Sacroiliac joint variation associated with diffuse idiopathic skeletal hyperostosis

Background Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by the ossification of vertebral bodies and peripheral entheses. However, variations in sacroiliac (SI) joint change in patients with DISH have not been fully clarified. The purpose of this study was to evaluate SI joint variation in patients with DISH in comparison with a non-DISH population. Methods A total of 342 SI joints in 171 patients (DISH+, n = 86; DISH-, n = 85) who had undergone lumbar spine surgery were analyzed by computed tomography examination. SI joint variations were classified into four types: Type 1, normal or tiny peripheral bone irregularity; Type 2, subchondral bone sclerosis and osteophytes formation; Type 3, vacuum phenomenon; and Type 4, bridging osteophyte and bony fusion. The type of bridging osteophyte in SI joints and the prevalence of ossification in each spinal segment from C1 to SI joint were also examined. Results The most common SI joint variation in the DISH+ group was bony fusion (Type 4), with 71.6% exhibiting anterior paraarticular bridging. On the other hand, SI joint vacuum phenomenon (Type 3) was the most frequent change (57.1%) in the DISH- group. The middle to lower thoracic spine and SI joints were highly affected in DISH and caused bony ankylosis. Conclusions Anterior paraarticular bridging was the most common type of SI joint change in patients with DISH who underwent lumbar spine surgery. The present results regarding variations of SI joint changes in DISH should help understand the etiology of DISH.