Evaluating Periarticular Screw Margins for Locking Plate Osteosynthesis of Proximal Humerus Fractures

Abstract

Introduction: The purpose of this study was to determine whether placing screws farther from the articular cortex could achieve comparable levels of purchase to the more deeply buried configurations currently recommended (between 5 and 8 mm from the articular surface), thus lowering the risk of screw cutout. Methods: Locking screws were inserted into synthetic composite models of osteoporotic bone at depths corresponding to 8, 11 and 14 mm from the articular surface of an anatomic reference model and subjected to mechanical testing. This protocol was then recapitulated in 24 paired cadaveric humeral specimens to assess the forces required to dislodge screws at depths of 8 and 14 mm from the articular surfaces. Results: The average pullout strengths of screws positioned 8, 11 and 14 mm from the articular surface in the synthetic bone composites were 145.64, 140.31 and 140.36 N respectively, demonstrating no significant difference. Pullout testing was performed with screw depths of 8 and 14 mm from the articular surfaces in 24 paired proximal humerus samples. The mean pullout strength of screws 8 and 14 mm from the articular surface were 23.92 and 21.79 N respectively (p=0.37). Conclusion: This study demonstrates no significant difference in locking screw purchase up to 14 mm of the articular margin. Increasing the periarticular distance of locking screws can help confer strength and stability to the implant, while simultaneously mitigating the risk of screw cutout. Clinical relevance: Biomechanical study comparing screw purchase of varying periarticular margins to decrease risk of screw cutout without sacrificing fixation.