This study compared the stability of periprosthetic femur fractures fixed using cortical allograft struts with a metal plate. Cadaveric specimens were loaded in single-leg stance and stair climbiing to 2250 N. Optimum stability in single-leg stance was achieved with two long struts medially and laterally. No clear advantage was noted in using a second strut in stair climbing. Cables rather than wires were useful in single-leg stance, but not in stair climbing. Allograft cortical struts are a biomechanically sound alternative to metal plates fixed with screws and cables for femur fracture fixation below a well-fixed femoral component.