Correlation analysis of clinical outcomes after THA in patients with pelvic skew
Authors: Lai Tianyu , Lan Yiping , Feng Eryou 
Published: April 2023

Abstract
Objective: THA (total hip arthroplasty) is the most effective treatment for end-stage hip disease. Patients with pelvic tilt often have bony structural deformities and peripheral soft tissue lesions, with subpelvic pelvic tilt being the most common type of pelvic tilt and prevalent in all types of hip disease. The purpose of this study was to investigate the effect of total hip arthroplasty on the orientation and function of the cup and the degree of tilt in patients with subpelvic pelvic tilt, and to summarize it.
Methods: The data of 897 patients who underwent THA from 2017.01 to 2021.01 in Orthopaedic District 1 were retrospectively analyzed, and 158 of them were included. Preoperative standing hip radiographs were taken to determine the pelvic skew angle, and the subpelvic pelvic skew was divided into 2 types according to the skew direction: type I for pelvic skew on the affected lower limb; type II for pelvic skew on the healthy lower limb. The cases were further divided into 2 subtypes according to the obtained pelvic skew angle: 0°-3° for type A; ≥3° for type B. Clinical observation and follow-up were performed at 1 day, 1 month, 3 months, 6 months, 1 year, and the last clinic visit (average 29 months) after surgery, and standing hip radiographs were taken to measure the cup position parameters and pelvic skew angle. The Harris score was used to evaluate the function of the affected hip joint before and after surgery.The preoperative and postoperative hip function was evaluated by Harris score.Repeated-measures ANOVA was used for intra-group comparisons, while between-group means were compared using the lsd-t test.
Results: 75 cases of type I and 83 cases of type II. The cup position parameters did not change over time for each subtype, and the cup position remained stable; preoperatively, the Harris score decreased as the degree of pelvic distortion increased for each subtype; over time, the Harris score improved significantly and the degree of pelvic distortion improved for each subtype compared with preoperatively, with statistically significant differences between time points (P < 0.001). At most postoperative time points, the mean Harris score for IB was smaller than that of the other subtypes (P < 0.05), and at the 1-year postoperative follow-up, the difference between the mean functional scores of IB and IIB patients was not statistically significant (P = 0.118 > 0.05), but the mean functional scores of IB patients tended to be smaller than those of IIB patients. At all postoperative time points, the mean pelvic skew angle was greater in patients with type IB than in all other subtypes (P < 0.05).
Conclusion: In the case of subpelvic pelvic tilt caused by multiple hip disorders, the surgeon was able to achieve the desired effect by using THA not only for the pelvis but also for the pelvis.It can improve the patient's function and correct the pelvic skew while the socket cup remains stable; however, for patients with pelvic skew on the affected side and the skew angle ≥3°, the postoperative functional improvement and pelvic skew correction are less. Adequate preoperative preparation, early surgery, and accurate reconstruction of the femoral eccentric distance are important for these patients to maintain hip stability, maintain pelvic balance, and improve hip function.