Background/Purpose: Despite the development of advanced imaging modalities such as MRI and CT, conventional radiography remains the cornerstone for the diagnosis and classification of Ankylosing Spondylitis (AS).  Ease of access and cost may be contributory continued use of X-rays. The AP pelvis radiograph has long been the established standard for the screening and grading of sacroiliitis, despite its well-documented poor reproducibility. There is a lack of recent research that compares the standard AP pelvis (APPx) view with dedicated sacroiliac views. To the best of our knowledge, no previous studies compared AP pelvis vs the angled frontal “Ferguson” view (SIJx), a modality that has been advocated anecdotally by many clinicians. Our aim was to compare the APPx view with the dedicated SIJx view in order to clarify if one modality has a clear advantage for diagnosis and grading of sacroiliitis. 

Methods: 103 patients who had simultaneous APPX and SIJx modalities on the same date with an established diagnosis of Axial spondyloarthritis (SpA), either through the modified NY criteria or through the 2009 ASAS criteria were randomly selected from the axial SpA registry. One independent coordinator randomized the sequence of these patients and prepared the x rays to be read on two separate computer terminals with all patient identifiers removed. Two rheumatologist independently reviewed both the SIJx and the APPx and scored the graphs according the modified NY criteria.  Intra-reader and inter-reader agreements were obtained for both the APPx  and SIJx evaluations by using the Cohen-weighted kappa statistic and the intraclass correlation coefficient (ICC). Mean SIJ scores were also calculated.

Results: A total of 206 radiographs were read (103 for each modality). Intra-observer reliability of the observers showed similar agreements with regards to right and left SIJ evaluation (Table 1) which was also reflected in the kappa for diagnosis of AS (fulfilling NY criteria) between the observers. The inter-rater agreement showed similar values between the imaging modalities. This agreement was also replicated when separately evaluating SIJ’s with score grading of 0 to 2. The SIJ dedicated view did not significantly influence the diagnosis and there was no statistically significant change for the overall population as outlined on Table 1. The average SIJ scores obtained from each observer showed similar values for both modalities. 

Conclusion: There was agreement between dedicated SIJ and the AP pelvis x-ray reads. Either modality can be employed to evaluate the sacroiliac joints for sacroiliitis with the dedicated SIJ imaging showing no clear superiority over the standard AP Pelvis view. 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/is-there-evidence-to-support-replacing-conventional-ap-pelvis-radiographs-with-dedicated-sacroiliac-joint-views-for-the-diagnosis-of-sacroiliitis/