Threaded locking structures for affixing bone anchors to a bone plate, and related systems and methods

This applicationis a reissue application of U.S. Pat. No. 11,013,541, issued May 25, 2021, whichis related to U.S. patent application Ser. No. 15/926,390,filed on Mar. 20, 2018, in the name of Bosshard, et al.; and Ser. No. 15/940,761, filed Mar. 29, 2018,in the name of Bosshard, et al., the disclosures of each of which are hereby incorporated by reference as if set forth in their entireties herein.

The present invention relates to bone plates and bone anchors for coupling to the bone plates, and particularly relates to threaded locking structures defined within a fixation hole of a bone plate for locking with a head of a bone anchor.

Bone plate systems for the internal fixation of bone fractures are well known. Conventional bone plate systems are particularly well-suited to promote the healing of a fracture. A bone anchor, such as a bone screw, is inserted through a fixation aperture or hole in a bone plate and is threaded into bone to compress, neutralize, buttress, tension bend, and/or bridge the fracture ends together. Bone screws that are capable of locking with the bone plate can be employed to transfer loads from one fractured bone part, over a plate, and onto another fractured bone part without drawing the bone against the plate, and to avoid loosening or backing out the bone screws with respect to the plate (which can lead to poor alignment and poor clinical results). One known embodiment of such a screw employs a screw head with external threads for engaging with a corresponding thread on the inner surface of a fixation hole to lock the screw to the plate. These screws, which are hereinafter referred to as “locking screws” or “locking compression screws”, and which can include standard-type locking screws that are configured to lock within fixation hole substantially only at a “nominal” orientation whereby the central screw axis is substantially aligned with the central hole axis, as well as “variable-angle” (VA) locking screws that are configured to lock within a fixation hole at either a nominal orientation or an “angulated” orientation whereby the central screw axis is oriented at an acute angle with respect to the respective central hole axis.

According to an embodiment of the present disclosure, a bone plate includes at least one hole extending through the bone plate from an upper plate surface to a lower plate surface along a central hole axis that is oriented along an axial direction. The at least one hole defined by an interior surface of the bone plate. The interior surface further defining a plurality of columns sequentially located about a circumference of the interior surface and a plurality of recesses located circumferentially between the columns. Each of the columns defines a plurality of thread segments each defining a root, a first thread surface extending from the root to a first crest, and a second thread surface extending from the root to a second crest. At least a portion of the first and second thread surfaces are offset from one another at a thread angle. The thread angle of at least one of the thread segments is in a range of about 5 degrees to about 59 degrees.

The present disclosure can be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific devices, methods, applications, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the scope of the present disclosure. Also, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise.

The term “plurality”, as used herein, means more than one. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable.

The terms “approximately” and “substantially”, as used herein with respect to dimensions, angles, and other geometries, takes into account manufacturing tolerances. Further, the terms “approximately” and “substantially” can include 10% greater than or less than the stated dimension or angle. Further, the terms “approximately” and “substantially” can equally apply to the specific value stated.

Standard-type locking screws and VA locking screws can both be susceptible to a phenomenon referred to herein as “timing error,” whereby factors relating to a bone plating procedure can cause an axial misalignment between external threads on the head of the bone screw relative to corresponding internal threads of a locking hole extending through the bone plate. Moreover, VA locking screws have a tendency to cause cross-threading within a locking hole in which they are inserted, particularly when the VA locking screw is inserted in the locking hole at an angulated orientation. Cross-threading can be caused by the external threads on the screw head not fitting within and thus cross-threading the internal threads of the locking hole. Regions of contact between the crests of the screw head threads and portions of the internal threads, particularly at or near the crests of the internal threads, can be particularly susceptible to cross-threading. Timing error and cross-threading are problematic because they reduce the interference fit (also referred to as the “form-fit”) between the internal threads of the aperture and the screw head threads, which can reduce stability between the screw head and the locking hole. The embodiments disclosed herein pertain to locking structures employed within a locking hole, which locking structures define internal threads having geometries that can avoid or at least reduce contact with the screw head crests. The internal threads can also deform in a direction along a central axis of the hole responsive to timing error. In this manner, the threaded locking structures described herein can lock with the heads of both standard-type and VA locking screws in a manner inhibiting or at least reducing cross-threading.

1 FIG. 2 4 5 6 6 8 4 5 9 6 9 9 26 6 26 26 8 6 25 8 26 29 27 8 8 4 Referring to, a bone fixation systemincludes a bone platehaving a plate bodythat defines therein one or more fixation holes, such as variable-angle (VA) locking holes. The VA locking holesare configured to receive anchor members, such as locking screws, for example, that are configured to affix the bone plateto one or more portions of bone. The plate bodydefines internal threadswithin the VA locking holes. Accordingly, the internal threadscan also be referred to as “plate hole threads” or simply “plate threads” or “hole threads.” The hole threadstraverse locking structures, such as columns, defined within the VA locking holes. Thus the locking structures and columnscan be referred to as “threaded locking structures” and “threaded columns”, respectively. The threaded columnsare configured such that, during insertion of a locking screwwithin the VA locking hole, a screw shaftof the locking screwbypasses the columns, which in turn engage external threadson the screw headof the locking screwin a manner providing enhanced locking engagement between the locking screwand the bone plate, as set forth in more detail below.

4 5 10 12 14 16 4 18 20 18 20 The bone platecan be a bridge plate, as shown, although other bone plate types and configurations are within the scope of the present disclosure. The plate bodycan define a first endand a second endspaced from each other along a longitudinal direction X and a first lateral sideand a second lateral sidespaced from each other along a lateral direction Y that is substantially perpendicular to the longitudinal direction X. The bone platecan also define an upper plate surfaceconfigured to face away from the bone and an opposed lower plate surfaceconfigured to face the bone. The upper and lower plate surfaces,are spaced from each other along a vertical direction Z substantially perpendicular to each of the longitudinal direction X and the lateral direction Y.

It is to be appreciated that, as used herein, the terms “longitudinal”, “longitudinally”, and derivatives thereof refer to the longitudinal direction X; the terms “lateral”, “laterally”, and derivatives thereof refer to the lateral direction Y; and the terms “vertical”, “vertically”, and derivatives thereof refer to the vertical direction Z.

6 18 20 22 22 22 6 22 20 18 18 20 The VA locking holesextend axially from the upper plate surfaceto the lower plate surfacealong a central hole axis. In the depicted embodiment, the central hole axisis oriented along the vertical direction Z, although in other embodiments the central hole axisof one or more of the VA locking holescan be oriented at an oblique angle with respect to the vertical direction Z. As used herein, an “axial direction” is defined as the direction along which the central hole axisextends. Moreover, the directional terms “axial”, “axially”, and derivatives thereof refer to the axial direction. Thus, as used herein, the directional term “axially upward” and derivatives thereof refers to the axial direction from the lower plate surfacetoward the upper plate surface. Conversely, the term “axially downward” and derivatives thereof refers to the axial direction from the upper plate surfacetoward the lower plate surface. Thus, “axially upward” and “axially downward” are each mono-directional components of the “axial direction”, which is bi-directional.

5 8 5 8 5 8 The plate bodyand the locking screwscan each comprise one or more biocompatible materials, such as titanium, titanium alloys (e.g., titanium-aluminum-niobium (TAN) alloys, such as Ti-6Al-7Nb), stainless steel, cobalt base alloys, composite materials, and polymeric materials and/or ceramic materials, by way of non-limiting examples. Preferably, the plate bodymaterial is less hard than the locking screwmaterial. This parameter contributes to the locking characteristics described below. In one example embodiment, the plate bodyprimarily or entirely comprises titanium and the locking screwsprimarily or entirely comprise TAN.

2 FIG. 6 8 8 8 4 4 100 8 8 101 102 6 8 23 22 6 8 23 1 22 1 8 8 Referring now to, the VA locking holescan be configured to provide enhanced affixation with multiple types of locking screws, including standard-type locking screwsa and VA locking screwsb, each optionally having various lengths, so as to allow a physician to implant the bone plateto one or more bones or bone segments as desired. By way of non-limiting example, as shown, the bone platecan be coupled to a long-bonevia locking screwsa,b in a manner affixing fractured segments,of the bone together. The VA locking holesdescribed herein can lock with standard-type locking screwsa at a nominal orientation whereby a central screw axisthereof is substantially aligned with the central hole axis. The VA locking holescan also lock with VA locking screwsb at either a nominal orientation or an “angulated” orientation whereby the central screw axisis oriented at an acute angle Awith respect to the respective central hole axis. Acute angle Acan also be referred to as the “angle of angulation” or simply the “angulation.” Both types of locking screwsa,b and their locking functionalities are described more fully in U.S. Pat. No. 9,314,284, issued Apr. 19, 2016, in the name of Chan et al. (the “Chan Reference”), the entire disclosure of which is incorporated by reference herein, as well as U.S. patent application Ser. Nos. 15/926,390 and 15/940,761, referenced above.

25 8 6 100 8 27 6 27 4 100 4 100 4 100 27 4 100 27 During a bone plating operation, the screw shaftof a locking screwcan be inserted through one of the VA locking holesand driven into the underlying bone. In particular, rotation of the locking screwcauses its threaded screw headto threadedly mate with the VA locking hole. As a result, the screw headfastens the bone plateto the underlying bonesubstantially without applying a compressive force onto the bone plateagainst the underlying bone. The bone platecan be spaced from the underlying bonewhen locked to the threaded screw head. Alternatively, the bone platecan abut the underlying bonewhen locked to the threaded screw head.

8 6 100 9 29 9 8 4 4 100 8 9 25 8 6 100 29 9 100 29 9 26 9 8 6 It is to be appreciated that, during a plating operation, the first locking screwinserted through one of the VA locking holesand into underlying bonehas the benefit of being able to generally mate with the hole threadsso that crests of the screw head threadadvance helically substantially along the troughs of the hole threads. However, once the first locking screwis locked to the bone platethereby fastening the plateto the underlying bone, the subsequent locking screwsoften lack the ability to have their external thread crests advance helically along the hole threadtroughs. This results because, once the screw shaftsof these subsequent locking screwsadvance through the VA locking holesand threadedly purchase into the underlying bone, the relative axial positions of the screw head threadsand the hole threadsare substantially a function of the screw's threaded purchase with the underlying bone. This axial misalignment of the screw head threadsrelative to the hole threadsis referred to herein as “timing error.” As described in more detail below, the threaded columns, and thus the hole threads, can be configured to deform axially to accommodate the timing error associated with locking screws. Such deformation can inhibit or at least reduces cross-threading within the VA locking holes.

3 4 FIGS.and 6 24 5 24 5 24 24 27 6 Referring now to, each of the VA locking holescan be defined by an interior surfaceof the plate body. Alternatively, the interior surfacecan be defined by an insert fitted within an axial aperture of the plate body. Typically, at least a portion of the interior surfaceis tapered as it extends axially downward. Thus, the interior surfaceis configured to prevent the screw headfrom passing completely through the VA locking hole.

24 26 26 18 20 6 26 24 24 28 26 28 18 20 26 28 24 6 26 28 6 The interior surfacecan define the columns. The columnsextend axially between the upper and lower plate surfaces,. Within each (or at least some of) the VA locking holes, the columnsare sequentially located about a circumference of the interior surface. The interior surfacealso defines a plurality of recessessequentially located circumferentially between the columns. The recessesextend axially between the upper and lower plate surfaces,. The columnsand recessescan be evenly spaced about the circumference of the interior surfacewithin the VA locking hole. However, in other embodiments, the columnsand/or recessescan be un-evenly spaced about the circumference of the VA locking hole.

24 30 6 18 32 6 20 30 32 24 34 30 26 34 28 34 22 24 36 32 36 22 36 28 The interior surfacecan define an upper perimeterof the VA locking holeat an interface with the upper plate surfaceand a lower perimeterof the VA locking holeat an interface with the lower plate surface. The upper and lower perimeters,can each be circular in shape, although other shapes are within the scope of the present disclosure. The interior surfacecan also define a lead-in surfacethat tapers axially downward from the upper perimeterto one or more of the columns. As shown, the lead-in surfacecan be circumferentially interrupted by one or more of the recesses. Alternatively, the lead-in surfacecan extend circumferentially continuously and uninterrupted along a full revolution about the central hole axis. The interior surfacecan also define an undercut surfacethat tapers axially upward from the lower perimeter. The undercut surfacecan extend circumferentially continuously and uninterrupted along a full revolution about the central hole axis. Alternatively, the undercut surfacecan be circumferentially interrupted by one or more of the recesses.

5 6 FIGS.and 6 26 28 22 26 26 26 26 22 28 28 26 26 28 26 26 28 26 26 26 28 Referring now to, in an example embodiment, the VA locking holecan include three (3) columnsand three (3) recessesevenly spaced about the central hole axis. The columnscan include a first columna, a second columnb, and a third columnc evenly spaced about the central hole axis. The recessescan include: a first recessa located circumferentially between the first and second columnsa,b; a second recessb located circumferentially between the second and third columnsb,c; and a third recessc located circumferentially between the third and first columnsc,a. It is to be appreciated that in other embodiments there can be fewer than three (3) or more than three (3) columnsand recesses, respectively.

5 FIG. 6 FIG. 28 37 28 37 28 37 37 37 22 37 37 37 37 22 1 28 28 37 37 28 28 28 39 39 22 39 2 22 28 39 6 6 22 As shown in, the first recessa can define a first recess axisa, the second recessb can define a second recess axisb, and the third recessc can define a third recess axisc. Each recess axisa-c can be parallel with the central hole axis, although other recess axisa-c orientations are possible. Each recess axisa-c can also be radially spaced from the central hole axisby radial distance R. Each of the recessesa-c can define a portion of a downward-tapering frusto-conical shape that defines a central cone axis coincident with the respective recess axisa-c. The frusto-conical shapes of the recessesa-c can be substantially identical. In the illustrated embodiment, the frusto-conical shapes are each a frustum of a right circular cone; however other recess geometries can be employed. Each recessdefines a radially-outermost region or trough. Each troughcan lie in a plane that also includes the central hole axis. As shown in one such plane in, the troughscan be oriented at an acute angle Ain a range of about 5 degrees to about 30 degrees relative to the central aperture axis. The recessescan be configured such that the troughsdefine the radially outermost locations of the VA locking hole, as measured in any reference plane that extends through the VA locking holeand is orthogonal to the central hole axis.

26 42 22 42 26 42 26 18 20 42 26 44 45 26 44 45 26 26 28 44 26 26 28 45 26 26 28 44 26 26 28 24 42 26 22 Each columncan define a first surfacesubstantially facing the central hole axis. The first surfacecan also be referred to as an “innermost surface” of the column. The first surfacesof the columnscan extend generally axially between the upper and lower plate surfaces,. The first surfaceof each columncan also extend between a first sideand a circumferentially opposed second sideof the column. The first and second sides,of each columncan define interfaces between the columnand the circumferentially adjacent recesses. For example, the first sideof the first columna can define an interface between the first columna and the third recessc; the second sideof the first columna can define an interface between the first columna and the first recessa; the first sideof the second columnb can define an interface between the second columnb and the first recessa; and so forth along the circumference of the interior surface. The first surfacesof the columnscan collectively define segments of another downward-tapering frusto-conical shape that defines a central cone axis coincident with the central hole axis.

9 26 28 18 20 28 9 50 6 50 52 52 26 54 The hole threadsextend through the columnsand at least portions of the recessesalong one or more thread paths between the upper and lower plate surfaces,. The one or more thread paths can be a single thread path (i.e., single-lead), a pair of non-intersecting thread paths (i.e., double-lead), or three or more thread paths (e.g., triple-lead, etc.). The thread paths can be helical. Portions of the recessescan optionally circumferentially interrupt the hole threadsso as to define a plurality of threaded regionsspaced about the circumference of the VA locking hole, as shown. Each threaded regioncarries one or more thread segmentsextending along the thread path(s). Axially aligned ones of the thread segmentscan traverse a respective one of the columnsso as to define column threads.

6 FIG. 42 26 46 44 45 26 46 26 22 46 56 54 46 54 48 58 54 26 46 48 22 46 3 22 48 4 22 46 48 54 60 46 48 22 60 5 22 60 46 48 46 48 26 With reference to, the first surfaceof each columncan define a column centerlinethat is disposed circumferentially equidistantly between the first and second sides,of the column. The column centerlinesof the columnscan lie in respective planes that also include the central hole axis. In each column, the column centerlinecan extend along the crestsof the column threads. Thus, the column centerlinecan also be referred to as the “crest centerline” of the respective column threads. A root centerlinecan extend along the rootsof the column threads. In each column, the crest centerlineand the root centerlinecan both lie in a single plane that includes the hole axis. The crest centerlinecan be oriented at an acute angle Ain a range from about 5 degrees to about 30 degrees relative to the central aperture axis. The root centerlinecan also be oriented at an acute angle Ain a range from about 5 degrees to about 30 degrees relative to the central aperture axis. The crest and root centerlines,can be parallel, as shown. The column threadscan also define a thread midline, which can lie in a common plane with the crest and root centerlines,and the central hole axis. The thread midlinecan define an acute angle Ain a range from about 5 degrees to about 30 degrees relative to the central aperture axis. In the illustrated embodiment, the thread midlineis parallel with, and equidistantly spaced between, the crest centerlineand the root centerline. It is to be appreciated that, in other embodiments, the crest and root centerlines,of a columncan be oriented at an oblique angle relative to one another.

46 22 2 22 6 6 60 22 3 48 22 4 2 54 3 54 4 54 The crest centerlinecan be radially spaced from the central hole axisby a radial distance Rmeasured along a reference plane M that is orthogonal to the central hole axisand located at the vertical center of the VA locking hole. Thus, the reference plane M can be characterized as the axial “mid-plane” of the VA locking hole. The thread midlinecan be radially spaced from the central hole axisby a distance Rmeasured along the hole mid-plane M. The root centerlinecan be radially spaced from the central hole axisby a distance Rmeasured along the hole mid-plane M. Distance Rcan be characterized as the mean crest radius of the column threads. Distance Rcan be characterized as the mean radius of the column threads. Distance Rcan be characterized as the mean root radius of the column threads.

7 FIG. 52 58 55 58 56 52 57 58 56 55 57 6 54 6 Referring now to, each of the thread segmentscan define a root, a first thread surfaceextending from the rootto a first, axially upper crest. Each thread segmentcan also define a second thread surfaceextending from the rootto a second, axially lower crest. The first and second thread surfaces,are offset from one another at an angle A, which defines the thread angle of the column threads. The thread angle Acan be in a range of about 20 degrees to about 40 degrees, preferably in a range of about 25 degrees to about 35 degrees, and more preferably about 30 degrees.

9 54 54 46 48 9 29 In embodiments where the hole threadsare double-lead threads, the column threadscan define a thread pitch P in a range of 0.2 mm to about 0.6 mm and preferably about 0.4 mm and a thread lead L in a range of about 0.4 mm to about 1.2 mm and preferably about 0.8 mm, each measured along the axial direction. The column threadscan also define a thread depth D measured from the crest centerlineto the root centerlinealong the radial direction R. The pitch P and lead L of the hole threadsare preferably equivalent to the pitch and lead of the screw head threads.

8 FIG. 2 FIG. 6 27 8 8 27 8 66 29 29 8 74 75 76 77 74 76 8 27 6 29 Referring now to, the VA locking holedescribed above can be configured to provide beneficial mating characteristics with the screw headof the standard-type locking screwa () and the VA locking screwb. The screw headof the VA locking screwb can have a generally spherical outer surfacethat defines the external screw head threads. The external screw head threadsof the VA locking screwb define a first thread profilemeasured at the thread rootsand a second thread profilemeasured at the thread crests. As depicted, the threads profiles,of the VA locking screwb are generally spherical, which provides the screw headwith a locking functionality as it advances within the VA locking hole. The external screw head threadshave a thread angle of about 60 degrees.

9 17 FIGS.through 6 8 29 9 26 26 6 29 With reference to, threaded engagement between the VA locking holesand the VA locking screwb will now be described. Although the following description of threaded engagement between the screw head threadsand the hole threadsis made in reference to a single threaded column, it is to be appreciated that the other columnsin the VA locking holecan engage with the screw head threadsin a similar, cooperative manner.

9 FIG. 54 6 8 29 54 54 56 54 56 54 1 1 1 54 1 56 54 6 Leads Referring now to, axial deformation of the column threadsis shown, which can compensate for timing error between the VA locking holeand the VA locking screwb. In this example, the timing error causes the screw head threadsto transmit axially downward forces to the column threads. The column threadsdisclosed herein are configured to have axial flexibility, particularly at the creststhereof. This allows the column threadsto deform axially responsive to the transmitted axially downward forces. One or more of the crestsof the column threadscan be configured to deform downward or upward, and non-destructively, at a maximum axial deformation distance Zthat is at least substantially equivalent to one half of the thread pitch P or to one half of the thread lead L divided by the number of leads. Accordingly, the maximum axial deformation distance Zcan be expressed by the equation: Z=0.5(P)=0.5(L)/(N). According to one example embodiment, the lead L is 0.8 mm, the pitch P is 0.4 mm, the column threadsare double-lead (N=2), and the resultant maximum axial deformation Zof the thread crestis 0.2 mm. The axial deformability of the column threadscan avoid, or at least reduce the timing-error and thus, avoid or at least reduce the occurrence of cross-threading within the VA locking hole.

10 FIG. 54 8 4 6 54 29 6 9 29 56 54 75 29 56 75 6 54 29 Referring now to, radially outward deformation of the column threadsis shown, such as, for example, to lock to the VA locking screwb to the bone plate. In this example, timing error is not present. During screw insertion in the VA locking hole, the column threadsengage the screw head threadsin an interconnecting manner so as to substantially achieve a form-fit in the VA locking hole. In this form-fit, contact between the hole threadsand the screw head threadscan occur predominantly via engagement between the crestsof one or more of the column threadsand the rootsof one or more associated screw head threads. This type of crest-to-rootcontact is at least partially provided by the shallower thread angle Aof the column threadsrelative to the thread angle of the screw head threads.

8 54 54 56 54 29 75 54 6 6 77 54 54 77 Once form-fit is achieved, further rotational advancement of the VA locking screwb with respect to the column threadscan commence deforming the one or more column threads, preferably at the crests. This deformation occurs primarily radially outward, although some measure of axial and/or circumferential deformation can occur, mostly when a timing-error is present. Moreover, the radial deformation can include plastic and elastic deformation, which compresses the one or more column threadsin a manner exerting a reactive compressive force against the associated screw head threads, primarily at the rootsthereof. The plastic and elastic radial deformability of the column threadscan also reduce cross-threading within the VA locking hole. Additionally, the thread angle Aand thread depth D can provide clearance for the screw head crestswithin the column threads, which can reduce contact between the column threadsand the screw head crests, thereby further reducing cross-threading.

54 54 56 55 57 29 75 78 79 54 29 4 8 2 56 54 75 29 8 5 Furthermore, as the one or more column threadsdeforms radially, the total engaged surface area between the column threads(including at the crestsand the upper and lower surfaces,) and the screw head threads(including at the rootsand the upper and lower surfaces,) increases. In this manner, the physical interface between the column threadsand the screw head threads, and thus between the plateand the VA locking screwb, also increases, providing a more stable bone fixation system. This principle of deforming the crestsof the column threadsvia engagement with the rootsof the screw head threadsis achieved, at least in part, by use of a harder locking screwmaterial relative to the hardness of the plate bodymaterial as mentioned above.

11 16 FIG.through 6 8 With reference to, engagement between the VA locking holeand VA locking screwsb at various angulations will now be described.

11 FIG. 11 FIG. 12 FIG. 8 6 56 9 56 8 23 56 52 26 29 46 99 54 29 6 27 8 Referring now to, the VA locking screwb can be locked within the VA locking holeof the present embodiment at a nominal orientation and such that the thread crestsof the plate hole threadsundergo an elastic and plastic deformation, dependent on the applied locking torque. As shown in, the applied locking torque is still small and the deformation of the thread crestsjust started. With a further advancement of the screwb along its central screw axis, the locking torque and the deformation of the thread crestswill increase further. Furthermore, as shown more clearly in the magnified view of, such locking can start at one and continue to two of the thread segmentsof a columnin contact with the screw head threadsat the crest centerline, as shown at interference regions. This beneficial locking mechanism is provided by at least in part by the plastic and elastic radial deformation of the column thread(s)responsive to contact with the screw head threads. It is to be appreciated that the VA locking holecan engage the headof a standard-type locking screwa inserted at a nominal orientation in a generally similar manner.

13 14 FIGS.and 14 FIG. 6 8 25 26 55 54 26 78 29 6 3 6 77 58 54 54 29 56 56 29 99 27 Referring now to, the VA locking holecan be configured such that, when the VA locking screwb is inserted at an angulation of about 15 degrees with the screw shaftextending toward a column, the upper surfaceof the column threadsof the columncan be substantially parallel with the upper surfacesof associated ones of the screw head threads. Such cooperative thread orientations can occur when the column thread angle Ais about 30 degrees and the screw head thread angle is about 60 degrees. As described above, the crest centerline angle Aand the thread depth D can cooperate with the column thread angle Ato increase the clearance between the screw head thread crestsand the rootsof the column threads. Additionally, at the illustrated angulation, contact between the column threadsand the screw head threadscan occur predominantly at, or at least proximate, the column thread crests. As shown in, respective ones of the column thread crestscan deform against portions of the screw head threadsat interference regionsin a manner providing locking engagement with the screw head.

15 16 FIGS.and 16 FIG. 6 8 25 39 28 26 57 54 26 79 29 3 6 77 58 54 54 29 56 56 29 99 27 Referring now to, the VA locking holecan be configured such that, when the VA locking screwb is inserted at an angulation of about 15 degrees with the screw shaftextending toward the troughof a recessopposite a column, the lower surfaceof the column threadsof the columncan be substantially parallel with the lower surfacesof associated ones of the screw head threads. As before, the crest centerline angle Aand the thread depth D can cooperate with the column thread angle Ato increase the clearance between the screw head thread crestsand the rootsof the column threads. Additionally, at the illustrated angulation, contact between the column threadsand the screw head threadscan occur predominantly at or at least proximate the column thread crests. As shown in, respective ones of the column thread crestscan deform against portions of the screw head threadsat interference regionsin a manner providing locking engagement with the screw head.

26 3 2 3 4 6 54 It is to be appreciated that one or more of the characteristics of the columns, such as, by way of non-limiting example, the crest centerline angle A, the mean radii R, R, R, the thread angle A, the thread depth D, the thread pitch P, and the thread lead L can be tailored as needed to provide desired locking characteristics. For example, adjustments to the thread geometry that reduce the form-fit can be offset by adjustments that increase the radial deformation of the column threads, and vice versa.

17 23 FIGS.through 1 16 FIGS.through 6 26 26 6 With reference to, additional embodiments of the VA locking holeswill now be described. For the sake of brevity, the following description will focus primarily on the differences between these embodiments and the embodiments described above with reference to. Although the following description focuses on a single threaded column, it is to be appreciated that the description can apply to the other columnsin the VA locking hole.

17 18 FIGS.and 54 55 57 52 81 82 81 55 57 58 82 82 81 56 81 82 81 7 82 8 7 8 7 8 54 Referring now to, in another embodiment, the column threadscan define multiple thread angles. For example, the first and second thread surfaces,of each thread segmentcan each define a first portionand a second portion. The first portionsof the first and second thread surfaces,can extend from the rootto the respective second portions. The second portionscan extend from the respective first portionstoward the respective crests. The axial space between the first portionscan be referred to as the “root depression.” In this embodiment, the axial space between the second portionscan be referred to as the “crest region.” The first portionscan define a first thread angle Aand the second portionscan define a second thread angle A. The first thread angle A, which can also be referred to as the “root depression angle,” can be in a range of about 20 degrees to about 40 degrees, or about 25 degrees to about 35 degrees. The second thread angle Acan be in a range of about 45 degrees to about 90 degrees. As shown, the first thread angle Acan be about 30 degrees and the second thread angle Acan be about 60 degrees. The column threadsof this embodiment can be characterized as “dual-angle” threads.

26 56 26 26 4 56 2 82 8 46 22 56 6 7 FIGS.and 6 7 FIGS.and 16 17 FIGS.and 6 7 FIGS.and In the present embodiment, the columndesign can optionally be substantially similar to that described with reference to, with the primary difference being that the crestsof the present example are truncated with respect to those shown in. Stated differently, one way of providing the columnshown inis to begin with the columnsshown inand remove bodymaterial at the creststhereof in a manner increasing the crest mean radius Rand forming thread portionsat the second thread angle A. Thus, the thread depth D in the present embodiment can be shallower than in those described above. To compensate for this, the crest centerlinecan optionally be located radially further from the central hole axisthan in the above embodiments, because less deformation will occur at the thread crests.

19 21 FIGS.through 19 FIG. 20 21 FIGS.and 54 58 77 54 54 8 56 26 54 99 27 As shown in, the geometry of the dual-angle column threads, particularly at the crest regions, can provide an increased form-fit relative to the embodiments described above. For example, at a nominal angulation, as shown in, the threaded locking engagement can be substantially entirely via form-fit. The geometry at the root depressions can provide clearance between the column thread rootsand the head thread crestsat various angulations. The root depression can also provide the column threadswith axial deformability, which allows the column threadsto deform downward or upward, such as when the VA locking screwb is inserted with timing error, for example. However, in the present embodiment, the axial deformability can be less profound at the creststhan in the above embodiments. As shown in, at angulations of 15 degrees away and toward the column, the column threadscan deform radially outward at interference regionsso as to achieve a locking press-fit with the screw head.

22 FIG. 54 9 55 57 52 83 82 56 83 9 7 8 9 Referring now to, in further embodiments, column threadscan define a third thread angle A. For example, the first and second thread surfaces,of the thread segmentscan each define a third portionextending from the respective second portionsto the respective crests. In this embodiment, the axial space between the third portionscan be referred to as the “crest region.” The third thread angle Acan be in a range of about 70 degrees up to about 179 degrees, or about 80 degrees to about 100 degrees. In one example embodiment, the first thread angle Acan be about 30 degrees, the second thread angle Acan be about 60 degrees, and the third thread angle Acan be about 90 degrees.

23 FIG. 54 46 22 55 57 48 46 54 10 48 46 10 48 46 10 1 2 55 57 1 2 3 60 10 58 10 56 Referring now to, the column threadscan optionally define an arcuate profile in a reference plane containing the crest centerlineand the central hole axis. For example, the first and second thread surfaces,can each extend radially inward from the root centerlineto the crest centerlinealong an arcuate profile path, such as an involute profile path, by way of a non-limiting example. In this manner, the columns threadsof the present embodiment define a varying thread angle Abetween the root and crest centerlines,. The varying thread angle Aat any radial location RD between the root and crest centerline,can be defined as follows: the varying thread angle Ais the angle between a pair of tangent lines T, Tintersecting the first and second thread surfaces,at respective locations L, Lalong a reference line Lparallel with the thread midlineand coincident with the radial location RD. In such embodiments, the varying thread angle Acan vary from an angle of about 5 degrees adjacent the rootto an angle Aof about 179 degrees as the crests, for example.

22 23 FIGS.and While the embodiments shown inhave less axial deformability than other embodiments disclosed herein, they provide better form fit and less plastic and elastic deformation.

24 FIG. 58 9 150 56 150 22 22 26 1 26 2 39 150 150 26 48 26 77 58 26 Referring now to, in additional embodiments, the rootsof the hole threadscan follow a root thread paththat is different than the thread path followed by the crests. In particular, the root thread pathcan revolve about the central hole axisso as to define a non-circular spline profile in a reference plane orthogonal to the central hole axis. In one such example, the radius of curvature of the spline, as viewed in the reference plane, is greater at the columns(RC) than at locations remote from the columns(RC), such as at the recess troughs, for example. Stated differently, in this example the root thread pathfollows a polyconic spline, wherein the curvature of the root thread path“flattens out” at the columns, such as at the root centerline. Thus, within the columns, any contact between a screw head thread crestand the thread rootbecomes more tangential. In this manner, cross-threading within the columnscan be further reduced or avoided.

25 26 FIGS.through 4 90 6 92 24 90 6 92 18 22 6 92 90 22 6 94 92 22 6 94 92 90 Referring now to, the bone platecan include a combination hole(also referred to as a “combi-hole”) that includes one of the VA locking holesdescribed above in combination with a compression hole. Thus, the interior surfaceof the combination holecan define both the VA locking holeand the compression hole, each extending from the upper plate surfaceto the lower plate surface. The VA locking holeand the compression holeof the combination holecan be open to each other along a direction that is perpendicular to one or both of the central hole axisof the VA locking holeand a central hole axisof the compression hole. The central hole axisof the VA locking holeand the central hole axisof the compression holeof the combination holecan be aligned with each other along the longitudinal direction L, or along any suitable alternative direction as desired.

24 4 96 92 90 30 6 92 6 32 6 92 6 The interior surfaceof the bone platecan thus also define a compression surfaceof the compression holeof the combination hole. Thus, the upper perimetercan define an upper opening to each of the VA locking holeand the unthreaded compression holethat is open to the VA locking hole. Similarly, the lower perimetercan define a lower opening to each of the VA locking holeand the unthreaded compression holethat is open to the VA locking hole.

96 4 96 92 4 100 At least a portion up to an entirety of the compression surfacecan be unthreaded. Accordingly, the unthreaded compression head of a compression screw is configured to bear against the bone plate, and in particular the compression surface, in the compression holeso as to apply a compressive force against the bone platetoward the underlying bone.

96 94 92 96 96 96 94 90 In one example, the compression surfacecan be concave in the axial direction with respect to the central hole axisof the compression hole. For instance, the compression surfacecan be dish shaped or spherical. Thus, the compression surfacecan be configured to be placed in surface contact with the compression head of the compression screw. Alternatively, the compression surfacecan be linear in the axial direction as it tapers radially inwardly toward the central hole axis. Additional details of the combination hole, as well as operation of the compression screw in the combination hole, can be according to the descriptions set forth in U.S. patent application Ser. Nos. 15/926,390 and 15/940,761, referenced above.

Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present disclosure is not intended to be limited to the particular embodiments described in the specification. As one of ordinary skill in the art will readily appreciate from that processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure.