Background: Sacroiliac joint (SIJ) abnormality is a potential source of low back pain (LBP), therefore numerous patients receive various treatments because of the degenerative changes of SIJ. However, the outcome is unfavorable for patients because these morphologic alterations are common but not the origins of LBP. Previous studies revealed lumbar fusion and transitional vertebra increased the prevalence of degeneration of SIJ. Lumbar disc herniation (LDH) is one of the most common lumbar diseases, but there is no study regarding the relationship between LDH and SIJ degradation. Objectives: The aim of this study was to investigate the severity of SIJ degeneration in patients with LBP with LDH. The relationship between degenerative changes of SIJ and LDH was also assessed. Study Design: Retrospective observational study. Setting: This study was conducted in 2 medical centers located in southeast and midwest China, respectively. Methods: Lumbar and pelvic computed tomography (CT) scans of patients with LDH (LDH group) from January 2016 to May 2020 were reviewed using a picture archiving and communication system. The control group was age, gender, and body mass index–matched patients with LBP without LDH. Patients underwent whole abdomen and pelvic CT examinations due to non-musculoskeletal disorders. Scores of SIJ degeneration were compared between patients with LDH and the control group. Differences in SIJ degeneration among patients with LDH with diverse characteristics, symptoms, and complications were also evaluated. Univariate and multivariate linear mixed model (LMM) was chosen to identify the factors associated with SIJ degeneration. Results: CT examinations of 782 patients with LDH were assessed, whereas 223 patients were in the control group. The SIJ degeneration score of the LDH group and control group were 6.00 (5.00) and 3.00 (4.00) (P < 0.05). Age and whether patients suffered from LDH were included in the LMM, which involved all reviewed patients (P < 0.05). Regarding the characteristics of LDH, the patients with more herniated discs had more severe SIJ degeneration. The score of SIJ degradation in patients with upper LDH was significantly higher than the other patients with LDH (12.00 [4.00] vs. 6.00 [4.00]; P < 0.05). Similarly, more significant SIJ degeneration was observed in patients with LDH who had secondary lumbar spinal stenosis (10.00 [4.00] vs. 5.00 [4.00]; P < 0.05). The scores of SIJ degradation were significantly greater in patients with LDH with sciatica, numbness, weakness, and/or cauda equina syndrome. Age and LDH were identified as associated factors for more serious degeneration of SIJ among patients with LDH. Limitations: The main limitation of this study was the retrospective observational nature. Hence our study described that SIJ degeneration was relevant to LDH, but the causal relationship was uncertain. Magnetic resonance imaging was not chosen in this study. Conclusions: The SIJ degeneration in patients with LDH was more serious than in individuals without LDH. SIJ degeneration was more significant in patients with LDH with more pathological alterations, symptoms, and complications. Age and LDH relate to SIJ degeneration. Therefore the diagnosis and selection of treatment for SIJ changes should comprehensively consider the coexistence of LDH. Key words: Lumbar disc herniation, low back pain, sacroiliac joint, degeneration, sciatica, numbness, weakness, cauda equina syndrome, computed tomography, linear mix model

BackgroundDegeneration of sacroiliac joints (SIJ) is common in the general population, which associates with age, gender and body mass index (BMI). This degenerative disease relates to various lumbar disorders. Lumbar facet joint osteoarthritis (LFJOA) is highly prevalent, but relationship between this disease and SIJ degeneration remains poorly evaluated.ObjectivesThis study aimed to investigate the relation between LFJOA and SIJ degeneration. We hypothesized that LFJOA patients might suffer more serious SIJ degeneration, thus multiple linear regression was employed to compare the effect of LFJOA and demographic characteristics on degeneration of SIJ.MethodsWe reviewed pelvic and lumbar computed tomography (CT) examinations of LFJOA patient with low back pain (LBP) through a picture archiving and communication system. The controls were age, gender and BMI-matched individuals who were free of LFJOA and LBP, and underwent pelvic and whole abdomen CT scans due to the non-musculoskeletal symptoms. Severity of SIJ degeneration was scored using a quantitative method which has been descripted by Bäcklund et al [1]. LFJOA was graded using a method which has been mentioned by Weishaupt et al [2]. Briefly, this method concerns facet joint space, osteophytes, hypertrophy of the articular processes, and subarticular bone erosions, which ranges from 0 to 3 for a joint. If there is a discrepancy between 2 joints in the same level, the greater one was used. LFJOA was defined at least one level ≥2 from L1-2 to L5-S1. Scores of SIJ degeneration were compared between LFJOA patients and the controls. Correlation analysis between SIJ degeneration score and number of LFJOA levels, number of LFJOA joints, sum of LFJOA grades were performed. Stepwise multiple linear regression model was used to find the most important contributor of SIJ degeneration among LFJOA, gender, age and BMI.Results(1) CT examinations of 992 LFJOA patients and 399 controls were reviewed. (2) Score of SIJ degeneration in LFJOA patients were higher than that of the controls (8.85±2.94 vs. 4.31±2.52, P<0.05). (3) SIJ degeneration score positively correlated with number of LFJOA levels (r=0.11, P<0.05), number of LFJOA joints (r=0.09, P<0.05) and sum of grades (r=0.10, P<0.05). (4) Results of multiple linear regression were shown in Table 1. LFJOA had the greatest standardized coefficient in the regression model.ConclusionLFJOA patients suffers more significant SIJ degeneration, and more severe LFJOA leads to more serious SIJ degeneration. Influence of LFJOA on SIJ degeneration is stronger than demographic characteristics.References[1] Bäcklund J, Clewett Dahl E, Skorpil M. Is CT indicated in diagnosing sacroiliac joint degeneration? Clin Radiol 2017;72(8):693.e9-693.e13.[2] Weishaupt D, Zanetti M, Boos N, et al. MR imaging and CT in osteoarthritis of the lumbar facet joints. Skeletal Radiol 1999; 28: 215-219.Abstract THU0432 – Table 1Stepwise multiple linear regression model for sacroiliac joints degeneration scoreIndependent variablesUnstandardized coefficientStan...