Background The functional disability experienced in juvenile idiopathic arthritis is primarily caused by degeneration of the osteocartilaginous structures due to the inflammatory process in the synovium. It is therefore essential for evaluating the therapeutic efficacy to closely monitor the structural damage during the disease course. During the past decade musculoskeletal ultrasound (US) has become an established diagnostic method in adult rheumatology and within recent years an increased attention for utilizing US in pediatric rheumatology has emerged. Previously we have found differences in joint cartilage thickness (Cth) between healthy children and JIA children measured by US (1). But are there any differences in Cth measured by US between healthy children and joints without a history of activity among JIA children’s.

Objectives To investigate a possible effect of the inflammatory process on joints never directly affected by arthritic activity during the history of the child’s disease course. Furthermore we wanted to compare joint cartilage thickness within the JIA group in joints with or without a history of activity.

Methods We included 95 Danish JIA children. Age, mean (range) 10,49 years (5-15), girls/boys (68/27). Subsets of JIA was: 15 systemic onsets, 8 RF-positive and 22 RF-negative poly articular JIA, 14 extended and 36 persistent oligo articular JIA. In total we investigated 941 joints with grey-scale US: 186 knee joints, 188 ankle joints, 188 wrist joints, 190 2nd MCP joints, and 189 2nd PIP joints. Cartilage thickness was measured perpendicular to the bone surface. History of joint activity was found by review of medical records. An age-, and sex-matched healthy cohort investigated in a previous study served as a control group (2), age, 10.9 (6-16), girls/boys (177/217). Linear regression analyzes were controlled for age, gender, subtype, and adjusted for clustered data (right/left extremities).

Results We found a significantly thicker cartilage in healthy children than in the healthy joints of JIA children: Knee joint: mean (95% CI), 1.06 mm (0.77-1.36 mm, p<0.001), Wrist joint: 0.44 mm (0.15-0.74 mm, p=0.003), and 2nd PIP-joint: 0.37 mm (0.27-0.48 mm; p<0.001). We found no difference in the ankle joint and 2nd MCP joint. Within the JIA group we found no significant difference between joints with or without a history of activity, but estimates pointed towards thinner cartilage in joints with a known history of activity.

Conclusions We found that the articular cartilage from the knee-, wrist-, and 2nd PIP-joints in JIA children without a history of active arthritis were thinner than joints in an age, and sex matched healthy cohort. No differences were found for the ankle- and 2nd MCP-joints. Our results suggest that even though a joint has never been directly affected by inflammatory activity, it may be negatively influenced by the inflammatory process in general.

1. D Pradsgaard et al: Joint Cartilage Thickness Measured by Ultrasound in Juvenile Idiopathic Arthritis, Poster, PRSYM, ACR Pediatric Rheumatology Symposium, Miami, June 2011

2. A Spannow et al.: Ultrasonographic measurements of joint cartilage thickness in healthy children: age- and sex-related standard reference values. 2010, J. Rheumatol, 37; 12 (2595-2601)

Disclosure of Interest None Declared