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Knowledge of entheseal development in children with JIA is critical.
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Ultrasound can differentiate earlier polyartheritis and enthesitis according to ILAR classification criteria.
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Knowledge of the normal vascularization about an enthesis is essential.
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Detection of hyperemia between the cortical bone and enthesis may be a specific sign for an inflammatory enthesitis.
Juvenile idiopathic arthritis (JIA) is inflammatory rheumatism that begins before the patient is 16 years old and that has a disease duration of at least 6 weeks and no identifiable cause. An international classification for arthritis has been suggested ( Table 18B-1 ), and new entities have been proposed: symmetric arthritis, oligoarthritis, rheumatoid arthritis with positive or negative rheumatoid factor, psoriatic arthritis, and enthesitis, which represents 20% of JIA cases. Enthesitis is defined as the association of one type of arthritis and one enthesitis or one arthritis and at least two other elements: sacroiliac pain, inflammatory spine, HLA-B27 positivity, anterior uveitis, spondyloarthropathy, or inflammatory enterocolopathy. It can also be associated with extra-articular manifestations, such as eye, heart, cutaneous, or digestive conditions.
| Definition |
Arthritis and enthesis, or Arthritis or enthesis with at least two of the following:
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Exclusions
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Enthesitis is similar to seronegative spondyloarthropathy in adults, which can evolve from the childhood disease. However, spinal inflammation in children is uncommon compared with adults. The juvenile form of enthesitis is much more common than the adult form of ankylosing spondylitis.
The juvenile spondyloarthropathies are diagnostically challenging. Early stages of disease remain difficult to differentiate from pauciarticular juvenile rheumatoid arthritis. Lower limb arthritis and enthesitis should raise the possibility of a juvenile spondyloarthropathy, because enthesitis is a highly specific feature, and inflammation of the sacroiliac joints is typically seen many years after the onset of clinical symptoms. It is important to have a tool that permits the diagnosis of enthesitis. In children, it is difficult to differentiate juvenile ankylosing spondylitis from other forms of juvenile arthritis, because the most helpful distinguishing feature is enthesitis. The problem is that pain located in the enthesis in children is common and may be caused by excessive physical exercise. In this chapter, we explain the development of enthesis in children to understand why ultrasound can be useful for detection of enthesitis and for earlier diagnosis of spondyloarthropathies. We briefly discuss the implication of mechanical disease in entheses of the lower limbs.
Enthesis Organ Concept
Benjamin and McGonagle explained that the concept of the enthesis organ is not unique to the Achilles tendon, but can be applied to many articular and extra-articular sites.
Inflammation of the enthesis, when associated with arthritis in children, is called the syndrome of seronegative enthesopathy associated with arthritis (SEA). The entheses most commonly involved in children are the plantar aponeurosis, calcaneal enthesis, and distal and proximal patellar ligament insertions.
Some studies have shown that SEA can develop into a spondyloarthropathy. The diagnostic delay is related to symptom development, which is about 8 years for men and 9 years for women. An early diagnosis should permit rapid treatment and stall the evolution of the disease. Histologic examination of enthesitis shows the hyperemia between the bone and tendon. Magnetic resonance imaging (MRI) with gadolinium shows, with a good sensitivity, enhancement of early inflammation of the enthesis. However, this tool is expensive, difficult to access, and requires sedation for the child. MRI cannot assess in real time all of the enthesis area.
Ultrasound is more accessible and can assess much of the joint in real time. Lehtinen and colleagues and Balint and coworkers were the first to describe the B-mode ultrasound pattern of enthesitis in spondyloarthropathies. Ultrasound-depicted enthesitis is usually characterized by loss of fibrillar tendon views, increased focal abnormalities at the tendon insertion, and calcium deposits, erosions, or new bone formation at the tendon insertion.
Ultrasound Features of Normal Entheses In Children
Achilles Tendon
Enthesis Development
The archetypal enthesis organ is the Achilles tendon. It is a common site of disease in patients with spondyloarthropathies, and it has rightly been described as premiere enthesis . However, knowledge of the normal sonographic appearance of the Achilles tendon insertion in children at different ages is crucial for the correct diagnosis of pathologic changes in that area. In 1986, Fornage and associates described four groups:
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From 2 months to 3 years, no ossification of the secondary center of calcaneus is visible. In about 70%, color Doppler identifies at least one small vessel.
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From 4 to 6 years, early signs of the secondary ossification center appear ( Fig. 18B-1 A).
F igure 18B-1
A, Ultrasound shows a normal calcaneal enthesis in 4-year-old girl. The secondary ossification center can be seen (arrow) . The interface of bone and cartilage has the appearance of a wave. B, In a 10-year-old boy, the secondary ossification center is not fused with the calcaneus. C, In an 11-year, 3-month-old girl, fusion between the ossification center (C) and the calcaneus has not yet occurred, and there is a gap in between the structures (arrow) . Ca, calcaneus; N, ossification center; T, tendon.
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From 7 to 11 years, a wavy interface is seen between the posterior bony contour of the calcaneus and the cartilage of the apophysis (60%) (see Fig. 18B-1 B).
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From 12 to 18 years, the apophyseal cartilage between the bony contour of the calcaneus and the ossification center appears as a hypoechoic gap, and the dorsal aspect of the ossification center is covered by the cartilage (see Fig. 18B-1 C).
Volpon and colleagues studied radiographs of the calcaneus in 392 children between the ages of 6 and 15 years. They showed that ossification of the secondary ossification center began at 7 years, and by 15 years, the nucleus was fused in all of the children studied.
Ultrasound also can detect retrocalcaneal bursitis, which is associated with severe enthesitis in most cases. In the literature, only one case of retrocalcaneal bursitis in JIA was described.
Tendon Thickness
The normal thickness of the tendon insertion has been evaluated in only two articles. Grechenig and colleagues studied 100 calcaneal entheses in asymptomatic children between the ages of 2 months and 18 years. The measurements were done in millimeters for the anteroposterior diameter of the distal Achilles tendon. The thickness increased with age by 3.7 ± 0.4 mm in the fourth group (12 to 18 years). Another study described detection of Achilles tendon xanthomata in children with familial hypercholesterolemia. The results showed an increase in the thickness of the tendon, but a different method of measurement was used.
Vascularization
Grechenig and associates used color Doppler to show vascularization at the apophyseal cartilage in the first group (2 months to 3 years) in 76% of cases. This appearance of vascularization has been found in one case in adolescents (12 to 18 years). Some data should be given about mechanical disease of the calcaneal apophysis. In these cases, ultrasound can be used to assess severe disease.
Plantar Aponeurosis
Enthesis Development
No study has been published concerning the normal development and the thickness of the plantar aponeurosis in children. Huerta and Alarcon Garcia assessed with ultrasound the thickness of the aponeurosis (96 fascia) in an asymptomatic population but with different ages. This article showed the important effect on results by different methods of measurement.
Vascularization
Vascularization of the plantar aponeurosis has never been studied with power Doppler in a population of children.
Quadricipital Enthesis
Enthesis Development
We found only one article about the normal development of the patella. However, many studies have described the ultrasound appearance of the tibial insertion of the patellar ligament in Osgood-Schlatter disease. We also found descriptions of the development of the patella in articles about congenital abnormalities of the extensor mechanism of the lower extremity, but these reports never described the ultrasound appearance of normal patellar development in children.
During development, the patella is an unossified area located anterior to the cartilaginous portion of distal femoral epiphysis ( Fig. 18B-2 ). Later, ossification of the patella begins. The patellar cartilage is hypoechoic and homogeneous, and the interface between bone and cartilage is rounded ( Fig. 18B-3 A). As ossification proceeds, the cartilage disappears (see Fig. 18B-3 B).
