Fig. 1. Selection process and flowchart of study population. A flowchart shows the selection process of study population. A total of 22,127 patients who underwent hip replacement arthroplasty (HRA) and 52,882 patients who underwent knee replacement arthroplasty (KRA) at 882 hospitals nationwide were finally enrolled in the analysis between January 1 and December 31, 2010. Multiple hospitalizations were defined as one episode of hospitalizaton if the interval between the two successive hospitalizations was less than 2 days. Index procedure: the first replacement arthroplasty during the study period. Index date: the first date of hospitalization during which the index replacement arthroplasty was performed.