Digital measurement and significance of the angle of inclination of the iliac ala relative to the square region

Objective To obtain the angle of inclination of the normal adult iliac ala relative to the square region by three-dimensional(3D) computed tomography(CT) reconstruction and digital measurement of adult intact pelvis, and to provide anatomical parameter support for clinical improvement of ilium and acetabulum fracture reduction quality. Methods Retrospective study. Complete adult pelvic data of CT three-dimensional reconstruction examinations were collected from General Hospital of Central Theater Command from January 2016 to December 2018. There were 60 males (120 sides), 40 females (80 sides), aged for an average 42.18 years old.The data were imported into Mimics 20.0 software in DICOM format, and the surrounding soft tissues, patella, and bilateral femurs were removed to create a complete bilateral independent three-dimensional hip bone model. The iliac wing was divided into three zones. The anterior, middle and posterior tilt angles of the ilium wing were marked according to pelvic-related bone markers and measured by Mimics software. The angle of inclination of the iliac ala relative to the square region were compared between the left and right sides of the same sex and between men and women. Results The angle of inclination of the iliac ala relative to the square region between male and female (mixed left and right) were 142.40°±5.62° and 142.03°±4.82° at the anterior part, while 130.78°±5.75°and 126.37°±6.17° at the middle part, 101.27°±5.40° and 100.46°±5.44° at posterior part. There was no significant difference between the left and right inclination angles of the same sex subjects (all P values>0.05). The anterior and posterior angles of inclination of the iliac ala relative to the square region that had no statistical differences ( all P values>0.05), the middle inclination angle was greater in men than in women. which was statistically significant (P<0.05). The angle of inclination of the iliac ala relative to the square region gradually decreased from front to back(all P values<0.05). Conclusions The angles of inclination of the iliac ala relative to the square region changes between different genders and different parts. The anatomical parameters can provide reference for the anatomical reduction of the ilium and acetabulum fracture during operation. To a certain extent, the quality of reduction of pelvic acetabular fractures can be improved from an overall perspective, and the rotation displacement of the fracture can be evaluated, compensating the deficiency of Matta's criterion. Key words: Ilium; Ala ossis ilium; Imaging, three-dimensional; Digital-anatomy