Dynamic test to diagnose loose uncemented femoral total hip components

A new computed tomographic rotation study was developed to determine the stability of uncemented femoral components after total hip arthroplasty. The computed tomographic rotation study measures femoral component version with the leg in maximum external and internal rotation. The component is considered rotationally unstable, and thus loose, if these angles differ by more than 2 degrees. The results of the computed tomographic rotation study were confirmed with intraoperative inspection in 50 patients: 13 patients (Group A) with definite radiographic loosening, 22 patients (Group B) with equivocal radiographic loosening, and 15 patients (Group C) with documented stability. The results of the computed tomographic rotation study agreed with intraoperative findings for all patients in Groups A and C, and 20 of 22 patients in Group B (1 false negative and 1 false positive). Statistical analysis of Group B showed that the computed tomographic rotation study had a sensitivity of 91.6% and a specificity of 90.0%. The positive predictive value was 91.6%. These results indicate that the computed tomographic rotation study can supplement equivocal radiographic findings in assessing loosening of an uncemented femoral component.