Abstract: BACKGROUND: Subspine impingement caused by low anterior inferior iliac spine is often neglected, resulting in missed diagnosis or poor treatment effect in some patients.  
OBJECTIVE: To compare and analyze the difference of hip joint of patients with anterior inferior iliac spine impingement and those without impingent, to investigate whether conventional X-ray and CT examination can directly or indirectly judge the existence of the low anterior inferior iliac spine.
METHODS:  Totally 15 patients diagnosed with anterior inferior iliac spine impingement and undergoing hip arthroscopic surgery in First Affiliated Hospital of Jinzhou Medical University from January 2016 to June 2019 were selected as trial group. Fifteen patients with non-iliac anterior inferior iliac spine impingement who underwent standard anteroposterior pelvic X-ray and three-dimensional CT examination of the pelvis were selected as control group. The angle α, the center-edge angle of the hip joint, the Tönnis angle, the neck shaft angle, the anteversion angle of the acetabulum, and the horizontal and vertical distance between the anterior inferior iliac spine and the acetabular anterior edge, and the width of the anterior inferior iliac spine were compared between the two groups using X-ray film and CT examination. Finite element analysis was used to simulate the physiological activities of the hip joint in patients with anterior inferior iliac spine, and to observe the absence and presence of local pressure change.  
RESULTS AND CONCLUSION: (1) The center-edge angle and the vertical distance of the anterior inferior iliac spine from the acetabular anterior edge of the trial group were smaller than those of the control group, but only the difference of vertical distance value between the groups was statistically significant (P < 0.05). The measured values of other indicators of the patients were slightly greater in the trial group than those in the control group, but the difference was not significant (P > 0.05). (2) Three-dimensional reconstruction of type II anterior inferior spinal impingement showed that anterior inferior iliac spine was proliferative, hypertrophic, and extends downward, but did not protrude to the acetabular anterior edge. The anterior inferior iliac spine gap disappeared. Moreover, the protruding hypertrophic part of the anterior inferior iliac spine did not make obvious contact with the proximal femur during the entire exercise loading process. (3) It is not possible to infer or judge whether there is a low anterior inferior iliac spine through X-ray and CT scans. The imaging diagnosis of the low anterior inferior iliac spine still mainly depends on three-dimensional reconstruction. Patients with anterior inferior iliac spine may not have abnormal contact between the distal end of the anterior inferior iliac spine hypertrophy and the proximal femur.

Key words: low anterior inferior iliac spine, impingement, imageology, dynamic simulation, hip impingement, hip arthroscopy