Comparison of ultrasonography and magnetic resonance imaging for the assesment of clinically defined knee enthesitis in spondyloarthritis

Abstract

Objective. Ultrasonography (US) and magnetic resonance imaging (MRI) are increasingly used imaging techniques for visualising entheses, however few studies have made a direct comparison of each. This study aimed to compare each technique for the detection of enthesitis in patients with spondyloarthritis (SpA) related knee swelling in order to make a lesion by lesion comparison. Methods. Consecutive SpA patients with knee synovitis were recruited: each had clinical assessment for enthesitis at 8 sites in the involved knee joint followed by US and MRI examinations. Inflammatory and structural changes at tendon and ligament insertions were scored and a lesion by lesion comparison was made. Results. 21 patients were recruited. Clinically defined involved knee joint enthesitis was evident in 18 of 21 (86%) patients in 61 of 168 (36%) evaluated sites. Clinical enthesitis was associated with more hypoechogenicity (16 vs. 4%, p=0.007) and thickening (16 vs. 6%, p=0.03) by US compared to non-tender sites. Considering all MRI findings only increased signal in the surrounding tissues was higher at tender sites (41 vs. 20%, p=0.01) and the insertions points themselves showed little abnormality. The positive agreements between individual lesions by both methods was very low (10-26%) with low kappa values (0.06-0.18) with no correlations between the MRI and US scores (r(2)=0.059). Conclusion. The difficulty in procuring gold standard histological validation is synovial joints makes the assessment of enthesitis using clinical and current imaging protocols of limited utility for diagnostic purposes.