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Background Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by ossification of the enthesis. The diagnosis has been mainly based on the chest or whole spine lateral plain film. Recently, chest or thoracolumbar computed tomography (CT) has been reported to be more reliable for the diagnosis of DISH. The purposes of this study were to investigate the prevalence and location of DISH and evaluate the prevalence of comorbidities, such as ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF), using whole spine CT. Methods Whole spine CT scans of patients over 16 years of age who were examined at Cheju Halla General Hospital between February 2011 and December 2016 were reviewed for this study. The diagnosis of DISH was made according to the modified Resnick criteria. The prevalence of DISH in each age decade and its location were evaluated. Also, the prevalence of OPLL and OLF in DISH patients was investigated. Results The overall incidence of DISH was 24.4% (40 of 164 cases). There was no case of DISH in patients in their 40s and younger. The percentile incidences of DISH in patients in their fifth, sixth, seventh, eighth, and ninth decades were 20.0% (4 of 20 cases), 32.3% (10 of 31 cases), 40.0% (10 of 25 cases), 34.5% (10 of 29 cases), and 27.3% (6 of 22 cases), respectively. A strong positive correlation between the age decade and the incidence of DISH was noted (r = 0.853, p = 0.007). DISH patients had higher incidences of OLF (22.5%) and OPLL (37.5%). The most common location of DISH was the middle thoracic spine (90.0%) followed by the lower thoracic spine (87.5%). There was one case of DISH involving only the cervical spine. Conclusions The incidence of DISH diagnosed by CT was higher than we expected. Whole spine CT can be a valuable modality to evaluate the location of DISH in the cervical and lumbar spine and the comorbidity rates of OLF and OPLL.

Background Several previous studies reported on the impact of upright standing and chair sitting on the sagittal spinopelvic alignment. However, there are no studies on the impact of the two Asian (Korean and Japanese) style floor-sitting positions on the sagittal spinopelvic alignment. The purpose of this study was to evaluate the impact of four different body postures (standing, chair sitting, kneel sitting, and cross-legged sitting) on the sagittal spinopelvic alignment. Methods Sixteen selected healthy volunteers (10 males and six females) were subjects of this pilot study. In all subjects, radiographs were taken in comfortable standing and sitting positions. All spinal curvatures including lumbar lordotic angle (LLA), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI) were measured on the radiographs. Results In standing position, the average LLA, SS, PT, and PI were 37.1°, 35.3°, 15.7°, and 51.0°, respectively. In chair sitting, the average LLA, SS, PT, and PI were 17.9°, 20.3°, 28.2°, and 49.5°, respectively. In kneel sitting (Japanese style), the average LLA, SS, PT, and PI were 31.8°, 38.3°, 14.2°, and 52.5°, respectively. In cross-legged sitting (Korean style), the average LLA, SS, PT, and PI were 9.8°, 13.4°, 38.3°, and 51.7°, respectively. LLA in standing (37.1°) and kneel sitting (31.8°) were very similar. Remarkable reduction in LLA was observed in Korean-style cross-legged sitting (9.8°), and LLA in chair sitting (17.9°) was about half of that in standing. SS was similar in standing (35.3°) and kneel sitting (38.3°), and it was reduced remarkably in cross-legged sitting (13.4°). PT was largest in cross-legged sitting (38.3°), and it was similar between standing (15.7°) and kneel sitting (14.2°). PIs were similar in all positions. Conclusions The kneel sitting position did not show significant differences with the standing position when assessed using four parameters related to the sagittal spinopelvic alignment, whereas chair sitting and cross-legged sitting positions significantly altered the spinopelvic alignment compared to the standing position.