Surgeon-stratified cohort analysis of 1976 cementless Zweymüller total hip arthroplasties from a single hospital with 23,255 component years of follow-up.

INTRODUCTION: The third-generation Zweymüller hip endoprosthesis has been used for decades with excellent results in arthroplasty registries, but surgeon-stratified reports on this implant are still scarce. The aim of the presented single-hospital cohort analysis of the third-generation Endoplus-Zweymüller primary total hip arthroplasty was to determine implant survival rates until the first revision/removal at 10/15/20/25 years after implantation and to find out whether implant survival depended on the operating surgeon, patient's age and gender, operated side (right/left), season of the year and the set of implanted components (SL-PLUS femur, BICON-PLUS acetabulum or both components).

MATERIALS AND METHODS: The retrospective observational cohort study included 1976 consecutive patients with primary BICON/SL-PLUS Zweymüller hip endoprosthesis implanted at the same operating theater block of the University Medical Centre Ljubljana, Department of Orthopaedic Surgery (Ljubljana, Slovenia) between January 1, 1993 and May 1, 2014. Survival analyses were performed with the Kaplan-Meier method and the Cox regression analysis after minimum 5 and maximum 26 years of follow-up.

RESULTS: At 10/15/20/25 years after implantation, the cumulative proportion of revision-free surviving Zweymüller total hip endoprostheses was 92/90/85/81% and the cumulative proportion with unremoved immobile components was 93/91/87/84%, respectively. After adjustment for age, gender and operated side, less experienced surgeons (odds ratios 2.34-5.00), season of the year at primary implantation (spring vs. winter odds ratio 1.74) and the use of BICON-PLUS acetabulum with femoral stem from another manufacturer (odds ratio 2.23) were significant risk factors of worse implant survival.

CONCLUSIONS: The study presents the largest published third-generation Zweymüller BICON/SL-PLUS total hip arthroplasty cohort from a single non-developmental hospital with 23,255 component years of observation. Study findings indicate the impact of environmental factors at primary implantation and variability between different surgeons on the long-term implant survival.