Metal-on-metal hip prosthesis has no advantages over other type

The metal-on-metal hip prosthesis has no advantages over the metal-on-plastic system. This is remarkable, as it was developed specifically as an alternative to the metal-on-plastic type, which is not very wear-resistant. The metal-on-metal prosthesis also has a negative effect on bone quality, as it gives off metal ions. Orthopaedic surgeon Wierd Zijlstra made these findings in the course of research he conducted at the Martini Hospital and the University Medical Center Groningen (UMCG). Zijlstra will be awarded his PhD on 23 November 2011 by the University of Groningen.

A total hip replacement can be a solution for patients with severe wear and tear to the hip joint. The original prosthesis consisted of a metal head that is free to move inside a plastic (polythene) socket. Pressure and movement cause wear and tear on the plastic, and the debris released attacks the bone, with the result that the prosthesis eventually comes loose and revision surgery is required.

Ten-year follow-up

Zijlstra is the first person to have conducted a study looking at the differences in results between metal-on-metal and metal-on-plastic prostheses over a ten-year period. The study showed that the metal-on-metal hip prosthesis is no better than the metal-on-plastic version. Zijlstra’s laboratory work indicates that bone cells are harmed by the cobalt and chromium metal ions given off by the prosthesis. The long-term results of Zijlstra’s study have been incorporated in a new recommendation on hip prostheses by the Dutch Orthopaedic Association (NOV). The NOV recommends caution with the use of metal-on-metal prostheses and regular check-ups.

Larger head

Zijlstra also looked into the size of the femoral head and found that while a total hip replacement with a 48mm head provides slightly greater hip joint mobility, the difference between that and the smaller 28mm head was small. The large head does not therefore have any advantages as regards mobility.

Curriculum vitae

Wierd Zijlstra (Assen, 1972) studied Medicine and Human Movement Sciences at the University of Groningen. He conducted his research at the Orthopaedics Departments of the Martini Hospital in Groningen and the University Medical Center Groningen (UMCG). His PhD thesis is entitled ‘Metal-on-metal total hip arthroplasty: clinical results, metal ions and bone implications’. Zijlstra specialized in hip and knee prosthesiology while working as an orthopaedic surgeon in Sydney and he is currently working at Medisch Centrum Leeuwarden.