The relationship between pelvic incidence and anatomical acetabular anteversion in female Japanese patients with hip osteoarthritis: a retrospective iconographic study.

PURPOSE This study aimed (1) to investigate the relationship between pelvic incidence (PI) and the anatomical acetabular anteversion (AA) relative to the spino-pelvic tilt (SPT) plane (anatomical AASPT), relative to the anterior pelvic plane (anatomical AAAPP), and functional standing AA; and (2) to compare AA and the sagittal spino-pelvic parameters of lumbo-pelvic complex types 1 (PI ≤ 30°) and 2 (PI > 30°), in Japanese females with hip osteoarthritis. METHODS We conducted a retrospective study on 110 Japanese females with unilateral hip osteoarthritis. PI, standing lumbar lordosis (LL), standing SPT, anatomical AASPT, anatomical AAAPP, and functional standing AA were measured and calculated using radiographs and computed tomography. The PI-LL difference was defined as the mathematical difference between the PI and standing LL angles. Pearson's correlation test was used to measure the relationship between the PI and AA. Student's t test was used to compare spino-pelvic parameters between lumbo-pelvic complex type 1 (n = 24) and type 2 (n = 86). RESULTS There was a significant relationship between the PI and anatomical AASPT (r =  -0.532, p < 0.001), but no significant relationship between the PI and anatomical AAAPP (r =  -0.021, p = 0.824) or functional standing AA (r = 0.104, p = 0.299). Lumbo-pelvic complex type 1 had a higher anatomical AASPT (22.4° ± 9.1° vs. 5.4° ± 15.1°, p < 0.001), similar anatomical AAAPP (15.0° ± 10.6° vs. 15.1° ± 15.3°, p = 0.981) and functional standing AA (12.4° ± 8.0° vs. 15.0° ± 14.1°, p = 0.254), a lower standing SPT (- 14.3° ± 11.0° vs. 13.7° ± 12.6°, p < 0.001), and a lower PI-LL difference (- 14.4° ± 18.5° vs. 6.4° ± 17.1°, p < 0.001) in comparison to lumbo-pelvic complex type 2. CONCLUSION Our findings will help to improve the understanding of hip anatomy and its relationship with the standing spino-pelvic alignment in Japanese females with hip osteoarthritis.