Additional file 1: Supplementary Table 1. Logistic regression analysis of factors associated with having confusion following elective primary hip and knee arthroplasty. Supplementary Table 2. Logistic regression analysis of factors associated with having a delayed discharge (length of stay over 3 days) following elective primary hip and knee arthroplasty. Supplementary Table 3. Reasons for reattendance/readmission in those with post-operative hyponatraemia. Supplementary Table 4. Comparison of demographics of hip and knee replacements patients in the current audit of 1,000 Joints and the 10th Annual National Joint Registry Report 2013