Delay in Diagnosis of Invasive Surgical Site Infections Following Knee Arthroplasty Versus Hip Arthroplasty

Background. The timing of diagnosis of invasive surgical site infection (SSI) following joint replacement surgery is an important criterion used to determine subsequent medical and surgical management. Methods. We compared time to diagnosis of invasive SSI following hip vs knee arthroplasty. SSIs were included in the analysis if they occurred within 365 days following procedures performed from 1 January 2007 through 31 December 2011 at 36 community acute care hospitals and 1 ambulatory surgery center in the Duke Infection Control Outreach Network. A Cox regression model was fitted to estimate the association between procedure type and time to diagnosis of SSI, adjusted for age, pathogen virulence, American Society of Anesthesiologists' score, and hospital surgical volume. Results. Six hundred sixty-one invasive SSIs were identified; 401 (61%) occurred following knee arthroplasties. The median time to diagnosis of SSI was 25 days (interquartile range [IQR], 17-48 days) following hip arthroplasty vs 42 days (IQR, 21-114 days) following knee arthroplasty (unadjusted hazard ratio [HR], 1.60; 95% confidence interval [CI], 1.37-1.87; P < .001). Time to diagnosis of invasive SSI remained significantly shorter for hip than for knee arthroplasties after adjusting for age, pathogen virulence, and hospital surgical volume (HR, 1.51; 95% CI, 1.28-1.78; P < .001). Conclusions. The diagnosis of invasive SSI was delayed following knee arthroplasty compared with hip arthroplasty. We hypothesize that differences in symptom manifestation and disparities in access to care may contribute to the observed differential timing of diagnosis. Our findings have important implications for the management of prosthetic joint infections, because treatment strategies depend on the timing of diagnosis.