MID-TERM RESULTS OF MÜLLER ROOF REINFORCEMENT RING IN TOTAL HIP ARTHROPLASTY

Abstract

The purpose of our study was to find out the midterm results of the Müller acetabular roof reinforcement ring in primary and revision total hip arthroplasty. From 1988 to 1998, 48 total hip arthroplasties using the acetabular roof reinforcement ring (39 patients) was performed by one surgeon (PDB).

We reviewed all patients who had a minimum of five year follow up. There were 37 hips (31 patients) with a mean follow up of 7 years (5 to 12 years). Acetabular deficiencies were classified according to the AAOS classification. Acetabular reconstruction was done using the Müller acetabular roof reinforcement ring with the polyethylene cup cemented to the ring, and morcellized cancellous bone graft. Müller straight stem femoral prosthesis was used in all cases for femoral reconstruction. All patients were followed up annually and outcome assessed using Harris hip score. There were 27 primary procedures and 10 revisions. 30 patients (81%) had cavitary, 2 (5%) had segmental and 5 (14%) had combined defects.

Survival analysis was done with failure defined as radiological evidence of loosening of the acetabular component. Statistical analysis was done using SPSS for Windows (SPSS Inc, Chicago, Illinois). 5 patients died due to unrelated causes and 2 patients were lost for follow up. The mean Harris hip score improved from 42 preoperatively to 82 postoperatively (p< 0. 001)(Wilcoxon Signed Rank test). Both mean pain and function score showed improvement from 12 to 39 postoperatively (p< 0. 001) and 12 to 32 (p< 0. 001) respectively. 5 patients had radiological loosening of the ring. The migration rate was 13%. The cumulative survival rate at 12 years, excluding all patients who died and were lost for follow up, was 79. 3% (95% confidence interval 71. 4 to 87. 2, standard error 4). There was no statistical difference in the failure rate between primary and revision procedures (chi-square test). This series show satisfactory medium term results with Müller roof reinforcement ring and cancellous bone graft in acetabular deficiencies with poor bone stock.