Abstract
Background
The aim of this study was to determine the change in standing pelvic sagittal alignment and associated impact on functional acetabular component position at follow-up after total hip arthroplasty (THA).
Patients and Methods
A retrospective review was performed on 91 consecutive patients who had undergone primary THA by a single surgeon via a posterior approach in the lateral decubitus position. Of these, 41 patients had high quality standing AP pelvis radiographs preoperatively, at six weeks postoperatively, and at one year postoperatively available for analysis. Pelvic ratio was defined as the ratio between the vertical distance from the inferior sacroiliac (SI) joints to the superior pubic symphysis and the horizontal distance between the inferior SI joints. Apparent changes in the functional acetabular component position were determined from the change in pelvic ratio between the preoperative and one year postoperative standing AP pelvic radiograph. A change of at least five degrees was considered clinically meaningful.
Results
From preoperative to 1 year postoperative, pelvic ratio decreased (posterior tilt) in 58.5% of cases, did not change significantly in 36.6% of cases, and increased (anterior tilt) in 4.9% of cases (Figure 1). Clinically meaningful changes in acetabular component abduction or anteversion on standing radiographs were observed in 63.4% of cases.
Conclusion
Changes in pelvic tilt occur during the first year after THA, and lead to clinically significant changes in functional acetabular position in the majority of cases. The magnitude and direction of these changes are variable. This brings into question the investment of time and cost of individualizing cup position given the fact that such a high percentage will change within year postoperatively due to the change in pelvic rotation that occurs as the natural history of recovery from THA.
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