Radiological inclination (RI) is determined in part by operative inclination (OI), which is defined as the angle between the cup axis or handle and the sagittal plane. In lateral decubitus the theatre floor becomes a surrogate for the pelvic sagittal plane. Critically at the time of cup insertion if the pelvic sagittal plane is not parallel to the floor either because the upper hemi pelvis is internally rotated or adducted, RI can be much greater than expected. We have developed a simple Pelvic Orientation Device (POD) to help achieve a horizontal pelvic sagittal plane. The POD is a 3-sided square with flat footplates that are placed against the patient's posterior superior iliac spines following initial positioning (figure 1). A digital inclinometer is then placed parallel and perpendicular to the patient to give readings of internal rotation and adduction, which can then be corrected. A model representing the posterior aspect of the pelvis was created. This permitted known movement in two planes to simulate internal rotation and adduction of the upper hemi pelvis, with 15 known pre-set positions. 20 participants tested the POD in 5 random, blinded position combinations, providing 200 readings. The accuracy was measured by subtracting each reading from the known value.Introduction
Methods
