Background/Purpose: Musculoskeletal ultrasound (MSUS) can enhance the clinical assessment of the pediatric enthesis. Doppler signals in particular are considered a sign of pathology but may not be specific for enthesitis. The normal pediatric enthesis can exhibit Doppler. The aim was to obtain data of knee and ankle entheses in healthy children at the peak of linear growth as a reference for patients.

Methods: 42 males and females, 11-14 years old, free of musculoskeletal (MSK) symptoms, conditions or medication affecting the MSK system, no MSK injuries in the past 3 months and no participation in sports more than 3 times per week took part. The Quadriceps insertion, proximal and distal patella tendon insertion and Achilles enthesis were examined in Power and Colour Doppler using an Esaote Mylab 70 XVG Gold with a linear probe 6 to 18 MHz. Doppler settings were optimized individually to obtain maximum sensitivity. Extremities were assessed in neutral and 30 degrees flexion. Images were acquired by one examiner and read by two. 10 volunteers were reassessed 2 days later. Presence of Doppler signals was assessed directly at the bone/cartilage interface as well as within 2mm, 5mm and 10mm using a scoring system 0=no Doppler signals via 1a=single signal, 1b=single confluent signal up to 3 b=3 and more confluent signals. Signals at the enthesis were differentiated from peri-tendinous and intra-cartilage signals. A marginal logistic regression model with generalized estimating equation for associations between ultrasound signal detection and distance, Doppler mode, position, location, and side of measurement was used. Agreement between observers and scan days was determined using prevalence- and bias-adjusted Kappa.

Results: Doppler signals were hardly ever present directly at the tendon bone junction but did show the highest prevalence within 2 mm of the enthesis with an Odds ratio (OR) of 4.58 (95 % CI 2.71-7.72), p<0.001, and 5 mm, OR 4.24 (95 % CI 2.18-8.25), p<0.001. Doppler signals were significantly less likely to be present in the proximal patella and Achilles tendon insertion compared with the Quadriceps and distal patella tendon insertion (p<0.001 each). There was no significant difference between right and left as well as the two degrees of flexion in the logistic regression model. The mean(range) for kappas between the first and second assessment at the various distances and entheses was 0.82 (0.45-1). The mean(range) for kappas regarding agreement between the two readers at the various distances and entheses was 0.87 (0.46-1).

Conclusion: We found Doppler signals especially within 2 and 5 mm of the enthesis of the Quadriceps and distal Patella tendon. Contrary to results in adults with Spondylarthritis, Doppler signals were not consistently more prevalent in the flexed or extended position. Results showed good agreement between the right and the left extremity and were stable over time. Our results indicate the need to differentiate various entheses in MSUS. Doppler signals may be more specific for pathology in the proximal Patella tendon and Achilles tendon than in the Quadriceps or distal Patella tendon insertion. The exam should be performed in various positions of the joint.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/differential-pattern-of-doppler-signals-at-lower-extremity-entheses-of-healthy-children/