Influence of Contralateral Hip Status on Pelvic Tilt After Total Hip Arthroplasty

Abstract

Background: Every degree of change in pelvic tilt (PT) leads to a 0.7° change in anteversion and a 0.3° change in inclination. This study aimed to determine the significance of contralateral hip arthritis on changes in PT using preoperative and postoperative anteroposterior radiographs. Methods: There were 193 primary total hip arthroplasties done by 2 surgeons at a single academic tertiary referral center reviewed between September 2021 and January 2023. PT was calculated as Tilt = −(ln[(B/A) × (1/0.483)]) / 0.051. Value A is the distance from the base of the SI joint to the superior margin of the obturator foramen; value B is the height of the obturator foramen. After exclusions, contralateral hips were identified as being normal (n = 75), arthritic (n = 39) (Tönnis grade 3/4), replaced (n = 34), or having undergone simultaneous bilateral total hip arthroplasty (n = 5) on postoperative films. Difference in PT was measured between preoperative and postoperative films taken 1-3 months after surgery. Analyses for statistical significance were calculated using t-tests and one-way analysis of variance. Results: Average change in PT in patients with normal contralateral hips was −5.2° with an absolute mean difference of 7.6°, −1.5° for arthritic contralateral hips with an absolute mean difference of 5.0°, −1.6° for replaced contralateral hips with a mean absolute difference of 4.3°, and 2.2° for bilateral hips with a mean absolute difference of 2.6° (P < .01). Conclusions: Differences in postoperative PT changes between healthy, arthritic, and replaced contralateral hip study groups were significant. Changes in preoperative to postoperative tilt may have implications for optimal cup placement.

Keywords

• Pelvic tilt
• Acetabular cup
• Contralateral hip
• Postoperative
• Standing x-ray
• Hip arthroplasty