Background: The tripod screw configuration has been shown to offer similar stiffness characteristics to a laterally placed plate. However, concern has been raised that the construct may be prone to failure in scenarios where the screw intersects at the fracture line. We performed a finite element analysis to assess potentially ideal and unideal screw placements in the tripod construct among Mason III radial head fractures.
Methods: A 3-dimensional proximal radius model was developed using a computed tomography scan of an adult male radius. The fracture site was simulated with a uniform gap in transverse and sagittal planes creating a Mason Type III fracture pattern comprising 3 fragments. Three configurations were modelled with varying screw intersection points in relation to the radial neck fracture line. A fourth configuration comprising an added transverse interfragmentary screw was also modelled. Loading scenarios included axial and shear forces to simulate physiological conditions. Von mises stress and displacement were used as outcomes for analysis.
Results: Some variation can be seen among the tripod configurations, with a marginal tendency for reduced implant stress and greater stiffness when screw intersection is further from the neck fracture region. The construct with an added transverse interfragmentary screws demonstrated greater stiffness (2269N/mm) than an equivalent tripod construct comprising three screws (612N/mm).
Conclusion: The results from this study demonstrate biomechanical similarity between tripod screw constructs including where screws intersect at the radial neck fracture line. An added fourth screw, positioned transversely across fragments increased construct stiffness in our model.
Keywords: Radial head; biomechanical; finite element analysis; fixation; fracture; headless screws; stability.
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