HIGH EARLY FAILURE RATE WITH A LARGE HEAD METAL ON METAL HIP REPLACEMENT: THE IMPORTANCE OF MRI IMAGING

Abstract

Introduction: Although good mid-term results have been reported with some metal on metal hip replacements, reported complications due to metal on metal (MOM) related reactions are a cause for concern. We have assessed the clinical outcome and MRI metallic artefact reduction sequence (MARS) findings in a consecutive series of patients with a large head metal on metal hip replacement.

Methods: 62 ASR XL Corail THRs and 17 ASR resurfacings were performed at our hospital between 2005 and 2008. All patients were reviewed and assessed with an Oxford hip score (OHS), a plain radiograph and a MRI imaging was obtained on 76 (96%) hips. Implant position was assessed using Wrightington cup orientation software.

Results: At a mean follow up of 32 months, 9 (15%) ASR XL Corail THRs, and 2(12%) ASR resurfacings had been revised. 10 revisions were performed for MRI confirmed MOM related pathology. Histology confirmed a MOM reaction in all 10 cases.

Of the 76 hips that were MRI scanned, 27 (36%) had typical features of a MOM reaction. These were classified as mild in 10 (13%), moderate in 13 (17%) and severe in 4 (5%).

78 patients completed an OHS and the mean score was 21. The mean OHS was 29 pre-operatively in those that had been revised, 25 in patients with abnormal MRI findings and 20 in those with a normal MRI. 10 patients with abnormal MRIs had a near perfect OHS (15 or less)

Conclusions: The ASR XL Corail THR has an unacceptably high early failure rate. MARS MRI is able to detect metal debris related soft tissue pathology around metal on metal THRs. These lesions are sometimes asymptomatic. We suggest that MARS MRI evaluation should form part of the routine evaluation of all metal on metal THRs, and in particular of this implant.