Proximal humeral fracture fixation: a biomechanical comparison of two constructs

Background Different options exist for stabilizing proximal humeral fractures. This study compared the mechanical stability of 2 common proximal humeral fixation plates in bending and torsion. Methods Tests were conducted on 40 synthetic and 10 matched pairs of cadaveric humeri (evenly fixed with DePuy S3 proximal humeral plating system [DePuy Orthopaedics, Warsaw, IN, USA] and Synthes proximal humerus locking compression plate [Synthes, Paoli, PA, USA]). Half of the humeri were tested by cantilevered bending in flexion, extension, varus, and valgus for 100 cycles of ±5 mm of displacement at 1 mm/s before loading to failure in varus. The other half were tested in torsion for 100 cycles of ±8° of rotational displacement at 1°/s before loading to failure in external rotation. Results Peak cyclic loads for synthetic constructs were higher for DePuy plates than Synthes plates in varus and valgus ( P < .0001), but a difference was not detected in extension ( P > .40) or flexion ( P = .0675). Peak cyclic loads for cadaveric constructs showed a significant difference in extension and flexion (Synthes > DePuy, P < .0001) and in varus (DePuy > Synthes, P < .05) but not in valgus ( P > .10). Bending stiffness during varus failure testing was higher for DePuy plates than Synthes plates ( P < .0001) for synthetic constructs. Regarding torsion of synthetic and cadaveric constructs, DePuy plates experienced higher peak cyclic torques over all cycles in both directions ( P < .0001). For synthetic constructs, DePuy plates showed higher torsional stiffness in external failure than Synthes plates ( P < .0001). Conclusions The DePuy plate was stiffer than the Synthes plate with varus and valgus bending, as well as in torsion. The Synthes plate tended to be stiffer in flexion and extension.