Treatment of recurrent THR dislocation using of a cementless dual-mobility cup: A 59 cases series with a mean 8 years' follow-up

Introduction: Instability is one of the most feared complications following total hip replacement (THR). In France, dual-mobility cups are widely used in acetabular revision for instability; few studies, however, have focused on this type of implant. Hypothesis: The gain in stability provided by the dual-mobility implant allows the risk of dislocation to decrease by the sole revision of the acetabular component in case of recurrent instability. Objectives: This hypothesis was tested over medium-term follow-up of a series of cementless dual-mobility cups implanted during isolated acetabular revision for recurrent dislocation. Patients and methods: A series of THR revision for instability was analyzed retrospectively. Inclusion criteria were: recurrent THR dislocation treated by cementless dual-mobility cup, between 1995 and 2001. Radiological analysis used Imagika (TM) software. Fifty-nine patients were included; nine died before radioclinical follow-up could be performed; none of the survivors were lost to follow-up. Mean follow-up was 8 years (range, 6-11 years). Results: There was one early dislocation without recurrence; the dislocation rate was 1.7%. At follow-up, mean PMA score was 16.5 (12-18) and mean Harris score 86.7 (49-99). Radiologically, there was no loosening or migration, but 19% of X-ray views showed less than 1 mm wide peri-acetabular radiolucency. With dislocation as censoring criterion, 8-year survivorship was 98% (95% CI: 95-100%). Discussion: The dislocation rate (1.7%) and clinical results were better than in most series of revision by constrained cup for recurrent dislocation. The high rate of peri-acetabular radiolucency would seem to relate to the external coating of the cup: aluminum oxide in the Novae-1 implant and aluminum oxide/hydroxyapatite in the Novae-E. Conclusion: The use of dual-mobility cups to treat THR instability gave satisfactory results. We recommend dual-mobility cups with hydroxyapatite surface treatment over a porous metallic substrate, rather than with an aluminum oxide or an aluminum oxide/hydroxyapatite bilayer coating.