

In this prospective study we studied the effect of the inclination angle of the acetabular component on polyethylene wear and component migration in cemented acetabular sockets using radiostereometric analysis.

A total of 120 patients received either a cemented Reflection All-Poly ultra-high-molecular-weight polyethylene or a cemented Reflection All-Poly highly cross-linked polyethylene acetabular component, combined with either cobalt–chrome or Oxinium femoral heads. Femoral head penetration and migration of the acetabular component were assessed with repeated radiostereometric analysis for two years. The inclination angle was measured on a standard post-operative anteroposterior pelvic radiograph. Linear regression analysis was used to determine the relationship between the inclination angle and femoral head penetration and migration of the acetabular component.

We found no relationship between the inclination angle and penetration of the femoral head at two years’ follow-up (p = 0.9). Similarly, our data failed to reveal any statistically significant correlation between inclination angle and migration of these cemented acetabular components (p = 0.07 to p = 0.9).

Introduction: Highly cross-linked polyethylene acetabular cups and Oxinium femoral heads were developed to reduce wear debris induced osteolysis. Laboratory tests have shown less wear with these new materials. This RSA-study was performed to compare these new materials in vivo with conventional bearing materials used in total hip arthroplasty.

Methods:150 patients were randomized to 5 groups. The patients received either a cemented Charnley mono-block stainless steel femoral stem with a 22.2 mm head or a cemented Spectron EF femoral stem with a 28 mm head. The Charnley stem articulated with a cemented Charnley Ogee acetabular cup. The Spectron EF stem was used with either cemented Reflection All-Poly EtO-sterilized ultra-high molecular weight polyethylene (UHMWPE) acetabular cups or cemented Reflection highly cross-linked polyethylene (XLPE) acetabular cups, combined with either Cobalt Chrome or Oxinium 28 mm femoral heads. Patients were followed up with repeated radiostereometric analysis (RSA) for two years to assess the rate of penetration of the femoral head into the cup (MTPM).

Results: At 2 years follow-up the mean MTPM (95 % CI) for Charnley Ogee (n=25) was 0.20 mm (0.11–0.29). For the Spectron EF femoral stem used with Reflection All-Poly UHMWPE acetabular cups the mean MTPM (CI) at 2 years was 0.40 mm (0.23–0.57) when combined with Cobalt Chrome femoral head (n=23) and 0.50 mm (0.29–0.71) when combined with Oxinium femoral head (n=16). When using the Spectron EF femoral stem with Reflection XLPE combined with Cobalt Chrome (n=27) or Oxinium (n=24) femoral head the mean MTPM (CI) at 2 years was 0.19 mm (0.10–0.28) and 0.18 mm (0.07–0.29), respectively. There were no differences in penetration between the Charnley/Ogee, XLPE/CoCr and XLPE/Oxinium groups (student t-test, p=0.5–0.8). There was no statistically significant difference between the two Reflection All-Poly UHMWPE groups (p=0.09). The groups with Reflection All-Poly cups had a statistically significant higher penetration than the three groups mentioned above (p< 0.001).

Discussion: The use of Reflection XLPE cups instead of Reflection All-Poly cups reduced femoral head penetration at 2 years. We used the Charnley Ogee cup as a reference due to a long clinical record. This cup was superior to Reflection All-Poly, but not Reflection XLPE, regarding femoral head penetration. Because the femoral head of Charnley Ogee is smaller than the Oxinium/Cobalt Chrome head it might be more clinical relevant to measure volumetric wear. The groups with Oxinium heads did not have less wear than the groups with Cobalt Chrome heads after 2 years follow-up. Further follow-up is needed to evaluate the benefits, if any, of Oxinium femoral heads in the clinical setting.