Anchoring a first object in a second object

A method of anchoring a first object in a second object, the method comprising:

• providing the first object, the first object extending along an axis between a proximal end and a distal end and having a circumferential surface extending around the axis, the circumferential surface comprising at least one helical protrusion of a first material,
• wherein the first material is a thermoplastic material;
• providing the second object, the second object comprising a porous material that is brittle;
• bringing the first object in contact with the second object;
• coupling mechanical vibration into the first object to cause the first object to be subject to a helical movement relative to the second object;
• and
• driving the first object with the at least one helical protrusion into the second object,
• wherein the driving of the at least one helical protrusion into the material of the second object causes the material of the second object to be abraded where the at least one helical protrusions drives into it so that the at least one helical protrusion creates a groove, the groove extending helically into the second object,
• wherein the mechanical vibration causes at least some of the thermoplastic material of the at least one helical protrusion to become flowable and to penetrate into the pores of the material of the second object to yield, after re-solidification, a positive fit connection with the second object.