A absorbable surgical screw fastener is provided which includes a head and a tapered shaft extending distally of the head. Buttress threads are provided about the tapered shaft to secure the fastener in tissue. The fastener includes slots formed in the head and buttress threads. A gap is provided between the buttress threads in the head to secure a prosthetic. There is also provided a surgical instrument having novel lockout structure to prevent inadvertent actuation.