Pelvic positioning during total hip arthroplasty (THA) affects functional position of the acetabular component. We sought to evaluate whether preoperative pelvic tilt correlated with intraoperative pelvic tilt while positioned on a traction table for direct anterior THA and furthermore to evaluate whether there was a consistent and predictable effect on pelvic tilt while positioned for surgery.
We evaluated the sagittal spinopelvic preoperative standing and supine pelvic tilt radiographic measurements as compared with intraoperative measurements of 25 patients. Changes in pelvic tilt were analyzed for statistical significance and interobserver reliability.
The mean standing pelvic tilt was 13.5° ± 5.7°. The mean supine pelvic tilt was 13.3° ± 6.1°. There was no statistically significant difference between standing and supine pelvic tilt (P = .866). The mean intraoperative pelvic tilt was 3.0° ± 6.2°. There was a statistically significant decrease in pelvic tilt between both standing to intraoperative comparison and supine to intraoperative comparison (P < .0001 for both). Difference in mean between these comparisons was 10.5° ± 4.6° (95% confidence interval, 8.7°-12.3°) and 10.3° ± 6.3° (95% confidence interval, 7.8°-12.8°), respectively.
Patient positioning on a traction table for direct anterior THA has a reliable effect on pelvic tilt in the magnitude of approximately 10° decreased pelvic tilt. This effect on pelvic tilt correlates to approximately 7.4° and 3° altered anteversion and inclination, respectively. Taking into account this change in pelvic tilt at the time of surgery will allow the hip arthroplasty surgeon to more accurately place acetabular components in the desired functional position.