Background Radiograph of anteroposterior (AP) view of pelvis is usually used to diagnose sacroiliitis. Magnetic resonance imaging (MRI) can detect lesions early in the disease course before they can be seen on radiography. The severity of sacroiliitis may be different as detected by MRI or by AP view X-ray. The oblique view of pelvis may provide additional information that make it closer to the finding of MRI than AP view X-ray.

Objectives To determine whether oblique radiographs of the sacroiliac (SI) joints provide significant diagnostic advantage to a single AP projection of the pelvis in establishing the presence and severity of sacroiliitis as compared with MRI.

Methods Radiographs (both AP pelvis and oblique projections) and MR images of 392 SI joints were obtained from 196 patients with an established diagnosis of spondyloarthritis (SpA) and were graded according to New York criteria by 3 readers (2 radiologists and 1 rheumatologist). The inconsistent results were re-discussed by all readers until consensus obtained. We compared the data of radiographs (both AP and oblique views) with the results of MRI.

Results 7.1% SI joints were graded 1, 26.5% graded 2, 51.0% graded 3, and 15.3% graded 4 on AP view radiographs; 14.3% SI joints were graded 1, 43.9% graded 2, 34.7% graded 3, and 7.1% graded 4 on oblique view radiographs; while 14.3% SI joints were graded 1, 40.8% graded 2, 39.8% graded 3, and 5.1% graded 4 on MRI. 60.2% SI joints were graded identically whether on AP or oblique view X-ray. The agreement rate between oblique views and MRI (90.8%) was significantly higher than that between AP views and MRI (63.3%) (p<0.05). 12 patients would be diagnosed of ankylosing spondylitis (AS) by AP view radiographs, while who would be read as having non-radiography SpA (nr-SpA) by oblique view X-ray or MRI. No patient was diagnosed of AS on oblique view X-ray or MRI, while who was read as having nr-SpA on AP view radiograph.

Conclusions Oblique radiographs had closer agreement in severity score of sacroiliitis with MRI than AP pelvis radiographs. Oblique view radiographs may provide advantage to a single AP projection of the pelvis in diagnosing sacroiliitis.

References

1. Van der Linden S, Valkenburg HA, Cats A: Evaluation of diagnostic criteria for ankylosing spondylitis. A proposal for modification of the New York criteria. Arthritis Rheum1984; 27(4): 361-8.

2. Battistone MJ, Manaster BJ, Reda DJ, Clegg DO. Radiographic diagnosis of sacroiliitis–are sacroiliac views really better? J Rheumatol. 1998 Dec;25(12):2395-401.

Disclosure of Interest None declared