Abstract
This paper examines the mechanics of the tibiotalocalcaneal construct made with a PHILOS plating system. A failed device consisting of the LCP plate and cortical, locking, and cannulated screws was used to perform the analysis. Visual, microstructure, and fractographic examinations were carried out to characterize the fracture surface topology. These examinations revealed the presence of surface scratching, inclusions, discoloration, corrosion pits, beach marks, and cleavage and striations on the fracture surface. Further examination of the material crystallography and texture revealed an interaction of S, Ni, and Mo-based inclusions that may have raised pitting susceptibility of the device made with Stainless Steel 316L. These features suggest that the device underwent damage by pitting the corrosion-fatigue mechanism and overloading towards the end to fail the plate and screws in two or more components. The screws failed via conjoint bending and torsion fatigue mechanisms. Computer simulations of variable angle locking screws were performed in this paper. The material of construction of the device was governed by ASTM F138-8 or its ISO equivalent 5832 and exhibited inconsistencies in chemistry and hardness requirements. The failure conditions were matched in finite element modeling and those boundary conditions discussed in this paper.
Highlights
The locking compression plates in fractures fixation represents a major improvement especially in elderly patients [1]
The other important advantage of the locking plate over the conventional plate is that the conventional plate depends on the friction between the bone and the plate only to provide the fixation, while the locking plate depends on locking the screw heads into the plate by the threaded holes
This paper examines the biomechanical behavior of the VALS and conditions that may have failed a tibiotalocalcaneal construct made with SS 316L
Summary
The locking compression plates in fractures fixation represents a major improvement especially in elderly patients [1]. Despite that, locking plates are mostly used with multiple fracture cases to optimize the alignment of the fracture area, reduce the gap between the bones, and provide maximum stability [3]. Conventional plating requires higher screw torque than the locking plates to provide the same amount of stability This high torque can lead to screw loosening especially in osteoporotic bones and that causes an increase in the gap at the fracture area and failure of the fixation device(s) [4]. Having the screws in a fixed angle within the plate assists in equivalent stress distribution across the plate [6] This advantage makes the locking plate a preferred choice when working on multiple fracture cases and bone with osteoporosis.
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