Mechanical analysis of modified femoral neck system in the treatment of osteoporotic femoral neck fractures

Abstract

Background: Despite the explicit biomechanical advantages associated with FNS, it is currently inconclusive, based on the existing literature, whether Femoral Neck System (FNS) outperforms Cannulated cancellous screws (CSS) in all aspects. Due to variances in bone morphology and bone density between the elderly and young cohorts, additional research is warranted to ascertain whether the benefits of FNS remain applicable to elderly osteoporosis patients. This study aimed to investigate the biomechanical properties of FNS in osteoporotic femoral neck fractures and propose optimization strategies including additional anti-rotation screw.

Methods: The Pauwels type III femoral neck fracture models were reconstructed using finite element numerical techniques. The CSS, FNS, and modified FNS (M-FNS) models were created based on features and parameterization. The various internal fixations were individually assembled with the assigned normal and osteoporotic models. In the static analysis mode, uniform stress loads were imposed on all models. The deformation and stress variations of the femur and internal fixation models were recorded. Simultaneously, descriptions of shear stress and strain energy were also incorporated into the figures.

Results: Following bone mass reduction, deformations in CSS, FNS, and M-FNS increased by 47%, 52%, and 40%, respectively. The equivalent stress increments for CSS, FNS, and M-FNS were 3%, 43%, 17%, respectively. Meanwhile, variations in strain energy and shear stress were observed. The strain energy increments for CSS, FNS, and M-FNS were 4%, 76%, and 5%, respectively. The shear stress increments for CSS, FNS, and M-FNS were 4%, 65% and 44%, respectively. Within the osteoporotic model, M-FNS demonstrated the lowest total displacement, shear stress, and strain energy.

Conclusion: Modified FNS showed better stability in the osteoporotic model (OM). Using FNS alone may not exhibit immediate shear resistance advantages in OM. Concurrently, the addition of one anti-rotation screw can be regarded as a potential optimization choice, ensuring a harmonious alignment with the structural characteristics of FNS.

Keywords: Femoral neck fractures; Femoral neck system; Finite element analysis; Osteoporosis.

Fig. 1

Conceptual diagrams of all models: Pauwels type III fracture model (A); CSS model (B); FNS model (C); CSS fixed model (D); FNS fixed model (E); M-FNS fixed mode (F)

Fig. 2

Schematic representation of mesh: Non-uniform meshing at the proximal end of the femur (A); Mesh details of the internal fixation (B)

Fig. 3

Schematic diagram of the simplified muscle loading model of the proximal femur: The coronal plane angle (α) was configured at 13° (A); The sagittal plane angle (β)was set to 3°(B)

Fig. 4

The band graph illustrated the total displacement of each model. The three charts above depicted the displacement within the NM (normal model). The subsequent three charts showcased the displacement within the OM ((osteoporotic model). Each chart was accompanied by a dedicated legend

Fig. 5

The band graph illustrated equivalent stress of each internal fixation model. The three charts above depicted the equivalent stress within the NM (normal model). The subsequent three charts showcased the equivalent stress within the OM (osteoporotic model). Each chart was accompanied by a dedicated legend

Fig. 6

The figure presented the peak details of each model. Equivalent stress, total displacement, shear stress, and strain energy were recorded. Each chart was individually titled, and they shared a unified legend

Fig. 7

The total deformation of each model under torsional conditions: NM (normal model); OM (osteoporotic model)