The lateral femoral wall thickness on the risk of post-operative lateral wall fracture in intertrochanteric fracture after DHS fixation: A finite element analysis

Background

Patients with a lateral femoral wall (LFW) fracture were reported to have high rates
of re-operation and complication. Although the LFW thickness was a reliable predictor
of post-operative or intra-operative LFW fracture, there was a paucity of literature
evaluating the critical stress distributions on the femur and screws of intertrochanteric
fractures treated with dynamic hip screw (DHS). This study aimed to investigate the
biomechanical performance of intertrochanteric fractures with different LFW thickness
treated with DHS device.

Methods

A three-dimensional model of the proximal femur was established by computed tomography
images. The intertrochanteric fracture model with three different LFW thickness (10mm,
20.5mm and 30mm respectively) was created, which was fixed by DHS. The von Mises stress
on the proximal femur, lateral femoral wall, DHS and the total displacement of the
device components were evaluated and compared for three different LFW thickness model.

Results

The maximum von Mises stress in the proximal fragment of the 10mm and 20.5mm model
increased by 80.56% and 57.97% when compared with the 30mm model. The peek von Mises
stress around the blade entry point of the 10mm and 20.5mm model increased by 89.26%
and 66.39% when compared with the 30mm model. The peek von Mises in the DHS located
near the junction of the barrel and side plate of each model and the 30mm model had
the smallest von Mises stress compared with the other two models. Furthermore, the
maximum displacement in the 30mm model was much smaller than that in the10mm model
and 20mm model.

Conclusions

The intertrochanteric fracture with a thinner LFW tended to have a higher risk of
LFW fracture stabilized by a DHS device. Thus, the intertrochanteric fractures with
a thinner LFW should not be treated by DHS alone and the intramedullary nail or an
addition of trochanteric stabilization plate(TSP) was recommended.