This retrospective single-center study followed the STROBE guidelines.

We retrospectively included all the children aged < 15 years who were operated on to treat septic arthritis of an articulation (hip, shoulder, or ankle) using procedures that commonly require fluoroscopic guidance, and who were treated from December 2015 to October 2020 with a minimum of two years of follow-up.

The exclusion criteria were septic arthritis of a joint that was easily puncturable without radiological guidance (a knee) or septic arthritis secondary to chronic osteomyelitis (because the surgical treatment is then different in terms of both the approach to and curettage of the bone lesion), a penetrating joint injury, and a follow-up period of less than two years.

Each diagnosis of septic arthritis was made in the emergency department on the basis of clinical findings (edema, pain, heat), biological data [biological inflammatory syndrome, blood count, C-reactive protein (CRP) level, and fibrinogen level], and radiological data (US, joint effusion).

The protocol followed the guidelines of the Helsinki Convention. Written informed consent was obtained from the parents of the children or their legal representatives. The study was approved by the institutional review board committee of Montpellier (number IRB-MTP_2021_05_202100781).

Each operation was an emergency operation, conducted in an operating room with the child under general anesthesia in the supine position. Needle puncture was performed using a short safety catheter (2.2 × 50 mm; 14-G hinge). The needle was inserted under US (US group) or fluoroscopic (non-US group) guidance, depending on the surgeon’s preference, employing the usual surgical approach (anterior for the hip, anterolateral for the ankle, deltopectoral for the shoulder) (Fig. 1). US guidance was provided by an L4-12T probe (Samsung). The needle axis was longitudinally aligned to the axis of the US probe. If possible, lavage employed physiological serum delivered using the puncture needle, which was left in place in the joint until a clear lavage fluid was obtained. The effectiveness of both puncture and lavage was monitored under US by watching the joint swell and deflate during the procedure (Fig. 2). Joint fluid was inoculated directly into blood culture bottles, and a portion was stored for direct examination and inoculation onto enriched media in the bacteriology laboratory. A 16 S RNA PCR test for Kingella kingae (KK) was routinely requested. If joint lavage using the puncture needle was difficult given the thickness of the joint fluid, or if the fluid was very purulent, the surgeon could choose to perform arthrotomic lavage, which also allowed an intra-articular drain to remain in place at the end of the procedure.

Ultrasound-guided puncture of septic arthritis of the right shoulder of a 4-year-old child. 1a. Ultrasound visualization of joint effusion. 1b. Joint puncture of the purulent fluid. 1c. Visualization of the puncture needle during the procedure

Ultrasound-guided puncture of septic arthritis of the ankle of a 2-year-old child. 2a. Ultrasound visualization of joint effusion. 2b. Joint puncture. Ultrasound allows us to check if the needle is in the joint and to identify and avoid vascular/neural elements, such as the dorsalis pedis artery. 2c. Disappearance of the effusion at the end of the procedure

IV antibiotic therapy was then started (cefazolin 150 mg/kg/day in four divided doses or clindamycin 40 mg/kg/day if a child was allergic to beta-lactams).

A biological check-up (blood count, assays of CRP and fibrinogen levels) was performed at 72 h, and then every 48 h until switching to per os. This occurred when the child was apyretic, and a biological check-up showed a CRP level < 20 mg/L and a fibrinogen level ≤ 4 g/L. If a cultured microbe was sensitive to certain antibiotics in the laboratory, these antibiotics were chosen. If no microbe was cultured, the per os treatment was amoxicillin with clavulanic acid (80 mg/kg/day in three divided doses) or clindamycin (25 mg/kg/day) if a child was allergic to beta-lactams; this continued for 15–20 days.

We systematically reviewed all patients 7–10 days after discharge, both clinically and biologically, and confirmed that the antibiotics had been stopped on schedule. All were followed-up again via consultations (clinical and radiological examinations) at 6 months, 1 year, and at the final follow-up; we noted all sequelae.

At the time of emergency admission, and on days 3, 5 (if the child was still hospitalized), and 10, we recorded age, sex, the joint involved, temperature, the white blood cell (WBC) and blood neutrophil counts, and the CRP and fibrinogen levels. We recorded the surgical procedures (arthrocentesis, or puncture with arthrotomy), the use of US or fluoroscopic assistance, if puncture was unsuccessful, and the appearance of the puncture fluid (clear, cloudy, or purulent). We later recorded any microbe isolated, the number of days in hospital, and whether surgical revision was necessary. At the final follow-up, patients were examined for late complications (reduced mobility, pain, limping, growth problems), and standard X-rays of the affected joints were taken.

The normality of the data distribution was assessed using the Shapiro–Wilk test. The Mann–Whitney test was employed to compare the groups. We considered p < 0.05 to indicate statistical significance. All statistical tests were performed using R software (version 4.3.2).