Results and outcome predictors after revision surgery for severe acetabular bone defects

INTRODUCTION The aim of this study was to assess results of different revision techniques for large acetabular bone defects identifying possible outcome predictors of the surgery. METHODS This retrospective study was carried out on 33 consecutive patients (22 females, 11 males) who underwent acetabular revision at our Institution for Paprosky grade II B and III (GIR 3or 4) acetabular bone defects. The average age at surgery was 67.1 years (range, 42 to 86). Burch-Schneider reinforcement cage and a cemented cup was used in 25 cases , trabecular metal revision shell in 6 cases, and LOR cup in 2 cases. The mean time between primary and revision procedure was 9.1 years and the mean follow-up was 48 months (range, 14 to 112). The Harris Hip Score (HHS) was obtained preoperatively and at latest follow-up. Pain at follow-up was evaluated using a 10-cm Visual Analog Scale (VAS). In 27 patients a follow-up radiographic evaluation was also performed. Determinants of HHS score at follow-up were assessed by linear regression analysis, using age, sex, BMI, rate of comorbidity (FCI), use of reinforcement ring, and time elapsed from the primary surgery as explanatory variables. RESULTS The average preoperative and follow-up HHS score was 41 ± 16 and 79 ± 13, respectively (p <0.001). The average pain reported on the VAS scale at follow-up was 3.2 ± 1.7. The overall re-revision rate was 18% (6/33patients). At the multivariate analysis the only negative determinant of HHS at follow-up was the level of comorbidity according to FCI (c = -5.3, p = 0.007). With the numbers available, the different surgical options were not associated with a difference in the functional outcome. Three Burch-Schneider reinforcement cages with long follow-up showed signs of radiographic loosening. In cases of intrapelvic acetabular protrusion of the primary cup, the use of revision tantalum trabecular metal components was associated with bone formation around the implant at latest follow-up. DISCUSSION Our results are in keeping with previously published data, that showed bone formation occurring on tantalum trabecular metal acetabular components. In the present study, comorbidity was a negative predictor of the functional outcome of revisions for severe acetabular bone defects. CONCLUSION Positive medium-term clinical results were detected with acetabular reinforcement cages and trabecular metal revision shells in severe acetabular bone defects. However, problems with the long-term duration of Burch-Schneider reinforcement cages might arise.