Iliac Dysmorphism Data
Introduction: Due to the complex anatomy of the pelvis, the boundaries of osseous fixation pathways (OFPs) are not readily visible on standard x-ray and computed tomography (CT) imaging. We hypothesized that the shape of the pelvis will be predictive of OFP size and sought to identify radiographic parameters that will help surgeons determine the feasibility of implant placement with standard imaging modalities. Methods: CT scans of 100 male and 100 female adult hemipelves without evidence of trauma were evaluated using the Intellispace Portal 7.0 (Koninklijke Philips – Amsterdam, Netherlands). Radiographic characteristics of the ilia were measured, such as axial angle on CT and inlet and outlet angles on x-ray (Figure 1). The dimensions of the anterior column, posterior column, supraacetabular, and gluteal pillar corridors were determined through manual best-fit analysis. Presence of sacral dysmorphism was identified. Corridor dimensions were sorted by clinically relevant parameters, such as less than 4.0mm and larger than 7.3mm. Student T test was used to assess for differences in iliac angles between these groups. Analysis of variance (ANOVA) was used to compare the interaction effects between corridor sizes. Results: The mean axial, inlet, and outlet angles were 155° (132.1-180), 150.8° (117.5-193.2), and 132.3° (102-152) respectively. Female pelves had significantly smaller corridors than male pelves, though there was no association with presence of sacral dysmorphism. The average axial angle in pelves with an SA corridor < 4mm was 160.7° and > 7.3mm was 154°. The average inlet angle in pelves with a gluteal pillar < 4mm was 144.3° and > 6.5mm was 152°. The average outlet angle in pelves with an anterior column corridor < 4mm was 128.9° and > 6.5mm was 134.8°. The average outlet angle in pelves with a posterior column corridor < 10mm was 129.2° and > 10mm was 133.1°. Pelves that have one small corridor are likely to have all small corridors and vice versa. Sacral dysmorphism does not correlate with iliac morphology or corridor size. Conclusions: Iliac morphology is associated with the size of iliac OFPs. Standard CT and x-ray imaging can be used to predict OFP size by identifying the shape of the ilium on axial, inlet, and outlet views. Currently, specialty imaging programs or intraoperative fluoroscopy are required to determine which implant, if any, could be successfully implanted into the pelvis. Using this technique, the determination could be made preoperatively and alternate fixation pursued if necessary. Additionally, we have shown that patients with one small corridor likely have associated small corridors throughout. Sacral morphology is not related to iliac morphology, so the utility of sacral OFPs must be separately assessed.