The Impact of Total Hip Arthroplasty on Pelvic Motion and Functional Component Position is Highly Variable

Background: This study's purpose was to determine the impact of THA implantation on pelvic motion, and to assess motion in patients with a history of lumbar fusion or prosthetic dislocation. Methods: This was an IRB-approved, prospective investigation of 3 cohorts: (1) patients without a history of lumbar surgery undergoing THA (group A), (2) patients with a lumbar fusion (group B), and (3) patients with a THA prosthetic dislocation (group C). All patients received both standing and sitting lateral pelvis images to measure sacral slope and pelvic tilt in the sagittal plane. Results: Fifty-eight patients were enrolled (24 group A, 27 group B, and 7 group C), with no differences in age, gender, or body mass index (P = .1-. 7). In group A, the mean change in sacral slope from standing to sitting was 22.1 degrees +/- 15.2 degrees preoperatively and 19.5 degrees +/- 14.8 degrees postoperatively. However, in 13 patients, the difference in pelvic motion from the standing to seated position, from preoperatively to postoperatively, was >5 degrees and in 10 patients, this difference was >10 degrees. The change in standing to sitting sacral slope was significantly less in patients with a lumbar fusion (9.8 degrees +/- 8.2 degrees) and history of prosthetic dislocation (12.5 degrees +/- 4.7 degrees) vs group A (P < .001 and P = .008). Conclusion: Implantation of a THA can increase or decrease sagittal plane pelvic motion from the standing to seated position with a high degree of variability. Thus, the ability to predict ideal component positioning from preoperative images may be challenging. (C) 2016 Elsevier Inc. All rights reserved.