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High-resolution ultrasound is a rapid, proven imaging technique for identifying enthesitis, synovitis, and effusion in inflammatory and infectious diseases and soft tissue or bone changes in osteomyelitis in children.
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Ultrasound makes injection procedures easier and more accurate.
The physician’s hands are not the only means for examining the musculoskeletal system of children in the clinical setting. For children, ultrasound is used as an extension of the physical examination. Although the precise role of ultrasound in pediatric rheumatology has not been fully defined, several published articles have reflected its usefulness as an imaging technique for diagnosis and therapeutic follow-up of pediatric inflammatory diseases (e.g., juvenile idiopathic arthritis [JIA]) and infectious diseases (e.g., osteomyelitis). There is no doubt that ultrasound makes injection procedures easier and more accurate.
Table 18A-1 lists the main applications of ultrasound for pediatric rheumatology in daily practice. This chapter discusses the normal ultrasound anatomy of joints and entheses in children and the main findings of common musculoskeletal diseases detected by gray-scale ultrasound and Doppler techniques.
| Painful hip |
| Arthritis: effusion and/or synovial hypertrophy |
| Transient synovitis |
| Inflammatory arthritis vs. septic arthritis |
| Legg-Perthes-Calvé disease |
| Slipped upper femoral epiphysis |
| Painful and/or swollen knee |
| Arthritis and bursitis: effusion and/or synovial hypertrophy |
| Tendinitis, enthesitis, and apophysitis |
| Baker’s cyst and other popliteal fossa cysts |
| Osteomyelitis |
| The painful and/or swollen hand or foot |
| Arthritis: effusion and/or synovial hypertrophy |
| Tendinitis and tenosynovitis |
| Osteomyelitis |
Hip Involvement
In the field of pediatric rheumatology, ultrasound was first applied to detect joint effusion in children with an antalgic gait. Commonly, an antalgic gait may reflect disease in the hip, which often results from transient synovitis, but it is rarely the first manifestation of JIA. It can also result from other potentially harmful diseases (septic arthritis, osteomyelitis).
Transient synovitis is the most common cause of painful hips in children. Ultrasound scanning usually is demanded when children present with fever, limping, and restriction of motion. It is also done for easily repeatable sonographic follow-up of children with transient synovitis who did not achieve clinically significant improvement in the usual time frame of 3 weeks. Using this approach, a higher incidence of Perthes disease has been observed in children with repeated episodes of transient synovitis.
The anterior-sagittal approach is commonly used in pediatric rheumatology because it can clearly demonstrate hip joint effusion in the anterior recess of the capsule. The joint capsule is normally concave anteriorly and close to the femoral neck; a minimum of about 1 mm 3 of fluid may be detected inside, allowing differentiation of both layers of the capsule ( Fig. 18A-1 , online only).
On gray-scale ultrasound, an effusion is diagnosed when the joint capsule bows anteriorly in addition to (1) distention of more than 5.2 mm with fluid measured from the middle of the femoral neck to the capsular outer margin or (2) when distention of the capsule is 2 mm or more than the contralateral asymptomatic side. The asymptomatic contralateral joint offers the best standard for comparison. A concave border of the anterior joint capsule seems to be a reliable indicator for the absence of effusion. In transient synovitis, effusion was identified as the only cause of distention of the anterior joint recess; no significant thickening of both layers of the capsule existed ( Fig. 18A-2 , online only).
The Doppler technique can visualize a minimum Doppler signal in a healthy hip due to feeding arteries of the femoral head. The power Doppler technique reflects blood flow in structures containing small vessels, such as the synovium. Some studies have confirmed its usefulness in the evaluation of fluid collections and musculoskeletal inflammatory processes ( Fig. 18A-3 , online only). Doppler ultrasound can demonstrate mild or no increased flow in the capsule in the hip affected with transient synovitis, whereas in Perthes disease, several changes in the superficial cartilaginous vascularity and intraosseous or deep transphyseal vascularity can be depicted by sonograms of the proximal femur in pathologic hips. Using power Doppler ultrasound, moderately to severely increased flow in and around the capsule can be visualized in patients with septic arthritis. Those findings underline the importance of using Doppler technique for the diagnosis of some diseases. Septic arthritis cannot be differentiated from inflammatory arthritis on the basis of effusion size (although there is more often debris within the effusion in the former) or on the basis of Doppler signal. Moreover, normal Doppler does not exclude it, and ultrasound guidance of arthrocentesis is necessary for diagnosis. In neonates, it is not unusual to find hip septic arthritis coexistent with osteomyelitis, and magnetic resonance imaging (MRI) allows its exclusion.
JIA can affect the hip joint, but it is characterized by insidious oligoarticular or polyarticular onset, and the hip is often affected bilaterally. In JIA, the ultrasound image over the anterior femoral neck demonstrates synovitis characterized by distended anterior capsule because of synovial thickening of both layers of the joint capsule and separated by turbid (hypoechoic) effusion, with or without power Doppler signal according to joint inflammatory activity.
Knee Involvement
Part of the added value of ultrasound is its accessibility to the clinician. In the painful pediatric knee, a quick bedside ultrasound longitudinal scan provides information about involvement of synovium, and/or entheses in a few seconds. Ultrasound can rule out a variety of disorders for pediatric consultation (fractures, masses). JIA is the most common rheumatologic disorder of childhood, where arthritis of the knee joint represents by far the most prevalent symptom of disease onset.
When a clinician begins to scan the pediatric knee joint, there are several points to be taken into consideration. Imaging of a child’s joint is unique and differs from that in an adult since the articular cartilage and the cartilage of the immature epiphysis are initially continuous with each other ( Fig. 18A-4 , online only). Ultrasound sonograms depict the unossified epiphysis as a hypoechoic or anechoic structure with evenly spread echoes, whereas the overlying articular cartilage is entirely anechoic.
At first, moderate to severe pannus and effusion were recognized on gray-scale ultrasound in active arthritis of the knee in children with JIA. Increased flow in synovial proliferation confirmed by the power Doppler signal on serial ultrasound examinations are indicators of highly vascularized, proliferative synovium and suggest active disease. Doppler ultrasound can be used for monitoring disease activity and evaluating any response to therapy based on the assessment of volume and distribution of the pannus and synovial vasculature. Routine use of ultrasound in the clinical setting led to the detection of subclinical synovitis and enabled early immunosuppressive therapy. The degree of knee joint vascularity has been correlated with serum levels of some inflammatory interleukins, such as interleukin-6 (which induces neoangiogenesis in vivo), in children with polyarticular JIA. Therapy with a humanized anti-interleukin-6 receptor antibody has proved efficacious in the treatment of JIA.
Doppler ultrasound detects indirect signs of increased vascularization associated with synovial or soft tissue because of inflammatory and infectious diseases ( Fig. 18A-5 , online only). Synovitis identified by a Doppler signal is not specific in defining the cause.
