Proximal Humeral Locking Plates: A Cadaveric Study of 5 Versus 7 Metaphyseal Locking Screws

The most common operative treatment of proximal humerus fractures is internal fixation with fixed-angle locking plates. Although this surgical technique has been refined, a significant failure rate remains. This study aimed to determine whether the number of locking screws in the humeral head affects the biomechanical strength and stability of the construct in bone from elderly individuals. Ten pairs of embalmed cadaveric humeri were osteotomized in a gap model and fixed with periarticular locking plates placed in the standard position. Five or 7 proximal locking screws were inserted. Mechanical testing was performed, and cyclic displacements and maximum force to failure were recorded. No significant difference was found between 5 and 7 locking screws in mean cyclic displacement on the medial (1.09 mm vs 1.12 mm, P=.834) or posterior (0.45 mm vs 0.42 mm, P=.791) sides of the fracture model. On testing to failure, 7 and 5 screws showed similar stiffness (336 N/mm vs 292 N/mm, P=.176), force at ultimate load (745 N vs 662 N, P=.309), and displacement at ultimate load (5.90 mm vs 4.36 mm, P=.080). All samples failed at diaphyseal fixation, and no screw cutout or varus collapse was observed. Results from this study suggest that there is no significant difference between 5 and 7 metaphyseal locking screws for stiffness of fixation of proximal humeral fractures in elderly patients. With the inherent possibility of screw penetration of the humeral head, fewer screws may lead to fewer complications. [Orthopedics. 2018; 41(5):306-311.].