Re-Revision Risk of Modular and Monobloc Revision Stems After Revision Total Hip Arthroplasty

Implant fracture of modular revision stems is a major complication after total hip arthroplasty revision (rTHA). Studies looking at specific modular designs report fracture rates of 0.3% to 0.66% whereas fractures of monobloc designs are only reported anecdotally. It is unclear whether the overall re-revision rate of modular designs is higher and if, whether stem fractures or other revision reasons are responsible for this elevation. All revisions within 5 years after implantation of a revision stems (n 0 =13,900; n 5 =2506) were analysed using Cox regression with design (modular: n=17, monobloc: n=27), BMI, Sex and Elixhauser Score as independent variables. One stage and two stage revisions were analysed separately (1-stage: modular n= 7,102; monobloc n= 4,542; 2-stage: 1,551 / 704). The revision volume of the hospitals was also considered (low: <20 revisions, medium: 21–50 revisions, high: >50 revisions). For the 1-stage revisions, the re-revision risk after 4 years was 14,3% [13.2%, 15.5%] for monobloc and 17.4% [16.40%, 18.40%] for modular stems (p< 0.001). Stem fracture was the reason for re-revision in 2.4% of the modular (fracture rate 0.42%) and 0.6% of the monobloc revisions. The difference in re-revision rates between the designs was mainly due to differences in dislocation and stem loosening. For the 2-stage revisions, the revision risks for either design were similar (21.7% [18,5%, 25.4%] vs. 23.0% [20.8%, 25.4%]; p=0.05). Patient characteristics influenced the comparison between the two designs in the 1-stage group but very little in the 2-stage group. Modular revision stem fractures only contribute very minor to re-revision risk. In 2-stage revisions, no difference in overall re-revision rates between designs was observed. This might indicate that the differences observed for 1-stage procedures are due to differences between the patient cohorts, not reflected by the parameters available or surgeon choice.