FEA of the transiliacal internal fixator as an osteosynthesis of pelvic ring fractures
Common Schanz screw systems can be used to stabilize pelvic ring fractures. In order to accommodate for different patient’s requirements, implants can be placed in cranio-caudal direction into the os ilium (T1), or into the supraacetabular bone canal, and
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Laboratory for Biomechanics, OTH Regensburg, Regensburg, Germany Regensburg University Medical Center Department of Trauma Surgery, Regensburg, Germany 3 Regensburg Center of Biomedical Engineering, OTH and University Regensburg, Regensburg, Germany 2
Abstract²Common Schanz screw systems can be used to stabilize pelvic ring fractures. In order to accommodate for GLIIHUHQWSDWLHQW¶VUHTXLUHPHQWVLPSODQWVFDQEHSODFHGLQ cranio-caudal direction into the os ilium (T1), or into the supraacetabular bone canal, and thus, in dorso-ventral direction (T2). Whereas both techniques are currently used, no data of the biomechanical behavior is available up to this date. The aim of this study is to analyze, whether T2 shows biomechanical advantages with respect to tissue and implant stresses due to the enlarged bone-implant interface. Forces acting on the pelvis were analyzed using motion capture data of a gait cycle obtained by the utilization of a musculoskeletal simulation program. A three dimensional finite element (FE) model of the pelvis with grayscale-based material properties was generated. The muscle and joint reaction forces at toe-off were applied to the FE model and instable pelvis fractures were implemented. The osteosynthesis systems were positioned within the model in order to enable the comparison between the two different surgical techniques. Stresses and displacements were analyzed for bone tissue, fracture zone and implant. T2 lead to approx. 30% larger displacements in the fracture zone. Von-Mises stresses were larger for T2 in the implant (80 MPa vs. 227 MPa), whereas T1 leads to larger stresses in the bone tissue (200 MPa vs. 140 MPa). Both implantation techniques showed a good biomechanical behavior. Differences could be found with respect to tissue strains and deformations in the fracture zone. If bone quality or fracture healing are of concern, T2 or T1 should be used, respectively. However, both techniques seem to be applicable for cases with no special requirements. Further analyses aim to investigate the behavior under cyclic loading. Keywords² finite element analysis, musculoskeletal simulation, internal fixator, pelvic ring fracture
© Springer Nature Singapore Pte Ltd. 2017 A. Badnjevic (ed.), CMBEBIH 2017, IFMBE Proceedings 62, DOI: 10.1007/978-981-10-4166-2_32
I. INTRODUCTION
A
LTHOUGH the incidence of pelvic ring fractures is low (0.3 to 8%) an increase over the last twenty years can be perceived [1, 2]. The causes for these fractures range from RUGLQDU\ZHLJKWEHDULQJ VRFDOOHG³LQVXIILFLHQF\IUDFWXUHV´RU ³IUDJLOLW\IUDFWXUHV´ XSWRKLJKHQHUJ\WUDXPDWD [2, 3]. Induced by high energy traumata, pelvic ring fractures are usually part of a polytrauma and, therefore, correlated with other fractures and injuries of the soft tissue. These complex pelvic traumata make the operative treatment difficult, considering the soft tissue related complications, morbidity and the risk of an implant malposition as well as neural damages. Insufficiency fractures usually occur in elderly people suffer
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