Ultrasound of the joints and entheses in healthy children

Tendon insertion pathologies such as enthesitis and apophysitis in children can result from trauma, overuse syndrome and arthritis. Knowledge of the US appearance of normal joints by age might aid diagnosis of pathologies. We describe the age-related sonographic features of the elbows, knees and feet in healthy children, providing a reference for the normal appearance of tendon insertions, apophyseal cartilage and bursae. This is a prospective cross-sectional study of 30 healthy children. Children were grouped according to age: group 1 (4-9 years, n = 11), group 2 (10-13 years, n = 9) and group 3 (14-18 years, n = 10). Children completed pain and function questionnaires and underwent a standardized joint examination by a pediatric rheumatologist. The common extensor, common flexor, quadriceps, patellar and Achilles tendons and plantar fascia insertions were evaluated with gray-scale and power Doppler ultrasound. The anterior elbow, suprapatellar and retrocalcaneal bursae were evaluated for fluid. We measured the apophyseal cartilage thickness at the enthesis. Correlation analyses examined associations between age and tendon thickness. We used ANOVA, with location as a repeated measure, to test for gender differences in cartilage thickness. Children had a median age of 12.4 years and 55% were boys. All 360 entheses appeared normal on gray-scale imaging. There was a strong linear relationship between tendon thickness and age. Tendon vascularity was only present in young children (group 1), in 7/22 (32%) quadriceps tendons. Peri-tendinous power Doppler signal was seen at seven sites: two patellar, four quadriceps and one common flexor tendon, and all these children were in group 2. Suprapatellar bursal fluid < 3 mm was detected in 9/60 (15%) knees. Of the children in group 1, boys had thicker apophyseal cartilage than girls at the medial epicondyle, patellar poles and os calcis (P < 0.05). Tendon vascularity may be a normal finding in young children, and mild peri-tendinous vascularity is not uncommon in children 10-13 years of age. Tendon thickness has a linear relationship with age; however cartilage thickness varies across sites and also differs as a function of gender.