Readmission Rates After Total Hip Arthroplasty—Reply

In Reply: Mr Zmistowski and colleagues note that the increase in readmissions that we observed between 1991 and 2008 might result from myriad factors, including the increase in comorbidities in primary and revision hip arthroplasty patients. Although our study presented only unadjusted readmission rates, we conducted additional analyses as they requested. Our observation of rising readmission rates persisted after adjusting for changes in patient demographics and comorbidity. Between 1991 and 2008, 30-day unadjusted readmission rates for primary total hip arthroplasty increased from 6.1% to 9.8% while adjusted readmission rates increased from 7.2% to 10.1%. For revision total hip arthroplasty between 1991 and 2008, unadjusted readmission rates increased from 8.9% to 15.9% while adjusted readmission rates increased from 10.6% to 16.1%. Thus, we think that the increase in readmission rates is unlikely to be attributable to changes in patient demographics or comorbidity alone.