Migration and Wear of a Dual Mobility Acetabular Construct at 3 Years Measured by Radiostereometric Analysis.

BACKGROUND

The anatomic dual mobility (ADM) acetabular component was introduced because of previously described low dislocation rates for this type of construct. The shape of the anatomic cup and the motion of polyethylene liner may have implications for acetabular cup fixation and polyethylene liner wear; therefore, the purpose of this study was to assess the migration patterns and wear rates of the ADM component using radiostereometric analysis.

METHODS

Uncemented ADM acetabular components were implanted in 27 patients. Radiostereometric analysis exams were taken at 6 follow-up visits over 3 years. Proximal translation and sagittal rotation of the cup and polyethylene total wear and wear rates were calculated. Oxford 12 Hip scores and satisfaction were recorded.

RESULTS

Mean proximal translation was below the 0.2 mm threshold at 2 years associated with acceptable long-term survivorship (0.16 mm [standard deviation {SD} 0.31] at 3 years). Mean sagittal rotation was 0.29 degrees (SD 1.03) and was greater in female subjects (P < .001). Following bedding-in, the annual wear rate was 0.02 mm/y, below the 0.1 mm/y threshold. There was no association between cup migration and polyethylene wear. Patient satisfaction at 3 years was 96%. Mean Oxford 12 Hip scores improved from 21 (SD 7) preoperatively to 43 (SD 7) 3 years postoperatively.

CONCLUSIONS

The ADM cup demonstrated stable migration at 3 years indicating low risk for aseptic loosening. Bedding-in in the first year was followed by low annual wear rates. These finding suggest no increased risk of the dual mobility and anatomic design on fixation or wear.