Aetiology and Management of Acute Septic Arthritis and Prosthetic Joint Infection Presentations to Orthopaedics: An Evaluation of Tertiary Centre Performance.

Background Septic arthritis (SA) and prosthetic joint infection (PJI) are common emergency referrals to orthopaedics in the United Kingdom. These infections carry a significant risk of harm due to chondrolysis and arthropathy and are a potential source of sepsis, requiring prompt assessment, investigation, and treatment. A joint aspirate is routinely sent for microscopy, culture , and sensitivities to aid treatment. In suspected PJI, this must be taken under sterile conditions to reduce the risk of iatrogenic PJI. Empirical antibiotics should then commence per the British National Formulary (BNF) or local policy. Due to the risks of delayed or ineffective treatment, evaluating local practice may identify areas to optimise treatment delivery and efficacy. Aims This study will evaluate the incidence of SA and PJI within a tertiary orthopaedic centre over 12 months. The culprit organisms and sensitivities, delivery of timely and appropriate antibiotics, serum infection markers, length of stay (LOS), and mortality will be reviewed. Methods Admissions to the orthopaedic unit between November 2023 and October 2024 were screened using the ICD-10 codes for pyogenic arthritis, prosthesis infection, or infection following a procedure. Further review confirmed cases of SA or PJI, excluding unsuitable admissions. Each patient's electronic record was examined for demographics, serum infection markers, LOS, 30-day mortality, relevant imaging, time to aspirate relative to admission, culture results, and timing and type of antibiotics initiated. Antibiotics used were compared to sensitivities and BNF recommendations to determine efficacy. Results A total of 27 admissions with SA and 24 of PJI were seen, accounting for 51 (1.9%) of 2,670 total admissions, relative to a mean annual arthroplasty incidence of 1,204 across the health board. The median age of PJI patients was 72 years, significantly higher than the median SA patient age of 52 years (p<0.01). Median LOS was also higher in PJI patients at 13.5 days compared to nine days in SA (p=0.036). Most infections were hip and knee joints at nine (33.3%) cases in SA, and 11 (45.8%) total knee replacements in PJI cohorts. Staphylococcus aureus was the most prevalent organism in each group; however, 11 (40.7%) of the SA aspirate cultures were negative. The median aspiration time, relative to admission, was 5.6 and 10.2 hours in SA and PJI, respectively. The median time to initiate antibiotics was 7.1 and 17.9 hours in SA and PJI, respectively. The majority of admissions received appropriate antibiotics at 20 (74.1%) of SA and 17 (70.8%) of PJI patients. Culture results confirmed sensitivity to recommended antibiotics in 14 (51.8%) of SA and 18 (75%) of PJI cases. The most initiated antibiotic overall was flucloxacillin.  There was no significant difference in infection markers. Conclusion This study finds that PJI patients were typically older, with a greater LOS and comorbidity. Large joint infections, such as hips and knees, were the commonest presentation. The majority of each cohort was appropriately treated per the BNF, with S. aureus being the commonest cause. Factors such as prehospital antibiotics may reduce the bacterial yield of aspirations. Both groups show prolonged time taken to aspirate and treat, in which quality improvement interventions may reduce. Other centres may benefit from similar evaluations of the infective microbiome and the speed and efficacy of septic joint treatment.