Patient weight more than body mass index influences total hip arthroplasty long term survival.

The effect of obesity on the long-term survival of total hip arthroplasty remains under discussion. Reviewing meta-analyses of large cohort studies a high body mass index has been correlated with a higher incidence of complications but not univocally with a lower implant survival rate. It has been suggested that body weight rather than body mass index might be a better parameter to evaluate prosthesis outcome. We reviewed 27,571 patients retrospectively with primary arthritis as a preoperative diagnosis. Patients were divided into 4 categories based on their body mass index, or into two groups based on the body weight (<80 kg and =80 kg). Implant survivorship was estimated with use of the Cox proportional hazards model with revision for aseptic loosening as the end point. Results were stratified for sex and implant tribology. When body mass index was used the 10 years implant survival in obese versus non-obese patients was not statistically different (p=0.058), but when body weight was used a statistically different implant survivorship was found for men (p=0.009). Therefore, weight rather than than body mass index influences survival of hip prostheses, and should be used as the discriminant parameter for further studies.