Correlation between biometric variables and size of prosthetic components in primary total hip arthroplasty: a registry study

Total hip arthroplasty (THA) is considered one of the most successful surgical procedures in Orthopaedics. The outstanding benefits that patients achieve undergoing this operation are well above the risks of postoperative complications and failures. The increase of life expectancy of the population and the higher functional demand of elderly patients have made this procedure very popular. Joint registries were born in the 1970s in Scandinavia and they represent a significant help for innovation and research. National registries are powerful tools for arthroplasty because they allow to organise the information collected during surgeries, with the intention to guide surgeons in their technical decisions. Recently, a new functional horizon has been set by the establishment of the firsts unified and universal registries, which go beyond the boundaries and limitations of the single nation. In this study, using the Swiss implant registry (SIRIS), we collected data from 395 patients that received a primary THA between 2012 and 2021 in two hospitals of the Cantone Ticino (Switzerland). The aim was to investigate the correlation between the biometric parameters of the patients (age, sex, height, weight and BMI) and the dimension of the femoral stem and the acetabular cup. Only one type of implant was considered in this study: the Corail uncemented stem (femoral component) with the Pinnacle cup (acetabular component). We observed the existence of a correlation between stem size and age, height, weight and sex of the patients and a correlation between acetabular diameter and sex, height, weight and BMI. However, only age, height and sex influenced significantly the size of both components, while weight and BMI didn’t show any influence. Particularly, as stature increases, bigger components are required in order to achieve the adequate press-fit fixation in larger bones. Males are in general higher the females, confirming the influence of sex as well. With increasing age, the dimensions of the femoral canal and the acetabulum tend to be bigger due to resorption bone, a characteristic feature of elderly patients. In conclusion, the biometric variables of age, sex and height have a strong influence on the dimension of the THA components and could guide surgeons in their practical choices.