Assessing the results of thrust plate prosthesis: a comparison of four different rating systems

OBJECTIVE: To evaluate four rating systems designed to assess patients following provision of a thrust plate prosthesis. SUBJECTS: Sixty-one patients undergoing total hip replacement with thrust plate prosthesis. DESIGN: Patients were evaluated preoperatively and six months postoperatively by four different hip rating systems (Harris, Iowa, Charnley and Merle d'Aubigne), both on a categorical and on a numerical basis. SETTING: Department of orthopaedics and traumatology in a university hospital. MAIN OUTCOME MEASURES: Patients were evaluated by four rating systems preoperatively and postoperatively either on a categorical or a numerical basis. RESULTS: All patients showed significant improvement after surgery in all rating systems. Although preoperative categorical evaluation revealed that the strongest correlation was between Charnley and Merle d'Aubigne scores (r = 0.876), numerical comparison of the rating systems showed strong correlation among all systems, both pre- and postoperatively. Responsiveness analysis revealed larger effect size for the Iowa and Harris hip scores. CONCLUSIONS: Our results suggest that hip rating systems should be compared numerically rather than by categorical evaluation and that the Iowa and Harris hip scores are more convenient in evaluating thrust plate prosthesis patients because they have larger effect sizes without floor and ceiling effects.