Reproducibility and Diagnostic Accuracy of Kellgren-Lawrence Grading for Osteoarthritis using Radiographs and Dual Energy X-ray Absorptiometry (DXA) images Running Title: Osteoarthritis grading using DXA

Introduction: Advances in image quality from modern Dual Energy X-ray absorptiometry (DXA) scanners now allow near radiograph-like quality images at a low radiation dose. This opens potential new applications for the use of DXA scanners to study other musculoskeletal conditions, such as osteoarthritis which is often investigated by visual assessment of radiographs. Together, osteoporosis and osteoarthritis are the two most common musculoskeletal conditions, both of which primarily affect older people. The aim of this study was to determine whether Kellgren-Lawrence grading of DXA images can be used to grade hip osteoarthritis as effectively as radiographs. Methodology: People who had attended for recent pelvic radiographs underwent DXA images of hips (50 hips from 25 people) using a GE Healthcare iDXA scanner. Three observers assigned Kellgren-Lawrence grades to each image and grading was repeated at least one week apart. Intraobserver and inter-observer reliability for radiograph and DXA were calculated using quadratic weighted kappa (QWK). People were recalled 12 months later and the tests were repeated with both the radiograph and DXA scans taken within 2 weeks of each other. Results: Hip DXA intra-observer reproducibility achieved a QWK range of 0.88-0.95 and interobserver reproducibility of 0.85-0.88, similar to QWK from hip radiographs. Intra-observer reliability between subject-matched radiograph and iDXA images revealed QWK ranging between 0.80-0.88. Conclusions: Reproducibility of hip osteoarthritis grading using DXA was comparable with that of radiographs in this study and similar to repeatability scores previously published in literature. Given the lower radiation dose and the opportunity to simultaneously investigate osteoporosis, DXA presents an attractive imaging option for osteoarthritis.