Background/Purpose: Enthesitis is one of the features of ankylosing spondylitis (AS). High prevalence of structural and inflammatory ultrasound lesions of peripheral entheses are found in AS patients. Furthermore, plain radiographs provide good imaging of peripheral enthesopathy at well-defined skeletal sites¹. There are several entheseal sites at the pelvis and hip region, but little is known about the presence of structural entheseal anomalies at these sites in AS. Our aim was to investigate the prevalence of radiographic entheseal lesions at the hip and pelvic region in patients with AS compared to control subjects.

Methods: The present analysis was performed in 214 patients from the Groningen Leeuwarden Axial SpA (GLAS) cohort study and 100 control subjects. The AS patients were included between November 2004 and December 2010 and had available anteroposterior (AP) pelvis radiographs at baseline. All patients fulfilled the modified New York criteria for AS. AP pelvis radiographs from control subjects matched for age and gender were obtained from the radiology department of the University Medical Center Groningen (UMCG).

Radiographs with blinded sacroiliac joints were randomized and scored by two trained readers. Anomalies with absolute agreement were reported. The entheseal sites scored were: trochanter major, trochanter minor, os ischium, crista iliaca, both left and right side and symphysis pubis. The following 3 anomalies were scored: cortical irregularities/erosions, calcifications and enthesophytes.

Results: Of the 214 AS patients, 148 (69%) were male, mean age was 42.5 ± 11.6 years, 171 (80%) were HLA-B27 positive and median symptom duration was 16 years (IQR 8-24). Patients had active disease with BASDAI 5.6 ± 1.9 and ASDAScrp 3.5 ± 0.9. Reader agreement on the entheseal lesions was overall moderate with Cohen’s kappa between 0.42 and 0.78.

Radiographic entheseal lesions at the hip and pelvic region were found in 160 (75%) patients and 58 (58%) controls. In total, 602 lesions were found of which 478 (80%) were present in AS patients. For both groups, the most prevalent lesion was irregularity/erosion (n=333 in 150 (70%) AS patients and n=85 in 50 (50%) controls), followed by enthesophytes (n=129 in 64 (30%) AS patients and n=37 in 21 (21%) controls). In both AS patients and controls, most lesions were found at the os ischii (n=275 in 138 (65%) AS patients and n=97 in 53 (53%) controls).

Conclusion: Radiographic entheseal lesions at the hip and pelvic region are more prevalent in AS patients compared to controls. Irregularities and erosions were most frequently found in both groups, especially at the os ischium. These new findings concerning structural entheseal lesions at the pelvis and hip region contributes to the knowledge of entheseal involvement in AS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/prevalence-of-radiographic-entheseal-lesions-at-the-hip-and-pelvic-region-in-patients-with-ankylosing-spondylitis-versus-controls/