Mortality and adverse joint outcomes following septic arthritis of the native knee: a longitudinal cohort study of patients receiving arthroscopic washout

BACKGROUNDThe short and long-term consequences of septic arthritis are uncertain. The purpose of this study was to determine the risk of mortality and adverse joint outcomes following septic arthritis of the native knee.
METHODSA retrospective cohort study of patients undergoing knee washout for septic arthritis, without prior knee surgery, was performed utilising the national hospital database for England over twenty-years. The rate of mortality within 90-days, and the 1-year and long-term rate of adverse joint outcomes (arthrodesis, amputation, arthroplasty), was determined. The mortality rate for patients with a primary admitting diagnosis of septic arthritis (ICD-10; M00) was compared to cases where this was a secondary diagnosis.
FINDINGS12132 patients were included (mean age 56.6 years; SD 24.9; 36% [4307/12132] female). Of the 10195 (84%) cases with septic arthritis as the primary admitting diagnosis, the 90-day mortality rate was 7.05% (719/10195; 95% CI 6.56-7.57) rising to 22.69% (418/1842; 95% CI 20.80-24.68) for patients aged over 79-years. Secondary septic arthritis was associated with adjusted odds for mortality of 2.10 (odds ratio; 95% CI1.79-2.46; p<0.001). The 1-year rate of arthrodesis was 0.13% (15/11393; 95% CI 0.07-0.22), amputation 0.40% (46/11393; 95% CI 0.30-0.54), and arthroplasty 1.33% (152/11393; 95% CI 1.13-1.56). Within 15-years, 8.76% (159/1816; 95% CI 7.50-10.15) underwent arthroplasty, corresponding to an annual risk of 6.14 times (risk ratio; 95% CI 4.95-7.62; p<0.001) that of the general population.
INTERPRETATIONThe consequences of septic knee arthritis (in a cohort of patients undergoing arthroscopic knee washout) are serious, with a 7% risk of mortality within 90-days, greater than 1% risk of adverse joint outcomes within 1-year, and 9% risk of knee arthroplasty within 15-years. These findings highlight the potentially devastating outcomes associated with sepsis from musculoskeletal joint infection.