Osteotomy across arcuate line in ilium needs prudence in curved periacetabular osteotomy.

Background: This study aimed to measure the optimal osteotomy angle and length, as well as the available width of the osteotomy site in the posterior column for the safe performance of periacetabular osteotomy. Methods: Fifty-six hips in 41 patients who underwent curved periacetabular osteotomy were evaluated. Computed tomography data were subjected to multiplanar reconstruction to measure parameters in two reference planes: the functional pelvic plane and the anterior pelvic plane. The optimal osteotomy angle, osteotomy length, and available width of the posterior column were defined. We assessed the possible factors affecting the optimal osteotomy angle. Results: The functional pelvic plane showed an average and maximum anterior pelvic tilt of 7.8° and 16.4°, respectively, from the anterior pelvic plane. The optimal osteotomy angles had comparable dispersions in the functional pelvic plane and anterior pelvic plane reference planes. Furthermore, as the rotation angle of the reconstructed axial views increased, i.e., the osteotomy site became closer to the arcuate line of the pelvis, the available width of the osteotomy site narrowed, and the length of the osteotomy site increased. We found significant correlations between the optimal osteotomy angle and sex, height, weight, body mass index, head lateralization index, and acetabular anteversion in all planes. The multiple regression analysis revealed that acetabular anteversion was significantly correlated with the optimal osteotomy angle in all planes, while height, weight, BMI, center edge angle, acetabular roof obliquity, and head lateralization index were correlated in some planes. Conclusions: Osteotomies near the arcuate line of the pelvis are considered particularly risky because long-distance osteotomies must be performed within a narrow width. The optimal osteotomy angle is affected by many factors, including acetabular anteversion, which varies from case to case.