# Septic arthritis following intra-articular corticosteroid injections: a retrospective analysis

## TL;DR

This study finds that septic arthritis after corticosteroid injections is rare but can occur up to 16 weeks later, suggesting longer monitoring is needed.

## Contribution

The study identifies a bimodal timing pattern for septic arthritis after corticosteroid injections, suggesting extended surveillance is necessary.

## Key findings

- The incidence of septic arthritis after large joint CSI was 0.093%.
- Infections often occurred between 1–3 and 7–10 weeks post-injection.
- Staphylococcus aureus and coagulase-negative Staphylococcus were the most common pathogens.

## Abstract

Septic arthritis is a rare but devastating complication of intra-articular corticosteroid injection (CSI), associated with significant medical morbidity and poor clinical outcomes. Although previous studies have examined risks associated with CSI, few have tracked patients long-term. This study evaluates the incidence, timing, and patient characteristics related to iatrogenic septic arthritis within 6 months of receiving a large joint CSI, offering new insights to inform clinical practice.

A retrospective, descriptive cohort study was conducted using SlicerDicer, a software stratification system within Epic, to identify patients diagnosed with septic arthritis within six months of receiving an intra-articular CSI of the hip, knee, or shoulder. Data were collected from a single institution over a 10-year period (July 1, 2010 to July 1, 2020). Individual chart review was used to obtain patient demographics, clinical characteristics, and procedural details for identified cases.

Of 15,021 intra-articular corticosteroid injections performed, 14 cases of septic arthritis were identified within 6 months of the procedure, resulting in an incidence rate of 0.093%. Of the affected patients, 21% had underlying inflammatory arthritis, and 21% had underlying comorbidities resulting in immunosuppression. The median time to diagnosis was 3.5 (range 1–16) weeks post-injection, with a bimodal distribution of infections occurring primarily between 1 and 3 and 7–10 weeks post-injection. Staphylococcus aureus (42%) and coagulase-negative Staphylococcus species (36%) were the most commonly isolated organisms.

Large joint intra-articular CSI presents a low risk (< 0.1%) for developing septic arthritis, but can present up to 16 weeks post-injection. The preliminary observation of bimodal timing and delayed presentation of septic arthritis suggests that a standard two-week surveillance window may not be long enough to fully capture all infections, particularly those involving lower-virulence organisms. These findings highlight the need for informed risk stratification and prolonged vigilance well beyond the immediate post-injection period to identify infectious complications after large joint CSI.