Finite element analysis of the modified intramedullary nail-II for managing reverse obliquity trochanteric fractures

Abstract

Cephalomedullary nails are widely used to fix unstable femoral trochanteric fractures nowadays. However, for reverse obliquity trochanteric (ROT) fractures, the fixation failure rate of existing cephalomedullary nails is high, resulting in many complications. Our team aimed to propose the modified intramedullary nail-II (MIN-II) to improve the fixation effects of ROT fractures and make biomechanical comparisons between MIN-II and three other cephalomedullary nails by finite element method. AO/OTA 31-A3.1 and 31-A3.3 ROT fracture models were established via a series of femoral CT data. Four cephalomedullary nails were constructed, including MIN-II, proximal femoral bionic nail (PFBN), InterTAN nail (ITN), and proximal femoral nail antirotation (PFNA). Then, these implants were assembled onto the above ROT fracture models. After setting boundary conditions, the mesh convergence test and model validation were performed. The evaluation indicators comprised von Mises stress (VMS) and displacement. To compare the mechanical stability of four implants, the percent difference (PD) was calculated. The values of maximal VMS on implants were 176.81 MPa, 292.04 MPa, 227.36 MPa, and 306.45 MPa in 31-A3.1 ROT fracture and 257.32 MPa, 349.90 MPa, 372.93 MPa, and 679.75 MPa in 31-A3.3 ROT fracture for the MIN-II, PFBN, ITN, and PFNA models under axial loads of 2100 N. Compared to the PFNA model, the PD reduction of MIN-II was 42.3% in 31-A3.1 ROT fracture and 62.1% in 31-A3.3 ROT fracture. The values of maximal displacement were 14.38 mm, 18.95 mm, 18.86 mm, and 20.53 mm in 31-A3.1 ROT fracture and 16.40 mm, 19.02 mm, 19.21 mm, and 20.56 mm in 31-A3.3 ROT fracture for the MIN-II, PFBN, ITN, and PFNA models. In comparison with the PFNA group, the MIN-II group showed a 30.0% reduction in 31-A3.1 ROT fracture and a 20.2% reduction in 31-A3.3 ROT fracture for this indicator, respectively. The values of maximal VMS on bones and maximal displacement of fracture surface exhibited similar trends for the four fixation groups. The modified intramedullary nail-II displayed the best biomechanical stability among the four cephalomedullary nails for the management of reverse obliquity trochanteric fractures. Hence, the MIN-II might be a good option for patients with ROT fractures.

Keywords: Biomechanical; Cephalomedullary; Finite element; Fracture; Modified; Reverse obliquity; Stability.

Fig. 1

Cephalomedullary nail models and the reverse obliquity trochanteric fracture models. (A) MIN-II. (B) PFBN. (C) ITN. (D) PFNA. (E) The MIN-II in AO/OTA 31-A3.1 fracture model. (F) The MIN-II in AO/OTA 31-A3.3 fracture model. MIN-II modified intramedullary nail-II, PFBN proximal femoral bionic nail, ITN InterTAN nail, PFNA proximal femoral nail antirotation.

Fig. 2

The bar plots of maximal VMS and displacement for the four fixation groups in 31-A3.1 and 31-A3.3 fracture models. (A) Maximal VMS on implants. (B) Maximal VMS on bones. (C) Maximal displacement. (D) Maximal displacement of fracture surface. VMS represents von Mises stress. MIN-II modified intramedullary nail-II, PFBN proximal femoral bionic nail, ITN InterTAN nail, PFNA proximal femoral nail antirotation.

Fig. 3

Maximal VMS on implants for the MIN-II, PFBN, ITN, and PFNA models in 31-A3.1 and 31-A3.3 fractures. VMS represents von Mises stress. MIN-II modified intramedullary nail-II, PFBN proximal femoral bionic nail, ITN InterTAN nail, PFNA proximal femoral nail antirotation.

Fig. 4

Maximal VMS on bones for the MIN-II, PFBN, ITN, and PFNA models in 31-A3.1 and 31-A3.3 fractures. VMS represents von Mises stress. MIN-II modified intramedullary nail-II, PFBN proximal femoral bionic nail, ITN InterTAN nail, PFNA proximal femoral nail antirotation.

Fig. 5

Maximal displacement for the MIN-II, PFBN, ITN, and PFNA models in 31-A3.1 and 31-A3.3 fractures. MIN-II modified intramedullary nail-II, PFBN proximal femoral bionic nail, ITN InterTAN nail, PFNA proximal femoral nail antirotation.

Fig. 6

Maximal displacement of fracture surface for the MIN-II, PFBN, ITN, and PFNA models in 31-A3.1 and 31-A3.3 fractures. MIN-II modified intramedullary nail-II, PFBN proximal femoral bionic nail, ITN InterTAN nail, PFNA proximal femoral nail antirotation.