Plating System Design Determines Mechanical Environment in Long Bone Mid-shaft Fractures: A Finite Element Analysis.

PURPOSE: Internal fixation device failure is rare but unavoidable. Fatigue-related mechanisms are responsible for most mechanical failures of orthopedic plates. Plate design needs to be optimized for both long fatigue life and bone healing. Only in this way can we reduce the occurrence of internal fixation failure. To address this issue, we aimed to provide a theoretical basis for improving the design of orthopedic plates.

MATERIAL AND METHODS: The finite element method was used to conduct a computational investigation. Three groups of plate models were designed with varied working lengths and other elements. By fixing these plates to tibial mid-shaft fracture models, parameters of the mechanical environment around the fracture site were recorded and analyzed.

RESULTS: Plate working length, existence of holes within the working length, and plate length are important factors that influence the mechanical environment of the fracture site. The screw-bone interface is the weakest part in internal fixation failure. Fractures fixed by traditional plates that had holes in the working length have larger interfragmentary movement, and these plates have more severe stress concentration than plates without holes in the working length.

CONCLUSIONS: We presented some suggestions for the plating system. First, partial weight bearing is recommended in the early postoperative period. Second, the working length of the plate does have an optimal range, depending on the fracture types. Finally, the hole within the working length should be removed to avoid stress concentration and facilitate fracture healing. Based on the findings from this study, recommendations can be developed to improve clinical practices and plating system design.