Development of a Patient-Specific Finite Element Model for Predicting Implant Failure in Pelvic Ring Fracture Fixation

Abstract

Introduction. The main purpose of this study is to develop an efficient technique for generating FE models of pelvic ring fractures that is capable of predicting possible failure regions of osteosynthesis with acceptable accuracy. Methods. Patient-specific FE models of two patients with osteoporotic pelvic fractures were generated. A validated FE model of an uninjured pelvis from our previous study was used as a master model. Then, fracture morphologies and implant positions defined by a trauma surgeon in the preoperative CT were manually introduced as 3D splines to the master model. Four loading cases were used as boundary conditions. Regions of high stresses in the models were compared with actual locations of implant breakages and loosening identified from follow-up X-rays. Results. Model predictions and the actual clinical outcomes matched well. For Patient A, zones of increased tension and maximum stress coincided well with the actual locations of implant loosening. For Patient B, the model predicted accurately the loosening of the implant in the anterior region. Conclusion. Since a significant reduction in time and labour was achieved in our mesh generation technique, it can be considered as a viable option to be implemented as a part of the clinical routine to aid presurgical planning and postsurgical management of pelvic ring fracture patients.

Figure 1

Postoperative X-ray 6 months after surgery.

Figure 2

Postoperative X-ray 3 months after surgery.

Figure 3

Four load cases simulated in this study.

Figure 4

Comparison of methods for FE model creation for completely patient-specific analysis (a) and for efficient patient-specific analysis (b).

Figure 5

Tension ((a) in MPa, minimum 0.086 MPa, maximum 155.07 MPa) and deformation ((b) mm, minimum 0.0247 mm, maximum 0.305 mm) along the transiliosacral screw at the posterior pelvic ring.

Figure 6

Zone of maximum tension at the infra-acetabular screw ((a) in MPa, minimum 0.0 MPa, maximum 86.816 MPa) and deformation ((b) mm, minimum 1.87 mm maximum 2.381 mm) at the plate near the right symphysis at the anterior pelvic ring.

Figure 7

Zones of maximum tension ((a) MPa, minimum 0.0225 MPa, maximum 101.66 MPa) and deformation ((b) mm, minimum 0.0259 mm and maximum 0.71952 mm) at the osteosynthesis of the posterior pelvic ring.

Figure 8

Zone of maximum tension (MPa, minimum 0.0 MPa, maximum 24.756 MPa) at the osteosynthesis of the anterior pelvic ring for Patient B.

Figure 9

Deformation (mm) at the plate near the right (minimum 0.816 mm, maximum 1.18 mm) (a) and left symphysis (b) at the anterior pelvic ring for Patient B (minimum 0.765 mm, maximum 1.585 mm).