FE-Analysis of Posterior Pelvic Ring Stability with Supra-acetabular Fixator
by Xishan Li
Date of Examination:2024-06-05
Date of issue:2024-06-07
Advisor:Prof. Dr. Wolgang Lehmann
Referee:Prof. Dr. Ralf Dressel
Referee:PD Dr. Wolfram Hahn
Persistent Address:
http://dx.doi.org/10.53846/goediss-10526
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Abstract
English
Background Unstable pelvic ring injuries remain a common problem in trauma patients, accounting for 14-20% of all cases, with a concerning mortality rate of 10-20%, mainly due to exsanguinating hemorrhage. The clinical urgency therefore requires immediate reduction and compression to control bleeding. Despite the emergence of the standard anterior external fixator as the treatment of choice, doubts remain regarding its efficacy in providing adequate stability to the posterior pelvic ring. To address this, this study aimed to develop a finite element model to evaluate the changes within the pelvic fracture space under the forces of the supra-acetabular fixator. Methods Therefore, using CT data from a patient who has had the SA fixator inserted following a type C pelvic fracture, established, pre-operative and post-operative models, the control group. The supra-acetabular fixator in the post-operative model was then attached to the pre-operative model, mimicking the positioning of the post-operative model, thereby establishing the experimental model. In terms of model validation, not only did the experimental and control models establish an internal self-control comparison, but the fracture gap was also fixed in silico with three nails, approximating the healthy models commonly used in literature. Comparisons were made to existing scientific data, and the overall outcomes substantiated the accuracy and reliability of the constructed experimental model. Observation points were strategically selected at identical locations within the anterior and posterior pelvic rings of both experimental and control models. Varying compression forces between 100-600N were then applied to the Schanz pins of the experimental model. This approach was used to determine if the changes in fracture gap were consistent with those of both the control group models and clinical observations. Results Finite element analysis of the experimental model, considering morphology, directional displacement at selected measurement points, and comparative distances before and after displacement, revealed a consistent expansion of the sacral fracture gap in the posterior pelvic ring with increasing applied loads. Meanwhile, a continuous contraction was observed at the symphysis pubis in the anterior pelvic ring. However, the symphysis pubis gap in the control group exhibited anterior-lateral contraction and posterior-medial expansion, while the experimental model displayed an overall reduction. This discrepancy likely arises from using a simplified healthy interpubic disc model to mimic the compression of pubic symphysis. Consequently, this study’s finite element model and evaluation methodology accurately reflect clinical outcomes. Under anterior load, traditional supra-acetabular fixators demonstrate an expansion rather than a compression of the posterior pelvic ring. Conclusion This research further clarifies the mechanical mechanisms of supra-acetabular fixators, revealing that in the type C pelvic fracture, the instability on the fractured side, combined with the pubic symphysis acting as a fulcrum during mechanical loading, inevitably leads to an enlargement of the sacral fracture gap due to the lever effect. Additionally, this investigation offers an assessed method for comparing the mechanical stability of various anterior external fixation devices in the pelvis fracture.
Keywords: Finite element analysis; Supra-acetabular fixator; Posterior pelvic ring; Pubic symphysis; Tile C pelvic fracture
Schlagwörter: Finite element analysis; Supra-acetabular fixator; Posterior pelvic ring; Pubic symphysis; Tile C pelvic fracture
