Flexible bone screw
Examples of devices and methods for stabilizing a fracture in a bone include a body having an elongate distal portion having an outer surface defining a screw thread and an elongate proximal portion having a non-threaded outer surface. In one example, a passage is formed through the proximal portion transverse to the longitudinal axis from a first opening on the surface of the proximal portion to a second opening on the surface of the proximal portion.
1. A bone screw for stabilizing bone fractures, the bone screw comprising:
a body defining a longitudinal axis extending between a proximal end and a distal end;
an elongate proximal portion of the body comprising a first material; and
an elongate distal portion of the body comprising a second material different from the first material such that a material composition of the body varies along a length of the body, the elongate distal portion having an outer surface defining a helical distal screw thread formed on a threaded distal portion, wherein the threaded distal portion is formed entirely of the second material, the helical distal screw thread having a minor diameter and a major diameter, wherein the second material has a lower stiffness than the first material, and
wherein a part of the body that is proximal to the helical distal screw thread has a diameter that is greater than the minor diameter of the helical distal screw thread.
2. The bone screw of claim 1 further comprising a passage formed through the elongate proximal portion transverse to the longitudinal axis from a first opening on an outer surface of the elongate proximal portion to a second opening on the outer surface of the elongate proximal portion.
3. The bone screw of claim 1 wherein the body comprises a sleeve surrounding a separate core, the sleeve and core being joined together to form the body.
4. The bone screw of claim 3 wherein the helical distal screw thread is formed on the sleeve.
5. The bone screw of claim 4 wherein the elongate proximal portion comprises the core extending proximally from the sleeve.
6. The bone screw of claim 4 wherein the sleeve comprises a polymeric material, the helical distal screw thread being formed in the polymeric material of the helical distal screw thread.
7. The bone screw of claim 6 wherein the core comprises a metal.
8. The bone screw of claim 6 wherein the sleeve comprises a resorbable polymer.
9. The bone screw of claim 8 wherein the core comprises a reinforced polymer.
10. The bone screw of claim 6 wherein the core comprises a slip resisting feature formed on a surface of the core and the sleeve is molded onto the core so that the polymeric material and slip resisting feature interdigitate.
11. The bone screw of claim 6 wherein the polymeric material comprises polyetheretherketone and the core comprises titanium.
12. The bone screw of claim 3 wherein the sleeve is pinned to the core.
13. The bone screw of claim 3 wherein the sleeve is threaded onto the core.
14. A bone screw for stabilizing bone fractures, the bone screw comprising:
a body defining a longitudinal axis extending between a proximal end and a distal end;
an elongate proximal portion of the body comprising a first material; and
an elongate distal portion of the body comprising a second material such that the elongate distal portion of the body has a second bending stiffness less than half of a first bending stiffness of the elongate proximal portion, the elongate distal portion having an outer surface defining a helical distal screw thread formed on a threaded distal portion, wherein the threaded distal portion is formed entirely of the second material, the helical distal screw thread having a minor diameter and a major diameter, and wherein the helical distal screw thread has a length, along the longitudinal axis, at least twice its minor diameter.
15. The bone screw of claim 14 further comprising a passage formed through the elongate proximal portion transverse to the longitudinal axis from a first opening on an outer surface of the elongate proximal portion to a second opening on the outer surface of the elongate proximal portion.
16. The bone screw of claim 14 wherein the body comprises a sleeve surrounding a separate core, the sleeve and core being joined together to form the body.
17. The bone screw of claim 16 , wherein
the core is formed of the first material;
the sleeve is formed of the second material;
the first material comprises titanium; and
the second material comprises polyetheretherketone.
18. The bone screw of claim 17 , wherein the sleeve is secured to the core via at least one selection from the group consisting of:
a pin passing through aligned holes in the sleeve and the core; and
sleeve threads of the sleeve that engage core threads of the core.
19. A bone screw for stabilizing bone fractures, the bone screw comprising:
a body defining a longitudinal axis extending between a proximal end and a distal end;
an elongate proximal portion of the body comprising a first material comprising a metal; and
an elongate distal portion of the body comprising a second material comprising a polymer, the elongate distal portion having an outer surface defining a helical distal screw thread formed on a threaded distal portion, wherein the threaded distal portion is formed entirely of the second material, the helical distal screw thread having a minor diameter and a major diameter;
wherein the first material is not present in the elongate distal portion, or is present in the elongate distal portion with a second thickness, perpendicular to the longitudinal axis, that is less than a first thickness, perpendicular to the longitudinal axis, of the first material within the elongate proximal portion, and
wherein a part of the body that is proximal to the helical distal screw thread has a diameter that is greater than the minor diameter of the helical distal screw thread.
20. The bone screw of claim 19 wherein:
the body comprises a sleeve surrounding a separate core, the sleeve and core being joined together to form the body;
the core is formed of the first material;
the sleeve is formed of the second material;
the helical distal screw thread is formed on the sleeve; and
the elongate proximal portion comprises the core extending proximally from the sleeve.
21. A bone screw for stabilizing bone fractures, the bone screw consisting essentially of:
a body defining a longitudinal axis extending between an elongate proximal portion and an elongate distal portion, the body comprising:
a core, formed of a metal, extending at least through the elongate proximal portion; and
a sleeve, formed of a polymer, surrounding and immovably joined to the core and extending through the elongate proximal portion and the elongate distal portion;
wherein:
the elongate distal portion comprises an outer surface defining a helical distal screw thread; and
the elongate distal portion is sufficiently flexible to bend in response to insertion of the distal end into a curved portion of a hole in human bone.