Dynamic bone anchor and method of manufacturing the same

A method of manufacturing a bone anchor comprising an anchor member having an open first end, an open second end, and a tubular section between the first end and the second end, a longitudinal axis extending from the first end to the second end, an outer surface, and a bone engagement structure for engaging a bone on at least a portion of the outer surface, and a longitudinal core member having a first portion, a second portion, and a tip portion, the second portion having an engagement structure configured to be inserted into the open first end of the anchor member and moved towards the second end of the anchor member for connecting the engagement structure to the anchor member, the first portion extending from the second portion to an end of the core member, and the tip portion having a solid core and extending from the second portion to an end of the core member opposite the first portion, wherein the core member is made at least partially of a first material that comprises a nickel-titanium (Ni—Ti) based shape memory alloy having a temperature sensitive property such that when the second portion of the core member is assembled inside the tubular section of the anchor member, the engagement structure of the second portion engages the anchor member at an interface with a low force at a first temperature, and the engagement structure engages the anchor member at the interface with a high force at a second temperature higher than the first temperature, resulting in a press-fit connection at the interface, and wherein when the interface has the press-fit connection, the tip portion is configured to project out of the second end of the anchor member and the engagement structure is entirely between the first end and the second end of the anchor member, the method including the steps of:

• inserting the core member into the tubular section, thereby deforming the second portion;
• and
• effecting a phase transition of at least the second portion of the core member into an austenitic state such that the second portion loses the deformation due to a shape memory effect of the shape memory alloy and is connected to the anchor member by a distortion-fit connection.

A dynamic bone anchor comprising:

• an anchor member having a first end, a second end, and a tubular section between the first end and the second end, a longitudinal axis extending from the first end to the second end, an outer surface, and a bone engagement structure for engaging a bone on at least a portion of the outer surface;
• and
• a longitudinal core member having a first portion and a second portion, the second portion configured to be received in the tubular section and connected to the anchor member, and the first portion configured to be spaced apart from the anchor member and movable with respect to the anchor member;
• wherein the core member is made at least partially of a first material that comprises a nickel-titanium (Ni—Ti) based shape memory alloy having a temperature sensitive property such that when the second portion of the core member is assembled inside the tubular section of the anchor member, the second portion engages the anchor member at an interface with a low force at a first temperature, and the second portion engages the anchor member at the interface with a high force at a second temperature higher than the first temperature, resulting in a press-fit connection at the interface,
• wherein the anchor member is made of a second material that is different than the first material, and
• wherein a free end of the first portion of the core member is connected to an anchor head made of a third material.