Development and validation of a Pediatric Internationally agreed UltraSound Hip synovitis protocol (PIUS-hip), by the PReS imaging working party

Abstract

Background: Whilst musculoskeletal ultrasound (MSUS) normal values for examination of the hip joint have been established for healthy children, equivalent values for patients with juvenile idiopathic arthritis (JIA), as well as internationally validated MSUS protocols for the optimal evaluation of synovitis are lacking. This study aimed to develop and validate the most sensitive MSUS protocol for the detection of hip synovitis in JIA.

Methods: In consecutive JIA patients with ≥ 1 clinically affected hip joint, affected and unaffected hips underwent MSUS. Disease, demographic and clinical findings were recorded. Synovitis was graded using the pediatric OMERACT score for B-Mode (BM) and power-Doppler Mode (PD) in the longitudinal and transverse scans and the sensitivity and specificity was analyzed. Additionally anterior recess size (bone to capsula distance), capsula thickness and femoral head cartilage thickness (transverse view) were measured. Published data provided further control data for anterior recess size (children without JIA). Interobserver reliability of BM and PD was tested using Fleiss-Kappa.

Results: 60 patients were enrolled who had 76 hips with and 32 without clinical arthritis. BM was positive (grade ≥ 1) in 74/76 of hips with clinical arthritis (97%, sensitivity 0.97 (0.93-1.0), specificity 0.85 (0.74-0.97) versus 2/32 (6%) in hips without arthritis. PD positivity frequency was 6 (8%) in hips with arthritis versus 0 in hips without. Anterior recess size (mean ± SD) was significantly wider in patients with clinical arthritis (9.9 ± 2.5 vs 5.5 ± 1.3, p-value 0.001). Use of the cut-off of ≥ 7.2 mm resulted in an area under the curve of at least 95%, with a sensitivity of 86% and specificity of 94%. Articular capsula and femoral head cartilage thickness did not differ between patients with and without arthritis. Recess size was comparable in the internal and external control groups (n = 449). Interobserver reliability of BM and PD positivity showed excellent agreement (kappa = 0.85).

Conclusions: The Pediatric internationally agreed UltraSound hip synovitis protocol (PIUS-hip) could be limited to one longitudinal scan including B-Mode scoring plus measurement of anterior recess size for maximal sensitivity and specificity for synovitis.

Keywords: Hip synovitis; Juvenile idiopathic arthritis; Ultrasound.

Fig. 1

Ultrasound probe placement and example B-Mode and Power-Doppler appearance in the anterior longitudinal view of the hip joint. The optimal placement of the US probe for evaluation of the anterior longitudinal view is shown (a), hip joint effusion with significant distension of the joint capsula (B-Mode Grade 3) is shown (b) and multiple PD signals outside of the joint capsule indicating physiological blood vessels or within the synovial membrane are shown (c)

Fig. 2

Ultrasound measurement of the anterior recess size, anterior and posterior capsula thickness. Example of anterior recess size, including the anterior and posterior capsula thickness in the anterior longitudinal view

Fig. 3

Ultrasound measurement of the femoral cartilage thickness performed in the transverse view. Example of the femoral head as seen in the transverse view. The double-headed arrow indicates femoral cartilage thickness

Fig. 4

Overview of the PIUS-Hip Ultrasound Protocol for Synovitis. The anterior longitudinal view, with ultrasound probe position, corresponding example of B-Mode image is shown, along with the pediatric OMERACT grading criteria for B-Mode findings. The measurement of the anterior hip recess is also shown, also performed in the anterior longitudinal view, which forms the second necessary image to fulfil the PIUS-protocol