An apparatus for operating on tissue comprises a body, an elongate shaft, an end effector, a compression member, and a firing beam. The end effector has a pair of jaws configured to open and close along a first plane. The end effector is capable of delivering RF energy to the tissue. The compression member is configured to drive the jaws to a closed position once the compression member has been distally driven into the end effector. The compression member is substantially inflexible along the first plane yet is flexible along a second plane that is transverse to the first plane. The firing beam is operable to sever tissue captured within the end effector. The compression member may be actuated distally to close the jaws upon tissue and provide uniform compression of the tissue along the length of the jaws before the firing beam is advanced through the tissue.
