Very little is known about the accuracy of CTA in diagnosing hip disease. Detailed imaging of the hip joint at MRI can be difficult in bulky or obese patients who have thick layers of overlying soft tissue that separate the joint from the MR imaging surface coil. It is easier to compensate for these types of patients when imaging with CT. As in other joints, CTA of the hip can be used to assess for intra-articular loose bodies (Fig. 10), masses (Fig. 11), and cartilage defects. The reliability of CTA in the evaluation of labral tears is unknown.
At least one recent study suggests that CTA is more sensitive in detecting surface defects than conventional MRI . In this study, 20 hips in 19 patients who had acetabular dysplasia were evaluated using both thin-section, 3D, fat-suppressed, gradient-echo MRI (noncontrast) and single-contrast CTA (0.5-mm-thick sections). CT arthrography had better interobserver variability than MRI for partial thickness cartilage defects (kappa = 0.78 for CT, kappa = 0.52 for MRI), and CT was significantly more sensitive than MRI in detecting defects .
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