An observational case-control study was designed to analyse the discriminative value of ultrasound (US)-detected joint effusion compared with physical examination in the assessment of sacroiliac joints (SIJ) in patients with spondyloarthropathy (SpA) with or without inflammatory back pain (IBP).
45 patients with SpA, classified according to European Spondylarthropathy Study Group criteria, and 30 healthy volunteers were studied. All patients had clinical evaluation of the SIJ, Bath ankylosing spondylitis (AS) metrology index, Bath AS disease activity index, Bath AS functional index, health assessment questionnaire, patient's and physician's visual analogue scale on global disease activity.
Ultrasound showed joint effusion in 38.9% of SIJ of patients with SpA and in 1.7% of SIJ of controls (p<0.001). The presence of IBP was significantly associated with SIJ effusion assessed by US alone or plus at least one SIJ test. SIJ effusion assessed by US alone or plus at least one SIJ test had a positive likelihood ratio (LR) (2.67 and 4.04, respectively) for the presence of IBP higher than LR of single clinical tests. Positive sacral sulcus test, iliac gapping and midline sacral thrust test were associated with SIJ effusion assessed by US, but all clinical tests, singly and in various combinations, had a low LR for the presence of SIJ effusion assessed by US.
The study suggests that high resolution sonography is useful in the assessment of SIJ involvement in SpA, resulting in images that are fast and inexpensive and may locate, complementing the physical examination, the origin of IBP.