Comparison of Sacroiliitis Grade Readings on the Same Plain Radiographs by the Same Observer at Different Periods

Background: This study aimed to investigate whether there is a difference between the readings of plain sacroiliac radiographs of patients with sacroiliitis by the same observer. Materials and methods: In the study, we included patients diagnosed with sacroiliitis through sacroiliac MRI who had undergone plain radiographs at our center between 2015 and 2022. The radiographic grading of patients was conducted by transferring their demographic and clinical information into a computerized environment so that these details would not be identifiable. The plain radiographs were numbered, and the responses were graded as grade 0, 1, 2, 3, or 4 for the right and left sacroiliac joints. The next day, using the same procedure, the same clinician re-evaluated the same plain radiographs in a different order without viewing the previous responses. This method was employed to prevent bias. The results (kappa value) were evaluated (0.00-0.20: slight agreement, 0.21-0.40: fair agreement, 0.41-0.60: moderate agreement, 0.61-0.80: substantial agreement, 0.81-1.00: perfect agreement). Results: The study population included 478 patients and 956 sacroiliac joints from plain radiographs, both on the right and left. Following the observer's classification of the sacroiliac joints into 0, 1, 2, 3, and 4, a moderate level of agreement was found in the second evaluation of the same observer a day later with the same grades (p<0.001, kappa: 0.576). When categorized as grade 0-1 and grade 2-4, there was moderate agreement (p<0.001, kappa: 0.519), and categorization into grades 0-2 and 3-4 showed substantial agreement (p<0.001, kappa: 0.715). Analyzing the categorization into grades 0-3 and grade 4 revealed a higher kappa value, indicating substantial agreement (p<0.001, kappa: 0.766). Conclusion: Intraobserver interpretation of radiographs may be more accurate than the interpretation of different specialists. While interpreting plain radiographs, we observed variability between adjacent grades but less variability between distant grades. However, these results need to be validated.