According to one aspect, an instrument may include a sheath having a distal end. The instrument also may include a fluid cannula at the distal end of the sheath. The instrument also may include a cutting electrode at the distal end of the sheath. At least one of: (i) an exterior surface of the fluid cannula, and (ii) a cutting electrode surface that faces the exterior surface, is longitudinally slidable along the other of the exterior surface and the cutting electrode surface during movement of at least one of the cutting electrode and the fluid cannula relative to the other of the cutting electrode and the fluid cannula.