Cirrhosis is a risk factor for total hip arthroplasty for avascular necrosis: A Danish nationwide cohort study

Deleuran, Thomas; Overgaard, Søren; Vilstrup, Hendrik; Jepsen, Peter

We examined one outcome: time to total hip arthroplasty for AVN. We followed the cirrhosis patients and the reference individuals from the index date to the date of total hip arthroplasty for AVN, date of death, or end of follow-up (December 31, 2011). We used stratifi ed Cox regression to estimate the hazard ratio (HR) of total hip arthroplasty for AVN in cirrhosis patients as opposed to reference individuals and adjusted these HRs for potential confounders. We found no violations of the proportional hazards assumption when we tested it using Schoenfeld residuals and checked it by inspecting the log-log plot. We used the cumulative incidence function with death as a competing risk to compute the 5-year risk of total hip arthroplasty for AVN. This analysis relies on non-informative censoring. There were 2 censoring events in our study cohort: end of study (on December 31, 2011) and migration. Both of these events are unlikely predictors of the risk of a total hip arthroplasty for AVN, so the censoring in our study cohort was non-informative. Alcohol intake is a well-known risk factor for AVN, and cirrhosis patients have a high prevalence of alcohol intake. We were concerned that the regression analysis would leave residual confounding, so we performed a supplementary analysis in which we used restriction to minimize confounding by alcohol intake. We repeated the regression analysis and restricted it to cirrhosis patients with unspecifi ed cirrhosis (ICD-10: K74.6) who had not been hospitalized for an alcohol-related disorder (see Supplementary data, Table 3 ), and the corresponding reference individuals. Reference individuals who had previously been hospitalized for an alcohol-related disorder were also left out of this analysis. All statistical analyses were performed using Stata version 12.1 and the R software package version 2.14 (R 2013).