Echotexture analysis of L4 supraspinous enthesis in ankylosing spondylitis

Background: Enthesopathy is a main characteristic of ankylosing spondylitis (AS). However, ultrasonographic features of supraspinous enthesis in AS have not yet been reported. Methods: Forty-seven AS patients and 22 healthy individuals were enrolled and completed the study. L4 supraspinous entheses were assessed through an ultrasound (US) unit with the participants in a lateral decubitus position. Entheseal echogenicity was interpreted upon inspection of the US image. An entheseal grayscale (GS) value determination, along with an echotexture analysis using a gray-level co-occurrence matrix algorithm, was performed. The thoracolumbar fascia just above the enthesis was also analyzed. An enthesis-To-fascia ratio (EFR) of each texture feature was used for the purpose of intergroup comparison. Results: The prevalence of abnormal entheseal echogenicity in the AS and healthy groups was 19.1% and 13.6%, respectively (P = 0.42). The AS group experienced a higher GS EFR (0.56 [0.10-1.08] vs. 0.40 [0.12-0.89], P = 0.007), higher contrast EFR (0.62 [0.15-1.23] vs. 0.49 [0.23-1.33], P = 0.049), higher variance EFR (0.44 [0.06-1.21] vs. 0.35 [0.13-1.10], P = 0.023), and lower homogeneity EFR (1.07 [0.97-1.27] vs. 1.11 [1.04-1.19], P = 0.011) in comparison to the healthy group. Conclusion: Echotexture analysis identified the subtle structural changes in L4 supraspinous enthesis in AS patients. It proved to be superior to the inspection method and may possess the potential for providing early detection of supraspinous enthesopathy in AS.