Variable angle locking structure for orthopedic applications

Abstract

To provide a bone anchor that prevents a screw from backing out from a plate after insertion of the screw into bone.SOLUTION: An embodiment includes a bone fixation system comprising: a bone anchor with a tapered head, the head being threaded; and a plate that includes a void, the void including one of a counterbore or a countersink; wherein: (a) no portion of the void is threaded; (b) the void includes an inner wall; (c) the inner wall includes reliefs along its perimeter.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] Embodiments of the present invention are in the field of orthopedic applications. [Background technology]

[0002] In orthopedic surgery, it is common to thread bone screws into bone through holes in fixation plates, allowing for stabilization of osteotomies, fractures, bone fragments, etc. After the screw is inserted into the bone, users often desire to lock the screw to the plate to prevent the screw from backing out of the plate. The desired angle at which the locked screw engages the hole in the plate can vary from normal to the central axis of the hole, depending on the patient's anatomy or additional hardware. Summary of the Invention

[0003] Features and advantages of embodiments of the present invention will become apparent from the appended claims, the following detailed description of one or more exemplary embodiments, and the corresponding drawings. Where considered appropriate, reference labels have been repeated among the figures to indicate corresponding or analogous elements. This disclosure includes the following [1] to

[27] . [1] A bone anchor; a plate; the bone anchor includes: (a)(i) a head and a body, the head coupled to the body; (a)(ii) the bone anchor having a longitudinal axis; (a)(iii) the body having an outer diameter perpendicular to the longitudinal axis, the head having an outer diameter perpendicular to the longitudinal axis; and (a)(iv) the outer diameter of the head is greater than the outer diameter of the body; (b)(i) the plate includes an aperture, (b)(ii) the aperture includes a longitudinal axis that traverses the aperture but does not intersect the plate, (b)(iii) the aperture includes a first opening and a second opening, (b)(iv) the aperture includes a protrusion, the protrusion projecting inwardly from a wall of the aperture and toward the longitudinal axis, (b)(v) the protrusion has a first surface and a second surface, (b)(vi) at least a portion of the first surface is coplanar with a first plane, and (b)(vii) the first plane intersects the longitudinal axis at a first angle, the first angle being between 85 degrees and 95 degrees. Bone fixation system. [2] the protrusion includes an inner wall connecting the first surface of the protrusion to the second surface of the protrusion; the inner wall of the projection has a first portion that is a first distance from the major axis, the first distance being perpendicular to the major axis; the inner wall of the projection has a second portion at a second distance from the major axis, the second distance being perpendicular to the major axis; The second distance is greater than the first distance. The bone fixation system according to [1] above. [3] the inner wall of the protrusion has a third portion at a third distance from the major axis, the third distance being perpendicular to the major axis; the third distance is greater than the first distance; The bone fixation system according to [2] above. [4] the third distance is greater than the second distance; the second distance is measured from a location of the second portion that is farthest from the major axis compared to other locations of the second portion; the third distance is measured from a location of the third portion that is farthest from the major axis compared to other locations of the third portion; The bone fixation system according to [3] above. [5] the inner wall of the protrusion defines an inner periphery of the protrusion; the inner wall of the projection has a fourth portion at the first distance from the major axis; the first portion is between the second portion and the third portion; the third portion is between the first portion and the fourth portion; The bone fixation system according to [3] above. [6] The bone fixing system according to [2], wherein the first plane is perpendicular to the longitudinal axis. [7] The bone fixing system according to [1], wherein the first plane is perpendicular to the longitudinal axis. [8] The bone fixation system of [1], wherein (b)(viii) at least a portion of the second surface is coplanar with a second plane, and the second plane intersects the longitudinal axis at a second angle, the second angle being between 85 degrees and 95 degrees. [9] The bone fixing system according to [8], wherein the second plane is perpendicular to the longitudinal axis.

[10] The bone fixing system according to [8], wherein the first plane is perpendicular to the longitudinal axis.

[11] The first surface is between the second surface and the first opening; the second surface is between the first surface and the second opening; the first surface is a first distance from the first opening, the first distance being parallel to the major axis; the second surface is a second distance from the second opening, the second distance being parallel to the major axis; The first distance is greater than the second distance. The bone fixation system according to [1] above.

[12] the plate does not include a thread between the first opening and the second opening; the first opening is in direct contact with a first outer surface of the plate; the second opening directly contacts the second outer surface of the plate; the first outer surface of the plate faces the second outer surface of the plate; The bone fixation system according to [1] above.

[13] the first opening has a first maximum diameter perpendicular to the longitudinal axis; the second opening has a second maximum diameter perpendicular to the longitudinal axis; The second maximum diameter is greater than the first maximum diameter. The bone fixation system according to

[12] above.

[14] the head of the bone anchor includes a third maximum diameter; the first maximum diameter is greater than the third maximum diameter; the protrusion forms a ring that encircles the inner portion of the opening; the ring has a minimum diameter; the minimum diameter of the ring is smaller than the third maximum diameter; The bone fixation system according to

[13] above.

[15] at least a portion of the head of the bone anchor is included in the most proximal fifth of the bone anchor; the portion of the head of the bone anchor including threads. The bone fixation system according to [1] above.

[16] the body of the bone anchor includes threads; the threads of the body of the bone anchor have a first thread height; the threads on the portion of the head of the bone anchor have a second thread height; The second thread height is less than the first thread height; The bone fixation system according to

[15] above.

[17] The threads of the body of the bone anchor have a first crest width; the threads of the portion of the head of the bone anchor have a second crest width; The second top width is greater than the first top width. The bone fixation system according to

[16] above.

[18] The bone fixation system according to [1], wherein the protrusion forms a ring that surrounds the inner portion of the opening.

[19] the head of the bone anchor has a circular cross-section, the cross-section being perpendicular to the longitudinal axis of the bone anchor; the outer diameter of the head is greater than the outer diameter of the body of the bone anchor including the tapered portion; the tapered portion includes a thread root that tapers outward at an angle between 10 degrees and 25 degrees; the head of the bone anchor includes a maximum diameter taken perpendicular to the longitudinal axis of the bone screw; the projection forms a ring that circumscribes an interior portion of the opening, the ring including a minimum diameter; the maximum diameter of the head of the bone anchor is 5 to 10 percent larger than the minimum diameter of the ring; at least a portion of the head of the bone anchor is included in the most proximal fifth of the bone anchor, and the portion of the head of the bone anchor includes a thread; The thread of the portion of the head of the bone anchor has a thread height, and the thread height is 0.0254 mm to 0.3048 mm; The thread of the head portion of the bone anchor has a crest width, the crest width being 0.0508 mm to 0.3048 mm; the first surface is between the second surface and the first opening, and the second surface is between the first surface and the second opening; the first surface is a first distance from the first opening, the first distance being parallel to the major axis and between 0.254 mm and 1.27 mm; the protrusion includes an inner wall connecting the first surface of the protrusion to the second surface of the protrusion; the inner wall of the projection has a first portion at a second distance from the major axis, the second distance being perpendicular to the major axis; the inner wall of the projection has a second portion that is a third distance from the major axis, the third distance being perpendicular to the major axis; The third distance is greater than the second distance, and the third distance is 0.508 mm to 1.016 mm; The third distance is greater than the second distance by a differential distance, and the differential distance is 0.127 mm to 0.381 mm; the first surface is a fourth distance from the second surface, the fourth distance is parallel to the major axis, and is between 0.254 mm and 5.588 mm; the first portion of the protrusion projects inwardly from the wall of the opening and toward the longitudinal axis a fifth distance, the fifth distance being between 0.254 mm and 0.127 mm; The bone fixation system according to [1] above.

[20] A bone anchor having a tapered head, the head being threaded; a plate including a void, the void including one of a counterbore or a countersink; No part of the gap is threaded; the cavity includes an inner wall; the inner wall includes a relief along its periphery; Bone fixation system.

[21] the cavity includes the counterbore; the counterbore includes a landing, the landing including a surface defined by a plane; the plane is perpendicular to the longitudinal axis of the cavity; the counterbore includes a sidewall, the sidewall extending parallel to the longitudinal axis of the cavity; The bone fixation system according to

[20] above.

[22] The bone anchor includes a material; the plate comprises the material; the bone anchor is monolithic; The plate is monolithic. The bone fixation system according to

[20] above.

[23] the bone anchor and the reliefs are collectively configured such that threads of the bone anchor head deform the landing adjacent at least one of the reliefs when the bone anchor is mated with the plate; the bone anchor and the relief are collectively configured to lock the bone anchor to the plate in response to the threads of the bone anchor head deforming the landing. The bone fixation system according to

[20] above.

[24] The bone fixation system according to

[23] , wherein the plate does not include an elastic member.

[25] A plate including a void, the void including one of a counterbore or a countersink; The plate does not include an elastic member, No part of the gap is threaded; the cavity includes an inner wall; the interior wall includes a relief along its periphery; the reliefs are configured such that threads of the bone anchor head deform the inner wall adjacent at least one of the reliefs when the bone anchor is mated with the plate. Bone fixation kit.

[26] the cavity includes the counterbore; the counterbore includes a landing, the landing including a surface defined by a plane; the plane is perpendicular to the longitudinal axis of the cavity; the counterbore includes a sidewall, the sidewall extending parallel to the longitudinal axis of the cavity; The bone fixation kit according to

[25] above.

[27] A bone fixation kit according to

[25] above, comprising the bone anchor. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 includes a bone anchor in one embodiment.

[0005] [Figure 2] 2A, 2B, and 2C include top views of a bone plate in one embodiment.

[0006] [Figure 3] 3A, 3B, and 3C include side views of a bone plate in one embodiment.

[0007] [Figure 4]4A, 4B, and 4C include side views of a bone plate in one embodiment.

[0008] [Figure 5] 5A, 5B, and 5C include cross-sectional views of different embodiments of bone plates. DETAILED DESCRIPTION OF THE INVENTION

[0009] Referring now to the drawings, similar structures may be provided with similar suffix reference designations. To more clearly illustrate the structures of various embodiments, the drawings included herein are diagrammatic representations of the structures. Thus, the actual appearance of a manufactured structure may appear differently, for example, in a photograph, while still incorporating the claimed structure of the illustrated embodiment. Furthermore, the drawings may show only structures useful for understanding the illustrated embodiment. Additional structures known in the art may not be included to maintain clarity of the drawings. For example, not all parts of a device are necessarily shown. "One embodiment," "various embodiments," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments necessarily include the particular feature, structure, or characteristic. Some embodiments may have some, all, or none of the features described for other embodiments. "First," "second," "third," etc., refer to a common object and indicate that different instances of the same object are being referenced. Such adjectives do not imply that the objects so described must be in a given order, either temporally, spatially, ranked, or in any other way. "Connected" can indicate that elements are in direct physical or electrical contact with each other, and "coupled" can indicate that elements cooperate or interact with each other, although these elements may or may not be in direct physical or electrical contact. A phrase such as "comprising at least one of A and B" includes situations of A, B, or A and B.

[0010] One embodiment includes a variable angle locking screw and plate system that does not require the plate to include threaded or tapered holes. Locking the screw to the plate allows biomechanical loads to be transferred from the screw to the plate more efficiently than with standard non-locking screw / plate systems. Load transfer can aid the healing process, for example, because osteotomy or fracture reduction is maintained.

[0011] One embodiment includes a bone fixation system comprising a bone anchor 101 and a plate 151. Although the plate in Figure 2A shows a single aperture, this is for clarity and embodiments may include one, two, three, four, five, six, or more holes.

[0012] The bone anchor includes a head 102, a body 103, and a longitudinal axis 104. The body has an outer diameter 105 perpendicular to the longitudinal axis, and the head has an outer diameter 106 perpendicular to the longitudinal axis. While the body is not tapered in FIG. 1 , other embodiments may have a tapered body in which (a) the root 107 (where the threads meet the unthreaded portion of the body) is tapered, (b) the crest (the outermost edge of the threads) is tapered, (c) both the root and crest are tapered at the same angle of incidence relative to the longitudinal axis, or (d) the root and crest are tapered at different angles of incidence relative to the longitudinal axis. In FIG. 1 , the head diameter outer diameter 106 is larger than the body outer diameter 105.

[0013] The plate includes an opening 152 having a longitudinal axis 153 that traverses the opening but does not intersect the plate. The opening includes a first opening 154 and a second opening 155. The opening includes a projection 156 that projects inward from a wall 157 of the opening and toward the longitudinal axis. The projection has a first surface 158 and a second surface 159. At least a portion of the first surface is coplanar with a first plane 160. The first plane 160 intersects the longitudinal axis at a first angle 161 that is 90 degrees. However, in other embodiments, the first angle is between 85 and 95 degrees, between 75 and 105 degrees, or between 65 and 115 degrees.

[0014] The protrusion 156 includes an inner wall 162 connecting the first surface of the protrusion to the second surface of the protrusion. The inner wall of the protrusion has a first portion 163 that is a first distance 164 from the major axis 153, the first distance being perpendicular to the major axis. The inner wall of the protrusion has a second portion 165 that is a second distance 166 from the major axis, the second distance being perpendicular to the major axis. The second distance is greater than the first distance because portion 165 is within a void, recess, or relief formed along wall 162. In one embodiment, the inner wall of the protrusion has a third portion 167 that is a third distance 168 from the major axis, the third distance being perpendicular to the major axis. The third distance is greater than the first distance.

[0015] In one embodiment, the third distance 168 is greater than the second distance 166 (not shown in FIG. 2A ). Thus, the relief may be formed at various depths that are not equal to one another. The second distance is measured from a position on the second portion that is farthest from the major axis compared to other positions on the second portion (i.e., the deepest portion of the relief), and the third distance is measured from a position on the third portion that is farthest from the major axis compared to other positions on the third portion.

[0016] In one embodiment, the inner wall of the protrusion defines an inner periphery of the protrusion. The inner wall of the protrusion has a fourth portion 169 that is a first distance 164 from the longitudinal axis.

[0017] In one embodiment, distance 166 is between 0.508 mm and 1.016 mm and is greater than distance 164 by a differential distance 184, which is between 0.127 mm and 0.381 mm.

[0018] In one embodiment, at least a portion of the second surface is coplanar with a second plane 170. The second plane intersects the major axis at a second angle 171 that is 90 degrees. However, in other embodiments, the second angle is between 85 degrees and 95 degrees, between 75 degrees and 105 degrees, or between 65 degrees and 115 degrees.

[0019] In FIG. 2C, the first surface 158 is a first distance 172 from the first opening, the first distance being parallel to the long axis. The second surface is a second distance 173 from the second opening, the second distance being parallel to the long axis. The first distance is greater than the second distance. This allows for a larger clearance for the plate to receive the bone anchor, which may allow for a larger insertion angle of the anchor into the plate. However, in other embodiments, these distances may be the same.

[0020] In one embodiment, distance 173 is between 0.254 mm and 1.27 mm, and distance 172 is between 0.254 mm and 5.588 mm. In one embodiment, protrusion portion 163 projects inwardly and toward the longitudinal axis from aperture wall 157 a distance 185 between 0.254 mm and 0.127 mm. In one embodiment, thickness 186 is between 1.00 mm and 2.75 mm.

[0021] The dimensions used herein are examples and various embodiments may or may not include such dimensions.

[0022] In one embodiment, plate 151 does not include threads between first opening 154 and second opening 155. First opening 154 directly interfaces with first outer surface 174 of the plate, second opening 155 directly interfaces with second outer surface 175 of the plate, and first outer surface 174 of the plate faces second outer surface 175 of the plate. Avoiding the use of threads allows for an increased locking angle without shearing the protruding material or creating burrs. Additionally, once a screw is locked into a thread structure at an angle, the threads can become damaged, making it difficult to relock at a different angle. Avoiding threads allows for high angulation and repeated locking. Additionally, unlike many other conventional locking structures, the locking structure is not limited to only one thread design or thread form.

[0023] In one embodiment, the first opening has a first largest diameter perpendicular to the major axis (twice the radius 176 in the example of FIG. 2C), and the second opening has a second largest diameter perpendicular to the major axis (twice the radius 177 in the example of FIG. 2C). In one embodiment, the second largest diameter is larger than the first largest diameter, although in other embodiments, the two diameters may be equal, or the first diameter may be larger than the second diameter.

[0024] In FIG. 3B , the head 102 of the bone anchor includes a maximum diameter 106. The maximum diameter 176′ of the plate opening 154 is larger than the maximum diameter 106. Also, the protrusion 156 forms a ring that circumscribes the interior portion of the opening. The ring has a minimum diameter 164′ that is smaller than the maximum diameter 106. As used herein, the “maximum” diameter can accommodate, for example, situations where the surface is not circular. For example, the opening 154 may be non-circular in some embodiments and therefore may include more than one diameter, such that the “maximum” diameter is the largest of the diameters.

[0025] In one embodiment, the maximum diameter 106 of the bone anchor head is 5 to 10 percent larger than the minimum diameter 164' of the ring.

[0026] In Figure 1, at least a portion of the head 102 of the bone anchor is included in the most proximal fifth (20 percent) of the bone anchor, and this portion includes the threads. In other words, at least a portion of the bone anchor head is threaded. In Figure 1, the body 103 of the bone anchor includes the threads. The threads on the body of the bone anchor have a first thread height 178, and the threads on the head portion of the bone anchor have a second thread height 179 that is less than the first thread height.

[0027] 1, the threads on the body of the bone anchor have a first crest width 180, and the threads on the head portion of the bone anchor have a second crest width 181 that is greater than the first crest width. However, in other embodiments, widths 180, 181 are equal to one another, and in still other embodiments, width 181 is less than width 180.

[0028] In FIG. 1, thread height 179 is between 0.0254 mm and 0.3048 mm, and crest width 181 is between 0.0508 mm and 0.3048 mm.

[0029] 1, 3C, and 4C, the head of the bone anchor has a circular cross-section, the cross-section being perpendicular to the longitudinal axis of the bone anchor, and the outer diameter of the head is greater than the outer diameter of the body of the bone anchor, which includes a tapered portion. The tapered portion includes a root that tapers outward at an angle 182 between 10 and 20 degrees. The threads on the head portion of the bone anchor include a crest that tapers outward at an angle 183 between 10 and 20 degrees. However, in other embodiments, the tapered portion includes a root that tapers outward at an angle 182 between 10 and 25 degrees, and the threads on the head portion of the bone anchor include a crest that tapers outward at an angle 183 between 10 and 25 degrees.

[0030] One embodiment provides a variable angle locking structure for orthopedic applications by allowing interference between the locking screw and the threaded hole. In one embodiment, the locking screw is a dual-lead locking screw with a tapered diameter extending 2.2 mm to 3.5 mm (measured from one or more crests). However, in other embodiments, the locking screw is a dual-lead locking screw with a tapered diameter extending 1.6 mm to 7.0 mm (measured from one or more crests). In one embodiment, the threaded portion extends the entire length of the screw. The minor angle of the screw head is tapered from 12 degrees to 17 degrees, representing 8 percent to 80 percent of the total length of the screw. The major angle of the screw head is tapered from 7 degrees to 15 degrees, but not the entire head. The proximal portion of the main screw head is not tapered for 5 percent to 15 percent of the screw head. The screw has a minor diameter at thread breakout 187 that is between 6 percent less and 3 percent greater than diameter 164'. However, in another embodiment, the screw has a minor diameter at thread breakout 187 that is between 10 percent less and 5 percent greater than diameter 164'.

[0031] In one embodiment, the diameter of the locking thread on the anchor head is 1 percent to 15 percent larger than diameter 164'. The difference in diameter provides interference with projection 156, causing deformation of the openings in the relief cuts of portions 165, 167 (and any other relief cuts or portions in projection 156).

[0032] In one embodiment, the anchor includes a diameter 106 that allows for limited interference with the top surface 174 under engagement angled up to 30 degrees from the axis 104. However, in another embodiment, the anchor includes a diameter 106 that allows for limited interference with the top surface 174 under engagement angled up to 50 degrees from the axis 104.

[0033] In one embodiment, space 188 is formed as a counterbore having a diameter 176' that is 15 to 35 percent larger than diameter 164'. The opening formed by sidewall 162 is coaxial with the counterbore and allows for mating with a captive screw. Diameter 164' provides interference with tapered head 102 and its captive threads. A radius 189 in the range of 0.0508 mm to 0.381 mm can be present at the bottom of the counterbore to help reduce stress or manufacturability.

[0034] The protrusion 156 includes a thickness 186 that is 40 to 60 percent less than the lead 190 of the thread (the lead is the axial advance of the helix or thread for one complete revolution (360°), and the lead of the thread is the axial movement of a single revolution).

[0035] The locking hole may have multiple relief cuts (see, e.g., portions 165, 167) oriented radially around the opening. The presence of the cuts (or more generally voids) allows deformation of the land to occur, which aids in an interference fit with the screw.

[0036] In one embodiment, the anchor and plate are made of the same material, which may include, for example, Ti-6Al-4V, although other biocompatible materials may be used in other embodiments, and the anchor and plate do not necessarily need to be the same material.

[0037] Embodiments are suitable for securing bone plates and anchors (such as screws) used in foot / ankle repair, however other embodiments are suitable for general orthopedic or medical (human or animal) applications, including but not limited to applications in the foot and ankle, spine, craniofacial, and / or veterinary fields.

[0038] Embodiments provide a variable angle locking structure without the use of tapered, threaded, or channeled plates.

[0039] The plate relief cuts or voids may include one, two, three, four, five, or more in alternative embodiments. In one embodiment, there is no bottom counterbore (e.g., no void 188'). Diameter 164' may range, for example, from 1.0 mm to 7.0 mm or more. Similarly, the anchor may have a diameter 106 that varies from 1.0 mm to 7.0 mm or more. In one embodiment, the screw is fully unthreaded, with the head of the screw having a thread-free cap. In one embodiment, the drive feature of the screw may be any feature that allows for the transmission of torque from the mating member. In one embodiment, the threads of the screw may be embodied in a left-handed thread configuration. In one embodiment, the number of thread leads may vary from one to four. In one embodiment, the screw head may be spherical as opposed to conical.

[0040] One embodiment includes a locking mechanism that locks using a mixture of "notches," "point load threading," and "screw head expansion," as well as a mechanism that does not use countersunk, threaded, or tapered hole geometries. Compared to prior art that uses a two-component system for locking, the locking mechanism addressed herein provides a higher degree of angulation without compromising locking strength. Advantages over prior systems include the ability to lock at angles greater than 30 degrees in one direction, which results in a 60-degree locking cone. However, in other embodiments, advantages over prior systems include the ability to lock at angles greater than 50 degrees in one direction, which results in a 100-degree locking cone. Additionally, one embodiment allows for multiple locking attempts at various angles (without using additional components such as bushings or locking caps). Instead, such an embodiment requires only a specific locking hole and screw geometry to achieve the same result.

[0041] One embodiment includes a screw with two or more continuous threads. The screw includes a conical head and a cylindrical body that make up the overall length of the screw 201. Embodiments of the screw may vary in length from 4 mm to 170 mm. In one embodiment, the length is between 8 mm and 50 mm.

[0042] In one embodiment, the screw has a tapered conical head that extends to the cylindrical body of the screw. In this embodiment, the screw is generally cylindrical between the tapered head and the tip of the screw.

[0043] In one embodiment, the screw head diameter is the critical dimension. The screw head diameter 106 is essential for interference, which allows the screw to lock into the plate and prevents the screw from translating through the hole without "seizing" or locking. The screw head diameter 106 can vary from 2.4384 mm to 4.572 mm. In this embodiment, the head diameter is equal to or greater than the diameter 164'. In one embodiment, the diameter 106 is 7 percent larger than the diameter 164'. However, in other embodiments, the diameter 106 is 4, 5, 6, 8, 9, 10, or more percent larger than the diameter 164'.

[0044] In one embodiment, the thread height 178 (for the threads on the body) ranges from 0.254 mm to 0.762 mm. In one embodiment, the height 178 is 0.381 mm. While the thread height is the same between the two threads in the embodiment of FIG. 1, in other embodiments the thread heights may differ where one thread has a greater height than the other.

[0045] In one embodiment, an important feature is that the thread height 181 on the head of the screw is different from the thread height 178 on the body of the screw. The thread height 181 is between 0.0254 mm and 0.3048 mm. In one embodiment, the thread height 181 is 0.1778 mm. The thread height 181 on the tapered head 102 allows for ideal locking within the opening formed by the protrusion 156. If the thread height 181 is too high, the threads may deform and shear away from the head of the screw, resulting in undesirable burrs on the loose body. Conversely, if the thread height 181 is too low, this locking may be achieved by not contributing to the cut of the protrusion 156.

[0046] In one embodiment, an important feature is the head's underangle 182 (i.e., the angle followed by the roots of the threads). This feature is important because it helps shape the geometry of the thread head. In various embodiments, the angle varies from 10 to 20 degrees, extending 80 to 100 percent of the tapered head 102 from the body 103 of the screw. However, in other embodiments, the angle varies from 10 to 25 degrees, extending 80 to 100 percent of the tapered head 102 from the body 103 of the screw. The angle 182 allows the threads on the head to bite into and wedge with the protrusion 156.

[0047] In one embodiment, an important feature is the major angle 183 of the head (i.e., the angle followed by the crest of the thread). This feature is important in one embodiment because it defines the geometry of the threads on the head. In various embodiments, the angle may range from 10 to 20 degrees. However, in other embodiments, the angle may range from 10 to 25 degrees. In one embodiment, the angle 183 is 15 to 17 degrees. In one embodiment, this angle is constant throughout the head of the screw. This angle allows the threads on the head to bite into and wedge against the protrusion 156.

[0048] In one embodiment, the leading flank angle 191 helps define the thread geometry and is between 30 and 40 degrees (or between 20 and 50 degrees in other embodiments). In one embodiment, the angle 191 is 35 degrees. In one embodiment, the trailing flank angle 192 helps define the thread geometry and is between 2 and 8 degrees (or between 2 and 30 degrees in other embodiments). In one embodiment, the angle 192 is 3 degrees. In one embodiment, the lead 190 of the thread (i.e., the pitch divided by each unique thread) is between 0.7366 mm and 1.524 mm. In one embodiment, the lead is 0.9906 mm. In one embodiment, the crest width 180 on the body of the thread (or the flat at the edge of the thread) is between 0.0254 mm and 0.1524 mm.

[0049] In one embodiment, an important feature is that the crest width 181 of the screw head is between 0.0508 mm and 0.3048 mm, with one embodiment having a value of 0.2032 mm. This is important because the crest needs to be small enough to create sufficient stress and / or strain on the projection 156, but large enough so that it does not shear off and create a loose body.

[0050] In one embodiment, thread diameter 105 is the largest diameter of the threads in the body of the screw. In one embodiment, all unique threads have the same diameter (e.g., if there are two unique threads on the screw, the threads are equal to each other). However, in one embodiment, all unique threads may have different diameters. In one embodiment, diameter 105 is approximately 2.6924 mm.

[0051] In one embodiment, the shaft diameter 193 (defined by the diameter formed by the thread roots of the body of the screw) may be equal for all unique threads and be approximately 1.8796 mm. However, in other embodiments, the diameter 193 may be different for different unique threads. In one embodiment, the tip of the screw may be rounded or sharp for self-drilling applications. In one embodiment, the thread root 107 is comprised of two or more geometric shapes, such as a radius (e.g., 0.2032 mm) and a 0.0254 mm flat.

[0052] With respect to the plate, in one embodiment, an important feature includes the use of an upper counterbore. As used herein, a counterbore is a cylindrical, flat-bottomed hole that enlarges another coaxial hole. The use of the counterbore creates a flat land 158 into which a locking screw can engage. The counterbore may have a depth 172 of 0.762 mm, but in other embodiments, may range from 0.254 mm to 1.27 mm. In an alternative embodiment (e.g., FIG. 5B), the top of the counterbore may have a countersink having a total included angle greater than 90 degrees from the central axis 153. As used herein, a countersink comprises a conical hole cut into a manufactured object. In an embodiment, a counterbore radius 189 may or may not be present, allowing for manufacturability of the land feature. Such a radius may be, for example, 0.254 mm.

[0053] In one embodiment, the opening relief is a key component. For example, in FIG. 2A, there are three reliefs, but in alternative embodiments there may be one, two, four, five, or more reliefs. The reliefs are oriented radially from the central axis 153 and comprise diameters 166 ranging from 0.508 mm to 1.016 mm that protrude into the projections 156. The reliefs allow deformation of the locking holes to occur without creating a loose body.

[0054] In one embodiment, protrusion 156 (e.g., land) is a radially oriented protrusion of material with upper and lower surfaces that may be parallel to one another. In one embodiment, there is no taper, angulation, or thread relief for the land (e.g., a 90-degree angle between wall 162 and surface 158). The land may increase along the minor axis of the locking hole (the opening formed by protrusion 156) if the underside of the locking plate is curved. The land has a thickness 186 and a length 185.

[0055] In one embodiment, thickness 186 is critical to the function of the locking mechanism and is between 0.254 mm and 5.588 mm, allowing the threads of the locking head to cut into the protrusion without significantly deforming the protrusion and allowing the screw to be pulled through the protrusion. Land thickness 186, in one embodiment, is constant around the perimeter of the opening. In one embodiment, thickness 186 varies. Such an embodiment may include, for example, a step of varying the thickness.

[0056] In one embodiment, 176' is 1.0668 mm larger than diameter 164'. The smaller the counterbore diameter, the less angulation the screw can lock into as it contacts top surface 174. In an alternative embodiment, the presence of a countersink above the counterbore avoids this consideration.

[0057] In one embodiment, the key feature is the depth 184 of the relief, which may or may not be equal for each of the reliefs. Typically, the reliefs have a depth 184 of 0.127 mm to 0.381 mm within the projection 156. In one embodiment, the depth 184 is 0.3048 mm. If the relief depth is too shallow, locking will be compromised. Similarly, if the depth is too deep, the land may be subjected to critical forces, causing it to deform excessively and shear from the locking plate.

[0058] In one embodiment, diameter 164' is a critical feature. This diameter is 7 percent smaller than head diameter 106, but can be 2-15 percent smaller. This diameter is critical to the design and allows for an optimal amount of interference that allows the screw to bite / wedge into the locking hole (the hole defined by protrusion 156) to form a solid, unitary structure. In one embodiment, the opening has a diameter of 4.0767 mm.

[0059] In one embodiment, the upper counterbore depth has sidewalls 157 parallel to axis 153. However, the counterbore can be combined with other features, such as a countersink (e.g., FIG. 5B). Figures 5A and 5C show other alternative designs. In one embodiment, the upper counterbore depth 172 is 0.889 mm.

[0060] In one embodiment, a bottom counterbore is present, although such a feature is optional. One embodiment includes a land having two parallel flat surfaces 160, 170. If the bottom counterbore is not present, the bottom surface 175 may have a radius of curvature that is not parallel to the top surface 174 of the land. The presence of the bottom counterbore or gap helps provide clearance for the locking screw at high angles. In one embodiment, the bottom counterbore has a diameter 176'' of 5.461 mm and a depth 173 of 0.127 mm.

[0061] An important feature in some embodiments is the distance 185 of the locking hole land protrusion from the counterbore wall 157. This value can vary from 0.254 mm to 0.762 mm in various embodiments. The protrusion is important to the locking mechanism because if the protrusion is too small, the screw angle and locking ability will be compromised. Additionally, if the protrusion is too long, the locking screw may translate through the locking hole.

[0062] In one embodiment, the angle of the upper counterbore wall 157 from the central axis 153 may be 0 degrees (parallel), but in other embodiments may range from 0 to 80 degrees. Additionally, the angle of the lower counterbore side wall from the axis 153 may be 0 degrees, but may range from 0 to 80 degrees.

[0063] The following examples relate to further embodiments.

[0064] Example 1. A bone anchor and a plate, wherein the bone anchor includes: (a)(i) a head and a body, the head coupled to the body; (a)(ii) the bone anchor having a longitudinal axis; (a)(iii) the body having an outer diameter perpendicular to the longitudinal axis, the head having an outer diameter perpendicular to the longitudinal axis; (a)(iv) the outer diameter of the head is greater than the outer diameter of the body; (b)(i) the plate includes an aperture; and (b)(ii) the aperture has a longitudinal axis extending along the longitudinal axis that intersects the aperture but does not intersect the plate. (b)(iii) the aperture comprises a first opening and a second opening; (b)(iv) the aperture comprises a protrusion, the protrusion protruding inwardly from a wall of the aperture and toward the longitudinal axis; (b)(v) the protrusion has a first surface and a second surface; (b)(vi) at least a portion of the first surface is coplanar with a first plane; and (b)(vii) the first plane intersects the longitudinal axis at a first angle, the first angle being between 85 degrees and 95 degrees.

[0065] In one embodiment, such a bone anchor may include what is called a "headless" screw. Such a screw may have a varying pitch or lead (e.g., a larger pitch or lead near the distal end and a smaller pitch or lead near the proximal end). However, the screw may taper slightly near the proximal end, or may still be tapered to some extent.

[0066] Example 2. The bone fixation system of example 1, wherein the protrusion includes an inner wall joining a first surface of the protrusion to a second surface of the protrusion, the inner wall of the protrusion having a first portion at a first distance from the major axis, the first distance being perpendicular to the major axis, and the inner wall of the protrusion having a second portion at a second distance from the major axis, the second distance being perpendicular to the major axis, the second distance being greater than the first distance.

[0067] Example 3. The bone fixation system of example 2, wherein the inner wall of the protrusion has a third portion that is a third distance from the major axis, the third distance being perpendicular to the major axis, and the third distance being greater than the first distance.

[0068] Example 4. The bone fixation system of Example 3, wherein the third distance is greater than the second distance, the second distance being measured from a position of the second portion that is farthest from the long axis compared to other positions of the second portion, and the third distance being measured from a position of the third portion that is farthest from the long axis compared to other positions of the third portion.

[0069] Example 5. The bone fixation system of Example 3, wherein the inner wall of the protrusion defines an inner circumference of the protrusion, the inner wall of the protrusion has a fourth portion at a first distance from the longitudinal axis, the first portion being between the second portion and the third portion, and the third portion being between the first portion and the fourth portion.

[0070] Example 6. The bone fixation system of Example 2, wherein the first plane is perpendicular to the long axis.

[0071] Example 7. The bone fixation system of Example 1, wherein the first plane is perpendicular to the long axis.

[0072] Example 8. The bone fixation system of Example 1, wherein (b)(viii) at least a portion of the second surface is coplanar with the second plane, and the second plane intersects the long axis at a second angle, the second angle being between 85 degrees and 95 degrees.

[0073] Example 9. The bone fixation system of Example 8, wherein the second plane is perpendicular to the long axis.

[0074] Example 10. The bone fixation system of Example 8, wherein the first plane is perpendicular to the long axis.

[0075] Example 11. The bone fixation system of Example 1, wherein the first surface is between the second surface and the first opening, the second surface is between the first surface and the second opening, the first surface is a first distance from the first opening, the first distance being parallel to the long axis, and the second surface is a second distance from the second opening, the second distance being parallel to the long axis, and the first distance is greater than the second distance.

[0076] Example 12. The bone fixation system of Example 1, wherein the plate does not include threads between the first opening and the second opening, the first opening directly abuts the first outer surface of the plate, the second opening directly abuts the second outer surface of the plate, and the first outer surface of the plate faces the second outer surface of the plate.

[0077] Example 13. The bone fixation system of Example 12, wherein the first opening has a first maximum diameter perpendicular to the longitudinal axis and the second opening has a second maximum diameter perpendicular to the longitudinal axis, the second maximum diameter being greater than the first maximum diameter.

[0078] Example 14. The bone fixation system of Example 13, wherein the head of the bone anchor includes a third maximum diameter, the first maximum diameter being greater than the third maximum diameter, and the protrusion forms a ring that circumscribes an inner portion of the opening, the ring having a minimum diameter, and the minimum diameter of the ring is less than the third maximum diameter.

[0079] Example 15. The bone fixation system of Example 1, wherein at least a portion of the head of the bone anchor is comprised in the most proximal fifth of the bone anchor, and wherein a portion of the head of the bone anchor comprises a thread.

[0080] Example 16. The bone fixation system of Example 15, wherein the body of the bone anchor includes threads, the threads of the body of the bone anchor have a first thread height, and the threads of the head portion of the bone anchor have a second thread height, the second thread height being smaller than the first thread height.

[0081] Example 17. The bone fixation system of Example 16, wherein the threads of the body of the bone anchor have a first crest width and the threads of the head portion of the bone anchor have a second crest width, the second crest width being greater than the first crest width.

[0082] Example 18. The bone fixation system of example 1, wherein the protrusions form a ring that circumscribes an inner portion of the opening.

[0083] Example 19. The head of the bone anchor has a circular cross section, the cross section being perpendicular to the longitudinal axis of the bone anchor, the outer diameter of the head being greater than the outer diameter of the body based on the bone anchor including a tapered portion, the tapered portion tapering outward at an angle of 10 degrees to 25 degrees, including a thread root, the head of the bone anchor having a maximum diameter taken perpendicular to the longitudinal axis of the bone anchor, the protrusions forming a ring circumferentially around the inner portion of the opening, the ring having a minimum diameter, the maximum diameter of the head of the bone anchor being the minimum diameter of the ring. the head portion of the bone anchor has a thread, the thread on the head portion of the bone anchor has a thread height, the thread height is 0.0254 mm to 0.3048 mm, the thread on the head portion of the bone anchor has a crest width, the crest width is 0.0508 mm to 0.3048 mm, the first surface is between the second surface and the first opening, and the second The surface is between the first surface and the second opening, the first surface being a first distance from the first opening, the first distance being parallel to the major axis and between 0.254 mm and 1.27 mm, the protrusion including an inner wall connecting the first surface of the protrusion to the second surface of the protrusion, the inner wall of the protrusion having a first portion at a second distance from the major axis and the second distance being perpendicular to the major axis, the inner wall of the protrusion having a second portion at a third distance from the major axis and the third distance being perpendicular to the major axis and the third distance being greater than the second distance. the third distance is 0.508 mm to 1.016 mm, the third distance is greater than the second distance by a differential distance, the differential distance being 0.127 mm to 0.381 mm, the first surface is a fourth distance from the second surface, the fourth distance is parallel to the major axis and is 0.254 mm to 5.588 mm, and a first portion of the protrusion protrudes inward from the wall of the opening and toward the major axis by a fifth distance, the fifth distance being 0.254 mm to 0.127 mm.

[0084] Example 19.5 The bone fixation system of Example 19, wherein the threads on the head portion of the bone anchor include a crest that tapers outward at an angle of 10 to 20 degrees.

[0085] Example 20. A bone fixation system comprising: a bone anchor having a tapered head, the head being threaded; and a plate including a void, the void comprising one of a countersink or a countersink, wherein no portion of the void is threaded, and the void includes an inner wall, the inner wall including a relief along its periphery.

[0086] Example 21. The bone fixation system of Example 20, wherein the void comprises a counterbore, the counterbore comprises a landing, the landing comprises a surface defined by a plane, the plane being perpendicular to the longitudinal axis of the void, the counterbore comprises a sidewall, the sidewall extending parallel to the longitudinal axis of the void.

[0087] Example 22. The bone fixation system of example 20, wherein the bone anchor comprises the material, the plate comprises the material, the bone anchor is monolithic, and the plate is monolithic.

[0088] Example 23. A bone fixation system as described in Example 21, wherein the bone anchor and reliefs are collectively configured such that when the bone anchor is mated with the plate, the threads of the bone anchor head deform a landing adjacent to at least one of the reliefs, and the bone anchor and relief are collectively configured to lock the bone anchor to the plate in response to the threads of the bone anchor head deforming the landing.

[0089] Example 24. The bone fixation system of example 23, wherein the plate does not include an elastic member.

[0090] For example, some prior art may use a wire (e.g., a nickel-chromium alloy with shape memory) that moves laterally while the screw is being inserted and then returns to an intermediate position and over the screw head to prevent backout of the screw, but such a resilient member is not included in one embodiment of the plate.

[0091] Example 25. A bone fixation kit comprising a plate including a void, the void comprising one of a countersink or a countersink, wherein the plate does not include a resilient member, wherein no portion of the void is threaded, the void includes an inner wall, the inner wall including a relief along its periphery, the relief configured such that threads on the bone anchor head deform the inner wall adjacent at least one of the reliefs when the bone anchor is mated with the plate.

[0092] Example 26. A bone fixation kit as described in Example 25, wherein the void includes a counterbore, the counterbore includes a landing, the landing includes a surface defined by a plane, the plane being perpendicular to the longitudinal axis of the void, and the counterbore includes a sidewall, the sidewall extending parallel to the longitudinal axis of the void.

[0093] Example 27. The bone fixation kit according to Example 25, comprising a bone anchor.

[0094] Example 5a. A bone fixation system described in any of Examples 3 to 4, wherein the inner wall of the protrusion defines an inner circumference of the protrusion, and the inner wall of the protrusion has a fourth portion at a first distance from the longitudinal axis, the first portion being between the second portion and the third portion, and the third portion being between the first portion and the fourth portion.

[0095] Example 6a. The bone fixation system of any of Examples 1-5, wherein the first plane is perpendicular to the longitudinal axis.

[0096] Example 8a. A bone fixation system described in any of Examples 1 to 6, wherein (b)(viii) at least a portion of the second surface is coplanar with the second plane, and the second plane intersects the longitudinal axis at a second angle, the second angle being between 85 degrees and 95 degrees.

[0097] Example 10a. The bone fixation system of any of Examples 1-9, wherein the first plane is perpendicular to the longitudinal axis.

[0098] Example 11a. A bone fixation system described in any of Examples 1 to 10, wherein the first surface is between the second surface and the first opening, the second surface is between the first surface and the second opening, the first surface is a first distance from the first opening, the first distance being parallel to the longitudinal axis, and the second surface is a second distance from the second opening, the second distance being parallel to the longitudinal axis, and the first distance is greater than the second distance.

[0099] Example 12a. A bone fixation system described in any of Examples 1 to 11, wherein the plate does not include a thread between the first opening and the second opening, the first opening is in direct contact with the first outer surface of the plate, the second opening is in direct contact with the second outer surface of the plate, and the first outer surface of the plate faces the second outer surface of the plate.

[0100] Example 15a. A bone fixation system according to any of Examples 1 to 14, wherein at least a portion of the head of the bone anchor is comprised in the most proximal fifth of the bone anchor, and wherein the head portion of the bone anchor comprises a thread.

[0101] Example 18a. The bone fixation system of any of Examples 1 to 17, wherein the protrusions form a ring that circumscribes an interior portion of the aperture.

[0102] Example 19a. The head of the bone anchor has a circular cross section, the cross section being perpendicular to the longitudinal axis of the bone anchor, the outer diameter of the head being greater than the outer diameter of the body of the bone anchor including a tapered portion, the tapered portion tapering outward at an angle of 10 to 20 degrees, including a thread root, the head of the bone anchor having a maximum diameter taken perpendicular to the longitudinal axis of the bone anchor, the protrusions forming a ring circumscribing an inner portion of the opening, the ring having a minimum diameter, the maximum diameter of the head of the bone anchor being greater than the minimum diameter of the ring. the head portion of the bone anchor includes a thread, the thread on the head portion of the bone anchor has a thread height, the thread height being 0.0254 mm to 0.3048 mm, the thread on the head portion of the bone anchor has a crest width, the crest width being 0.0508 mm to 0.3048 mm, the first surface is between the second surface and the first opening, and the second surface is between the first surface and the second opening. and a second opening, the first surface being a first distance from the first opening, the first distance being parallel to the major axis and being 0.254 mm to 1.27 mm; the protrusion including an inner wall connecting the first surface of the protrusion to the second surface of the protrusion, the inner wall of the protrusion having a first portion being a second distance from the major axis and the second distance being perpendicular to the major axis; the inner wall of the protrusion having a second portion being a third distance from the major axis and the third distance being perpendicular to the major axis, the third distance being greater than the second distance, the third distance being 0.254 mm to 1.27 mm. A bone fixation system as described in any of Examples 1 to 18, wherein the third distance is 0.508 mm to 1.016 mm, the third distance is greater than the second distance by a differential distance, the differential distance being 0.127 mm to 0.381 mm, the first surface is a fourth distance from the second surface, the fourth distance is parallel to the major axis and is 0.254 mm to 5.588 mm, and the first portion of the protrusion protrudes inward from the wall of the opening and toward the major axis by a fifth distance, the fifth distance being 0.254 mm to 0.127 mm.

[0103] Example 22a. The bone fixation system of any of Examples 20 to 21, wherein the bone anchor comprises the material, the plate comprises the material, the bone anchor is monolithic, and the plate is monolithic.

[0104] As used herein, monolithic means formed from a single unit. For example, a plate may be formed by forging, machining a block of material, additive manufacturing, etc. Such a unit does not include parts joined via welds or adhesives.

[0105] Example 23a. A bone fixation system described in any of Examples 20 to 22, wherein the bone anchor and relief are collectively configured so that when the bone anchor is mated with the plate, the threads of the bone anchor head deform a landing adjacent to at least one of the reliefs, and the bone anchor and relief are collectively configured to lock the bone anchor to the plate in response to the threads of the bone anchor head deforming the landing.

[0106] Example 24a. The bone fixation system of any of Examples 20 to 23, wherein the plate does not include an elastic member.

[0107] Example 27a. A bone fixation kit according to any of Examples 25 to 26, comprising a bone anchor.

[0108] Example 6a'. The bone fixation system of Example 5a, wherein the first plane is perpendicular to the longitudinal axis.

[0109] Example 8a'. The bone fixation system of any of Examples 5a to 6a, wherein (b)(viii) at least a portion of the second surface is coplanar with the second plane, and the second plane intersects the longitudinal axis at a second angle, the second angle being between 85 degrees and 95 degrees.

[0110] Example 10a'. The bone fixation system of any of Examples 5a, 6a, and 8a, wherein the first plane is perpendicular to the longitudinal axis.

[0111] Example 11a'. A bone fixation system described in any of Examples 5a, 6a, 8a, and 10a, wherein the first surface is between the second surface and the first opening, the second surface is between the first surface and the second opening, the first surface is a first distance from the first opening, the first distance being parallel to the longitudinal axis, and the second surface is a second distance from the second opening, the second distance being parallel to the longitudinal axis, and the first distance is greater than the second distance.

[0112] Example 12a'. The bone fixation system of any of Examples 5a, 6a, 8a, 10a, and 11a, wherein the plate does not include threads between the first opening and the second opening, the first opening is in direct contact with the first outer surface of the plate, the second opening is in direct contact with the second outer surface of the plate, and the first outer surface of the plate faces the second outer surface of the plate.

[0113] Example 15a'. The bone fixation system of any of Examples 5a, 6a, 8a, 10a, 11a, 14a, wherein at least a portion of the head of the bone anchor is comprised in the most proximal fifth of the bone anchor, and wherein the head portion of the bone anchor comprises a thread.

[0114] Example 18a'. The bone fixation system of any of Examples 5a, 6a, 8a, 10a, 11a, 14a, or 17a, wherein the protrusions form a ring that circumscribes an interior portion of the aperture.

[0115] Example 19a'. The head of the bone anchor has a circular cross section, the cross section being perpendicular to the longitudinal axis of the bone anchor, the outer diameter of the head being greater than the outer diameter of the body of the bone anchor including a tapered portion, the tapered portion tapering outward at an angle of 10 to 20 degrees and including a thread root, the head of the bone anchor including a maximum diameter taken perpendicular to the longitudinal axis of the bone anchor, the protrusions forming a ring circumscribing an inner portion of the opening, the ring including a minimum diameter, the maximum diameter of the head of the bone anchor being 5 percent greater than the minimum diameter of the ring. the bone anchor is between 0.0254 mm and 0.3048 mm in diameter, the bone anchor is between 0.0508 ... the first surface is a first distance from the first opening, the first distance being parallel to the major axis and between 0.254 mm and 1.27 mm; the protrusion includes an inner wall connecting the first surface of the protrusion to the second surface of the protrusion, the inner wall of the protrusion having a first portion at a second distance from the major axis and the second distance being perpendicular to the major axis; the inner wall of the protrusion having a second portion at a third distance from the major axis and the third distance being perpendicular to the major axis, the third distance being greater than the second distance and the third distance being between 0.508 mm and 1.016 mm; The bone fixation system of any of Examples 5a, 6a, 8a, 10a, 11a, 14a, 17a, and 18a, wherein the third distance is greater than the second distance by a differential distance, the differential distance being 0.127 mm to 0.381 mm; the first surface is a fourth distance from the second surface, the fourth distance being parallel to the major axis and being 0.254 mm to 5.588 mm; and the first portion of the protrusion protrudes inward from the wall of the opening and toward the major axis by a fifth distance, the fifth distance being 0.254 mm to 0.127 mm.

[0116] Example 23a'. A bone fixation system as described in Example 22a, wherein the bone anchor and reliefs are collectively configured such that when the bone anchor is mated with the plate, the threads of the bone anchor head deform a landing adjacent to at least one of the reliefs, and the bone anchor and relief are collectively configured to lock the bone anchor to the plate in response to the threads of the bone anchor head deforming the landing.

[0117] Example 24a'. The bone fixation system of any of Examples 22a and 23a, wherein the plate does not include a resilient member.

[0118] The foregoing description of embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. This specification and the following claims include terms such as left, right, top, bottom, above, below, upper, lower, first, second, etc., which are used for descriptive purposes only and should not be construed as limiting. For example, terms specifying relative vertical position refer to a situation in which the device side of a substrate is the "top" surface of that substrate; the substrate may actually be in any orientation such that the "top" side of the substrate is lower than the "bottom" side in a standard Earth reference frame and still be included in the meaning of the term "top." The term "on" as used herein (including in the claims) does not, unless otherwise specified, indicate that a first structure "on" a second structure is directly on and in direct contact with the second structure; there may be a third or other structure between the first structure and the second structure on the first structure. The embodiments of the devices or articles described herein can be manufactured, used, or shipped in a number of positions and orientations. Those skilled in the art will recognize that many modifications and variations are possible in light of the above teachings. Those skilled in the art will recognize various equivalent combinations and substitutions for the various components shown in the figures. Accordingly, it is intended that the scope of the invention be limited not by the detailed description, but by the claims appended hereto. The present invention includes the following aspects. [Aspect 1] 1. A bone fixation system comprising a bone anchor having a longitudinal axis and a plate, The bone anchor comprises: a threaded head having a proximal end with a circular cross section perpendicular to the longitudinal axis of the bone anchor; a threaded body extending from the threaded head; and Equipped with The plate is an opening extending through the plate along a longitudinal axis of the opening; Equipped with The opening is a first plate opening; a second plate opening; a sidewall extending into the plate from the first plate opening; a protrusion projecting from the sidewall to the interior surface toward the longitudinal axis of the opening; Equipped with The protrusion is a first surface extending from the sidewall of the aperture between the first and second plate openings of the aperture; a second surface disposed between the first surface of the projection and the second plate opening of the aperture; an inner wall extending parallel to the longitudinal axis of the opening and joining the first surface of the projection to the second surface of the projection, the inner wall forming a circular ring circumscribing an interior portion of the opening, the ring having a minimum diameter, measured perpendicular to the longitudinal axis of the bone anchor, that is less than a maximum diameter of the threaded head of the bone anchor; Equipped with the bone fixation system, wherein for all non-zero angles up to 50 degrees between the long axis of the bone anchor and the long axis of the opening, the threads of the threaded head of the bone anchor are configured to interference-fit engage with the protrusion so as not to deform the protrusion, thereby locking the bone anchor within the opening in the plate. [Aspect 2] the inner wall of the projection has a first portion that is a first distance from the major axis, the first distance being perpendicular to the major axis; the inner wall of the projection has a second portion that is a second distance from the major axis, the second distance being perpendicular to the major axis; 2. The bone fixation system of claim 1, wherein the second distance is greater than the first distance. [Aspect 3] the inner wall of the projection has a third portion that is a third distance from the major axis of the opening when measured perpendicular to the major axis of the opening; 3. The bone fixation system of aspect 2, wherein the third distance is greater than the first distance. [Aspect 4] the third distance is greater than the second distance; the second distance is determined from a location of the second portion that is farthest from the longitudinal axis compared to other locations of the second portion; 4. The bone fixing system of claim 3, wherein the third distance is determined from a position of the third portion that is farthest from the longitudinal axis compared to other positions of the third portion. [Aspect 5] the inner wall of the protrusion defines an inner periphery of the protrusion; the inner wall of the projection has a fourth portion at the first distance from the longitudinal axis; the first portion is between the second portion and the third portion; 4. The bone fixation system of aspect 3, wherein the third portion is between the first portion and the fourth portion. [Aspect 6] 3. The bone fixation system of aspect 2, wherein the first plane is orthogonal to the longitudinal axis. [Aspect 7] 2. The bone fixation system of claim 1, wherein the first plane is perpendicular to the longitudinal axis of the opening. [Aspect 8] 2. The bone fixation system of claim 1, wherein the second surface is coplanar with a second plane that intersects the longitudinal axis of the opening at a second angle between 85 degrees and 95 degrees. [Aspect 9] 9. The bone fixation system of claim 8, wherein the second plane is perpendicular to the longitudinal axis of the opening. [Aspect 10] 9. The bone fixation system of aspect 8, wherein the first plane is perpendicular to the longitudinal axis of the opening. [Aspect 11] the first surface is a first distance from the first plate opening as measured parallel to the major axis; 2. The bone fixation system of claim 1, wherein the second surface of the protrusion is at a second distance from the second plate opening that is less than a distance from the first plate opening of the opening to the first surface of the protrusion, when measured parallel to the long axis of the opening. [Aspect 12] the plate does not include threads between the first plate opening and the second plate opening; the first plate opening is in direct contact with a first outer surface of the plate; the second plate opening is in direct contact with the second outer surface of the plate; 2. The bone fixation system of claim 1, wherein the first outer surface of the plate opposes the second outer surface of the plate. [Aspect 13] the first plate opening has a first maximum diameter measured perpendicular to the major axis of the opening; 13. The bone fixation system of claim 12, wherein the second plate opening has a second maximum diameter measured perpendicular to the longitudinal axis of the opening, the second maximum diameter being greater than the first maximum diameter of the first plate opening. [Aspect 14] 14. The bone fixation system of claim 13, wherein the first maximum diameter of the first plate opening is greater than the maximum diameter of the threaded head of the bone anchor. [Aspect 15] at least a portion of the head of the bone anchor is contained within the most proximal fifth of the bone anchor; 2. The bone fixation system of claim 1, wherein the portion of the head of the bone anchor includes a thread. [Aspect 16] the threads of the threaded body of the bone anchor have a first thread height; 16. The bone fixation system of claim 15, wherein the threads of the portion of the head of the bone anchor have a second thread height that is less than the first thread height. [Aspect 17] 17. The bone fixation system of claim 16, wherein the threads of the threaded body of the bone anchor have a first crest width that is smaller than a second crest width of the threads of the threaded head of the bone anchor.

Claims

1. 1. A bone fixation system comprising a bone anchor having a longitudinal axis and a plate, The bone anchor comprises: a threaded head having a proximal end with a circular cross section perpendicular to the longitudinal axis of the bone anchor; a threaded body extending from the threaded head; and Equipped with The plate is an opening extending through the plate along a longitudinal axis of the opening; Equipped with The opening is a first plate opening; a second plate opening; and a sidewall extending into the plate from the first plate opening; a protrusion projecting inwardly from the sidewall toward the longitudinal axis of the opening; Equipped with The protrusion is a first surface extending from the sidewall of the aperture between the first and second plate openings of the aperture; a second surface disposed between the first surface of the projection and the second plate opening of the aperture; an inner wall extending parallel to the longitudinal axis of the opening and joining the first surface of the projection to the second surface of the projection, the inner wall forming a circular ring circumscribing an interior portion of the opening, the ring having a minimum diameter, measured perpendicular to the longitudinal axis of the bone anchor, that is less than a maximum diameter of the threaded head of the bone anchor; Equipped with the bone fixation system, wherein for all non-zero angles up to 50 degrees between the long axis of the bone anchor and the long axis of the opening, the threads of the threaded head of the bone anchor are configured to provide an interference fit engagement with the protrusion without significantly deforming the protrusion, thereby locking the bone anchor within the opening in the plate.

2. the inner wall of the projection has a first portion that is a first distance from the major axis, the first distance being perpendicular to the major axis; the inner wall of the projection has a second portion that is a second distance from the major axis, the second distance being perpendicular to the major axis; The bone fixing system of claim 1 , wherein the second distance is greater than the first distance.

3. the inner wall of the projection has a third portion that is a third distance from the major axis of the opening when measured perpendicular to the major axis of the opening; The bone fixing system of claim 2 , wherein the third distance is greater than the first distance.

4. the third distance is greater than the second distance; the second distance is determined from a location of the second portion that is farthest from the longitudinal axis compared to other locations of the second portion; The bone fixing system of claim 3 , wherein the third distance is determined from a location of the third portion that is furthest from the longitudinal axis compared to other locations of the third portion.

5. the inner wall of the protrusion defines an inner periphery of the protrusion; the inner wall of the projection has a fourth portion at the first distance from the longitudinal axis; the first portion is between the second portion and the third portion; The bone fixing system of claim 3 , wherein the third portion is between the first portion and the fourth portion.

6. A bone fixation system as described in claim 2, wherein the first surface is coplanar with a first plane perpendicular to the longitudinal axis of the opening.

7. A bone fixation system as described in claim 1, wherein the first surface is coplanar with a first plane perpendicular to the longitudinal axis of the opening.

8. The bone fixation system of claim 1 , wherein the second surface is coplanar with a second plane that intersects the longitudinal axis of the opening at a second angle between 85 degrees and 95 degrees.

9. The bone fixing system of claim 8 , wherein the second plane is perpendicular to the longitudinal axis of the opening.

10. A bone fixation system as described in claim 8, wherein the first surface is coplanar with a first plane perpendicular to the longitudinal axis of the opening.

11. the first surface is a first distance from the first plate opening as measured parallel to the major axis; 2. The bone fixation system of claim 1, wherein the second surface of the projection is at a second distance from the second plate opening that is less than a distance from the first plate opening of the opening to the first surface of the projection, measured parallel to the longitudinal axis of the opening.

12. the plate does not include threads between the first plate opening and the second plate opening; the first plate opening is in direct contact with a first outer surface of the plate; the second plate opening is in direct contact with the second outer surface of the plate; The bone fixation system of claim 1 , wherein the first outer surface of the plate opposes the second outer surface of the plate.

13. the first plate opening has a first maximum diameter measured perpendicular to the major axis of the opening; 13. The bone fixation system of claim 12, wherein the second plate opening has a second maximum diameter measured perpendicular to the longitudinal axis of the opening, the second maximum diameter being greater than the first maximum diameter of the first plate opening.

14. The bone fixation system of claim 13 , wherein the first maximum diameter of the first plate opening is greater than the maximum diameter of the threaded head of the bone anchor.

15. at least a portion of the head of the bone anchor is contained within the most proximal fifth of the bone anchor; The bone fixing system of claim 1 , wherein the portion of the head of the bone anchor includes threads.

16. the threads of the threaded body of the bone anchor have a first thread height; The bone fixation system of claim 15, wherein the threads of the portion of the head of the bone anchor have a second thread height that is less than the first thread height.

17. 17. The bone fixation system of claim 16, wherein the threads of the threaded body of the bone anchor have a first crest width that is less than a second crest width of the threads of the threaded head of the bone anchor.

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