Abstract
Introduction
Literature describes pelvic rotation on lateral X rays from standing to sitting position. EOS full body lateral images provide additional information about the global posture. The projection of the vertical line from C7 (C7 VL) is used to evaluate the spine balance. C7 VL can also measure pelvic sagittal translation (PST) by its horizontal distance to the hip center (HC). This study evaluates the impact of a THA implantation on pelvic rotation and sagittal translation.
Materials and Method
Lumbo-pelvic parameters of 120 patients have been retrospectively assessed pre and post- operatively on both standing and sitting acquisitions (primary unilateral THA without complication). PST is zero when C7VL goes through the center of the femoral heads and positive when C7VL is posterior to the hips' center (negative if anterior). Three subgroups were defined according to pelvic incidence (PI): low PI <45°, 45°<normal PI<65° or high PI>65°.
Results
Pre-operatively PST standing was −0.9 cm (SD 4.5; [−15.1 to 7.2]) and PST sitting was 1.3cm (SD 3.3; [−7.7 to 11.8]). The overall mean change from standing to sitting was 2.2 cm ([−7.2 to 17.4]) (p<0.05).
Post-operatively PST standing was 0.2 cm (SD 4.7; [−17 to 8.1]) and PST sitting was 1.4cm (SD 3.5; [−7.3 to 10.4]). The overall mean change from standing to sitting was 1.2 cm ([−14.2 to 22.4]) (p<0.05).
In low PI group pre and post-operatively, PST increased significantly from standing to sitting (p<0.05; with HC going anterior to C7VL). When comparing pre and post operative changes, standing PST significantly increased (p=0.001). Pre to postoperative PST variation (sitting-standing) decreased significantly (p=0,01).
In normal PI group pre-operatively, PST increased from standing to sitting (p=0.004). When comparing pre and postoperative changes, PST increased (p=0.006). Pre to postoperative PST variation (sitting-standing) decreased significantly (p=0,04).
In high PI group pre and post operatively, PST increased from standing to sitting (p=0.034) while there are no significant changes from pre to post-operative status in standing and in sitting.
Discussion
Anteroposterior pelvic tilt is not the only adaptation strategy for postural changes from standing to sitting positions. Anteroposterior pelvic translation (quantified by PST) is an important adaptation mechanism for postural changes. Comparison of pre and post-operative values of PST points out the importance of pelvic translation for low and standard PI patients after THA.
The anteroposterior translation appears to change significantly in different functional positions pre and post operatively. This is an important variable to consider when assessing the patients' posture change or investigating the causes of the hip dislocation after total hip arthroplasty or spinal fusion.
Conclusion
Pelvic translation must be considered as a significant mechanism of adaptation after THA. Further studies are needed to study the impact on subluxation or dislocation.
