Joint space narrowing (JSN) is a measurable outcome of tissue degeneration in arthritis. JSN is usually assessed by conventional radiography. Ultrasonographic (US) measurement of joint cartilage thickness has been validated in healthy children, and US measurement of the distal femoral cartilage has been validated in a group of patients with juvenile idiopathic arthritis (JIA). Our aim was to compare the measures of cartilage thickness of the proximal cartilage site in the second metacarpophalangeal (MCP), second proximal interphalangeal (PIP), and knee joints as assessed by US to joint space width (JSW) as measured by computerized radiography in children with JIA.
The study included 74 children with JIA aged 5-15 years (median 11.3 yrs). MCP and PIP joints were assessed at one midline spot. Knee joints were assessed at the medial and lateral femoral condylar areas. Only the proximal cartilage site in the joints was assessed by US, whereas the complete JSW was assessed by radiography.
We assessed 136 second MCP, 138 second PIP, and 146 knee joints. We found a high level of agreement between US and radiographic measures of cartilage thickness and JSW: r = 0.82-0.86 (second MCP), r = 0.50-0.55 (second PIP), and r = 0.52-0.81 (knee); p < 0.001 for all 8 assessed sites.
US measurements of cartilage thickness of the proximal site of the second MCP, second PIP, and knee joints correlated well with radiographic JSW measurements in the finger and knee joints of children with JIA. However, US does not measure the distal cartilage, which may limit its use in the assessment of JSN.