Degeneration of the sacroiliac joints (SIJs) is a common finding, while its underlying cause and development remain incompletely understood. The aim of this investigation was to describe the spatial distribution of degenerative SIJ changes across age groups and to investigate for the first time their relationship to anatomical form and sex. For this IRB-approved investigation, demographic data of 818 patients without SIJ disease were retrieved from electronic patient records. High-resolution computed tomography (CT) datasets of all patients were analysed retrospectively for seven predefined age groups (ten-year increments, from < 25 to ≥ 75). A structured scoring system was applied to assess sclerosis, osteophytes, joint space alterations, and anatomical form. Chi-square tests were used to compare frequencies of degenerative lesions, and logistic regression analyses were performed to investigate associations between demographic data, anatomical form, and the presence of structural lesions. Sclerosis and osteophytes were common findings, with an overall prevalence of 45.7% and 46.8%, respectively. Female sex had an odds ratio (OR) of 0.15 (95% CI: 0.08–0.27) for the presence of ventral osteophytes and of 4.42 (95% CI: 2.77–7.04) for dorsal osteophytes. Atypical joint forms were significantly more prevalent in women with 62.1% vs. 14.1% in men (p < 0.001). Accessory joints increased the likelihood of dorsal sclerosis (OR 2.735; 95% CI 1.376–5.436) while a typical joint form decreased its likelihood (OR 0.174; 95% CI 0.104–0.293). Sex and anatomical joint form have a major impact on the development of degenerative lesions of the SIJs and their spatial distribution.

Objectives The aim of this investigation was to determine the prevalence of variant sacroiliac joint forms in symptomatic patients with mechanical joint disease (MJD) and axial spondyloarthritis (axSpA) compared with control patients. Method A total of 973 patients were included in this cross-sectional study (95 axSpA; 61 MJD; 817 controls); clinical diagnosis, age and gender were noted. An established scoring system was used to classify joint forms on computed tomography scans of the pelvis. Frequencies of joint forms were compared between groups (axial spondyloarthritis; mechanical joint disease; controls). Results Patients with MJD exhibited the highest proportion of atypical joints (80.3% in MJD vs 44.1% in axSpA and 37.5% in controls; p&lt; 0.001). Overall, females had a significantly higher proportion of atypical joints than men (65.0% vs 17.8%; p&lt; 0.001); proportions of atypical joints were significantly higher in males with symptomatic joint disease than in male controls: 32.2% in axSpA, 55.0% in MJD, 13.9% in controls; p≤ 0.001. Two specific joint forms were significantly more prevalent in symptomatic patients than in controls: the iliosacral complex (16.2% vs 4.2%; p&lt; 0.001) and the crescent-shaped ilium (9.1% vs 2.8%; p&lt; 0.05). Conclusions Our data demonstrate a strong association between atypical joint forms and symptomatic joint disease.

ObjectiveTo assess the diagnostic accuracy of radiography (X-ray, XR), CT and MRI of the sacroiliac joints for diagnosis of axial spondyloarthritis (axSpA).Methods163 patients (89 with axSpA; 74 with degenerative conditions) underwent XR, CT and MR. Three blinded experts categorised the imaging findings into axSpA, other diseases or normal in five separate reading rounds (XR, CT, MR, XR +MR, CT +MR). The clinical diagnosis served as reference standard. Sensitivity and specificity for axSpA and inter-rater reliability were compared.ResultsXR showed lower sensitivity (66.3%) than MR (82.0%) and CT (76.4%) and also an inferior specificity of 67.6% vs 86.5% (MR) and 97.3% (CT). XR +MR was similar to MR alone (sensitivity 77.5 %/specificity 87.8%) while CT+MR was superior (75.3 %/97.3%). CT had the best inter-rater reliability (kappa=0.875), followed by MR (0.665) and XR (0.517). XR +MR was similar (0.662) and CT+MR (0.732) superior to MR alone.ConclusionsXR had inferior diagnostic accuracy and inter-rater reliability compared with cross-sectional imaging. MR alone was similar in diagnostic performance to XR+MR. CT had the best accuracy, strengthening the importance of structural lesions for the differential diagnosis in axSpA.

Our study shows a very high prevalence of fat metaplasia adjacent to the sacroiliac joint in asymptomatic patients, while erosions are extremely uncommon.

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