The "true" incidence of surgically treated deep prosthetic joint infection after 32,896 primary total hip arthroplasties A prospective cohort study

Background and purpose - It has been suggested that the risk of prosthetic joint infection (PJI) in patients with total hip arthroplasty (THA) may be underestimated if based only on arthroplasty registry data. We therefore wanted to estimate the "true" incidence of PJI in THA using several data sources. Patients and methods - We searched the Danish Hip Arthroplasty Register (DHR) for primary THAs performed between 2005 and 2011. Using the DHR and the Danish National Register of Patients (NRP), we identified first revisions for any reason and those that were due to PJI. PJIs were also identified using an algorithm incorporating data from microbiological, prescription, and clinical biochemistry databases and clinical findings from the medical records. We calculated cumulative incidence with 95% confidence interval. Results - 32,896 primary THAs were identified. Of these, 1,546 had first-time revisions reported to the DHR and/or the NRP. For the DHR only, the 1-and 5-year cumulative incidences of PJI were 0.51% (0.44-0.59) and 0.64% (0.51-0.79). For the NRP only, the 1-and 5-year cumulative incidences of PJI were 0.48% (0.41-0.56) and 0.57% (0.45-0.71). The corresponding 1and 5-year cumulative incidences estimated with the algorithm were 0.86% (0.77-0.97) and 1.03% (0.87-1.22). The incidences of PJI based on the DHR and the NRP were consistently 40% lower than those estimated using the algorithm covering several data sources. Interpretation - Using several available data sources, the "true" incidence of PJI following primary THA was estimated to be approximately 40% higher than previously reported by national registries alone.