Quantitative analysis of regional specific pelvic symmetry.

Understanding bilateral pelvic symmetry can be useful for analyzing complex pelvis anatomy and simplifying difficult procedures for pelvic fractures. This paper aims to quantify the degree of regional pelvic symmetry using computer-based methods. CT scans of 30 intact pelvises were digitized into 3D models and regions were defined: the ilium, acetabulum, pubis, and ischium. The right hemipelvis was aligned with the left, and deviations between the two models were quantified using method 1 (global registration) and method 2 (local registration). Symmetry was evaluated using the root mean square (RMS) of the deviations and the percentage of points within preset thresholds of ± 2 mm and ± 1 mm. The results showed that > 86% of points are within the ± 2 mm deviation threshold and average RMS are < 1.33 mm. For all regions, method 2 showed lower deviations than method 1. The pubis and ischium regions showed a large difference in symmetry between the two methods indicating high local symmetry, but a degree of global asymmetry. Conversely, the acetabular and iliac regions showed similar levels of symmetry with the two methods. When evaluated locally, the pelvic regions can be considered highly symmetric; the acetabulum is highly symmetric globally as well. These findings can be used in future studies to assess the feasibility of patient-specific implants using the mirrored contralateral hemipelvis as a template for unilateral pelvic fracture fixation. The left image shows the "cut planes" used to define four pelvic regions: the ilium, acetabulum, pubis, and ischium. The right image shows a deviation color map (DCM) used to quantify bilateral pelvic symmetry. The scale and color illustrate the degree of deviation of the left hemipelvis with the right hemipelvis with the units in millimeters (mm).

Development and application of the average pelvic shape in virtual pelvic fracture reconstruction.

BACKGROUND: With unilateral pelvic fractures, the contralateral hemipelvis can be used as a template in virtual reconstruction; however, this cannot be applied for bilateral fractures. Therefore, statistical shape modelling was used to build average pelvic shapes that can serve as templates when reconstructing bilaterally fractured pelvises. METHODS: Four average shape models were created for male and female, left and right hemipelves from 20 male and 20 female subjects. They were used as templates to reconstruct eight unilaterally fractured pelvises. RESULTS: The average root-mean-square of deviations between the reconstructed and intact hemipelves was 1.46 ± 0.32 mm, which is less than the 2 mm threshold for causing hip joint complications. CONCLUSION: This indicates that the reconstructions are reliable and the average shape models can be used to reconstruct bilaterally fractured pelvises. The proposed technique can potentially provide quick and accurate treatment plans for pelvic fracture patients, which is necessary for recovery.

Virtual reconstruction of unilateral pelvic fractures by using pelvic symmetry.

PURPOSE: Pelvic fractures are known to be one of the most difficult injuries to treat. The objective of this study is to introduce a novel technique for virtual unilateral pelvic fracture reconstruction. Since the pelvis exhibits remarkable left-right symmetry, the contralateral hemipelvis can be used as a template for rebuilding the fractured hemipelvis. METHODS: CT scan data of the pelvic region of eight subjects with acute unilateral pelvic fractures were involved in this study. Computer-aided design software was used to create 3D models of these pelvises. The contralateral hemipelvis of each subject was then reflected across the sagittal plane, and the fractured hemipelvis was rebuilt by aligning the bone fragments with their equivalent location on the reflected side. To evaluate the quality of this reduction process, a 3D deviation analysis was conducted to calculate the differences between the reflected intact hemipelvis and the reconstructed hemipelvis. RESULTS: Results showed that the average root mean square (RMS) of deviations and average percentage of points within a ± 2 mm predefined threshold was 1.32 ± 0.22 mm and 88.4 ± 3.78%, respectively. The deviation color maps obtained indicated that the largest differences were along the fracture lines and on the non-articular surfaces of the pelvises. CONCLUSION: These results allowed us to conclude the validity of this procedure, since the average RMS difference was below 2 mm and the average percentage of points within ± 2 mm was high. The proposed technique will allow surgeons to provide their patients with more accurate reconstruction procedures which can potentially improve surgical outcomes.

Investigation of pelvic symmetry using CAD software.

Severe pelvic fractures often prove difficult for surgeons as they require patient-specific surgical treatment plans and customized equipment. Developing virtual patient-specific 3D pelvis models would ease the surgical planning process and enable development of custom fixation plates. This paper aims to examine pelvic symmetry to conclude whether the contralateral side may be used as a reference model for the fractured side of the pelvis. Fourteen subjects with intact pelvises were involved in this study. CT scans of the pelvises were converted to 3D models and the right sides of the pelvises were reflected and aligned with the left sides. A deviation analysis was then performed for each set of models and results showed that the average root mean square (RMS) of values was 1.14 ± 0.26 mm and the average percentage of points below a deviation threshold of ± 2 mm was 91.9 ± 5.55%. The deviation color maps (DCMs) showed that the largest deviations were on the non-articular surfaces. The volume and surface area of each model were also examined and showed no significant differences between left and right sides. These results indicate that the pelvis displays bilateral symmetry and this concept can be used to develop fully intact patient-specific 3D pelvis models for fracture reconstruction using the unfractured contralateral side. Graphical Abstract.