Preoperative description of severe acetabular defects caused by failed total hip replacement

Purpose: The reconstruction of severe acetabular defects, caused by failed hip prostheses, is difficult and complex. Current radiographic descriptions of the defects are inadequate. We sought to more accurately describe remaining bone and improve surgical planning using 3D physical models based on CT data. Method: Nineteen patients (20 hips) with failed total hip replacements and severe acetabular defects were selected. Plain radiography and CT were performed. Solid 3D physical models of each pelvis were constructed using the CT data. Bone loss in structurally important regions was measured from radiographs, models, and intraoperative observation. Comparisons were made of the radiograph-based and model-based bone loss measurements, surgical plans, and interobserver variability. Results: There was no statistical difference between the model-based measurements and the intraoperative measurements. Radiographs statistically underestimated bone loss by at least 20% (p < 0.01), Interobserver bone loss grading was poor for the radiograph-based measurements (kappa = 0.06) but was substantial for the model-based measurements (kappa = 0.73). In only half the cases was prosthesis type correctly selected based on radiographs. Model-based planning selected the correct prosthesis type in all cases. Conclusion: The physical models were substantially more accurate than radiographs for measuring acetabular defects and for surgical planning.