Patent Publication Number: US-2023136340-A1

Title: Bone screw having an overmold of a shank

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application incorporates by reference the entire disclosure of U.S. Pat. No. 10,335,201, titled SPINAL IMPLANT SYSTEM AND METHODS OF USE, filed Jan. 25, 2017; U.S. Pat. No. 10,653,455 titled SPINAL IMPLANT SYSTEM AND METHODS OF USE filed Sep. 12, 2017; U.S. Pat. No. 6,790,209, titled ROD REDUCER INSTRUMENTS AND METHODS, filed Jul. 1, 2002; U.S. App. No. 17/128,615, titled LOCKING CAP MODULE AND CONNECTOR and filed Dec. 12, 2020, U.S. App. No. 17/167,734, titled LOCKING CAP MODULE AND CONNECTOR and filed Feb. 4, 2021, U.S. App. No. 17/307,674 titled DORSAL ADJUSTING IMPLANT AND METHODS OF USE and filed Mar. 4, 2021, and U.S. App. No. 17/318,279 titled TOP LOADING QUICK LOCK CONSTRUCT and filed Mar. 12, 2021. 
    
    
     FIELD 
     The present technology is generally related to bone screws for use in a medical context that may be formed of a first portion mechanically coupled to a second portion, for example. In some embodiments, the first portion may be referred to as a substrate and the second portion may be referred to as an overmold that may be formed directly on top of the substrate component. In some embodiments, the first portion (substrate) may be formed of a metallic material such as titanium and the second portion (overmold) may be formed of a plastic material such as Polyether ether ketone (PEEK). 
     BACKGROUND 
     A bone screw and/or pedicle screw may be implanted in a human patient for a variety of medical uses. At least one use involves the installation of a pedicle screw into a boney anatomy of a patient and the subsequent attachment of a receiver or connector to the pedicle screw for stabilization and/or fixation of the boney anatomy. Conventional bone screws and pedicle screws are formed of metallic materials, which are highly visible on an X-ray, and in some unwanted circumstances may block and/or otherwise hinder visibility of certain elements of patient anatomy. 
     SUMMARY 
     The techniques of this disclosure generally relate to a bone screw formed of a metallic first portion and a second portion formed of a plastic component directly on the first portion by an overmold or additive manufacturing process. In other embodiments, the first portion and the second portion may be threaded together or attached together by an adhesive, e.g., an epoxy. 
     In one aspect, the present disclosure provides for a bone screw. The bone screw may include a first portion extending from a first end to a second end in a longitudinal direction, for example. In various embodiments, the first portion may have a head that defines the first end and a shank that defines the second end, for example. In various embodiments, the first portion may include a metallic material and/or is formed of a metallic material, for example or may be of other materials including carbon fiber. In various embodiments, a second portion may be mechanically coupled to the first portion and surround the shank, for example. In various embodiments, the second portion may have an exposed thread pattern and an exposed leading tip, for example. In various embodiments, the second portion may include a thermoplastic material and/or be formed of a thermoplastic material, for example or may be of other materials including carbon fiber. 
     In another aspect, the disclosure provides for a bone screw product formed by an overmold process, for example. The bone screw product may include a substrate portion extending from a first end to a second end in a longitudinal direction, for example. In various embodiments, the substrate portion may have a head that defines the first end and a shank that defines the second end, for example. In various embodiments, the substrate portion may be formed of a metallic material, for example. In various embodiments, the bone screw product may include an overmold portion formed directly on top of the shank portion by an overmold process, for example. In various embodiments, the overmold portion may have an exposed thread pattern and an exposed leading tip, for example. In various embodiments, the overmold portion may include a thermoplastic material and/or be formed of a thermoplastic material. Additionally, in various embodiments, the overmold portion may surround the shank of the substrate portion and the head of the substrate portion may remain exposed. 
     In another aspect, the disclosure provides a spinal implant system. The spinal implant system may include a bone screw, for example. In various embodiments, the bone screw may include a first portion extending from a first end to a second end in a longitudinal direction, the first portion may have a head that defines the first end and a shank that defines the second end, for example. In various embodiments, the first portion may include a metallic material and/or be formed of a metallic material. In various embodiments, the second portion may be mechanically coupled to the first portion and surrounding the shank, for example. In various embodiments, the second portion may include an exposed thread pattern and an exposed leading tip, for example. In various embodiments, the second portion may include a thermoplastic material and/or be formed of a thermoplastic material, for example. The spinal system may further include a receiver having a rod receiving passageway extending through a first sidewall and through a second sidewall of the receiver, for example. In various embodiments, the receiver may have a threaded passageway configured to receive a set screw for securing the rod within the rod receiving passageway, for example. Additionally, the receiver may further include a base portion and at least one locking ring, for example. In various embodiments, in a coupled position, the head portion of the bone screw is securely coupled to the receiver via the base portion and the at least one locking ring. 
     The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a front view of a bone screw. 
         FIG.  2    is an exploded parts view of a receiver and a bone screw for attaching to the receiver. 
         FIG.  3    is a front view of a head portion and shank portion of a bone screw. 
         FIG.  4    is a transparent view of a bone screw including a head portion, shank portion, and an overmold. 
         FIG.  5    is an X-Ray image of an entirely metallic spinal support system including a bone screw, receiver, and rod. 
         FIG.  6    is an X-Ray image of a first bone screw including both metallic and non-metallic materials. 
         FIG.  7    is an X-Ray image of a bone screw including both metallic and non-metallic materials. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure relate generally, for example, to spinal stabilization systems, and more particularly, to bone screws having a metallic head and shank portion and a non-metallic overmold. In some embodiments, the head and shank may be formed of titanium and the overmold may be formed of PEEK. Embodiments of the devices and methods are described below with reference to the Figures. 
     The following discussion omits or only briefly describes certain components, features and functionality related to medical implants, installation tools, and associated surgical techniques, which are apparent to those of ordinary skill in the art. It is noted that various embodiments are described in detail with reference to the drawings, in which like reference numerals represent like parts and assemblies throughout the several views, where possible. Reference to various embodiments does not limit the scope of the claims appended hereto because the embodiments are examples of the inventive concepts described herein. Additionally, any example(s) set forth in this specification are intended to be non-limiting and set forth some of the many possible embodiments applicable to the appended claims. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations unless the context or other statements clearly indicate otherwise. 
     Terms such as “same,” “equal,” “planar,” “coplanar,” “parallel,” “perpendicular,” etc. as used herein are intended to encompass a meaning of exactly the same while also including variations that may occur, for example, due to manufacturing processes. The term “substantially” may be used herein to emphasize this meaning, particularly when the described embodiment has the same or nearly the same functionality or characteristic, unless the context or other statements clearly indicate otherwise. 
     Referring to  FIGS.  1 - 4    generally, various bone screw embodiments and implant systems are disclosed. The components of bone screw  100  can be fabricated from biologically acceptable materials suitable for medical applications, including metals, synthetic polymers, ceramics and bone material and/or their composites. For example, the components, individually or collectively, can be fabricated from materials such as stainless steel alloys, commercially pure titanium, titanium alloys, Grade 5 titanium, super-elastic titanium alloys, cobalt-chrome alloys, superelastic metallic alloys (e.g., Nitinol, super elasto-plastic metals, such as GUM METAL®), ceramics and composites thereof such as calcium phosphate (e.g., SKELITE™), thermoplastics such as polyaryletherketone (PAEK) including polyetheretherketone (PEEK), polyetherketoneketone (PEKK) and polyetherketone (PEK), carbon-PEEK composites, PEEK-BaSO4 polymeric rubbers, polyethylene terephthalate (PET), fabric, silicone, polyurethane, silicone-polyurethane copolymers, polymeric rubbers, polyolefin rubbers, hydrogels, semi-rigid and rigid materials, elastomers, rubbers, thermoplastic elastomers, thermoset elastomers, elastomeric composites, rigid polymers including polyphenylene, polyamide, polyimide, polyetherimide, polyethylene, epoxy, bone material including autograft, allograft, xenograft or transgenic cortical and/or corticocancellous bone, and tissue growth or differentiation factors, partially resorbable materials, such as, for example, composites of metals and calcium-based ceramics, composites of PEEK and calcium based ceramics, composites of PEEK with resorbable polymers, totally resorbable materials, such as, for example, calcium based ceramics such as calcium phosphate, tri-calcium phosphate (TCP), hydroxyapatite (HA)-TCP, calcium sulfate, or other resorbable polymers such as polyaetide, polyglycolide, polytyrosine carbonate, polycaroplaetohe and their combinations. 
     Generally,  FIGS.  1 - 4    illustrate various views and embodiments of a bone screw  100  and example implant systems  1000 .  FIG.  1    is a front view of a bone screw  100  and  FIG.  2    is an exploded parts view of a receiver  20  and a bone screw  100  for attaching to the receiver  20 . In the example embodiment, bone screw  100  may extend in a longitudinal direction from a proximal end  100 P to a distal end  100 D, for example. The proximal end  100 P may include a first portion  30  comprising a head  31  having a drive interface  34 , for example. The distal end  100 D and medial portion may comprise a second portion  10 , for example. The second portion  10  may be securely connected to the first portion  30  as will be explained in detail below. 
     In various embodiments, the first portion  30  may comprise a metallic material, be formed substantially of a metallic material, and/or be formed purely of a metallic material, e.g., titanium, titanium alloys, etc. However, it shall be understood that other biocompatible materials having similar material properties may also be used. In various embodiments, the second portion  10  may comprise a thermoplastic material, be formed substantially of a thermoplastic material, and/or be formed purely of a thermoplastic material, e.g., PEEK and PEEK composites. However, it shall be understood that other biocompatible materials having similar material properties may also be used. 
     Second portion  10  may include at least one thread pattern, for example first thread pattern  14   a  and second thread pattern  14   b . In the example embodiment of  FIG.  1   , first thread pattern  14   a  has a different thread pitch than second thread pattern  14   b , however other embodiments may include a continuous symmetrical thread pattern  14   c  (see  FIG.  2   ). Additionally, second portion  10  may include a tip  12 . Tip  12  may be a self-taping tip, a blunt tip, a pointed tip, a chisel tip, etc. In at least one embodiment, tip  12  is formed of a metallic material and the remaining part of second portion  10  is formed of a non-metallic material, e.g., any of those materials explained previously. In another embodiment, tip  12  is coated with a metallic material. In the example embodiment of  FIG.  1   , bone screw  100  is a fenestrated type screw having two openings  13  on a first side of bone screw  100  and another two openings  13  on a second side of bone screw  100  (not visible) which may be used in conjunction with Fenestrated Screw Cement, such as that sold by Medtronic under the brand name HV-R™ or a Bone Cement such as that sold by Medtronic under the brand name Kyphon™ Xpede™, for example. However, other embodiments may be formed with more or less openings  13  and/or as other types of bone screws  100 , e.g., solid (see  FIG.  2   ), cannulated, hybrid, self-taping, self-drilling, etc. 
       FIG.  2    illustrates an embodiment of bone screw  100  for use in conjunction with an implant receiver  20 , for example. Implant receiver  20  may include a threaded passageway  24  for rotatably supporting and receiving set screw  50 , for example. Threaded passageway  24  may extend in the vertical direction and define a vertical axis of which set screw  50  may move upward and downward in upon rotation of set screw  50 . Additionally, implant receiver  20  may include a passageway  22  for receiving rod  40 , for example. Passageway  22  may extend in the horizontal direction and define a horizontal axis which rod  40  may be coaxially aligned with, for example. In the example embodiment, passageway  22  may be shaped like an oval when viewed in a side perspective view. In other embodiments, passageway  22  may be shaped like a circle, or a square or include an open top end, for example. In various embodiments, passageway  22  may have a size and shape generally corresponding to a size and shape of rod  40 , for example. In various embodiments, a side view cross section of rod  40  may have an oval like shape generally corresponding to a size and shape of passageway  22  and/or any other shape corresponding to passageway  22 , for example. In various embodiments, the rod may be formed of a non-metallic material, for example, PEEK or Carbon Fiber. 
     In the example illustrations, it is shown that set screw  50  may have an exterior thread pattern  51  having a timing and/or pitch including a size and shape generally corresponding to the timing and or pitch of threads  25  of threaded passageway  24  for example. Additionally, set screw  50  may include a breakoff portion  52  and a drive end  53  for coupling to a driver (not illustrated) to rotate set screw  50 , for example. Drive end  53  may take any shape, for example a hexalobular shape, a hexaganol shape, a torx shape, etc. In operation, an end user may secure rod  40  within passageway  22  of implant receiver  20  and securely tighten set screw  50  by rotating set screw  50  at drive end  53  such that set screw  50  advances downward and secures rod  40  against the lower walls of passageway  22 , for example. 
     In the example illustration, it is shown that implant receiver  20  may include a base portion  21  having a lower cavity configured to securely couple to bone screw  100  and support a crown  2  in a position above the head portion  31  of bone screw  100 , for example. Crown  2  may include curved support surfaces  3  having a size and shape corresponding to a lower portion of the curved surface of rod  40 , for example. Accordingly, crown  2  may support rod  40  from beneath rod  40  by directly contacting an underside of rod  40 . Spinal implant system  1000  may further include an upper ring  8  and a lower ring  9 . Upper and lower rings  8 ,  9  may be C-shaped and configured to securely couple head portion  31  of bone screw  100  within lower cavity of base portion  21 , for example. Additional examples of how implant receiver  20  may securely connect to a bone screw  100  via an internal cavity of base portion  21  are also disclosed in detail in each of U.S. Pat. No. 10,335,201, titled Spinal Implant System and Methods of Use; and U.S. Pat. No. 10,653,455 titled Spinal Implant System and Methods of Use; U.S. App. No. 17/167,258, titled Instrument for locking Orthopedic Screws, which are all incorporated herein by reference in their entireties. 
     In practice, a surgeon may initially couple the implant receiver  20  to bone screw  100  by pushing implant receiver  20  down against the bone screw  100  by, e.g., an instrument for locking orthopedic screws. For example, a surgical instrument may push implant receiver  20  down such that the upper and lower rings  8 ,  9  are seated around the head portion  31  of bone screw  100  and nested within and retained by corresponding cavities of base portion  21 , for example. In seating upper and lower rings  8 ,  9  in corresponding cavities the head portion  31  of bone screw  100  experiences a mechanical stress. As explained previously, the first portion  30  of bone screw  100  may be formed of a metallic material. At least one advantage of this material choice is that the metallic first portion  30  is durable enough to sustain the wear and tear associated with coupling receiver  20  to the head portion  31  of bone screw  100 . For example, the head portion  31  can sustain the reduction of receiver  20  and sustain the forces of the upper and/or lower rings  8 ,  9  as they compress the side surfaces of head portion  31  thereby pinning the upper portion  30  of bone screw  100  in the lower cavity  21  of receiver  20 . Another advantage of this material choice is that metallic first portion  30  is also durable enough to withstand intra-operative correction forces. 
       FIG.  3    is a front view of a first portion  30  of a bone screw  100  comprising an upper portion  38  including the head portion  31  and a lower shank portion  39 . First portion  30  may be formed as a single unitary component from stock material by a machining process, a casting process, or a molding process, for example. In the example embodiment, first portion  30  may extend in a longitudinal direction along axis L-A from a proximal end  30 P to a distal end  30 D and extend in a widthwise direction from a first lateral side  30 L to a second lateral side  30 L along axis W-W, for example. In various embodiments, the shank portion  39  may include various contours and textured surfaces such as indentations, outdents, diamond tread, etc. In the example embodiment, shank portion  39  includes a helical thread pattern  32  traversing the outside surface of shank portion  39  from head portion  31  to a necked down portion  36 , for example. In various embodiments, necked down portion  36  may comprise an area of first portion  30  that has a shortest distance from side to side in the widthwise wise direction, e.g., a smallest diameter section. Additionally, shank portion  39  may include a plurality of scallops  33  (indentations and/or oblong indentations) adjacent the distal end  30 D, for example. In the example embodiment, four scallops  33  are symmetrically disposed at the distal end  30 D of first portion  30  and the distal end  30 D flares back out from necked down portion  36 , e.g., distal end  30 D comprises a larger diameter section than necked down portion  36  (when viewed in cross-section). In other embodiments, the distal end  30 D of first portion  30  may include a rectangular geometry. 
       FIG.  4    is a transparent view of a bone screw  100  including a first portion  30  comprising the upper portion  38  and a second portion  10  comprising an overmold, for example. In various embodiments, the first portion  30  may comprise a metallic material, be formed substantially of a metallic material, and/or be formed purely of a metallic material, e.g., titanium, titanium alloys, etc. However, it shall be understood that other biocompatible materials having similar material properties may also be used. In various embodiments, the second portion  10  may comprise a thermoplastic material, be formed substantially of a thermoplastic material, and/or be formed purely of a thermoplastic material, e.g., PEEK and PEEK composites. However, it shall be understood that other biocompatible materials having similar material properties may also be used. 
     Example embodiments in accordance with the principles of this disclosure may be formed by an overmold manufacturing process, for example. In various embodiments, first portion  30  may serve as a substrate for which second portion  10  may be overmolded on top of. For example, in various embodiments the first portion  30  serves as a substrate material or part that may be placed into an injection molding tool and/or injection mold and then the overmold material may be injected into, onto, and/or around the first portion  30  which serves as a substrate. The overmold material may be melted in a fluid form and include any relevant biocompatible material, such as PEEK, as explained previously. Thereafter, the overmold material may cure or solidify around the first portion  30  thereby taking the particular shape of the injection mold and securely coupling to the substrate. After the overmold material cures or solidifies, the two materials become joined together as a single part, e.g., bone screw  100 . In the example embodiment, the first portion  30  and the second portion  10  are mechanically interlocked together due to the various geometrical contouring of first portion  30 , e.g, threads  32 , necked down portion  36 , scallops  33 , and widened distal end  30 D function in coordination to transfer rotational forces and axial separation forces between the two different materials of first portion  30  and second portion  10  such that they do not become separated during ordinary usage. 
     Referring generally to  FIGS.  5 - 7   , experimental testing of embodiments in accordance with the principles of this disclosure will be discussed.  FIG.  5    is an X-Ray image of an entirely metallic spinal support system  200  including a bone screw, receiver, and rod In the example illustration, it is shown that the metallic material is highly visible on the contrasting X-ray image.  FIG.  6    is front view of an X-Ray image of a first bone screw  100  (top screw) form completely of continuous fiber reinforced thermoplastic. Additionally  FIG.  6    illustrates a second bone screw  100  (bottom screw) formed of a titanium first portion  30  and a second portion  10  formed as a PEEK overmold by an overholding process as explained above.  FIG.  7    is a side view of  FIG.  6   . As seen by the various X-Ray images of  FIGS.  5 - 7   , bone screw  100  embodiments including a metallic first portion are visible by X-Ray, but are not nearly as highly contrasting as bone screws  200  formed of entirely metallic materials. Additionally, bone screw  100  embodiments (bottom screw) are capable of showing a trajectory of the bone screw  100  because the first portion  30  includes an elongated shank portion extending in a direction along the longitudinal axis of the bone screw  100 . Accordingly, the different material choices have distinct advantages in the context of X-ray imaging because the total mass of metallic material may be reduced, thereby also reducing interference or obfuscating viewing angles of X-Ray imaging. Bone screws  100  may be particularly advantageous when taking X-ray images of tumor patients or those patients with weakened boney anatomy where a surgeon may require high quality X-ray imaging to perform a procedure, verify a procedure, and/or assess future procedures, for example. 
     It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. For example, features, functionality, and components from one embodiment may be combined with another embodiment and vice versa unless the context clearly indicates otherwise. Similarly, features, functionality, and components may be omitted unless the context clearly indicates otherwise. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). 
     Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified, and that the terms “comprises” and/ or “comprising,” when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.