Radiographic entheseal lesions of the pelvic region are more prevalent in radiographic axSpA than in age- and sex-matched controls and are associated with more severe spinal disease.

Objectives: In axial spondyloarthritis (axSpA), entheseal involvement is common, which contributes significantly to disease burden and may also lead to structural damage. Although radiographs of the pelvis are widely available in axSpA, information on entheseal damage and associated characteristics are lacking. Therefore, we assessed the prevalence of radiographic entheseal lesions at the pelvic region in radiographic (r-) axSpA compared with controls and explored associations with patient and disease characteristics.

Methods: Pelvic radiographs of 167 consecutive r-axSpA patients were randomized with 100 pelvic radiographs from age- and sex-matched controls. Radiographs were blinded for patient information and sacroiliac joints and bilaterally evaluated for erosions/cortical irregularities, enthesophytes, and calcifications by two trained readers at the greater and lesser trochanter, os ischium, and iliac crest.

Results: Entheseal lesions were observed in 127 (76%) of r-axSpA patients and 58 (58%) controls. R-axSpA patients showed significantly more (bilateral) entheseal lesions than controls at all entheseal sites. Most lesions were found at the os ischium, erosions/cortical irregularities were most prevalent, and calcification was the most specific lesion in r-axSpA. Patients with lesions were significantly older, had longer symptom duration, and more severe spinal radiographic damage than patients without lesions. Enthesophytes were found significantly more often in patients with body mass index (BMI) ≥ 25.

Conclusion: Structural entheseal lesions observed at pelvic radiographs are not specific but occur often in r-axSpA patients. Treating physicians should keep in mind that these entheseal lesions are associated with more severe axial disease and high BMI which may be relevant for treatment decisions. Key Points • Pelvic radiographic entheseal lesions are significantly more prevalent in r-axSpA patients than in controls. • Radiographic entheseal lesions are associated with longer symptom duration and more spinal radiographic damage. • Pelvic enthesophytes are found significantly more often in r-axSpA patients with BMI ≥ 25.