Diagnostic Accuracy of Plain X-Ray in Diagnosing Avascular Necrosis of Hip Joint, Keeping Magnetic Resonance Imaging (MRI) as Gold Standard

Abstract

Avascular necrosis of the femoral head is an important cause of hip pain and functional limitation. Magnetic resonance imaging is considered the reference standard for early diagnosis; however, plain radiography remains widely available and cost-effective, especially in resource-limited settings. Objective: To determine the diagnostic accuracy of plain X-ray in diagnosing avascular necrosis of the hip joint, using magnetic resonance imaging as the gold standard. Methods: This cross-sectional validation study was conducted in the Department of Radiology, Sheikh Zayed Hospital, Rahim Yar Khan, from January 10, 2025, to July 10, 2025. A total of 188 patients aged 30–70 years with clinically suspected non-traumatic avascular necrosis of the hip joint were included through non-probability consecutive sampling. Patients with traumatic hip pathology or contraindications to MRI were excluded. All participants underwent plain radiography followed by MRI using a 1.5-Tesla scanner. The diagnostic performance of X-ray was calculated in terms of sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy, with MRI used as the reference standard. Results: The mean age of the patients was 48.34 ± 6.86 years. There were 96 males (51.1%) and 92 females (48.9%). MRI confirmed avascular necrosis in 99 patients (52.7%), while X-ray identified avascular necrosis in 102 patients (54.3%). Plain radiography showed 87 true-positive, 15 false-positive, 12 false-negative, and 74 true-negative cases. The sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy of plain X-ray were 87.88%, 83.15%, 85.29%, 86.05%, and 85.64%, respectively. A significant association was observed between X-ray and MRI findings (p < 0.001). Diabetes mellitus was also significantly associated with avascular necrosis (p < 0.001). Conclusion: Plain X-ray demonstrated good diagnostic accuracy for detecting avascular necrosis of the hip joint and may be used as an effective first-line imaging modality, particularly where MRI availability is limited. However, MRI remains essential for early detection, confirmation of equivocal cases, and accurate disease staging.