Sacroiliac Joint Variations on Magnetic Resonance Imaging in Patients with Low Back Pain

Aim: To investigate the frequency of anatomical variations on the sacroiliac joint (SIJ) and reveal their clinical importance by distinguishing the findings that mimic sacroiliitis in patients referred to magnetic resonance imaging (MRI) for low back pain. Materials and methods: This retrospective study included all SIJ MRI examinations performed in our hospital with patients ≥ 18 and < 65 years of age for a period of 24 months. According to the Assessment of Spondyloarthritis International Society (ASAS) criteria, data collection consisted of the patients’ age at the time of imaging, gender, and the presence of active and chronic sacroiliitis. Lumbosacral transitional vertebra (LSTV) was classified according to the Castellvi classification system. Moreover, all images were assessed for the presence of major sacroiliac joint variations described in the literature. Structural and edematous changes were also noted. Results: A total of 1,020 MRI examinations were included, and SIJ variations were identified in 323 of them. The frequency order of anatomical variants of SIJs are as follows: (1) LSTV (114 patients, 12.2%), (2) Accessory sacroiliac joint (80 patients, 7.8%), (3) Iliosacral complex (66 patients, 6.4%), (4) Sacral defect (61 patients, 5.9%), and (5) Isolated synostosis (2 patients, 0.2%). Structural and edematous findings were frequently observed in LSTV and accessory SIJ. Conclusion: We conclude that the lumbosacral transition segments and various anatomical SIJ variations are common in the low back pain population, especially in women. Moreover, these variations may be associated with degenerative and edematous signal intensity changes that mimic sacroiliitis.

Keywords:

magnetic resonance imaging, sacroiliac joint, anatomy lowback pain,

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