The Optimal Fibular Strut Bone Graft Fixation Angle for Unstable Proximal Humerus Fractures: A Finite Element Analysis

Adding a fibular strut bone graft to locking plate fixation has been introduced to improve stability and prevent varus collapse. The purpose of this study was to perform finite element analysis (FEA) of the biomechanical characteristics of different insertion angles of the fibular strut graft in proximal humerus fractures. Proximal humerus fractures with metaphyseal comminution and instability were simulated by creating wedge-shaped osteotomies medially and laterally for varus and valgus models, respectively. Three-dimensional finite element models were reconstructed from computed tomography images. A locking compression plate with a length of 90 mm (three holes) was applied to the proximal humerus fracture model. Fibular allografts were inserted at 0° and 30° to the humeral shaft. Axial and traction forces of 70°, 90°, and 110° relative to the vertical axis were applied to each model to simulate stress on the plate and graft. At axial loads, stresses in both the plate and the graft were lower when the graft was inserted at 0° than at 30°. Under traction loads, plate stress was lower with 30° insertion. Graft stress was also lower with 30° in most experimental conditions in both the valgus and varus models. These findings suggest that oblique insertion may provide biomechanical advantages under traction forces in unstable proximal humerus fractures.