Effects of shooting position on X-ray evaluation index of developmental hip dysplasia

Abstract

Objective To explore the impacts of the imaging positions on the sagittal tilt of the pelvis and the imaging parameters of the hip joint. Methods From December 2015 to October 2016, a total of 78 female DDH patients (DDH group) who received Bernese periarticular osteotomy were enrolled, aged 28.41±9.91 years (range 18-49 years) with 135 hips. There were 21 cases on one side and 57 cases on both sides. Another 26 female volunteers without spinal and hip disease were enrolled as the control group, aged 23.54±5.58 years (range 18-49 years) with 52 hips. X-ray films of the anterior and posterior pelvis were performed in both groups. The pelvic sagittal tilt was evaluated by measurement (pubic symphysis to sacrococcygeal distance, PSSC), with lateral center-edge angle of Wiberg (LCEA), Tonnis angle (TA), and Sharp angle (angle of Sharp, SA) assessed the degree of hip dysplasia and assessed the horizontal positional relationship between the femoral head and the acetabulum using tear drop distance (TD). All data were measured twice by two measurers independently. The correlation between hip parameters and X-ray position was analyzed. Results The average PSSC in the supine and standing positions of the control group were 53.73±16.22 mm and 36.45±14.21 mm, respectively with significant difference-17.28±8.07 mm (t=-10.913, P=0.000). The PSSC of the supine and standing positions of the DDH group were 56.76±13.54 mm and 48.62±15.44 mm, respectively with significant difference-8.13±13.02 mm (t=-5.516, P=0.000). The PSSC of the standing DDH group was larger than that in the control group. There was no significant difference in the PSSC between the two groups in the supine position. Furthermore, there were no significant difference in the supine and standing PSSC between the unilateral and bilateral DDH patients (P>0.05). In the control group, the hip in supine and standing position, LCEA averaged 30.33°±4.69° and 29.70°±3.83° (P>0.05), and TA averaged 4.05°±3.51° and 4.36°±3.07° (P>0.05), respectively. SA averaged 40.53°±4.34° and 41.79°±3.16° (P>0.05), and TD averaged 6.80±0.98 mm and 6.65±1.30 mm (P>0.05), respectively. In the DDH group, the hip in supine and standing positions, LCEA averaged 3.07°±12.07° and 1.69°±12.11° (P 0.05), respectively. SA averaged 48.01°±4.68° and 48.49°±4.74° (P>0.05), respectively, and TD averaged 10.51±3.51 mm and 10.93±4.23 mm (P>0.05), respectively. Conclusion From supine to standing, the pelvis backward is the main trend in sagittal plane. In standing, the pelvis of female DDH patients is forward contrast with normal women. There was no difference in pelvic tilt between unilateral and bilateral DDH patients. Female DDH patients from the supine to standing, hip coverage decreased, while the femoral head appeared horizontally outward. The hip joint of DDH patients is unstable. Key words: Hip dislocation, congenital; Pelvis; Photogrammetry; Osteotomy