Kit of parts for a modular femur head prosthesis, in particular, a reoperation prosthesis, and a femur head prosthesis from such a kit of parts

A femur head prosthesis adapted for implantation in a femur bone comprising:

• a shaft having a longitudinal axis, a distal portion adapted for implantation into the femur bone and a proximal end portion defining a support surface substantially perpendicular to the longitudinal axis and a guide surface parallel to the longitudinal axis;
• an artificial ball joint;
• a neck having a proximal end receiving the artificial joint ball and a distal end portion defining a support surface substantially perpendicular to the longitudinal axis of the shaft and abutting against the shaft support surface, the distal end portion further defining a guide surface parallel to the longitudinal axis and conforming to the shaft guide surface;
• and
• a fastener coupling the neck to the shaft and having an extensible screw that is elastically pre-stressed with a predetermined bias force, the screw comprising a threaded section and first and second thickened guide sections separated from one another by an extensible section having a transverse cross-section which is smaller than a core cross-section of the threaded section.

A method for anchoring a femoral prosthesis into a femur bone of a patient comprising:

• securing a distal end portion of a shaft into a cavity of the femur bone;
• mounting a neck to a proximal end portion of the shaft by:
• positioning a transverse support surface of a distal end portion of the neck against a transverse support surface of the proximal end portion of the shaft;
• and
• pressing the transverse support surface of the distal end portion of the neck against the transverse support surface of the proximal end portion of the shaft;
• conforming a guide surface of the distal end portion of the neck to a guide surface of the proximal end portion of the shaft such that the guide surfaces are parallel to a longitudinal axis of the shaft;
• inserting an extensible screw through the neck into the proximal end portion of the shaft to press the neck against the support surface of the shaft;
• and
• tightening the extensible screw by means of a torque wrench with a bias force which is defined as a predetermined upper value of the tightening torque of the torque wrench, and which corresponds to a predetermined greatest bending moment introduced by a main load force applied at the neck in a laterally offset position with respect to the longitudinal axis of the shaft.

A femur head prosthesis comprising:

• a neck portion having a proximal portion adapted for receiving an artificial joint ball, the neck portion defining a neck bore therethrough;
• a shaft portion having a distal portion adapted for insertion into a femur bone, the shaft portion defining a shaft bore;
• said neck and shaft portions having distal and proximal transverse support surfaces, respectively, transverse to the axis, said transverse support surfaces abutting one another;
• the neck bore and the shaft bore meeting at a bore intersection and defining an axis;
• the neck bore and the shaft bore defining a first common-diameter, centering surface at said bore intersection;
• at least one of the neck bore and the shaft bore defining a second centering surface;
• the neck portion having a fastener support surface oriented transverse the axis;
• an elongate fastener comprising a head, engaging the fastener support surface, and a fastener shaft, extending through the neck bore and into the shaft bore;
• and
• said fastener shaft comprising:
• a fastener portion secured to the shaft portion;
• a first centering surface region sized and positioned to be adjacent to the first centering surface on both sides of said bore intersection;
• a second centering surface region sized and positioned to be adjacent to the second centering surface;
• and
• a reduced-diameter region between the first and second centering surface regions.