关键词: 全髋关节置换, 髋关节, 臀中肌, 骨盆倾斜, 股骨头旋转中心高度, 骨盆倾斜角度变化比值, 骨盆稳态

Abstract: BACKGROUND: Pelvic tilt, which is often seen in hip diseases, is also a common functional problem after total hip arthroplasty.
OBJECTIVE: To investigate the mechanism of occurrence and recovery of pelvic tilt after unilateral total hip arthroplasty in patients with femoral head necrosis.
METHODS: The clinical data of 100 patients with femoral head necrosis who underwent unilateral total hip arthroplasty in the Department of Femoral Head Necrosis, Bone Injury Center of First Affiliated Hospital of Guangzhou University of Chinese Medicine were collected retrospectively from June 2021 to February 2023. The patients were divided into three groups, namely, groups A (< 2°, n=48), B (2°-3°, n=34), and C (> 3°, n=18), according to the severity of pelvic tilt on postoperative 3 day. Statistical data were collected and compared between the pre- and postoperative periods of patients of these three groups in terms of the angle of the coronal plane of the pelvis tilt, the length of the gluteus medius muscles of the bilateral sides, the heights of the rotational centers of the femoral heads, the difference in the lengths of the gluteus medius muscles of the bilateral sides and the heights of the rotational centers of the femoral heads, and the ratio of changes in the angle of the pelvic tilt. Pearson correlation coefficient was used to examine the correlation between pelvic tilt angle and other indexes. 
RESULTS AND CONCLUSION: (1) Pelvic tilt aggravation occurred in the short term after surgery. (2) The ratio of change in pelvic tilt angle from postoperative 3 days to postoperative 1 month time period differed between the groups, with group C > group B > group A. There was a difference between group C and the other groups in the time period from postoperative 1 to postoperative 3 months, with the ratio of change being the smallest in group C. There was no difference in the ratio of change between the groups in the time period from postoperative 3 days to postoperative 3 months. (3) The difference in bilateral gluteus medius muscles decreased gradually after surgery, and there was no difference in the comparison of bilateral gluteus medius muscles in the time period from postoperative 3 months. (4) The difference between bilateral centers of rotation increased after surgery, and the difference between bilateral heights at 3 months after surgery was smaller than that before surgery. (5) The pelvic tilt angle at 3 days after surgery, the duration of the disease and the pelvic tilt angle at 3 months after surgery were significantly correlated (all P=0.000), and the difference between bilateral gluteus medius muscles before surgery and the pelvic tilt angle at 3 days after surgery was significantly correlated (P=0.006) (6) The functional pelvic tilt occurred in the patients with femoral head necrosis after total hip arthroplasty. Correction of the pelvic tilt after surgery was based on the adaptive restoration of the functional pelvic tilt angle after surgery. Functional pelvic tilt arises as a compensatory adaptation of the organism based on the short-term postoperative reconstruction of bony structures and the survival of cumulative soft tissue damage.

Key words: total hip arthroplasty, hip joint, gluteus medius, pelvic tilt, heights of rotational center of femoral head, ratio of change in pelvic tilt angle, pelvic homeostasis