CAUSES OF DISLOCATION OF TOTAL HIP-ARTHROPLASTY - CT STUDY OF COMPONENT ALIGNMENT

We reviewed radiographs and CT scans of 38 total hip arthroplasties wh ich had dislocated (36 posteriorly; 2 anteriorly) and compared the ali gnment of the prosthetic components with those of 14 uncomplicated art hroplasties. No difference was found between the alignment of the pros thetic components in the two groups. In the seven patients who had reo perations, the cause of dislocation diagnosed by CT was confirmed in o nly two cases (one retroversion of the cup and one protruding osteophy te). Muscular imbalance rather than malposition of the components was the major factor determining dislocation. CT allows accurate measureme nt of cup and neck anteversion but contributes little to preoperative planning.