Three-dimensional computed tomography analysis on bony birth canal after bilateral periacetabular osteotomy

Background: Curved periacetabular osteotomy (CPO) is one of the joint preserving procedures for developmental dysplasia of the hip. CPO requires osteotomy of the medial wall of the acetabulum, which may cause narrowing of the bony birth canal and this step may result in increased risk of cesarean delivery. We analyzed the narrowest part of the bony birth canal using three-dimensional computed tomography (3D-CT) before and after bilateral CPO. Methods: Between February 2007 and March 2014, there were 29 cases of bilateral CPO in which both pre- and post-operative 3D-CT were available. Transverse diameters of the pelvic inlet, contraction, outlet, expansion, and teardrop were analyzed. Among them, the narrowest part of the bony birth canal was investigated, which being smaller than the normal lower threshold value for vaginal delivery (95 mm) was considered as a risk for cesarean delivery. Results: The transverse diameters of both pelvic expansion and teardrop significantly decreased after CPO (both p < 0.01), while other diameters showed no significant changes. Among these two diameters, the narrowest diameter of the bony birth canal was the pelvic teardrop in all 29 cases. That in 24 patients (82.8%) was greater than 95 mm, while that in five patients (17.2%) showed less than 95 mm. Conclusions: Based on 3D-CT analysis, the narrowest part of the bony birth canal after bilateral CPO was the pelvic teardrop. In this study, 82.8% of the patients showed pelvic teardrop diameter greater than 95 mm, while that of the other patients (17.2%) were less than 95 mm. (C) 2017 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.