To compare the ultrasonic findings of healthy children and children with temporary hip synovitis, and to investigate the effective ultrasonic diagnostic indices and their diagnostic value in temporary hip synovitis.

From January 2020 to July 2022, 320 healthy children and 200 children with temporary hip synovitis were recruited from the Chongqing Medical University Children's Hospital. The breadth of the anterior femoral neck space (ultrasonoimagedata joint space, UJS), joint effusion, joint capsule wall thickness, joint shape, and blood supply of the joint capsule were measured. The diagnostic efficacy of ultrasonic markers, alone or in combination, in hip transient synovitis was examined by receiver operating characteristic (ROC) curve analysis.

Approximately 3.7% of healthy children (24/640) had a protruding hip capsule, and 10% (64/640) had a small amount of physiologic fluid accumulation in the joint cavity. The average UJS was (0.55±0.10) cm. The mean thickness of the anterior and posterior walls of the articular capsule was (0.25±0.07) cm and (0.25±0.06) cm, respectively, with no statistical difference (P>0.05). The majority (78.4%, 228/261) of children with synovitis presented a convex articular capsule profile. Fluid accumulation was observed in the lumen of 261 affected hip joints, with an average value of (0.84±0.21) cm. The UJS on the affected side was (0.89±0.21) cm. The wall thickness of the articular capsule was (0.25±0.47) cm, and there was no significant difference in the thickness of the anterior and posterior walls of the articular capsule between children with temporary hip synovitis and the healthy group (P>0.05). There was no significant difference in blood supply between the healthy side and affected side (P>0.05). Among the five ultrasonic indexes (UJS, articular effusion, bilateral UJS difference, bilateral articular effusion difference, and articular capsule contour), the area under the ROC curve of bilateral UJS difference was 0.98, which was larger than that of the other ultrasonic indexes, and the best cut-off value was 0.1 cm. Among the joint indexes, the diagnostic efficiency of UJS >0.66 cm ＋articular effusion difference >0.16 cm was the best, and the area under the ROC curve was 0.97.

The articular capsule and synovial membrane in children with synovitis do not significantly thicken, and the blood supply does not significantly increase. The difference of bilateral UJS and the difference of UJS combined with bilateral joint effusion have good diagnostic efficacy for temporary hip joint synovitis, which provides a basis for ultrasound diagnosis of temporary hip joint synovitis..