Differences of Anteroposterior Pelvic Radiographs Between Supine Position and Standing Position in Patients with Developmental Dysplasia of the Hip.

OBJECTIVE: To explore the difference in pelvic tilt and hip joint parameters with developmental dysplasia of the hip (DDH) comparing the anteroposterior (AP) pelvic radiographs taken in supine and standing positions.

METHODS: A prospective study of DDH patients undergoing Bernese periacetabular osteotomy (PAO) was conducted. AP pelvic radiographs were taken in supine and standing positions before surgery The pelvic tilt and hip joint parameters from the two radiographs were compared. Contrast parameters included the distance between the pubic symphysis to sacrococcygeal distance (PSSC), lateral center-edge angle (LCEA), Tönnis angle (TA), and angle of sharp (SA).

RESULTS: A total of 110 young DDH patients were enrolled, including 32 men and 78 women, aged 18-49 years. The male PSSC was 45.63 ± 13.69 mm in supine position and 36.91 ± 12.33 mm in standing position (P < 0.05). The female PSSC was 56.76 ± 13.54 mm in supine position and 48.62 ± 15.44 mm in standing position (P < 0.05). In this study, LCEA <20° in AP pelvic radiographs in the supine position was found in 52 men and 135 women. For male patients, in supine position and standing position, LCEA were 5.51° ± 11.88° and 4.45° ± 12.22°, respectively (P < 0.05); TA were 20.20° ± 9.63° and 21.30° ± 9.97°, respectively (P < 0.05), and SA comparison showed no significant differences. For female patients, in supine position and standing position, LCEA were 3.07° ± 12.07° and 1.69° ± 12.11°, respectively (P < 0.05), TA were 22.62° ± 9.31° and 23.82° ± 9.45°, respectively (P < 0.05), and SA were 48.01° ± 4.68° and 48.49° ± 4.74°, respectively (P < 0.05).

CONCLUSION: Compared with the supine position, the young DDH patients have pelvic tilt backward and a decrease in hip coverage in the standing position.