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

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.

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.

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).

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.