From a surgical point of view, total hip arthroplasty is a well-standardized operation that has proven to be very effective. However, failure can sometimes occur in the immediate postoperative period or even some years after. According to the NICE guidelines, for a hip prosthesis to be considered safe its mean survival rate should be at least 90% at ten years1. Although the failure rate is low, it varies greatly and can be influenced by several factors, such as the type of prosthesis used and the patient's characteristics, and whereas the patient's characteristics are practically unchangeable, factors related to s and their choices can be modified. The literature includes numerous studies analysing factors that influence hip prosthesis failure, but they often concern small series of patients. Poon observed that weight and age influenced the outcome of total hip arthroplasty (THA) using cemented prostheses2. Kobayashi studied a consecutive series of 293 primary cemented Charnley prostheses and found that rapid wear of polyethylene and abnormal geometry of the femoral medullary canal affect prosthesis survival3. Kolundzic found that demographic factors explained only a minor part of the survival variability of 82 cementless acetabular cups4.
The largest series concerned only patients treated using cemented prostheses. Among them Berry analysed 2000 primary Charnley prostheses at 25 years' follow-up and found that age, gender and underlying diagnosis affected long-term survivorship of both components5. Dawson compared 598 cemented prostheses and found no significant differences between the performance of the two models6. As clearly stated the weakness of all the long-term studies depends on the fact that they assess the success or failure of old technologies and designs7. Comparison among prostheses with different fixation (cementless vs cemented) is limited to few clinical trials that indicate the better performance of cementless components8-10.
Analyses performed on data from northern European registers only partially fill this gap since there is a clear-cut prevalence of cemented prostheses with metal-polyethylene couplings.
In fact, 93.1% of prostheses implanted in patients in Sweden between 1979-200411, and 80% of those used in Norway between 1987-200412 were cemented. The figure is lower in Denmark, 49.8% between 1995-200413, and in Finland 55% from 1980-200314. The data collected for the UK were only for 2004, and although they included cemented prostheses in 49% of cases, they cannot be used for an effective analysis15.
However, an analysis of the data from the Norwegian resister Furnes revealed that in over 53,000 operations some diseases (femoral neck fracture sequelae, congenital hip dysplasia, and rare diseases) represent risk factors for prosthesis survival16. When limiting the analysis to young osteoarthritic patients, Eskelinen found that age and gender influence the result17. The Danish register identified age and gender as confounding factors in the evaluation of prosthesis survival13.
None of these analyses, due to the nature of the operations analyzed, considered the influence of the type of prosthesis fixation among the possible risk factors. Only when analysing the Finish data Visuri find that low age, male gender, uncemented prostheses and first 10 year-period of surgery were risk factors for loosening of the prostheses18. Therefore, we analyzed the data of a series of patients with a minimum of six years' follow-up taken from the RIPO register (Register of Orthopedic Prosthetic Implantology), which includes cemented and uncemented prostheses, to determine the influence of patient characteristics's experience, and type of prosthesis used, on the o