Effectiveness of a Pre-Operative Lateral Decubitus Position Radiologic Examination Using a Goniometer and Rod in THRA

ABSTRACT

PURPOSE: For inserting an acetabular cup with the correct inclination angle, we checked the pelvic tilts using the lateral decubitus position X-ray and a goniometer and pointer. The accuracy of the cup inclination at the targeted angles was evaluated after insertion of the cup at an adjusted angle with using a goniometer and pointer. MATERIALS AND METHODS: Between January 2008 and December 2009, 56 hips in 50 patients who underwent total hip replacement arthroplasty (THRA) were enrolled. The mean age at the time of surgery was 63.8 years. There were 31 male patients (36 hips) and 19 female patients (20 hips). The preoperative diagnoses included osteonecrosis of the femoral head in 27 hips, secondary osteoarthritis in 10 hips and femoral neck fracture in 14 hips. The preoperative pelvic tilts were evaluated according to the lateral decubitus position X-ray with using a goniometer and pointer. The target inclination angle was 40degrees for 27 hips that underwent ceramic-on-ceramic THRA. The target inclination angle was 45degrees for the 29 hips that underwent ceramic-on-polyethylene THRA. The inclination of the cup was evaluated after inserting the acetabular cup at the adjusted angle using a goniometer and pointer. RESULTS: The mean inclination angle of the acetabular cup was 39.3degrees for the ceramic-on-ceramic THRA and 44.4degrees for the ceramic-on-polyethylene THRA. There were no significant differences between the 40degrees and 45degrees (P=0.059, P=0.071). CONCLUSION: The pelvic tilt can be evaluated by checking the lateral decubitus X-ray with a goniometer and pointer. Insertion of an acetabular cup at the adjusted angle could be a credible method for reducing the variability of cup inclination.