Ultrasound of Joints in Children: ESPR 2022 Standard Positions

Why the Pediatric Protocol Differs from the Adult One

Ultrasound of joints in children cannot be mechanically transferred from the adult MSK protocol. According to the ESPR MSK Task Force 2022, the main source of errors is age-related anatomy: epiphyseal and joint cartilage, incomplete ossification centers, wide cartilaginous layers, and physiological vascularity near growth zones. What appears as a cortical contour defect or intra-articular soft tissue content in adults may be normal cartilage or unossified epiphysis in children.

The goal of the ESPR standard is not to replace the clinical diagnosis but to unify the technique: consistent child positioning, repeatable planes, assessment of typical joint recesses, tendons, bursae, bone-cartilage contour, and Doppler vascularization. This is especially important in juvenile idiopathic arthritis, trauma, pain of unclear origin, and treatment monitoring.

General Technical Principles

The examination is performed with a high-frequency linear transducer; for deep joints or larger children, a transducer providing sufficient depth and focus is chosen. Scanning is conducted in gray scale in longitudinal and transverse planes, then color or power Doppler is added to assess synovial and periarticular tissue hyperemia.

Critical factors include minimal transducer pressure, sufficient gel, and a calm limb position. Excessive compression can remove a small effusion from the recess and suppress a low-velocity Doppler signal. In case of a doubtful finding, comparison with the contralateral joint is useful, but symmetrical vascularization near growth zones should not automatically be interpreted as synovitis.

What Must Be Described in the Protocol

• Joint and side, limb position, standard approaches used.
• Presence of effusion, synovial thickening or villosity, compressibility of contents.
• Doppler signal in the synovium: present or absent, localization, comparison with gray scale changes.
• Condition of the joint cartilage and accessible bone contour: erosions, irregularity, post-traumatic changes.
• Periarticular structures: tendons, tendon sheaths, entheses, bursae, para-articular soft tissues.
• Age-related features that may explain the visible picture: cartilaginous epiphysis, ossification centers, growth zone.

Standard Positions: Practical Table

Shoulder Joint

In children, a significant part of the humeral head is cartilaginous, so posterior and lateral approaches provide a good acoustic window. The protocol must distinguish between intra-articular effusion, tenosynovitis of the long head of the biceps, and fluid in the subacromial-subdeltoid bursa. Doppler signal is assessed only after optimizing the gray scale image and reducing transducer pressure.

Elbow, Wrist, and Hand

In the elbow, small volumes of fluid are more often seen in the anterior and posterior recesses. Cartilaginous parts of the capitellum and radial head may appear hypoechoic; they need to be distinguished from synovial tissue. In wrist arthritis, the radiocarpal and midcarpal levels are typically examined because inflammation may be segmental.

In the hand and fingers, ultrasound is useful for differentiating arthritis, tenosynovitis, and periarticular edema. For small joints, it is especially important to position the transducer strictly along the axis of the phalanx: an oblique cut creates a false impression of contour irregularity or soft tissue thickening.

Hip Joint

The hip joint is predominantly examined from the anterior approach along the femoral neck. Ultrasound effectively identifies anterior effusion and synovial thickening but does not replace MRI when bone marrow involvement, avascular changes, or deep intraosseous processes are suspected. In young children, the unossified femoral head improves visualization of cartilaginous structures, while in adolescents, the acoustic window gradually narrows due to ossification.

Knee

The knee is a common target for pediatric ultrasound in arthritis and trauma. The suprapatellar recess is assessed in longitudinal and transverse planes, then the medial and lateral parapatellar recesses are examined. A posterior approach is needed for the popliteal area, including cystic formations and pathology of tendon-ligament structures. Condylar cartilage in children is well visualized and should be described separately from joint fluid.

Ankle and Foot

In the ankle, inflammatory changes may localize in the anterior tibiotalar recess, tendon sheaths, or retrocalcaneal bursa. Therefore, the ESPR standard focuses not only on the joint space but also on periarticular tendons. In the foot, the dorsal approach to the metatarsophalangeal joints is convenient for detecting synovitis, while the plantar approach is used for local soft tissue pain syndromes.

Age-Related Interpretation Traps

• Hypoechoic epiphyseal cartilage is not equivalent to effusion or synovial hypertrophy.
• An irregular contour appearance in the ossification center zone may be a normal maturation stage.
• Doppler signal near the physis and in periarticular vessels may be physiological.
• In younger children, ultrasound better shows cartilaginous structures, while in adolescents, the role of acoustic shadowing from bone increases.
• The absence of effusion on ultrasound does not exclude bone, bone marrow, or deep intra-articular structure pathology.

Practical Conclusion

The ESPR 2022 standard sets a reproducible minimum for pediatric joint ultrasound: correct positioning, typical recesses, cartilage and periarticular structure assessment, Doppler without compression, and mandatory age consideration. The conclusion should not substitute description with universal 'thickness norms': for children, the document emphasizes morphology, localization, side comparison, and clinical context.