DXA IMAGES ARE A RELIABLE ALTERNATIVE TO PELVIC RADIOGRAPHS FOR PERFORMING HIP MORPHOLOGY MEASUREMENTS

INTRODUCTION

Large cohort studies on hip OA usually obtain anteroposterior (AP) pelvic radiographs. Nevertheless, the image quality of a hip dual-energy x-ray absorptiometry (DXA) has increased significantly with new-generation scanners using narrow-angle fan-beam technology. Therefore, DXA images are increasingly used to study hip morphology, especially in large population studies. One of the main advantages of hip DXA images is the lower radiation burden of 0.36-70 µSv compared to hip or pelvic radiographs with an effective dose of 600-700 µSv. However, the image acquisition method is different between radiographs and DXA images. Therefore, whether hip morphology measurements are consistent between DXA images and radiographs is unknown.

OBJECTIVE

We investigated the agreement and reliability of the measurements performed on DXA and radiographs.

METHODS

We included 750 hips from 411 participants from the Rotterdam study, a population-based cohort study, who received a hip DXA and pelvic radiograph on the same day. The participants had a median age of 67.3 years (range 52.2 – 90.6), 45.5% were male, with a median BMI of 26.2 kg/m² (range 16.9 – 39.5). The acetabular depth-width ratio (ADR), modified acetabular index (mAI), alpha angle (AA), Wiberg and lateral center edge angle (WCEA, LCEA), extrusion index (EI) and triangular index ratio (TIR) were automatically determined on both imaging modalities, based on 38 landmark points. The intraobserver and intermethod agreement were studied using Bland-Altman methods, and the reliability was assessed using ICCs or concordance correlation coefficients (CCC) for non-normal distributed variables. Intraobserver reliability was tested with a 2-way random-effects model, single rater, absolute agreement ICC. Intermethod reliability was tested with a 2-ways mixed-effects model, single rater, absolute agreement ICC.

RESULTS

The mean values of each measurement on both DXA and pelvic radiograph, as well as the intraobserver and intermethod mean difference with limits of agreement (95% CIs) from the Bland-Altman methods, are summarized in Table 1. The limits of agreement for the intraobserver agreement within each imaging modality consistently demonstrated equal or narrower limits of agreement compared to the intermethod agreement.

Table 2 shows the intraobserver and intermethod reliability for all measurements. The intraobserver reliability was better than the intermethod reliability. However, the intermethod reliability was overall good.

CONCLUSION

DXA images and pelvic radiographs can both reliably be used to study hip morphology. Due to the lower radiation burden, DXA images can be an excellent alternative to pelvic radiographs for research purposes.