Biomechanical Simulation and Comparison of Scepter Plate and PHILOS Systems for Greater Tuberosity Humerus Fracture Fixation

This paper presents a biomechanical study of a proximal humerus locking plate (PHILOS) and a new locking plate for the humerous fracture treatment of greater tuberosity. A new locking plate is designed in a scepter shape. Fiber wire is applied to reduce the number of screws. The finite element model was conducted to evaluate the biomechanical behavior of the scepter locking plate-screw-wire fixation under natural loading conditions, i.e., contraction force 200 N and 100 N on supraspinatus and infraspinatus tendons, respectively, and compared to the PHILOS plate-screw-wire fixation. The model consists of cortical bones of the humerus, supraspinatus and infraspinatus tendons, both locking plates, screws, and fiber wires. The maximum von Mises stress and factor of safety on the PHILOS plate and scepter locking plate are 334.1 N/mm2, 2.07, and 590.9 N/mm2, 1.17, respectively. The maximum strain of two crack surfaces and maximum displacement of fracture gap of the PHILOS system model and scepter locking plate system model were 0.3937%, 0.54 mm, and 0.492%, 0.49 mm, respectively. The proper strain and maximum displacement of fracture gap that can promote primary healing are less than 2% and 1 mm, respectively. The results indicate that the scepter locking plate-screw-wire fixation exhibits comparable or non-inferior biomechanical behavior and no effect on the healing process, including stiffness and stress concentration, but 21% smaller, 45% shorter, and 74% lower volume and weight than the PHILOS plate-screw-wire fixation. The scepter locking plate also obtains smaller incisions and reduces soft tissue trauma. These findings suggest that the scepter locking plate design, including screw-wire fixation, is more specifically tailored to the humerus fracture treatment of greater tuberosity than PHILOS plate-screw-wire fixation and may offer advantages in surgical technique and outcome. This scepter locking plate system could be a viable alternative for the fracture treatment of greater tuberosity.