Disassembly of cemented bipolar prothesis of the hip.

A case of spontaneous disassembly of a bipolar prothesis after hemiarthroplasty due to a dislocation of the hip in an 85-year-old woman is presented, which is a rare complication. Open reduction was performed and original components were used because there was no acetabular and polyethylene linear erosion. The result was satisfactory at final follow-up (36 months), and radiographs showed no acetabular erosion, polyethylene wear, femoral subsidence, or component migration. To date, only 6 cases of disassembly of bipolar components have been reported in the English literature. In almost all cases, the injury was caused without any significant force, as only 2 patients reported a fall. Most were elderly women. We classified them into 3 types according to the etiology: iatrogenic disassembly (type I), erosion of the polyethylene liner (type II), and spontaneous disassembly (type III). Spontaneous disassembly is uncommon and seemed to be caused by a failure of the locking mechanism between the head components, resulting in an intraacetabular dislocation. Open reduction is required and revision surgery is judged by the locking mechanism between components. When there is no acetabular and polyethylene linear erosion, we believe that the original components can be used again. Although the potential disadvantage of bipolar systems shown here does not outweigh the advantages, we should rethink the status of bipolar hemiarthroplasty.