Proposal for a New Fixation Method for Pauwels Type III Femoral Neck Fracture-Metaphyseal Stem: A Finite-Element Analysis.

Objective: To evaluate the biomechanical behavior of a metaphyseal stem specifically designed for the fixation of Pauwels type-III femoral neck fractures using finite-element analysis.

Methods: Three different constructions were studied: the dynamic hip screw with a superior anti-rotation screw (DHS + ARS), multiple cannulated screws in an inverted triangle configuration (ASNIS), and the Metaphyseal Nailing System (MNS), a new implant developed by the authors. Vertical and total displacement, localized and total maximum and minimum principal, and the Von Mises peak stresses were evaluated.

Results: Results are shown for the DHS + ARS, ASNIS, and MNS models, respectively. Vertical displacement (mm) was 1.49, 3.63, and 1.90; total displacement (mm) was: 5.33, 6.02, and 6.30; localized maximum principal (Mpa) was: 2.77, 4.5, and 1.7; Total maximum principal (Mpa) was: 126, 223, and 531; localized minimum principal (Mpa) was: -1.8, -3.15, and -0.39; total minimum (Mpa) was: -121, -449, and -245; and Von Mises peak stress (MPA) was: 315.5, 326.1, and 286.0.

Conclusion: The present FEM study showed that the MNS device increases general stresses and reduces localized stresses, when compared to the DHS + ARS and ASNIS constructions used to fix Pauwels type-III femoral neck fracture in synthetic models. In this sense, the MNS showed a low fracture focus shift, conducive to the consolidation environment. The significant reduction in the maximum principal stress, allows to affirm that the main deforming force, the shear, in this fracture pattern, was considerably reduced and the low value of Von Mises obtained, consistent with an implant capable of making an effective load sharing.