Ultrasonography assessment of heel entheses in patients with spondyloarthritis: a comparative study with magnetic resonance imaging and conventional radiography

The aim of the present study was to determine the agreement between ultrasonography (US), magnetic resonance imaging (MRI), and conventional radiography (CR) in the detection of findings indicative of enthesopathy in spondyloarthritis (SpA) patients. A cross-sectional study was performed in 40 SpA patients. Heel entheses (Achilles tendon and plantar fascia) were bilaterally examined by US, MRI, and CR. The three imaging modalities were carried out by three independent operators blinded to the other imaging modality data. Soft tissue abnormalities indicative of enthesopathy as thickening, structural changes, and bursitis were assessed by both US and MRI, and cortical bone abnormalities indicative of enthesopathy as erosions and enthesophytes were assessed by the three imaging modalities. The unweighted kappa values between US and MRI were 0.80, 0.66, 0.69, 0.70, and 0.70 for thickening, structural changes, bursitis, enthesophytes, and bone erosions, respectively. With respect to the detection of enthesophytes, the unweighted kappa values between CR and both US and MRI were 0.78 and 0.76, respectively. At last, for the recognition of bone erosions, the unweighted kappa values between CR and both US and MRI were 0.38 and 0.45, respectively. Using MRI as standard reference method, US was more sensitive with respect to CR revealing bone erosions. The present study provides evidence about the high overall agreement between US and MRI for all abnormal comparable findings at entheseal level and between US, MRI, and CR for the detection of enthesophytes in SpA patients.