Objectives: We evaluated the efficacy of preoperative planning for implant placement with consideration of pelvic tilt in total hip arthroplasty (THA), and the accuracy of a computed tomography (CT)-based computer navigation system for implant positioning.
Methods: We examined 54 hips of 48 patients (38 females, 10 males; mean age 60.1 [range 38-89] years) who underwent THA and were followed-up for one year postoperatively. Preoperative planning included determination of cup inclination, cup anteversion, and stem antetorsion, using the anterior pelvic plane (APP) in the supine position as a reference. In the anterior tilt group (preoperative APP ≥10 degrees while standing), the standing APP value minus 10 degrees was the target reference, as the pelvis in such patients tends to tilt backward by up to 10 degrees after THA. For patients with lumbar-lordotic angles ≤30 degrees due to lumbar compression fractures, etc., in the posterior tilt group (preoperative APP ≤−10 degrees while standing), the midpoint between the supine and the standing APP values was the target reference, as the pelvis in such patients tends to tilt backward somewhat further after THA. Cup inclination, cup anteversion, and combined anteversion (CA) in the supine and the standing positions were examined one year after THA. The accuracy of the computer navigation system was also examined.
Results: The mean CA was 34.6±7.5 degrees in the supine position and 39.5±7.5 degrees in the standing position. CA did not differ among the three subgroups (anterior, intermediate, posterior tilt) in either the supine or the standing position, indicating that the implant placements were equally effective. The desired CA (37.3 degrees) was midway between those in the supine and the standing positions for each subgroup. The mean absolute errors between preoperative planning and postoperative CT measurement were 3.2±2.3, 3.6±3.1, 6.0±8.7, and 6.3±7.1 degrees for cup inclination, cup anteversion, stem antetorsion, and CA, respectively.
Conclusions: We obtained favorable THA results with preoperative planning for implant placement with pelvic tilt by demonstrating that supine and standing CA were unaffected by preoperative pelvic tilt at one year postoperatively. The mean absolute error of CA between preoperative planning and postoperative measurement was 6 degrees with the use of a CT-based navigation system for implant positioning.