Effectiveness of an acetabular positioning device in primary total hip arthroplasty.

To evaluate the efficacy of a commercially available acetabular positioning device, we performed a prospective evaluation of 40 consecutive patients undergoing primary total hip arthroplasty. All surgery was performed by the same surgeon, in the same operating room, and on the same operating table. The acetabular positioning device was designed to place the component in 45 degrees of abduction. At 6 weeks, all radiographs were evaluated by 3 investigators not involved with the surgery. Each radiograph was evaluated by each reviewer on 3 separate occasions, blinded to the findings of the other reviewer to assess interobserver and intraobserver variability. The mean cup abduction angle was 42.1 degrees, with a range from 23 degrees to 57 degrees (SD 8.3 degrees). Intraobserver and interobserver variability were 0.2 and 0.3 degrees, respectively. The findings of this study demonstrate a wide variability in acetabular cup placement in primary total hip arthroplasty. We believe this is due to movement of the pelvis, which may occur during preparation, draping, and retracting during surgery. We feel surgeons should not rely solely on positioning devices when implanting the acetabular component in total hip arthroplasty. Identification of bone landmarks and determination of superolateral implant coverage noted on preoperative templating is advocated to improve the precision of component position.