Comparison of stress shielding between endobutton and screw fixation in the latarjet procedure using three-dimensional finite element analysis

Abstract

BackgroundThe Latarjet procedure is a well-established surgical technique for the treatment of recurrent anterior shoulder instability. Endobutton fixation systems have recently emerged as an alternative to conventional screw fixation, with the potential advantage of providing a more homogeneous stress distribution across the graft. The purpose of this study was to compare the distribution of Von Mises stress (VMS) in coracoid grafts fixed with screws versus endobuttons using three-dimensional finite element (FE) analysis.MethodsThree-dimensional FE models of the glenoid and coracoid graft were constructed using computed tomography data. Two fixation scenarios were evaluated: [1] Group A - fixation with two cortical screws, and [2] Group B - fixation with an Endobutton system. Identical graft dimensions, positions, and loading conditions were applied. A 50-N anteriorly directed force was applied at the graft-glenoid interface. Material properties were defined as homogeneous, isotropic, and linearly elastic. VMS values were calculated using Abaqus software.ResultsScrew fixation produced localized stress concentrations around the screw holes with limited proximal load transfer, resulting in a heterogeneous graft stress pattern. In contrast, the Endobutton construct demonstrated a more uniform stress distribution across the graft. Although the screw group exhibited a higher mean von Mises stress (16.7 MPa [0.8-23.1]) compared with the Endobutton group (12.3 MPa [5.4-20.9]), a substantially greater proportion of graft volume exceeded the predefined high-stress threshold (>= 15 MPa), indicating localized stress concentration. The Endobutton model showed fewer high-stress regions and improved stress homogeneity.ConclusionEndobutton fixation in the Latarjet procedure results in a more uniform stress distribution across the coracoid graft than screw fixation, which may reduce the risk of graft osteolysis and enhance osteointegration. These findings warrant further validation with cadaveric and clinical studies.