A fractured hollow bone can be supported by forming a rigid plastics implant within a cavity of the bone, extending across the fracture. An access port aids removal or revision of the implant. The port comprises a hollow cylinder, with a distal end inserted through an aperture in an end of the bone into the cavity to surround a proximal end of the implant. The access port is connectable to a source of torsional-mode ultrasonic vibrations, which soften the plastics material of the implant, improving engagement between the implant and a threaded formation within the distal end of the access port. Removal of the source allows the access port to act as a guide passage, in line with the elongate implant. A cutting tool introduced through the access port is thus guided so that it can be used to hollow out the implant. Once sufficiently hollowed-out, the implant collapses within its surrounding balloon. The engagement of the access port with the proximal end of the implant allows the implant and balloon to be drawn out of the cavity. A particularly suitable cutting tool has a roughly cylindrical operative head comprising four equally-spaced fins separated by four part-circular grooves. The fins and grooves extend helically of the operative head. The distal end is concave. When activated by torsional-mode ultrasonic vibrations, the distal tips of the fins produce an effective longitudinal cutting action. Debris and softened plastics material flow proximally along the grooves away from the distal end where most cutting occurs.
