Deformable threaded locking structures, and related systems and methods
A bone fixation system includes a plate body that defines an interior surface that defines at least one hole defining a central axis. The internal surface defines plate threads within the hole. The system includes a bone screw having a shaft extending from head along a central axis, wherein the head has an exterior surface that defines threads that are configured to threadedly engage the plate threads. The plate threads and head threads each have a cross-sectional profile in a respective reference plane extending along the respective central axis. The cross-sectional profiles each comprise roots, crests, and flanks extending therebetween. The roots, crests, and flanks collectively deviate from a reference cross-sectional profile that is V-shaped in the respective reference plane and defines crest reference points at apices at a first side thereof and root reference points at apices at a second side thereof opposite the first side. Such deviation causes a thread height measured from the crests to the roots to be less than a reference height measured from the crest reference points to the root reference points, such that a ratio of the thread height of the head threads to the reference height of the head threads is from 0.50:1 to 0.80:1, and a ratio of the thread height of the plate threads to the reference height of the plate threads is from 0.50:1 to 1.00:1.
1. A bone fixation system, comprising:
a bone plate having a body that defines an interior surface that defines at least one hole that defines a central axis, the interior surface defining plate threads; and
a bone screw having a head and a shaft extending from the head along a central axis of the bone screw, the head having an exterior surface that defines head threads that are configured to threadedly engage the plate threads,
wherein the plate threads and the head threads each have a cross-sectional profile in a respective reference plane extending along the respective central axis, the cross-sectional profiles each comprising:
roots;
crests; and
flanks extending from the roots toward the crests, wherein the roots, crests, and flanks collectively deviate from a reference cross-sectional profile that is V-shaped in the respective reference plane and defines crest reference points at apices at a first side thereof and root reference points at apices at a second side thereof opposite the first side,
such that a thread height measured from the crests to the roots is less than a reference height measured from the crest reference points to the root reference points,
wherein a first ratio of the thread height of the head threads to the reference height of the head threads is in a range of 0.50:1 to 0.80:1, and a second ratio of the thread height of the plate threads to the reference height of the plate threads is in a range of 0.50:1 to 1.00:1.
2. The bone fixation system of claim 1 , wherein the bone screw is formed of a material selected from the group comprising stainless steel, titanium, a titanium-aluminum-niobium (TAN) alloy, a titanium-aluminum-vanadium (TAV) alloy, and a cobalt-chrome alloy.
3. The bone fixation system of claim 2 , wherein the bone plate is formed of a material selected from the group comprising stainless steel, titanium, a titanium-aluminum-niobium (TAN) alloy, a titanium-aluminum-vanadium (TAV) alloy, a cobalt-chrome alloy, and nitinol.
4. The bone fixation system of claim 1 , wherein the flanks of the plate threads define a plate thread angle in a range of about 20 degrees to about 60 degrees.
5. The bone fixation system of claim 4 , wherein the flanks of the head threads define a head thread angle in a range of about 30 degrees to about 55 degrees.
6. The bone fixation system of claim 5 , wherein a ratio of the thread height of the plate threads to the thread height of the head threads is in a range of 1.0:1 to 2.0:1.
7. The bone fixation system of claim 5 , wherein the flanks of the plate threads have a first portion that defines the thread angle and a second portion that defines a second thread angle, wherein the second portions of the flanks are located between the first portions and the crests, respectively, the thread angle is in a range of about 25 degrees to about 40 degrees, and the second thread angle is in a range of about 40 degrees to about 120 degrees.
8. The bone fixation system of claim 7 , wherein the first and second portions are substantially linear.
9. The bone fixation system of claim 4 , wherein the flanks of the plate threads are arcuate.
10. The bone fixation system of claim 1 , wherein the crests of the head threads each define relieved crest profiles in the respective reference plane.
11. The bone fixation system of claim 10 , wherein at least some of the relieved crest profiles of the heads threads are rounded and define a radius in a range of about 0.06 mm to about 0.25 mm.
12. The bone fixation system of claim 11 , wherein rounded crest profiles of the head threads define a crest width that is 0.05 mm or greater.
13. The bone fixation system of claim 12 , wherein crests of the head threads are defined at apices of the rounded crest profiles, and the cross-sectional profile of the head threads defines an arcuate crest trajectory axis that intersects the apices of the rounded crest profiles.
14. The bone fixation system of claim 1 , wherein the crests of the plate threads are coincident with a crest trajectory axis that is linear in the respective reference plane.
15. The bone fixation system of claim 14 , wherein the crest trajectory axis is oriented at an angle in a range of about 5 degrees to about 30 degrees relative to the central axis of the hole.
16. The bone fixation system of claim 14 , wherein the crests of the plate threads define linear crest profiles that extend along the crest trajectory axis extending in the respective reference plane.
17. The bone fixation system of claim 14 , wherein the crests of the plate threads define rounded crest profiles.
18. The bone fixation system of claim 1 , wherein the interior surface further defines:
a plurality of columns sequentially located about a circumference of the interior surface, wherein the plate threads traverse each of the columns; and
a plurality of recesses located circumferentially between the columns.
19. The bone fixation system of claim 18 , wherein the thread height and the reference height are substantially constant within each of the columns along at least one revolution about the central axis of the hole.
20. The bone fixation system of claim 18 , wherein each of the columns defines a plurality of first surfaces that extend from a first side of the column to a second side of the column, the first surfaces define the crests, wherein, in a second reference plane that is orthogonal to the central axis of the hole, each of the recesses extends tangentially from the first side of one of the columns to the second side of an adjacent column, the first surfaces of the columns are symmetrically oriented about the central axis of the hole, and the recesses have a substantially common radius in the second reference plane.
21. The bone fixation system of claim 20 , wherein the interior surface defines three columns and three recesses, such that at least an axial portion of the interior surface through which the second reference plane extends defines a trigonal profile in the second reference plane.
22. The bone fixation system of claim 20 , wherein at least an axial portion of the interior surface through which the second reference plane extends defines a quantity of columns and recesses selected from the group comprising:
four columns and four recesses, such that the at least an axial portion of the interior surface defines a tetragonal profile in the second reference plane;
five columns and five recesses, such that the at least an axial portion of the interior surface defines a pentagonal profile in the second reference plane; and
six columns and six recesses, such that the at least an axial portion of the interior surface defines a hexagonal profile in the second reference plane.
23. The bone fixation system of claim 20 , wherein the plate threads traverse each of the columns and recesses such that the thread height and the reference height are substantially constant along each of the columns and recesses along at least one revolution about the central axis of the hole.