Diagnostic accuracy of digital radiography for the diagnosis of osteonecrosis of the femoral head, revisited

Background: The radiographic diagnosis of osteonecrosis of the femoral head (ONFH) is challenging for radiologists. Purpose: To measure the sensitivity and specificity of digital radiography for diagnosing ONFH and to evaluate the diagnostic value of the frog-leg view. Material and Methods: Patients diagnosed with ONFH by magnetic resonance imaging (MRI) (n = 132) and normal controls (n = 69) were included. Two radiologists independently graded the likelihood of ONFH and subchondral fracture on radiographs. First, the anteroposterior (AP) and frog-leg radiographs were assessed as a whole. Subsequently, randomly ordered unilaterally cropped AP radiographs were analyzed. Sensitivity and specificity were measured using MRI as reference standard. A subgroup analysis for pre-collapse ONFH was performed. The effect of within-subject correlation was analyzed using a generalized-estimating-equation approach. Inter-reader agreement was assessed with κ statistics. McNemar’s test was used to determine the additional diagnostic value of the frog-leg view. Results: Among the 402 hips from 201 individuals, 191 were classified as normal, 73 as pre-collapse ONFH, and 138 as post-collapse ONFH. The sensitivity and specificity ranges for ONFH were 76–89% and 77–97%, respectively. For pre-collapse ONFH, the sensitivity and specificity were 52–71% and 78–97%, respectively. The κ ranges for the likelihood of ONFH and pre-collapse ONFH were 0.59–0.66 and 0.35–0.59, respectively. The frog-leg view did not provide additional value for diagnosing ONFH. Conclusion: Diagnostic performance of digital radiography for ONFH revealed low sensitivity and poor-to-moderate inter-reader agreement for diagnosing pre-collapse ONFH. There was no additional value of the frog-leg view.