[Hydroxyapatite-coated Esop modular femoral stem: three to ten year outcome in 155 cases].

PURPOSE OF THE STUDY: Primary and secondary stability of the Esop prosthesis depends exclusively on cementless metaphyseal anchoring. This modular implant is composed of an hydroxyapatite-coated metaphysis on which a diaphyseal piece is added intraoperoperatively simply to act as a centering device. The purpose of this retrospective analysis of a consecutive series was to assess primary and secondary stability of the Esop implant by measuring axial migration over time.

MATERIAL AND METHODS: Between 1995 and 2001, 172 primary total hip arthroplasties (THAs) were performed with the Esop femoral implant and the Atlas III acetabular implant. Six patients lost to follow-up and eleven patients who died were excluded from the analysis. The review thus concerned 155 THA in 128 patients (66 women and 32 men), mean age 57 years (age range 28-77 years), 53% with an occupational activity at the time of surgery. Degenerative hip disease and aseptic osteonecrosis were present in 87% of patients. Imagika, a dedicated software, was used to measure axial migration and overall offset of the THA at four distinct times: on the immediate pre- and postoperative films, after introduction of weight-bearing, and at last follow-up (mean 61 months, range 35-114 months). Survival and clinical and radiographic outcome were also assessed with the Postel-Merle-d'Aubigné (PMA) score.

RESULTS: THA survival was 98%, all causes of failure included. The PMA score showed 97% excellent, very good or good outcome. Axial migration greater than 5 mm was demonstrated in ten hips (6.4%). Among these ten, seven exhibited migration during the first month than did not move further up to last follow-up. Comparison between the pre- and postoperative images revealed a 10 mm reduction in offset in 38% of hips, showing that the hip rotation center was medialized.

DISCUSSION: Migration observed in ten implants corresponded to restablization at weight-bearing in seven. There was no correlation with the clinical outcome or poor radiological osteointegration.

CONCLUSION: Primary and secondary stabilization of the Esop implant is satisfactory. In this series, the rotation center of the hip was globally medialized so that it would be useful to have available lateralized implants.