VI. Outcomes of Revision for Failed Metal on Metal Hip Replacement
D W Murray
In 2009, we published results of our first series of revisions for failed metal on metal hip resurfacing.1 We found that the results depended profoundly on the reason for revision. When the revision was for a soft tissue reaction, which we called a pseudotumour, the results were poor, otherwise they were good. For non- pseudotumour revision the outcome scores, as assessed by the Oxford Hip Score (OHS), were similar to the outcome scores of matched primary hip replacements and the level of complications was acceptable. In contrast, if the revisions were for pseudotumours then the outcome scores following revision were nearly as bad as the pre-operative scores of patients due to have a hip replacement. In addition, the incidence of complications was unacceptably high: About 50% of patients had major complications, which included dislocation, loosening of the acetabular component and nerve or vessel injury. In addition, about one third have required re-revision. The dislocations were primarily the result of massive soft tissue damage, particularly to the abductor muscles. It is not clear why the acetabular loosening occurred but it may be that the remaining metal debris interfered with bone in-growth. During the re- revisions it was noted that the majority had recurrence of pseudotumours. This was probably because there was remaining metal debris which continued to cause soft tissue damage. This also probably explains why there were further neurovascular problems.
At the time we were doing the revisions during our first series we did not appreciate the amount of soft tissue damage that metal debris could cause. Therefore our primary indication for revision was patient symptoms. By the time patients with pseudotumour develop significant symptoms there is often severe soft tissue destruction. As a result of this soft tissue destruction the results of revision were poor. In view of this, we recommended that consideration should be given to early revision when there is pseudotumour. It is therefore important that if patients have symptoms following metal on metal hip replacement that they are investigated with cross-sectional imaging, such as an ultrasound or MRI scan and possibly metal ions. For some types of metal on metal hip replacement it is sensible to do this imaging, even if the patients are asymptomatic. On the basis of the symptoms and investigations a decision about revision can be made. If it is not clear whether to revise or not then it is sensible to repeat the scan after a period to determine if the lesion is enlarging. With earlier revision for pseudotumour our results of revision surgery have improved. However, with aggressive lesions the results are still disappointing.
1. Grammatopolous G, Pandit H, Kwon YM, Gundle R, McLardy-Smith P, Beard DJ, Murray DW, Gill HS. Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg Br 2009;91-8:1019-24.