Age-dependent arthrosonographic reference values of the hip joint in healthy children and adolescents - a cross-sectional multicenter ultrasound study.

Background: Musculoskeletal US is a noninvasive imaging method for diagnosing and monitoring inflammatory rheumatic diseases.

Objectives: To develop age- and gender-related arthrosonographic reference intervals for the hip joint of healthy children and adolescents.

Materials And Methods: In a cross-sectional US study, we examined both hip joints of 445 children and adolescents with an age range of 1 year to 18 years. We measured the distance between the bone surface and the outer margin of the joint capsule to define the bone-capsule distance, the joint capsule and cartilage thickness, and the capsule layer thickness. Reference values were calculated. The shape of the joint capsule and bone-capsule junction zone were analyzed qualitatively. An intraobserver analysis was performed.

Results: Bone-capsule distance, capsule thickness and the anterior capsule layer increase with age. In contrast, joint cartilage decreases. The posterior capsule layer exhibited constant thickness across all age groups. The difference between both body sides and gender was collectively less than 0.5 mm. The intraobserver variations were within the calculated reference intervals. The insertion of the capsule to the bone was mostly a peaked one. The capsule shape had a convex or straight configuration in a neutral position and a concave position during outward rotation. The intraobserver analysis revealed good to very good concordance.

Conclusion: We propose age- and gender-related reference intervals for the bone-capsule distance, joint capsule and cartilage thickness of the hip.