Abstract
Introduction
While research has been carried out widely for sagital pelvic tilt, research reports for coronal pelvic obliquity are few. The aim of this study is to evaluate changes of the pelvic obliquity before and after total hip arthroplasty.
Material and Methods
This retrospective study includes 146 cases of hips that were received total hip arthroplasty. There were 20 cases of revision, and 2 cases of re-revision. 17 cases were received bilateral total hip arthroplasty. The standing plain X-ray was used for evaluation of the pelvic obliquity in both before and 1-year after surgery. The correlation of pelvic obliquity was assessed between before and after surgery. 146 cases were classified into 3 groups (A, B, and C) according to the severity of the pelvic obliquity (0º−3º, 3º−6º, and >6º). Among the groups, statistical analysis was evaluated in the leg length discrepancy and the range of motion of the hip (flexion, extension, abduction, adduction, internal and external rotation) before and after surgery with 95% confidence intervals.
Results
The mean pelvic obliquity angle was 2.6º with the range of 0 to 15.9º preoperatively, while the mean angle was 2.0º with the range of 0 to 8.8º postoperatively. There was statistical correlation in pelvic obliquity between before and after surgery. The mean leg length discrepancy was −8.3 before surgery, and was 0.1 after surgery. Comparing three groups of pelvic obliquity, preoperative leg length discrepancy was significantly longer in larger pelvic obliquity groups. The range of motion in hip flexion was also significantly smaller in larger pelvic obliquity groups. There were not significant differences in postoperative leg length discrepancy and other parameters.
Discussion
The most important finding of present study was that postoperative pelvic obliquity related only the preoperative leg length discrepancy and the range of motion in hip flexion. We expected that pelvic obliquity is improved by correction of leg length difference. Nevertheless, there were not significant differences in postoperative leg length discrepancy. This indicated that contracture of the hip joint is contribute to pelvic obliquity more than leg length discrepancy.
Previous study reported that pelvic obliquity would be improved by physical therapy 4 to 6 month after surgery. However, in our data, pelvic obliquity still remained at 1-year follow up. Moreover, postoperative pelvic obliquity related the preoperative range of motion in hip flexion. Therefore, preoperative pelvic obliquity is one of the most important parameter to make decision of postoperative leg length discrepancy.
There is certain limitation in our study. We did not assess patient outcome in each groups. Extensive studies are needed to reveal correlation between pelvic obliquity and patient outcome.
Conclusion
Pelvic obliquity related the preoperative leg length discrepancy and the range of motion in hip flexion. Contracture of the hip joint may cause pelvic obliquity.
