Patent Description:
A variety of conditions can result in the need for manipulation or treatment of spinal conditions, and many spinal procedures require the use of one or more bone screws. In particular, bone screws can be used in the spine to correct deformities and treat trauma and/or degenerative pathologies. For example, bone screws can be used in instrumentation procedures to affix rods and/or plates to the spine, can be used to immobilize part of the spine to assist fusion by holding bony structures together, and can be used in a variety of other operations to treat spinal conditions. Bone screws can provide a means of anchoring or securing various elements to a spinal segment during these procedures.

In such operations, it is important to accurately insert bone screws at an entry point of choice. It is also important to reduce the tendency of bone screws to turn or skive out of the entry point during the initial insertion attempt. Another desirable attribute would be reducing the number of instruments needed to prepare the boney anatomy for insertion. Initial screw insertion can be a significant challenge, adding difficulty and danger to an operation while possibly requiring additional equipment to prepare an entry point for correct screw placement. One approach to reduce the need for additional equipment is to create a flute, or a vertical cut or groove, in the thread of the screw. This flute feature forms a vertical edge to cut bone as the screw is rotated into bone. However, this approach results in reduced fixation within the boney anatomy once the screw is completely inserted. This reduced fixation potential is amplified with shorter screws.

Accordingly, there remains a need for bone screws having an improved structure for initial screw insertion that reduces the need for additional instruments to prepare an entry point and does not sacrifice potential screw fixation, especially in shorter screw lengths.

<CIT> describes a bone fixation screw that employs plural interleaved and axially symmetrical spiral threads. The threads are machined at the screw tip to form symmetrically disposed leading cutting edges. An interference-screw embodiment has a central axial cannula and a female hexagonal drive socket.

The invention is defined by the independent claim, with embodiments described in the dependent claims. Associated surgical methods are also described herein to aid understanding of the invention. These surgical methods are not claimed.

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations may be within the scope of the present invention as defined by the claims.

When advancing bone screws into bone, particularly in the cervical spine, surgeons are often required to advance the screws at a variety of angles and from a variety of positions. These varying advancement conditions can make successfully advancing the screw a challenge. Thus various screws are provided herein that are configured to be implanted in bone, such as in the cervical spine, that can be advanced at a variety of angles with or without a guide hole in the bone. While the bone screws are described in connection with spinal operations and particularly placement in the cervical spine, the screws can be used in connection with any type of bone, tissue (such as in a suture anchor or for lagging soft tissue to bone such as in a shoulder), or in other non-surgical applications.

In an exemplary embodiment, a bone screw is provided with an elongate shank having a distal end or tip that is configured to cut bone as the bone screw is threaded into bone. The screw can have at least two threads extending along the elongate shank. The distal tip portion of the bone screw can have a distal facing surface, and each of the threads and the distal facing surface can define cutting edges that are positioned radially outward from a central longitudinal axis of the elongate shank. The cutting edges can be distal of at least a portion of the distal facing surface to allow the cutting edges to contact bone upon placement of the screw against bone at a variety of angles relative to the surface of bone. As a result, when the screw is rotated, the cutting edges can be configured to engage and cut into bone, allowing the screw to create its own path into bone.

<FIG> illustrate one embodiment of a bone screw <NUM> with an elongate shank <NUM> having a proximal end <NUM>, a distal end <NUM>, and a central longitudinal axis L1. The screw <NUM> can include a head <NUM> at the proximal end having a drive feature <NUM> configured to couple with a driver tool (not shown) for advancing the screw <NUM> into bone. The screw can also have two or more threads formed therealong that terminate at a distal tip on the distal end <NUM> that is configured to cut bone.

The head <NUM> of the bone screw <NUM> can have various configurations, and various drive features can be formed in or on the head. As illustrated in <FIG>, the drive feature <NUM> can be configured to receive a driver tool, such as a screw driver, a hexagonal driver, etc. Any complementary mating features can be used, however. In other embodiments, the head can be shaped to be received in a drive socket of a driver tool, or alternatively the bone screw can be headless, and the shank can mate with a driver tool (not shown).

The elongate shank <NUM> of the bone screw <NUM> can also have various configurations. The elongate shank <NUM> is shown in <FIG> with the threads removed. As shown, the illustrated shank <NUM> has a cylindrical body with a constant diameter extending along a majority thereof, representing a minor diameter of the bone screw <NUM>. The shank can be tapered distally, for example at the distal end, transitioning from a larger diameter to a smaller distal-most diameter. For example, the diameter can be constant along approximately <NUM> to <NUM>% of the total length of the shank <NUM>, with the tapered distal end being <NUM> to <NUM>%. In other embodiments, the shank <NUM> can taper along the entire length with a larger diameter at a proximal end of the shank tapering to a smaller diameter at a distal end thereof. Accordingly, tapering of the shank can be continuous along the length of the shank such that the diameter decreases at a constant rate along the length thereof, or tapering can be located just at a distal end thereof such that only a distal portion of the shank is tapered while a proximal portion has a constant diameter.

As indicated above, the elongate shank can include threads formed therealong. In the illustrated embodiment, the screw <NUM> has two threads <NUM> formed on an external surface thereof, but two or more threads can be used, for example two, three, four, or five threads. In the illustrated embodiment, the threads <NUM> start on opposite sides (e.g., <NUM> degrees apart) of the shank <NUM> so that they are opposed to each other and extend in a rotating pattern along at least part of the elongate shank <NUM> between the proximal end <NUM> and the distal end <NUM> to form a helix. Regardless of the number of threads formed therealong, the threads are preferably positioned equidistant from each other around the shank <NUM> such that the thread starts are balanced with each other. The threads <NUM> can each have a distal-most end that terminates at or near a cutting edge <NUM>, as discussed in further detail below. The threads <NUM> can have an approximately constant thread pitch as well as a constant lead along the entire length of the shank <NUM>.

In the illustrated embodiment, each of the threads <NUM> has a proximal surface <NUM> that faces proximally, a distal surface <NUM> that faces distally, and an outer-most radial surface <NUM> that can extend at an angle between and relative to the proximal and distal facing surfaces <NUM>, <NUM>. A thread profile of each of the threads <NUM> can be, for example, square or rectangular in shape. In other embodiments, the thread profile of the threads can be triangular with no radial surface, rounded, etc., and a height and a width of each of the threads can vary. In the illustrated embodiment, the threads are not symmetrical, such that the proximal surface <NUM> extends to the outer-most radial surface <NUM> at a steeper angle relative to a plane perpendicular to the longitudinal axis L1 as compared to the distal surface <NUM>, as seen in <FIG> and <FIG>. However, symmetrical threads can be used in various embodiments.

Other exemplary thread forms are disclosed, for example, in <CIT>, and in <CIT>.

The threads discussed herein, including the number of threads, the pitch, the lead, major and minor diameters, and thread shape, can be selected to facilitate engagement with bone. Additionally, the diameters of the threads can vary similar to the diameter of the elongate shank discussed above, wherein diameters of the thread(s) represent major diameters of the bone screws. As discussed above with the diameter of the elongate shank representing a minor diameter, the major and minor diameters of a bone screw can taper from one end to the other of a bone screw, such as from a proximal end to a distal end. The major and minor diameter taper can be the same or different. The start of the major and minor diameter taper can be at the same location along an elongate shank of a bone screw or can be different, resulting in constant crest width or varying crest width. The major diameter can represent the largest diameter of a screw thread, whereas the minor diameter can represent the smallest diameter of a screw thread. While threads are shown herein, other surface features can be used in other embodiments. For example, in some embodiments, bone screws can be configured to permit the screw to rotate in one direction but resist or prevent rotation in the opposite direction and/or can include cleats, spikes, friction-fit features, etc., formed thereon.

The screw <NUM> can also have a variety of different distal tip configurations. For example, as illustrated in <FIG>, the distal end <NUM> of the bone screw <NUM> can have a distal facing surface <NUM> that forms the distal-most surface of the bone screw <NUM>. As best shown in <FIG> and <FIG>, the distal facing surface <NUM> can have an outer edge extending therearound and defining a perimeter of the distal facing surface <NUM>. While the shape of the distal facing surface <NUM> can vary, in the illustrated embodiment, the distal facing surface <NUM> is substantially oblong, with concave and convex regions formed along the outer edge defining the perimeter. In an exemplary embodiment, the distal facing surface <NUM> has opposed convex regions <NUM> that are positioned radially about the central longitudinal axis and that define the majority of the outer perimeter. Smaller opposed concave regions <NUM> extend along opposed ends of the distal facing surface <NUM> and are spaced further radially outward of the convex regions <NUM>.

The shape of the distal facing surface <NUM> can vary, but in the illustrated embodiment it has a slight tip or point formed at the mid-point thereof, aligned with the central longitudinal axis L1. This can result in a slight conical shape of the distal facing surface <NUM>, for example as illustrated in <FIG>, such that when viewed along a cross-section extending through the axis L1, the distal end <NUM> of the screw <NUM> can be convex. The distal facing surface <NUM> of the screw <NUM> can thus define an acute angle A1 with a plane extending perpendicular to the central longitudinal axis L1 and extending through the mid-point at the distalmost point. In certain exemplary embodiment, the angle A1 can be, for example, about <NUM> degrees. This conical shape can facilitate effective docking of the bone screw <NUM> in bone while still allowing the cutting edges <NUM> to directly engage bone.

As illustrated in <FIG>, the distal end <NUM> can also have the two or more cutting edges <NUM> formed thereon that are configured to facilitate cutting of bone during rotation of the bone screw <NUM> into bone. The cutting edges <NUM> can be formed along a portion of the outer perimeter of the distal facing surface <NUM>. In the illustrated embodiment, the cutting edges <NUM> are formed along the concave regions <NUM> of the perimeter of the distal facing surface <NUM>, and on opposed sides of the bone screw at a location radially outward of the central longitudinal axis A1. The cutting edges <NUM> can be defined by an intersection of the distal facing surface <NUM> and the proximal surface <NUM> of each thread <NUM>. The distal surface <NUM> of each thread can terminate prior to the cutting edge <NUM>, as best shown in <FIG>. In particular, in the illustrated embodiment, the proximal surface <NUM> and the outer-most radial surface <NUM> of each thread taper toward one another at the distal terminal end of the thread, terminating at one end of the cutting edge <NUM>. As a result of this configuration, the distal surface <NUM> of each thread at the distal end of the bone screw extends between the outer-most radial surface <NUM> of the thread and the distal facing surface <NUM> of the bone screw.

Continuing to refer to <FIG>, and as indicated above, each cutting edge <NUM> can have a concave curved shape, defining a portion of the outer perimeter of the distal facing surface <NUM>. While curved, the cutting edges <NUM> can generally extend radially between the longitudinal axis L1 and the outer diameter of the bone screw <NUM>. As a result of the shape and position of the cutting edges <NUM>, the cutting edges <NUM> are configured to cut bone as the screw is rotated into bone, thereby forming a path for the threads. Effective engagement and cutting can also be achieved even at extreme non-perpendicular angles relative to a bone surface, which are often required in the cervical spine. For example, a user can advance the screw <NUM> into bone even when the screw <NUM> is at an oblique or acute angle relative to the surface of bone, such as about <NUM> to <NUM> degrees. The distal end or tip of the bone screw <NUM>, including the cutting edges <NUM>, can thus be configured to maximize the efficiency of the bone screw <NUM> and to minimize the torque and downward force required to drive the bone screw <NUM> into bone.

While bone screw <NUM> does not have any inner lumen or cannulation, an inner lumen may be provided for certain applications, as may be desired. For example, <FIG> illustrates a bone screw <NUM> similar to bone screw <NUM> with an elongate shank <NUM> having a proximal end <NUM>, a distal end <NUM>, and a longitudinal axis L2. The illustrated screw <NUM> also includes a head <NUM> having a drive feature <NUM> configured to couple with a driver tool (not shown) for advancing the screw <NUM> into bone. The screw can have two or more threads <NUM> formed therealong that terminate at a distal tip on the distal end <NUM> with leading cutting edges that are configured to cut bone. An inner lumen <NUM> is shown extending entirely therethrough along the axis L2, and the inner lumen <NUM> can be configured to receive a guidewire for facilitating placement of the bone screw in bone and/or bone cement to assist in anchoring the bone screw.

Additionally, the distal end of the bone screw can be altered to bring the cutting edges of the bone screw into even greater engagement with bone. For example, a concave distal facing surface can be used to allow the cutting edges to have greater direct and immediate engagement with bone when advancing a screw into bone. As illustrated in <FIG>, a bone screw <NUM>, similar to bone screw <NUM>, can have an elongate shank <NUM> having a proximal end <NUM> and a distal end <NUM>. The screw <NUM> can include a head <NUM> with a drive feature <NUM> configured to couple with a driver tool (not shown) for advancing the screw <NUM> into bone. The screw can have two or more threads <NUM> formed therealong. Each of the threads <NUM> can have a proximal surface <NUM> that faces proximally, a distal surface <NUM> that faces distally, and an outer-most radial surface <NUM> that can extend between and at an angle to the proximal and distal facing surfaces <NUM>, <NUM>. The threads <NUM> can terminate at a distal tip on the distal end <NUM> with leading cutting edges <NUM> that are configured to cut bone, similar to the cutting edges <NUM> discussed above.

In this embodiment, the distal facing surface <NUM> is concave, with the mid-portion being positioned more proximal than the outer edges of the distal facing surface <NUM>. When viewed along a longitudinal cross-section as shown in <FIG>, the distal end <NUM> of the screw <NUM> can have a bowl shape such that the bone screw is configured to allow direct and unobstructed contact between the cutting edges <NUM> and bone when the screw <NUM> is advanced into bone. In other words, the cutting edges <NUM> are more distal then the mid-portion of the distal facing surface <NUM>. The distal facing surface <NUM> can thus have sidewalls that extend at an acute angle relative to a plane extending perpendicular to the longitudinal axis L3. In certain exemplarmy embdoiments, the angle can be about -<NUM> degrees.

Similar to the prior embodiment, and as illustrated in <FIG>, the cutting edges <NUM> can be formed along an outer perimeter of the distal facing surface <NUM> on opposed sides thereof. Each cutting edges <NUM> can be defined by an intersection between the distal facing surface <NUM> and the proximal surface <NUM> of each of the threads <NUM>, similar to cutting edges <NUM>. The cutting edges <NUM> can extend radially outward between a longitudinal axis L3 of the bone screw <NUM> and an outer diameter of the bone screw <NUM>. Each cutting edge <NUM> can also have a curved concave shape. The outer perimeter of the distal facing surface <NUM> can also include convex regions, similar to those discussed above with respect to surface <NUM>. In use, because the distal facing surface <NUM> is concave, the cutting edges <NUM> protrude distally into even greater engagement with bone, without any point of contact on the distal end <NUM> of the screw <NUM> until the cutting edges <NUM> engage bone. The cutting edges <NUM> can thus effectively cut bone from a variety of different angles, allowing a user to place the screw <NUM> into bone in numerous different operational situations while allowing the screw <NUM> to create its own path into bone. For example, a user can advance the screw <NUM> into bone even when the screw <NUM> is at an oblique or acute angle relative to the surface of bone, such as about <NUM> to <NUM> degrees. The cutting edges <NUM> can be configured to maximize the efficiency of the bone screw <NUM> and to minimize the torque and downward force required to drive the bone screw <NUM> into bone while also removing any distal protrusion that can accidentally interfere with operation of the cutting edges <NUM>.

Similar to the inner lumen <NUM> of the bone screw <NUM>, an inner lumen can be formed in a bone screw with a concave distal end. For example, <FIG> illustrates a bone screw <NUM> similar to the bone screw <NUM> with an elongate shank <NUM> having a proximal end (not shown), a distal end <NUM>, and a longitudinal axis L4. The illustrated screw <NUM> includes a head with a drive feature (not shown) configured to couple with a driver tool (not shown) for advancing the screw <NUM> into bone. The screw can have two or more threads <NUM> formed therealong that terminate at a distal tip on the distal end <NUM> with leading cutting edges <NUM> that are configured to cut bone. An inner lumen <NUM> can be formed through the elongate shank <NUM> along the axis L4, and the inner lumen <NUM> can be configured to receive a guidewire for facilitating placement of the bone screw in bone and/or bone cement to assist in anchoring the bone screw.

The distal facing surface in the bone screws disclosed herein can have various features formed thereon. For example, a leading nub or protrusion can be located on a distal end of a bone screw to allow a user to align the bone screw with a pilot hole formed in bone. For example, <FIG> illustrate a bone screw <NUM> similar to bone screw <NUM> with an elongate shank <NUM> having a proximal end <NUM> and a distal end <NUM>. The screw <NUM> can also include a head <NUM> with a drive feature <NUM> configured to couple with a driver tool (not shown) for advancing the screw <NUM> into bone. The screw can have two or more threads <NUM> formed therealong. Each of the threads <NUM> can have a proximal surface <NUM>, a distal surface <NUM>, and an outer-most radial surface <NUM> that can extend at an angle to the proximal and distal surfaces <NUM>, <NUM>. The threads <NUM> can terminate at a distal tip on the distal end <NUM> with cutting edges <NUM> that are configured to cut bone. The distal tip configuration, including the cutting edges <NUM>, can have the same configuration as the bone screws discussed above. However, in this embodiment, a nub <NUM> extends distally from a central or mid portion of a distal facing surface <NUM> of the bone screw <NUM>. The nub <NUM> can have a variety of shapes, such as a generally conical shape. For example, the nub <NUM> can be cylindrical at a proximal base connecting to the distal facing surface <NUM> and can taper to a rounded or curved tip at a distal-most end. The nub <NUM> can be aligned with the central longitudinal axis and can be configured to fit into a pilot hole punched or drilled into bone to allow a user to quickly and easily line up the screw <NUM> with the bone, for example using the conical shape to ensure the screw <NUM> is securely positioned in the pilot hole. The diameter of the nub <NUM> is preferably smaller than the minor diameter of the threads <NUM> of the screw <NUM> to allow the cutting edges <NUM> to be formed and to help ensure that the threads <NUM> are large enough to still engage bone as the screw <NUM> is advanced into bone.

In certain embodiments, the bone screws and shanks disclosed herein can be part of a bone anchor assembly. For example, as illustrated in <FIG>, the bone screw <NUM> can be used with a polyaxial receiver <NUM> and a compression cap <NUM>. The receiver <NUM> can be in the form of a U-shaped body having screw extension tabs <NUM> extending proximally therefrom. The receiver <NUM> can have an inner cavity configured to seat the head <NUM> of the bone screw <NUM>. The elongate shank <NUM> can extend through an opening in a distal end of the receiver <NUM>. The compression cap <NUM> can be configured to be received in the receiver <NUM> and positioned proximally from the bone screw <NUM>. A spinal rod (not shown) can be positioned between the screw extension tabs <NUM>, and it can be seated in a proximal portion of the compression cap <NUM>. The assembly can also include a set screw (not shown) configured to be received between the screw extension tabs <NUM>, and it can apply a distal force to the spinal rod and the compression cap <NUM> to lock the rod within the receiver <NUM> and to lock the bone screw <NUM> in place relative to the receiver <NUM>. The outer surfaces of each of the screw extension tabs <NUM> can include a feature, such as a recess, dimple, notch, projection, or the like, to facilitate connection of the receiver <NUM> to instruments. For example, the screw extension tabs <NUM> can include an arcuate groove at the respective free end of the tabs. Such grooves are described in more detail in <CIT>. Additionally, the bone screw <NUM> can be a favored angle screw, for example as disclosed in <CIT>, and in <CIT>. Alternatively, the bone anchor assembly can be a conventional (non-biased) polyaxial screw in which the bone screw pivots in the same amount in every direction. The surgical instruments disclosed herein can be configured to operate in conjunction with bone anchor assemblies of the type known in the art. Further information on screws can be found in U. Patent Application Publication No. <CIT>. In some embodiments, a kit can be provided that includes one or more of the screws disclosed herein along with one or more screw assemblies, such as that illustrated in FIG. For example, an exemplary kit can include a plurality of screws and/or screw assemblies of varying type and size, such that a surgeon can select the appropriate screw and/or screw assembly for a particular application.

In use, the bone screws <NUM>, <NUM>, <NUM>, <NUM>, <NUM> can be inserted into a body of a patient, either as part of a screw assembly or as part of another procedure. Using the bone screw <NUM> as an example, the distal end <NUM> of the bone screw <NUM> can be placed against bone, such as a vertebral pedicle, e.g., in the cervical spine of a patient. A driver tool (not shown) can engage the drive feature <NUM>, and the driver tool can be rotated to rotate the bone screw <NUM>, e.g., clockwise, relative to the bone. As the cutting edges <NUM> rotate, they can cut away bone and cause the screw <NUM> to advance forward into the bone. The threads <NUM> can engage bone, which can secure the bone screw <NUM> in bone. The driver tool can continue to be rotated until the bone screw <NUM> is fully driven into the bone. For example, a user can position at least two cutting edges <NUM> formed along an outer perimeter of the distal facing surface <NUM> of the bone screw <NUM> in contact with a bone surface in the cervical spine of a patient. The cutting edges <NUM> can engage the bone surface, and the cutting edges <NUM> can be defined by a portion of the outer perimeter of the distal facing surface <NUM> and the proximal surface <NUM> of at least two threads <NUM>. Rotating the bone screw <NUM> can cause the cutting edges <NUM> to cut away bone to advance the bone screw into bone. The bone screw <NUM> can be positioned at an angle other than <NUM> degrees relative to the bone surface, and a distal protrusion on the distal facing surface <NUM> can be inserted into a guide hole formed in the bone. A central region of the distal facing surface <NUM> can be positioned proximal of the cutting edges <NUM> such that the central region does not contact the bone surface when the at least two cutting edges are positioned in contact with the bone surface.

The screws disclosed herein can be formed from any of a variety of materials. In some embodiments, the screws can be formed from non-absorbable materials, such as polysulfone, or metals such as titanium and titanium alloys. In other embodiments, the screws can be formed from or can include a coating made of a biocompatible, bioabsorbable material that can reduce immunological problems associated with having a foreign substance within the body over a prolonged period of time. Exemplary materials from which the screws disclosed herein can be formed include bioabsorbable elastomers, copolymer combinations such as polylactic acid-polyglycolic acid (PLA-PGA), and bioabsorbable polymers such as aliphatic polyesters, poly(amino acids), copoly(ether-esters), polyalkylenes oxalates, polyamides, tyrosine derived polycarbonates, poly(iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters, polyoxaesters containing amine groups, poly(anhydrides), polyphosphazenes, biomolecules (i.e., biopolymers such as collagen, elastin, bioabsorbable starches, etc.) and blends thereof. In some embodiments, the screws can be formed from polylactic acid, or a composite blend of tricalcium phosphate and polylactic acid. One or more coatings can be used on the bone screws, for example coatings to promote bone growth or improve bone adherence to the bone screw. The screws disclosed herein can be formed from a single, unitary material and structure or can be formed from one or more materials listed above.

The screws disclosed herein can be provided in any of a variety of sizes, depending on patient anatomy, procedure type, screw assembly size, and various other parameters which will be readily apparent to one having ordinary skill in the art. In some embodiments, the screws disclosed herein can have a variety of lengths, for example, about <NUM> to <NUM> or about <NUM> to <NUM>, and can have a variety of diameters, such as about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>.

Claim 1:
A bone screw (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), comprising:
an elongate shank (<NUM>) defining a central longitudinal axis, the elongate shank having a proximal end (<NUM>), a distal end (<NUM>) with a conical distal tip region that tapers distally inward, and a distal facing surface (<NUM>); and
at least two threads (<NUM>) formed on the elongate shank, each thread terminating at the distal end in a leading cutting edge (<NUM>) positioned radially outward of the central longitudinal axis and defined by an intersection between a proximal-facing surface (<NUM>) of the thread and the distal facing surface (<NUM>) of the conical distal tip region,
wherein the distal facing surface has an oblong shape with first and second curved edges extending along opposed sides thereof,
characterized in that the first and second curved edges each have a concave region (<NUM>) and a convex region (<NUM>), and wherein the leading cutting edge of each of the at least two threads extends along the concave region.