Can the Difference Between the Operative and Radiographic Cup Inclination Angle Be Reduced by Applying a Pillow Between the Patient's Legs in Total Hip Arthroplasty Performed In The Lateral Decubitus Position?

During hip replacement surgery the cup is placed on specific planned angles. Cup placement has an effect on the patients' pain-free range of movement, dislocation rates and satisfaction. However, the angles of the cup orientation (i.e. the tilt and rotation), which are preoperatively planned and postoperatively measured on radiographs, have a high variability even when an experienced surgeon is performing the surgery. One of the reasons this occurs is because the operated leg can move the pelvis to a different position in the time between set-up and actual implantation which may lead to the cup being placed in a non-optimal position. This study aims to see if the difference between planned and achieved cup angles and pelvic movement can be lessened by putting a pillow in between the legs to keep it in a stable horizontal position.