There are differences in the reasons for revision when M/M and M/P bearing surfaces are compared. The cumulative incidence of reason for revision demonstrates a higher incidence of revision for loosening/lysis, metal related pathology and infection for the M/M group. The cumulative incidence for these three revision diagnoses for M/M at thirteen years is 4.8%, 8.0% and 1.8% respectively compared to MoP 2.5%, 0.0% and 0.8% respectively (Figure MM7). It is uncertain why there is a higher incidence of reported infection. The diagnosis of infection is reported to the Registry at the time of surgery and has not been confirmed by linking to results of microbiological investigation. The differences in the reasons for revision between M/M and M/P are more evident in the M/M prostheses with a head size greater than 32mm. Metal related pathology is largely confined to head sizes greater than 32mm. The cumulative incidence of metal related pathology at ten years is 9.5% for head sizes greater than 32mm and 0.3% for head sizes 32mm or less. The incidence of metal related pathology is potentially higher as it is possible that undiagnosed metal related pathology contributes to the increased rate of loosening/lysis and infection reported in M/M articulations with larger head sizes (Figure MM8). The Registry has also identified that lysis, as the sole diagnosis for revision, is reported with the highest frequency in metal on metal articulations. In the M/M bearing group, the Metasul articulation is the principal recorded femoral head used with a head size of 32mm or less. It accounts for 85.2% of all the M/M bearings with this head size. In order to determine if the higher revision rate of M/M articulations with greater than 32mm head sizes is prosthesis specific, the Registry has analysed all prosthesis head/acetabular combinations with head size greater than 32mm with more than 200 procedures. There are 13 combinations that meet these criteria and the cumulative percent revision ranges from 4.3% to 37.2% at seven years (Table MM10).
Posted on: Tue, 28 Oct 2014 10:03:38 +0000
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