Abstract
AIMS: Modular revision stem fracture is a rare but difficult complication after hip arthroplasty revision. The purpose of this German Arthroplasty Registry (EPRD)-based study was to investigate whether the overall re-revision rate and the re-revision reasons of modular revision stems compared with monobloc stems are different. METHODS: A total of 291 re-revisions occurring within five years after implantation of a revision stem (n = 2,039) documented in the EPRD were analyzed using Kaplan-Meier survival analysis and Cox regression. Stem type (modular: n = 1,026, monobloc: n = 1,013) and revision reason were investigated as independent variables, while BMI, sex, age, hospitals' annual revision volume, and Elixhauser score were treated as confounding variables. Cases with an infection at index surgery were analyzed separately. RESULTS: Re-revision risk after five years was similar for either stem type (modular: 18.7% ( 95% CI 15.9 to 21.9); monobloc: 15.6% (95% CI 13.2 to 18.4); p = 0.200). One stem fracture of a modular revision stem was reported. The main reasons for re-revision were infection (modular/monobloc: 50%/60% of all revisions; p = 0.200), dislocation (19.8%/9.6%; p = 0.045), and loosening (12.2%/11.4%; p > 0.999). An Elixhauser score of 4 and above was associated with a higher hazard ratio (HR) for re-revision for either stem type (modular/monobloc: HR 2.01; p = 0.026/HR 2.44; p = 0.004), as well as a BMI category above 25/40 (modular/monobloc: HR 1.73 to 3.25; all p < 0.025/HR 3.61; p < 0.001). An infected index surgery increased the re-revision risk after one year to 26.0% (95% CI 22.2% to 30.3%) compared with 8.3% for noninfected cases (95% CI 7.0% to 9.8%) (p < 0.001) independent of stem type. CONCLUSION: A high BMI increases the HR for revision for either stem design but not due to mechanical implant failure. Infection at the index operation increases re-revision risk significantly, and is also the dominant reason for re-revision independent of stem type.