A surgical instrument having a handle, elongate shaft, and a pair of curved jaw members 3801 having a curved slot 3811 forming a curved track for a retractable blade assembly. The blade assembly has a greater lateral flexibility at a distal region than at a proximal region to aid the blade in curving. The blade assembly may have apertures to vary the flexibility such as a slot having a greater width in the distal region than it has in the proximal region, or a plurality of spaced apertures spaced further apart in the proximal region, or the blade may have a difference in thickness between the distal and proximal regions. The distal end of the blade may also be provided with a low friction coating so that it can slide more easily between the jaw members. The coating may be a polymer composite such as PTFE applied by chemical vapour deposition (CVD) or physical vapour deposition (PVD).
