Importance of Locking Plate Screw Number and Placement for Mid-Diaphyseal Humeral Fracture Fixation
Nana, Arvind MD, MBA
Kosmopoulos, Victor PhD
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Purpose: Single large-fragment plate constructs are currently the norm for internal fixation of mid-diaphyseal humerus fractures. In cases where anatomy limits the size of the humerus available for fixation however, recent studies support the use of a dual small fragment locking plate construct. This study aims to compare the simulated performance of both a single locking plate and a dual-locking plate construct with decreasing number of locking screws and with changes in screw fixation location. Materials & Methods: Mid-diaphyseal humeral fracture fixation using a single (Model S) and a dual (Model D) locking plate construct were simulated using the finite element method, a numerical technique commonly used to computationally approximate solutions for complex structural mechanics problems. Different configurations were tested by removal of either one or two screws from the superior half of the fixation construct and compared to a control having no screws removed. Models are labelled based on the location of the screw removed with 1 denoting the most superior screw and 4 denoting the inferior screw adjacent to the fracture (e.g., S1 denotes removal of the most superior screw from the single plate model). Results: Model D4 was the only construct to show an increase in stiffness as compared to the original dual plate construct without any screws removed. For the single-plate constructs, models S1-S3 all resulted in less than 2.5% stiffness reductions as compared to the control. Noteworthy, three of the single plate constructs, having two screws removed (models S12, S13, and S23), showed less than a 6% reduction in construct stiffness. In contrast, all of the dual-plate constructs with 2 screws removed showed high stiffness reductions (greater than 55%). Conclusions: Results support that screw number and/or location and construct type (single vs. dual) are important factors to consider in achieving successful fixation. Position and screw number were shown to be particularly important in the dual-plating constructs.