The aim of this study was to determine the biomechanical behavior of 2 different implants used in the fixation of proximal humeral fractures. The 2 implants in this study are specifically designed for the fixation of proximal humeral fractures, and both are based on the concept of fixed-angle locking screws. A reproducible 3-part fracture was created in paired human cadaveric bone and then fixed via the locking screw implants. Stress/strain curves for the bone-implant construct were created for loads applied in different directions to determine the relative stiffness below the yield point. After this, each construct was tested to failure with a valgus bending load. The locking nail implant provided a significantly stiffer construct to valgus, extension, and flexion cantilever bending loads below the failure threshold. The valgus load to failure was significantly higher for the nail. The mode of failure was different between implants.