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

Background: The short-term and long-term consequences of septic arthritis are uncertain. We aimed to determine risk of mortality and adverse joint outcomes following septic arthritis of the native knee.

Methods: We did a retrospective cohort study in patients who received arthroscopic knee washout for septic arthritis in England between April 1, 1997, and March 31, 2017, using data in the national Hospital Episode Statistics database. Patients with previous knee surgery to the same knee were excluded. Mortality within 90 days, adverse joint outcomes (arthrodesis, amputation, arthroplasty) within 1 year, and arthroplasty within 15 years were determined. Mortality in patients with a primary admitting diagnosis of septic arthritis (ICD-10) was compared with that in patients in whom septic arthritis was a secondary diagnosis.

Findings: 12 132 patients were included (mean age 56·6 years [SD 24·9]) of whom 4307 (36%) were female. In 10 195 (84%) patients with septic arthritis as the primary admitting diagnosis, 90-day mortality was 7·05% (95% CI 6·56-7·57; 719 patients), rising to 22·69% (20·80-24·68; 418 patients) in 1842 patients older than 79 years. Secondary septic arthritis diagnosis versus primary diagnosis was associated with an adjusted odds ratio for mortality of 2·10 (95% CI 1·79-2·46; p<0·0001). In 11 393 patients with at least 1 year follow-up, the 1 year rates were 0·13% (95% CI 0·07-0·22; 15 patients) for arthrodesis, 0·40% (0·30-0·54; 46 patients) for amputation, and 1·33%; (1·13-1·56; 152 patients) for arthroplasty. Within 15 years, 159 (8·76%; 95% CI 7·50-10·15) of 1816 patients had received arthroplasty, corresponding to an annual risk of arthroplasty that was about six times that of the general population (risk ratio 6·14, 95% CI 4·95-7·62; p<0·0001).

Interpretation: The consequences of septic knee arthritis in patients undergoing arthroscopic knee washout are serious. These findings highlight the potentially devastating outcomes associated with sepsis from musculoskeletal joint infection.

Funding: National Institute for Health Research.