Joint cartilage is a major target of the erosive process in chronic arthritis. The occurrence of cartilage loss in children with juvenile idiopathic arthritis (JIA) represents, therefore, an early indicator of joint damage and raises the need to intensify therapy before irreversible structural changes develop. Until a few years ago, most experience in joint imaging in JIA was based on conventional radiography1. Joint space narrowing and erosions seen on plain films have traditionally been considered important markers of disease progression and have been observed early in the disease course in a higher-than-expected proportion of children with JIA2. However, radiographs are inadequately sensitive in the detection of the initial structural changes in JIA.
Moreover, accurate assessment of joint damage in children is complicated by the age-related variations in the thickness of articular cartilage and the ongoing skeletal maturation. In growing children, bones are extensively cartilaginous, and ossification centers appear progressively and complete their growth over several years. In young children the epiphyses are highly vascularized and the metaphyseal vessels anastomose with epiphyseal vessels throughout the growth plate. In children with chronic arthritis, inflammation affecting the epiphyseal cartilage may extend to the ossification centers, causing excessive growth, deformities, or epiphyseal erosions. As a result, irreversible cartilage destruction may occur before bone changes are radiographically evident.
Newer imaging modalities, particularly ultrasound (US) and magnetic resonance imaging (MRI), have played an increasing role in the identification of early signs of synovitis and damage in JIA3. US is particularly suited for use in children because of its noninvasiveness, rapidity of performance, relatively low cost, ability to scan multiple joints at one time, repeatability, safety, and high patient acceptability. US enables visualization of the soft tissues and principal components of the joints and can detect the cartilage of unossified epiphyses …
Address correspondence to Dr. S. Magni-Manzoni. E-mail: silvia.magnimanzoni{at}opbg.net