Usefulness of Measuring Acetabular Anterior Coverage Using a Tomosynthesis Imaging System

Purpose The purpose of this study was to compare the usefulness of measuring acetabular anterior coverage by tomosynthesis and false profile (FP) radiography. Methods 70 hips in 35 patients who were diagnosed with early stage osteoarthritis of the hip, and 60 hips from 30 healthy volunteers were analysed. Plain FP radiographs were taken, and vertical-centre-anterior margin (FP-VCA) angles were measured. Acetabular anterior coverage was measured in the natural standing position using a tomosynthesis imaging system in the sagittal plane. As with FP radiography, we measured vertical-centre-anterior margin (TS-VCA) angles. Results The median values of the FP-VCA angle, and TS-VCA angle were 43.8°, 54.4°, respectively. The TS-VCA angle was significantly larger than the FP-VCA angle. For FP radiographs, the intraobserver intraclass correlation coefficient (ICC) was 0.68, and the interobserver ICC was 0.79. For tomosynthesis sagittal images, the intraobserver ICC was 0.85, and the interobserver ICC was 0.92. There was a strong positive correlation between the TS-VCA angle and the FP-VCA angle. When the FP-VCA angle was 25°, the TS-VCA angle was 35° in regression analysis. Conclusions Measuring acetabular anterior coverage using sagittal plane tomosynthesis correlates well with FP radiography. Regardless of the presence of acetabular deformities, tomosynthesis demonstrated high reproducibility, simple posture setting, low effective doses, and high versatility. A cut-off value of 35° was useful for the detection of developmental dysplasia of the hip joint using the TS-VCA angle.