Biomechanical investigation of positive reduction in the femoral neck fracture

Abstract-Text (inkl. Referenzen und Bildunterschriften)

Introduction

Achieving an anatomic reduction is critical for patients with femoral neck fractures (FNFs), but can be challenging in certain cases. The concept of 'Gotfried positive reduction' offers an alternative approach for such situations. This concept entails positioning the distal femoral neck fragment at the inferior medial edge of the proximal fragment in the anteroposterior (AP) view. However, in some clinical cases, increasing the Gotfried positive reduction may result in internal fixator failure and even hip varus.

Objective

The aim of this study is to analyze the effect of Gotfried's positive reduction on the FNF with different Pauwels angles.

Methods

3D models representing negative, anatomic, and positive femoral neck fracture (FNF) reductions stabilized with dynamic hip screws (DHS) and cannulated screws (CS), each associated with different Pauwels groups (Pauwels I, II, and III), were generated using finite element (FE) technology based on CT data. A 2100N load was applied to the femoral head in alignment with the mechanical axis of the femur. Parameters investigated, included von Mises stress, displacement, and von Mises strain. The stress distribution of the internal fixation was chosen as the key indicator to assess stability.

Results

The anatomic reduction model showed the minimum von Mises stress of the internal fixator for three groups (68.487 MPa, 98.991 MPa, and 161.11 MPa). With increasing positive reduction, there was a proportional increase in stress within the internal fixation. For Pauwels type I and type II FNFs, positive reductions of 1 mm (86.042 MPa, 115.3 Mpa) and 2 mm (108.77 MPa, 151.7 Mpa) were considered acceptable. For Pauwels type III FNFs, a positive reduction of 1 mm (167.9 Mpa) was acceptable. Negative reduction should be avoided.

Conclusion

Excessive positive reduction may increase the risk of internal fixation failure in FNF.