Abstract
INTRODUCTION
The risk of dislocation in large diameter metal on metal hip replacement is significantly lower than in standard THR. This is due to the increased primary arc, increased jump distance and possibly a suction effect. Our unit has performed over 1500 of these cases with an overall revision rate of <1%. We report a case series of dislocations in 5 large diameter metal on metal hips undertaken at our unit.
METHOD
All cases were reduced closed and investigated for cause of dislocation. Radiological investigation included plain film radiographs and CT to exclude component mal-position and MRI to document soft tissue deficiency. Metal ion levels were measured and microbiological investigation was undertaken.
RESULTS
In all cases component positioning was acceptable. Metal ion levels were significantly elevated with levels comparable to published work. MRI showed significant soft tissue defects in all patients. At revision all were found to have necrotic areas associated with a large turbid effusion. Histology confirmed metal related inflammatory change and microbiology specimens confirmed the absence of infection.
DISCUSSION
The local detrimental effects of metal debris are well documented. We believe this is the first series with a proven link between these soft tissue problems and dislocation. Every case of large diameter metal on metal hip in our unit that has dislocated has been proven to be associated with metallosis and has required revision.
