Superior 11-year survival but higher polyethylene wear of hydroxyapatite-coated Mallory-Head cups

Hydroxyapatite (HA) coating of implant surfaces is believed to improve longevity of uncemented total hip arthroplasty (THA). However; it is speculated that HA particles may cause third body wear of the polyethylene (PE) liner with subsequent osteolysis and aseptic loosening of implants. We performed a retrospective comparison of two patient populations with cementless Mallory-Head acetabular components. The patients were identified in the Danish hip arthroplasty Registry (DHR); 77 patients had HA-coated cups and 73 patients had non-HA coated cups. Anteroposterior (AP) radiographs were analysed for PE wear, osteolysis was quantified and survival of the acetabular components was compared. The mean follow-up was 11 years. There were no cup revisions in the HA group and 7 cup revisions in the non-HA group (P<0.01). The reason for revision in all cases was aseptic loosening of both stem and cup. The amount of osteolysis was significantly increased around cups in the non-HA group. The two-dimensional linear PE wear-rate of 0.18 mm/year was higher (P<0.001) in the group with HA coated cups compared with 0.12 mm/year in the group with non-HA coated cups. The mean age was lower (P=0.001) in the HA group (57 years) compared with the non-HA group (63 years). After 11.1 years of follow-up non-HA coated cups had a higher revision rate. Increased PE wear with HA-coated cups did not have a negative influence on the revision rate, but may result in a need for revision surgery over time.