Computational evaluation of the axis-blade angle for measurements of implant positions in trochanteric hip fractures: A finite element analysis.

Background: Recently, a novel approach axis-blade angle (ABA) was developed to measure implant positions during trochanteric hip fracture surgery. It was defined as the sum of two angles α and β measured between the femoral neck axis and helical blade axis in anteroposterior and lateral X-ray films, respectively. Although its clinical practicability has been confirmed, the mechanism is yet to be investigated by means of finite element (FE) analysis.

Methods: Computed tomography images of four femurs and dimensions of one implant at three angles were obtained to construct FE models. For each femur, 15 FE models in an arrangement (intramedullary nails at three angles multiplying five blade positions) were established. Under the simulation of normal walking loads, the ABA, von Mises stress (VMS), maximum/minimum principal strain and displacement were analyzed.

Results: When the ABA increased, all outcome indicators initially decreased till reaching inferior-middle site and then increased while the blade positions within the femoral head shifted from the superior-anterior quadrant toward the inferior-posterior quadrant, where the ABA were higher. Only the peak VMS of implant models in the inferior-posterior quadrant (particularly the inferior-middle site within) with blades in did not reach the yielding (risky) cut-off.

Conclusions: From the perspective of angles, ABA, this study demonstrated the inferior-posterior quadrant as the relatively stable and safe regions, especially the inferior-middle site within. This was similar but more elaborate compared with previous studies and clinical practice. Therefore, ABA could be employed as a promising approach to anchor the implants into the optimal region.