Patent Description:
Bone screws are utilized in a wide variety of orthopedic applications including procedures in which the bone screws are used to reduce bone fragments or to connect one or more structures to a bone. In this regard, it is desirable for such bone screws to maintain their respective positions within a bone for extended periods of time including for the life of the patient. While certain existing bone screws may be utilized with plates, implants or the like that employ backout prevention features, there exists a continued need for improved fixation within the bone. Document <CIT> discloses a hinged bone screw including a shank and a receiver, cooperating for hinged movement of the shank with respect to the receiver. Document <CIT> discloses a surgical implant having a body which includes a solid thread and a porous region.

The present disclosure describes exemplary embodiments of bone screws that include both solid and porous portions. The porous portions of these screws promote bone ingrowth to help facilitate long term fixation of such screws, while the solid portions provide structural support. Moreover, the solid and porous portions each comprise an exterior of each of the described screws such that the solid and porous portions come in contact with bone when applied thereto. In this regard, the ratio of bone contacting surface area defined by the porous portions relative to that of the solid portions may be predetermined such that the amount of bone growth into the porous portions is controlled so that the removal torque of the screw can be overcome by ordinary surgical instruments even after ingrowth has occurred over an extended period of time in order to remove the screw from the bone without having to cut the bone surrounding the screw. The bone screws described herein may be made via an additive manufacturing process, which can allow the porous portions to be disposed in locations on the screw difficult or impossible to achieve by other manufacturing processes and so that the porous and solid portions are integrated with each other to form a unitary/monolithic screw.

In one aspect of the present disclosure, a bone fastener includes a head, and a screw portion extending from the head. The screw portion includes a shaft and a thread extending along and about the shaft. The thread having a height extending from a root to a tip thereof. The thread also having first and second portions disposed between the root and the tip. The second portion includes a porous structure configured to promote bone ingrowth and having a porosity greater than that of the first portion.

Additionally, the height of the thread may increase toward a distal end of the bone fastener. Also, the shaft may taper inwardly toward the distal end of the bone fastener. The first portion of the thread may be positioned further from the shaft than the second portion. Moreover, the first portion and the second portion may collectively define an outer bone contacting surface of the thread, and the first portion may have a solid structure.

Continuing with this aspect, a height of the second portion may be constant along a length of the shaft. Also, a height of the first portion may increase toward a distal end of the bone fastener. The height of the thread may include the heights of the first portion and second portion. A height of the second portion may be about <NUM> or greater. The head, shaft and first portion of the thread may each comprise a solid structure that has a porosity smaller than that of the second portion.

In another aspect of the present disclosure, a bone fastener includes a head, and a screw portion extending from the head. The screw portion includes a shaft and a thread extending helically along and about the shaft and defines a helical depression therebetween. The screw portion also includes a plurality of porous fenestrations disposed within the helical depression and extends into the shaft. The porous fenestrations are filled with a porous structure configured to promote bone ingrowth. The porous structure includes a portion of an external surface of the bone fastener and is surrounded by a solid structure having a porosity smaller than that of the porous structure. Also a porous liner at least partially surrounds the channel and is disposed within the shaft of the screw portion. The porous liner includes a porous structure interconnected within the porous structure of at least two of the porous fenestrations.

Additionally, the porous fenestrations may each define a circular opening having a diameter of <NUM> to <NUM>. The porous fenestrations may extend into the shaft <NUM> or greater. The bone fastener may further include a channel extending along the length of the bone fastener and through both the screw portion and head of the bone fastener. At least some of the porous fenestrations may extend through the shaft and into communication with the channel such that the porous structure extends from the channel to an exterior of the bone fastener.

Continuing with this aspect, each porous fenestration may be offset from an adjacent porous fenestration by <NUM> to <NUM> degrees about a longitudinal axis of the bone fastener. Each porous fenestration may be offset from an adjacent porous fenestration by <NUM> degrees about a longitudinal axis of the bone fastener. A bone fastener may include a head, first and second screw portions each including a shaft, and a thread extending along and about the shaft. A shank may be disposed between the first and second screw portions. The shank may be threadless and having a plurality of porous portions interspersed within a solid substrate such that an exterior surface is both solid and porous. The plurality of porous portions may be a plurality of fenestrations that extend into the solid substrate of the shank and may be filled with a porous structure that is configured to promote bone ingrowth. The fenestrations may be helically arranged about the shank. The porous fenestrations may each define a circular opening having a diameter of <NUM> to <NUM>. The porous portions may extend into the solid substrate about <NUM> or greater.

In a further aspect of the present disclosure, a bone fastener includes a screw portion having a shaft and a thread, and a head positioned at a proximal end of the screw portion. The head includes a proximal portion and a distal portion. The distal portion of the head defines a bone contacting surface that faces in a direction toward a distal end of the screw portion. The distal portion has a porous structure configured to promote bone ingrowth and has a porosity greater than that of the proximal portion and the screw portion. The distal portion of the head defines a porous ring that extends about a longitudinal axis of the bone fastener.

Additionally, the porous structure of the distal portion may extend partially into a solid structure of the head. The head may be tulip shaped and may have a slot extending through the head in a direction transverse to a longitudinal axis of the screw, the slot may be configured to receive a spinal rod therein. The head may include a threaded inner surface.

The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings in which only the embodiment of <FIG> falls within the scope of the invention as claimed and in which:.

As used herein, when referring to the disclosed devices, the term "proximal" means closer to the operator or in a direction toward the operator and the term "distal" means more distant from the operator or in a direction away from the operator. Also, as used herein, the terms "about," "generally," and "substantially" are intended to mean that slight deviations from absolute are included within the scope of the term so modified.

<FIG> depict a cannulated bone screw <NUM> according to an embodiment of the present disclosure. Bone screw <NUM> generally includes a head <NUM>, screw portion <NUM> extending from head <NUM>, and a channel <NUM> extending through screw portion <NUM> and head <NUM>. Such channel <NUM> may be configured to receive a k-wire and/or a flowable material such as bone cement, medicament, bone marrow aspirate, and the like. However, in some embodiments, screw <NUM> may not include channel <NUM>.

Head <NUM> includes an underside <NUM> and a topside <NUM>. Underside <NUM> defines a first radial surface <NUM>. Topside <NUM> includes an upward extending post <NUM> and a plurality of downwardly extending grooves <NUM> (see <FIG>) positioned about post <NUM>. Such grooves <NUM> are adapted to engage a complementary driver tool. However, other configurations for engaging a driver tool that are known in the art are contemplated. Post <NUM> defines a second radial surface <NUM> that has a radius smaller than that of first radial surface <NUM>. In this regard, head <NUM> is a dual radius head which is configured to be driven by a driver while also being configured to polyaxially anchor other components to a bone, such as a stabilizing rod and coupling element to a vertebra. Examples of screws similar to screw <NUM>, as well as components, such as stabilizing rods, coupling elements, and drivers, that can be used in conjunction with screw <NUM> are disclosed in <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>, all of which are assigned to the same entity as the present invention. However, it is to be understood that the present invention can be utilized in a connection with any type of screw designed to be implant into bone.

Screw portion <NUM> extends distally from head <NUM> and includes a shaft <NUM>, helical thread <NUM>, distal tip <NUM>, and one or more cutting flutes <NUM>. Shaft <NUM> extends from head <NUM> and tapers inwardly toward a distal end of screw <NUM>. Shaft <NUM> also defines a minor diameter of screw. In this regard, the minor diameter of screw <NUM> gradually decreases in a distal direction. Distal tip <NUM> extends distally from shaft <NUM> and is also tapered in the distal direction. As depicted distal tip <NUM> is threadless. However, in some embodiments distal tip <NUM> may be fully or partially threaded. Cutting flutes <NUM> may extend along both shaft <NUM> and distal tip <NUM> to facilitate self-tapping. However, in some embodiments, particularly those that are not self-tapping, screw <NUM> may not include a cutting flute.

Thread <NUM> of screw <NUM> helically extends along and about shaft <NUM>. Thread <NUM> has a height (h) defined between a root <NUM> and a crest <NUM> of thread <NUM>, as depicted in <FIG>. Thread <NUM> has a single start and defines a major diameter of screw <NUM>. However, in some embodiments, screw <NUM> may include multiple threads defining multiple starts. In the particular embodiment depicted, the major diameter is constant along the length of the majority of shaft <NUM>. Thus, because the taper of shaft <NUM> and the constant outer diameter of thread <NUM>, the root <NUM> to crest <NUM> height (h) of thread <NUM> increases in a distal direction, as is best shown in <FIG>. However, it should be understood that screw <NUM> may have other configurations, such as a constant minor diameter and a variable major diameter, or a constant major and minor diameter.

Thread <NUM> includes a first portion <NUM> and a second portion <NUM> between root <NUM> and crest <NUM>. First portion <NUM> and second portion <NUM> are positioned adjacent each other with first portion <NUM> positioned further from shaft <NUM> than second portion <NUM>. In this regard, first portion <NUM> is positioned at a radial extent of thread <NUM> and defines crest <NUM>. Second portion <NUM> is positioned adjacent to shaft <NUM> at a base of thread <NUM>. However, at a distal end of thread <NUM> near the start of thread <NUM>, first portion <NUM> may not be positioned over second portion <NUM>, as shown in <FIG>.

First portion <NUM> has solid structure, while second portion <NUM> has a porous structure. The porous structure of second portion <NUM> has a porosity that promotes bone ingrowth over time when tissue is in contact therewith, as well as to aid in initial fixation prior to ingrowth. For example, the porous structure of second portion <NUM> may have an average pore diameter between <NUM>-<NUM> microns with a <NUM>-<NUM>% porosity. However, preferably the porosity may be between <NUM>-<NUM>% and may either be constant throughout the porous structure or gradient such that the porous structure has a varying porosity. In contrast, the solid structure of first portion <NUM>, to the extent it may have a porosity, does not have a porosity that promotes bone ingrowth and has therefore has a porosity less than that of the porous structure of second portion <NUM> and generally no porosity whatsoever. However, the solid structure of first portion <NUM> provides strength and stability to thread under different loading conditions. The remainder of screw <NUM> other than thread <NUM>, which includes head <NUM>, shaft <NUM>, and distal tip <NUM>, may have a solid structure similar to that of first portion <NUM> of thread <NUM>. The porous portions of screw <NUM>, as well as the solid portions thereof, may be formed through use of an additive manufacturing process as described below, and may be made from the same material or different material that is capable of bonding with each other through the additive manufacturing process.

Porous second portion <NUM> has a constant height along the length of shaft <NUM>. As mentioned above, the root-to-tip height (h) of thread <NUM> increases in the distal direction. Thus, since porous second portion <NUM> of thread <NUM> has a constant height along the length of shaft <NUM>, solid first portion <NUM> of thread <NUM> has a variable height along the length of shaft <NUM>, as best seen in <FIG>. In this regard, the height of first portion <NUM> decreases in the proximal direction. In other embodiments of screw <NUM>, porous second portion <NUM> may have a variable height along the length of shaft <NUM> while solid first portion <NUM> has a constant height. In even further embodiments of screw <NUM>, first and second portions <NUM>, <NUM> of thread <NUM> may each have variable heights along the length of shaft <NUM>. However, it is preferable that that the height of porous portion <NUM> be about <NUM> or greater.

Porous second portion <NUM> and solid first portion <NUM> comprise a bone contacting surface that is therefore both porous and solid. In this regard, solid first portion <NUM> helps provide strength while screw <NUM> is driven into bone and porous second portion <NUM> facilitates bone ingrowth at opposite sides of thread <NUM> to promote long term fixation of screw <NUM> and to prevent inadvertent backout thereof during the period of time that screw <NUM> is implanted. However, it may be necessary at some point to remove screw <NUM> from the bone even after extended periods of time over which bone ingrowth has occurred. In this regard, the surface area of porous structure of second portion <NUM> that is exposed to bone is proportional to or smaller than that of the surface area exposed to bone of the solid structure <NUM> so that the resistance afforded by bone ingrowth can be overcome through torsion applied to screw <NUM> using standard driver instruments. In one embodiment of screw <NUM>, height "h" of thread <NUM> may be <NUM>% comprised of the porous second portion and <NUM>% of the solid first portion. In other embodiments, the height "h" of thread <NUM> can comprise <NUM>% to <NUM>% of the surface area of thread.

In a method of use, a driver is engaged to topside <NUM> and screw <NUM> is driven into bone, such as a vertebrae. As screw <NUM> is driven into the bone, solid first portions <NUM> of thread <NUM> and thread flute <NUM> cut through the cortical and cancellous layers of the bone. Once fully seated, the natural roughness of porous second portion <NUM> of threads <NUM> may help prevent backout of screw <NUM> via frictional resistance. Thereafter, implantable equipment may be connected to screw <NUM>, such as components of a spinal rod system or a bone plate for fracture reduction and stabilization, for example. Over time, bone may grow into porous structure <NUM> of screw <NUM> helping to further secure screw <NUM> to the bone. If after a such ingrowth occurs it is necessary to remove screw <NUM> from the bone via a revision procedure or the like, screw <NUM> may be reengaged with a driver instrument and rotated such that the bonds formed between screw <NUM> and bone via bone ingrowth are broken thereby allowing screw <NUM> to be removed without the need to cut excess bone surrounding screw <NUM> for its removal.

<FIG> depict a screw <NUM> according to another embodiment of the present disclosure. Screw <NUM> is similar to screw <NUM> in that screw <NUM> includes a head <NUM>, screw portion <NUM> extending from head <NUM>, and a channel <NUM> extending through screw portion <NUM> and head <NUM>. In addition, head <NUM> is similar to head <NUM> in that it includes a topside <NUM> that defines a post <NUM> and plurality of grooves <NUM> for engaging a corresponding driver and an underside <NUM> that defines a radial surface <NUM> with a radius larger than a radial surface <NUM> of post <NUM>. Also, screw portion <NUM> includes a shaft <NUM>, thread <NUM>, and distal tip <NUM> similar to that of screw <NUM>. However, screw <NUM> differs with respect to its solid and porous configuration.

As shown, screw <NUM> includes a plurality of porous fenestrations <NUM> that extend into shaft <NUM> from an outer surface thereof and in a helical arrangement between thread <NUM>. In other words, the fenestrations are positioned in a helical depression that is defined by thread <NUM>. Each fenestration <NUM> may be positioned at a predetermined angle relative to adjacent fenestrations <NUM>. For example, each fenestration may be distributed every <NUM> to <NUM> degrees in a helical pattern about screw <NUM> and relative to each adjacent fenestration <NUM>, but preferably every <NUM> degrees. Fenestrations <NUM> are depicted as defining round openings in the solid structure of shaft <NUM>, which may have a diameter <NUM> to <NUM>, but preferably <NUM>. However, fenestrations <NUM> can define various different shaped openings, such as rectangular, ovular, triangular, and the like, for example. Porous fenestrations <NUM> are filled with a porous structure such that the porous structure forms a portion of an external surface of screw <NUM> at the respective openings of porous fenestrations <NUM>. As described below, porous fenestrations <NUM> provide strength to screw <NUM> relative to a complete absence of structure in fenestrations <NUM> and allows for bone ingrowth into its porous structure and for injection of materials therethrough, such as bone cement, bone marrow aspirate, and biologics.

In addition to porous fenestrations <NUM>, screw <NUM> includes one or more porous liners <NUM> lining channel <NUM>. Such porous liners <NUM> may be fully cylindrical so as to form a sleeve that has an opening coaxial with channel <NUM>. However, in some embodiments, porous liners <NUM> may be partially cylindrical and thus may not encircle channel <NUM>. In this regard, liners <NUM> along with the solid structure of shaft <NUM> define channel <NUM>. Liners <NUM> extend along at least a portion of shaft <NUM> of screw portion <NUM> and may extend between a plurality of fenestrations <NUM>. Porous liners <NUM>, as shown, do not extend entirely through the radial extent of shaft <NUM>. However, porous liners <NUM> are preferably in communication with some or all of porous fenestrations <NUM>. In this regard, a flowable material such as bone cement and medicament can be injected through channel <NUM>, porous liners <NUM>, and selected fenestrations <NUM> so that the bone cement or medicament can be delivered to the bone from multiple locations along the length of screw <NUM>. Alternatively, bone marrow aspirate can be aspirated from the bone from multiple locations along the length of screw <NUM>. Even further, bone graft material can be packed into channel <NUM> to bolster bone ingrowth.

While porous liners <NUM> are depicted in <FIG> as affording communication of porous fenestrations <NUM> with channel <NUM> of screw <NUM>, it is also contemplated that screw <NUM> may not have porous liners <NUM> and instead each porous fenestration <NUM> or a select number thereof may extend entirely through shaft <NUM> so as to communicate directly with channel <NUM>. In this regard, porous fenestrations <NUM> may form a uniform column of porous material that extends entirely through shaft <NUM>.

The porous structure of liners <NUM> and fenestrations <NUM> is similar to that previously described for promoting bone ingrowth. Additionally, in some embodiments, the porous structure in each fenestration <NUM> may have the same porosity, while in other embodiments the porosity may differ fenestration-by-fenestration. Moreover, the porosity in each fenestration <NUM> may be uniform or it may differ such that the porosity of each fenestration <NUM> increases in an outwardly radial direction. In addition, the remaining features of screw <NUM> other than porous fenestrations <NUM> and liners <NUM> are comprised of a solid structure so as to reinforce screw <NUM> and provide strength to screw <NUM> as well as to help control the surface area ratio between the porous and solid structure to allow for bone ingrowth that can be overcome by a predetermined amount of torque applied to screw <NUM>.

In a method of use, a driver is engaged to topside <NUM> and screw is driven into bone, such as a vertebrae. As screw <NUM> is driven into the bone, the solid thread <NUM> cuts into the cortical and cancellous layers of the bone. Once fully seated, bone cement or medicament may be injected or, alternatively, bone marrow aspirated, through channel <NUM> and porous fenestrations <NUM> to treat the bone or provide additional fixation support thereto such as described in <CIT>. Also, implantable equipment may be connected to screw <NUM>, such as components of a spinal rod system, such as one of the systems mentioned above. Over time, bone may grow into the porous structure <NUM>, <NUM> of screw <NUM> helping to further secure screw <NUM> to the bone. If after a such ingrowth occurs, it is necessary to remove screw <NUM> from the bone via a revision procedure or the like, screw <NUM> may be reengaged with a driver instrument and rotated such that the bonds formed between screw <NUM> and bone via bone ingrowth are broken thereby allowing screw <NUM> to be removed without the need to cut excess bone surrounding the screw for its removal.

<FIG> depicts a screw <NUM> according to a further embodiment of the present disclosure. Screw <NUM> includes a head <NUM> and screw portion <NUM> extending from head <NUM>. Head <NUM> is a tulip-shaped head that includes a U-shaped slot <NUM> extending through head <NUM> and transverse to an axis of screw <NUM>. Such slot <NUM> is configured to receive a spinal rod therein and may be internally threaded for threaded engagement to a set screw (not shown) or the like, as disclosed in <CIT>. Head <NUM> also includes a proximal solid portion <NUM> and a distal porous portion <NUM>. Distal porous portion <NUM> comprises a distal end of head <NUM> adjacent to screw portion <NUM> of screw <NUM>. In this regard, distal porous portion <NUM> defines a distally facing surface so that when screw <NUM> is driven into bone, porous portion <NUM> sits directly against the bone, such as a transverse process/facet junction. In the embodiment depicted, distal porous portion <NUM> forms a ring that extends about the axis of screw <NUM> and has a proximal-distal length of about <NUM> to <NUM>, but preferably <NUM>. In addition, distal porous portion <NUM> does not extend full thickness through head <NUM> and instead preferably extends into head <NUM> from the exterior thereof. In this regard, the entire internal surface <NUM> of head <NUM> is solid. The distance into which the porous portion <NUM> extends into head <NUM> may be about <NUM> to <NUM>, but preferably <NUM>. In addition, this distance or thickness of porous portion may vary along the proximal-distal length of porous portion <NUM> to account for regions of high stress. However, in some embodiments porous portion <NUM> may span full thickness between inner surface <NUM> and an exterior of tulip-shaped head <NUM>, such that porous portion <NUM> comprises a portion of internal surface <NUM>. Also, screw portion <NUM> may be similar to screw portion <NUM> with the exception that screw portion <NUM> may be entirely solid.

In a method of use, a driver is engaged to screw <NUM>, and screw <NUM> is driven into bone, such as a vertebrae. Once fully seated, distal porous portion <NUM> is positioned directly against the bone. In this regard, the bone, such as a transverse process/facet junction, may be abraded before screw insertion so that porous portion <NUM> directly abuts the abraded bone to help facilitate bone ingrowth. Implantable hardware may then be connected to the screw <NUM>. For example, a spinal rod may be inserted into slot <NUM> such that it extends therethrough in a direction transverse to an axis of screw <NUM>. A set screw may then be threaded to head <NUM> over the spinal rod for securing rod to screw <NUM>. Over time, bone may grow into porous portion <NUM> of screw <NUM> helping to further secure screw <NUM> to the bone. If after such ingrowth occurs, it is necessary to remove screw <NUM> from the bone via a revision procedure or the like, all hardware may disengaged from screw <NUM>. Screw <NUM> may then be reengaged with a driver instrument and rotated such that the bonds formed between distal porous portion <NUM> and bone via bone ingrowth are broken thereby allowing screw <NUM> to be removed without the need to cut excess bone surrounding screw <NUM> for its removal.

<FIG> depicts a bone screw <NUM> according to an even further embodiment of the present disclosure. Screw <NUM> is a lag screw and has a head <NUM>, first screw portion 420a, second screw portion 420b, and shank <NUM>. Screw <NUM> may be used with other orthopedic devices, such as bone plates, or by itself. First screw portion 420a is positioned adjacent head <NUM> while second screw portion 420b is positioned at a distal end of screw <NUM>. Screw <NUM> may be cannulated, like screw <NUM>, or not cannulated. First and second screw portions 420a-b are threaded and have a solid structure.

Shank <NUM>, which is disposed between first and second screw portions 420a-b, is unthreaded and includes a solid exterior surface <NUM> that is interrupted by a plurality of porous fenestrations <NUM> arrayed about shank <NUM>. Fenestrations <NUM> are similar to fenestrations <NUM> of screw <NUM> in that they are organized in a helical pattern with a fenestration <NUM> positioned every <NUM> to <NUM> degrees, but preferably every <NUM> degrees about shank <NUM>. However, in some embodiments, fenestrations <NUM> may be arranged in a non-helical pattern, such as in linear rows. Moreover, fenestrations <NUM> may extend through shank <NUM> such that they communicate with a channel (not shown) for aspiration of bone marrow aspirate or for delivery of a flowable material to the bone. This may be facilitated by one or more porous liners lining the channel, such as porous liners <NUM> of screw <NUM>. However, in some embodiments, fenestrations <NUM> may not extend entirely through shank <NUM> to the channel or may have fenestrations <NUM> that communicate with the channel and some that do not. However, where fenestrations <NUM> do not extend through shank <NUM> to the channel, fenestrations preferably extend <NUM> or greater through the exterior of shank <NUM>.

Fenestrations <NUM> are shown as defining a round opening, which may have a diameter of <NUM> to <NUM>, but preferably <NUM>. Moreover, each fenestration <NUM> may have the same diameter, or, in some embodiments, fenestrations <NUM> may have a variable diameter such that some of the fenestrations <NUM> have a smaller diameter than other fenestrations <NUM>. For example, some of fenestrations <NUM> may have a diameter of <NUM> while others may have a diameter of <NUM>. While fenestrations <NUM> are shown as defining a round, porous opening in the solid structure of shank <NUM>, fenestrations <NUM> can define other shaped openings such as a square, ovular, or triangular shaped opening, for example.

<FIG> depicts a bone screw <NUM> according to yet another embodiment of the present disclosure. Screw <NUM> is similar to that of screw <NUM> with the exception that shank <NUM> is entirely porous rather than having porous portions arrayed within a solid exterior. In this regard, screw <NUM> has a solid head <NUM>, a solid first screw portion 520a, a solid second screw portion 520b, and a porous shank <NUM> disposed between solid screw portions 530a-b. Porous shank portion <NUM> may have uniform porosity throughout the thickness of shank <NUM>. However, in other embodiments, the porosity may increase in a radial direction from an axial center of screw. In even further embodiments, shank <NUM> may not be entirely porous. Instead, the porous structure may extend inward toward the axis of screw <NUM> about <NUM> or greater from an exterior of shank <NUM> while the core of shank <NUM> may be a solid, cylindrical structure which underlies the porous structure of shank <NUM>. In embodiments where a channel extends through screw <NUM> similar to channel <NUM> of screw <NUM>, such solid core of shank may form a hollow, cylindrical structure.

The exemplary screws described herein may be formed layer-by-layer using an additive layer manufacturing (ALM), i.e., 3D printing, process so no separate connection mechanism is necessary to bring together any of the components of such bone screws. In some examples, ALM processes are powder-bed based and involve one or more of selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM), as disclosed in <CIT>; <CIT>; <CIT>; and <CIT>. Assembly of a bone screw with solid and porous portions using ALM is discussed in greater detail below.

In some arrangements, the above described bone screws are formed using an ALM fabrication process, such as SLS, SLM or EBM described above, fused deposition modeling (FDM), or other appropriate 3D printing technologies known to those skilled in the art. When employing powder-bed based technologies, articles are produced in layer-wise fashion according to a predetermined digital model of such articles by heating, e.g., using a laser or an electron beam, multiple layers of powder, which preferably may be a metallic powder, that are dispensed one layer at a time. The powder is sintered in the case of SLS technology and melted in the case of SLM technology, by the application of laser energy that is directed in raster-scan fashion to portions of the powder layer corresponding to a cross section of the article. After the sintering or melting of the powder on one particular layer, an additional layer of powder is dispensed, and the process repeated, with sintering or melting taking place between the current layer and the previously laid layers until the article is complete. The powder layers similarly may be heated with EBM technology. Additive manufacturing techniques such as the ALM processes described above may be employed to form the solid and porous layers and any other components, as applicable. In some instances, materials for one layer may be different than the materials for successive layers. This process allows for porous portions to extend full thickness through a particular structure, such as the thread <NUM> of screw <NUM> and the shank <NUM> of screw <NUM>, for example. It also allows porous portions to be formed in locations impossible to reach by other methods, such as the liners <NUM> of screw <NUM> which are located about channel within screw <NUM>.

Each of solid and porous layers of the above described screws may be constructed from biocompatible metals, such as titanium, titanium alloys, stainless steel, cobalt chrome alloys, tantalum, niobium, another metal, or a biocompatible polymer, such as polyether ether ketone (PEEK). All constituent porous and solid portions of the above described screws may be a common material, such as one of those listed above, or different materials can be employed for each part. Particular combinations of materials and their use for specific parts of herein described bone screws are a matter of design choice and may include the combination of different metals, different polymers, or metals combined with polymers. For example, the solid portions of the herein described screws can be made from a metal while the porous portions may be made from a polymer.

Each of the screws describe herein may have other features that may enhance the function of the screw from those described herein. For example, each of the screws described herein may include serrations on their respective threads. Examples of such serrated threads are described in <CIT>.

Moreover, each of the screws described above are not limited to the particular porous and solid configurations described above. Indeed, each of the above screws can have alternative solid/porous configurations and/or combinations as those previously described. For example, screw <NUM> may also include the fenestrations <NUM> described with respect to screw <NUM>. In such an embodiment, thread <NUM> may have a solid and porous structure as described with relation to screw <NUM> while also having porous fenestrations distributed in a helical array between thread <NUM> as described with relation to screw <NUM>. In another example, screw <NUM> may include the solid/porous thread <NUM> of screw <NUM> and/or porous fenestrations <NUM> of screw <NUM> in addition to having the porous ring <NUM> of tulip-shaped head <NUM>.

Also, while the above described solid/porous configurations are associated with particular bone screws, it should be understood that the described solid/porous configurations can be applied to any general purpose bone screw or other specialized bone screws not described herein. Examples of such screws are disclosed in <CIT> and <CIT>. Moreover, the solid/porous configurations are not limited to screws used in spinal procedures.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the scope of the present invention as defined by the appended claims.

Claim 1:
A bone fastener comprising:
a head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>); and
a screw portion (<NUM>, <NUM>, <NUM>, 420a, 420b, <NUM>, 520a, 520b, <NUM>) extending from the head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), the screw portion (<NUM>, <NUM>, <NUM>, 420a, 420b, <NUM>, 520a, 520b, <NUM>) having a shaft (<NUM>, <NUM>) and a thread (<NUM>, <NUM>, <NUM>) extending along and about the shaft (<NUM>, <NUM>), the thread (<NUM>, <NUM>, <NUM>) having a height (h) extending from a root (<NUM>) to a tip (<NUM>) thereof, the thread (<NUM>, <NUM>, <NUM>) also having first and second portions (<NUM>, <NUM>), the first portion (<NUM>) and the entire second portion (<NUM>) disposed between the root (<NUM>) and the tip (<NUM>), the second portion (<NUM>) having a porous structure configured to promote bone ingrowth and having a porosity greater than that of the first portion (<NUM>), wherein the remainder of the bone fastener other than thread, said remainder including the head, the shaft, and a distal tip (<NUM>) of the screw portion, has a solid structure similar to that of first portion of thread,
wherein the first portion (<NUM>) of the thread (<NUM>, <NUM>, <NUM>) is positioned further from the shaft (<NUM>, <NUM>) than the second portion (<NUM>).