Construction and validation of a finite element model of pelvis after subtotal sacrectomy

Quan LI; Zhiyu ZHANG; Longpo ZHENG; Zhengdong CAI

ABSTRACT

BACKGROUND:

For the sacroiliac joint has complex structure and locates deep,its biomechanical properties have not been fully understood,even less about the study of reconstruction.

OBJECTIVE:

To construct a finite element model of pelvis after subtotal sacrectomy,and validate its effectiveness,which is supposed to be useful for evaluating reconstructions of sacroiliac joint.TIME AND

SETTING:

The establishment and validation of three-dimensional finite element model was performed in the Orthopaedic Laboratory of Changhai Hospital,Second Military Medical University between January and March 2008.MATERIALSThe CT scan images of adult males who had no pathological changes in lumber and pelvis were downloaded from CT work station in Changhai hospital.The CT scan included low lumber and whole pelvis,and got 132 DICOM images in all.

METHODS:

Two three-dimensional finite element pelvis models were established① an intact pelvis model,② a defective pelvis model on which subtotal sacrectomy was performed cephalic to the S1 neural foramina.According to the biomechanical experiment of Hugate RR Jr,axial loads of 3 000 N and 1 000 N were applied on intact and defective pelvis models,respectively.The max axial displacements and stiffness on the L5 of two models were calculated and following comparison with the result in the literature.MAIN OUTCOME

MEASURES:

The max axial displacements and stiffness on the L5 were observed and considered as the index reflecting sacroiliac joint stability.

RESULTS:

The max axial displacements of the L5 on intact and defective pelvis models were 7.99 mm and 7.68 mm,respectively.The stiffness of the L5 on intact and defective pelvis models were 375 N/mm and 130 N/mm,respectively.The max axial displacements of the L5 on intact and defective pelvis models in the literature were(10.73?5.10) mm and(11.71?5.74) mm,and the stiffness were(353?231) N/mm and(101?49) N/mm,respectivly .

CONCLUSION:

In this experiment,we were successful to establish the finite element model of pelvis after subtotal sacrectomy.The calculated result was similar with the reference.The model could be used to evaluate different ways to reconstruct the sacroiliac joint.