PREOPERATIVE DESCRIPTION OF SEVERE ACETABULAR DEFECTS CAUSED BY FAILED TOTAL HIP-REPLACEMENT

Purpose: The reconstruction of severe acetabular defects, caused by fa iled hip prostheses, is difficult and complex. Current radiographic de scriptions of the defects are inadequate. We sought to more accurately describe remaining bone and improve surgical planning using 3D physic al models based on CT data. Method: Nineteen patients (20 hips) with f ailed total hip replacements and severe acetabular defects were select ed. Plain radiography and CT were performed. Solid 3D physical models of each pelvis were constructed using the CT data. Bone loss in struct urally important regions was measured from radiographs, models, and in traoperative observation. Comparisons were made of the radiograph-base d and model-based bone loss measurements, surgical plans, and interobs erver variability. Results: There was no statistical difference betwee n the model-based measurements and the intraoperative measurements. Ra diographs statistically underestimated bone loss by at least 20% (p < 0.01), Interobserver bone loss grading was poor for the radiograph-bas ed measurements (kappa = 0.06) but was substantial for the model-based measurements (kappa = 0.73). In only half the cases was prosthesis ty pe correctly selected based on radiographs. Model-based planning selec ted the correct prosthesis type in all cases. Conclusion: The physical models were substantially more accurate than radiographs for measurin g acetabular defects and for surgical planning.