Efficacy of the Anatomical-Pelvic-Plane Positioner in Total Hip Arthroplasty in the Lateral Decubitus Position

Total hip arthroplasty in the lateral position involves particularly large variance in the sagittal tilt of pelvis fixation, which affects the imprecision of the cup anteversion leading to poor outcomes. We have added an additional compression pad to an existing device, also to be used in the lateral position, but theoretically enabling fixation on the anatomical pelvic plane (APP) serving as the reference plane. The present study aims to evaluate the usefulness of this device in comparison with the conventional device.

We have studied 141 patients who underwent total hip arthroplasty at our hospital. Two frontal plain x-rays of the pelvis were obtained preoperatively for each patient after pelvis fixation; one with the conventional lateral fixation device and the other with an APP lateral fixation device. The sagittal tilt of the pelvis in each position was measured with 3D templating software, and variance in the sagittal tilt was compared between the 2 devices.

The mean bias in sagittal tilt relative to the functional pelvic plane (FPP) in the conventional device was −5.0° ± 4.8° (minus mean backward tilt) and was within 5° relative to the functional pelvic plane in 43%. The mean bias in the sagittal tilt relative to the APP in the APP lateral position device was 1.7° ± 3.1° (forward tilt) and was within 5° relative to the APP in 89%. The APP lateral device significantly reduced the variance in the sagittal tilt.

This device holds promise as a means of reducing the sagittal tilt in a simple, minimally invasive, and highly cost-effective manner.