Correlation between Pelvic Inclination and Radiological Shape of the Pelvic Cavity.

This study was designed to identify the change in radiological shape of the pelvic cavity caused by sagittal pelvic inclination and to learn the correlation between inclination and progression of osteo-arthritis (OA) of the hip joint.As a preliminary study, antero-posterior (AP) and lateral radiographs of 10 bleached pelves were taken simultaneously in seven different sagittal tilt angles.The degree of sagittal tilt of the pelvis (A) was then compared to the longitudinal: transverse axis length (L/T) ratio of the radiological shape of the pelvic cavity in AP radiographs. This study revealed a linear relationship between the two parameters that led to the equation: A=-67.0°×L/T+55.7° in males and A=-69.0°×L/T+61.6° in females. Using this the sagittal pelvic tilt can be calculated from the radiological shape of the pelvic cavity.Applying this equation to pelvic radiographs of 212 patients; 52 normal hips and 160 with OA hip of varying severity, pelvic tilt was calculated to investigate whether it relates to the aging of the patient or involves progression of OA.There was a significant correlation between age and pelvic tilt angles of patients in both normal and OA hip groups; the pelvis tended to incline posteriorly with increasing age. Further studies are required to elucidate the participation of the pelvic inclination on progression of OA of the hip.