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Musculoskeletal ultrasound (MSUS) is an important tool for evaluating disease activity, therapeutic progress, and remission status of rheumatic diseases in children. Knowledge of age-related normal findings is essential when interpreting pathological findings such as those seen in juvenile idiopathic arthritis. To evaluate normal findings of the knee joint, we recorded age-related stages of musculoskeletal development in the knee of 435 healthy children between 1 and 18 years of age using high-resolution B-mode MSUS. We determined approximate age- and sex-related norms for the suprapatellar recess size, ossified patella size, and distal femoral intercondylar cartilage thickness. In almost all age-groups, over 64 % of children had visible fluid accumulation in the suprapatellar recess. Significant correlations were found between chronological age and the suprapatellar recess size and ossified patella length (p < 0.05). An age-dependent decrease in intercondylar cartilage thickness of the distal femoral epiphysis was found in children between 10 and 18 years of age. High-resolution B-mode MSUS is an excellent tool for assessing joint and skeletal development in children. Our reference data can be used to discriminate better between normal physiological findings and pathological abnormalities.

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

We examined 445 healthy girls and boys between 1 year and 18 years of age. A cross-sectional multicentre grey-scale ultrasound study was performed to examine the shoulder joint on both sides. The children were divided according to their gender and were further classified into six age groups, which constituted three-year age ranges, to record anatomical development changes. We measured the capsule-bone distance (BCD) as a representation of the intracapsular cavity, as well as the thickness of the joint capsule and joint cartilage. Values were expressed in mean±standard deviation (SD) and minimum-maximum (min-max). The shape of the joint capsule and capsule-bone junction zone was qualitatively analysed. The joint cartilage thickness decreased with increasing age in all joints independently from sex and body side. However, the BCD and the capsule thickness increased with age. There was no intraarticular fluid visible. The joint capsule had a predominantly concave form, whereas the capsule-bone junction was mostly sharp. This study is the first describing age-related normal values of the intracapsular cavity, joint capsule and cartilage thickness as well as their respective shape in a large cohort of healthy children. The findings could be helpful to differentiate between physiological and pathological joint conditions and thereby distinguishing age-related variations from alterations caused by inflammation.

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