Medical screw implants for generating distraction between two bones

Abstract

Devices and methods for generating distraction between two or more bones to alleviate pressure on nerves are disclosed. A screw for securing a first bone fragment to a second bone fragment, said screw comprising: a proximal threaded region designed to grip bone; a distal threaded region designed to grip bone, wherein said proximal threaded region has a thread pitch greater than said distal threaded region.

Description

[0001] MEDICAL SCREW IMPLANTS FOR GENERATING DISTRACTION BETWEEN

[0002] TWO BONES

[0003] CROSS-REFERENCE TO RELATED APPLICATION

[0004] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Serial No. 63 / 670332, titled “MEDICAL SCREW IMPLANTS FOR GENERATING DISTRACTION BETWEEN TWO BONES” and filed on July 12, 2024, the entire disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

[0005] FIELD OF THE INVENTION

[0006] The present invention relates to scrcw-bascd devices for generating distraction between two or more bones to alleviate pressure on nerves and thus pain. The invention finds particular utility in the ability to generate a gap between two or more bones in order to relieve pressure on nerves, and thus reduce pain. While the invention has applications throughout the body, its utility will be illustrated in the context of distracting two adjacent spinal facets.

[0007] BACKGROUND

[0008] In the field of orthopaedics, it is common to relieve pain by reducing pressure on nerves. This can be accomplished in several different ways. One way it can be accomplished is by directly removing the bone that is pressing on the nerves. Another option is inserting a intervertebral cage between two adjacent vertebrae where the intervertebral disc has failed. The cage can restore the disc height and relief pressure on exiting nerves. Another method is to use a spinous process plate. The spinous process plate can be implanted between two adjacent vertebra and relieve pressure on exiting nerves. Alternatively, implants can be inserted into the facet joint to create space between the facets and relieve pressure on exiting nerves. While all of these procedures are effective at alleviating nerve pain, they are all invasive procedures. Thus, there exists a clinical need for minimally invasive implants that can generate distraction between two adjacent vertebrae in order to alleviate nerve pressure. SUMMARY

[0009] The present invention provides a novel orthopaedic screw-based implant which can generate distraction between two or more bones to alleviate nerve pressure and thus pain.

[0010] The screw-based implant can be metallic (such as titanium alloy) and manufactured via an additive manufacturing process (such as EBM or Laser additive manufacturing). Alternatively, the screw may be made out of a polymer such as polyether ether ketone (PEEK) or Polyetherketoneketone (PEKK) and manufactured via an additive manufacturing process (such as EBM or Laser additive manufacturing). The screw may be headless or headed. The screw may have a porous region either in the middle of the screw (between a distal and proximal threaded region) or may have a porous region located in the thread valleys. The screw may be fenestrated to allow for bone in growth. The screw may be treated after manufacturing to remove the passive titanium oxide coating, and selectively oxidize the screw so as to contain calcium and phosphorus within the titanium oxide layer

[0011] In one embodiment, the screw is a cannulated headless distraction screw with a distal and proximal threaded region. A thread pitch differential exists between the proximal and distal threads. The proximal threads are courser (fewer threads per inch) than the distal threads (more threads per inch). Between the threaded regions is a central shaft.

[0012] In another embodiment, the screw is a cannulated headed distraction screw with a distal and proximal threaded region. A thread pitch differential exists between the proximal and distal threads. The proximal threads are courser (fewer threads per inch) than the distal threads (more threads per inch). Between the threaded regions is a central shaft.

[0013] In either embodiment, the central shaft may be comprised of only solid metal, or it may be comprised of solid metal covered in porous metal. The porous metal may have a pore sizes engineered to allow for bone in-growth and on-growth. The screw may have one or more fenestrations that radiate axially from the central axis of the screw. The screw may have a nanorough surface, and an oxide layer rich in calcium and phosphorous.

[0014] The disclosure contemplates all combinations of any one or more of the foregoing aspects and / or embodiments, as well as combinations with any one or more of the embodiments set forth in the detailed description and any examples. BRTEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings arc not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

[0016] Figs. 1 and 2 are schematic views showing a novel headless distraction screw formed in accordance with the present invention.

[0017] Fig. 3 is a schematic cross-sectional view of a novel headless distraction screw formed in accordance with the present invention.

[0018] Fig. 4 is a schematic view showing a novel headed distraction screw formed in accordance with the present invention.

[0019] Fig. 5 is a schematic view of the nano-rough surface found on all screw embodiments disclosed with the present invention.

[0020] Fig. 6 is an EDS spectrum showing the presence of calcium and phosphorous in the oxide layer of the screw disclosed with the present invention.

[0021] Fig. 7 is a schematic view of the screw head containing a left handed reverse thread formed in accordance with the present invention.

[0022] Fig. 8 is a schematic view of the screw head and a removal tool formed in accordance with the present invention.

[0023] Fig. 9 is a schematic view of a removal tool engaging the screw head formed in accordance with the present invention.

[0024] Fig. 10 is a schematic view showing how insertion of the novel screw formed in accordance with the present invention generates distraction between two adjacent bones.

[0025] DETAILED DESCRIPTION

[0026] In accordance with one or more embodiments, orthopedic screw implants are disclosed. The implants may generally create distraction between two or more pieces of bone to decompress one or more nerves and reduce pain. In some embodiments, the screws may create a gap between two or more bones, reduce pressure on one or more nerves, and relieve pain. The screws can generate distraction between two or more bone fragments, have a micro and nano surface roughness to allow for bone on growth and have a surface finish the enhances the bioactivity of the screw. Structural features of the screw implants, such as but not limited to void space, surface roughness and porosity, as disclosed herein may generally promote bone growth and fusion. In some non-limiting embodiments, the disclosed screw implants may find particular utility in orthopedic applications. In one specific embodiment, the implants may be used for facet fixation.

[0027] Looking first at Fig. 1 there is shown a novel headless distraction screw 100 for generating distraction between two or more bone fragments and to relieve pressure on nerves. Headless distraction screw 100 is additively manufactured from metal such as titanium or titanium alloy such as Titanum-6Aluminum-4Vanadium; however, it can be made of any other biocompatible metal or polymer. In one embodiment, headless distraction screw 100 is additively manufactured from poly ether ether ketone (PEEK) or Poly etherketoneketone (PEKK). Headless distraction screw 100 has a proximal threaded region 110, a distal threaded region 120, and a central shaft 130. Proximal threaded region 110 may have a larger diameter than distal threaded region 120. In one embodiment proximal threaded region 110 may have a major diameter ranging from 4mm to 8mm, and preferably between 4mm and 6.5mm. Distal threaded region 120 maybe have a major diameter between 4mm and 8mm, and preferably between 4 and 6.5mm. Proximal threaded region 110 may have a shallower thread than distal threaded 120. In one embodiment proximal threaded region 110 has a thread depth of 0.5 to 2.5mm, and preferably between 0.75 and 1.5mm. Distal threaded region 120 has a thread depth of between 1.0 and 2.0mm and preferably between 1.25 and 1.75mm. In a preferred embodiment, the proximal threads 110 have a courser thread pitch than distal threaded region 120, so as to generate distraction between bone fragments during insertion. Proximal threaded region 110 has a thread pitch of between 1.0 and 5.5 mm, preferably 3.5mm and distal threaded region 120 has a thread pitch of between 1.0 and 6mm, preferably 2.5mm. When used to fixate a facet joint, the screw thread pitch differential is capable of creating a gap between the two facets of between 0.5mm and 3.5mm. This represents a clinically relevant distraction distance between the two facets in order to relieve pressure on nerves and alleviate pain. Screw 100 may have a total length of between 20mm and 70mm, and preferably between 15mm and 60mm.

[0028] Looking now at Fig. 2, headless distraction screw 100 has a drive feature 140 to allow for the screw to be inserted and removed. Looking now at Fig. 3, headless distraction screw 100 has a central cannulation 150. Central cannulation allows the screw to be inserted over a guidewire or k-wirc.

[0029] In an alternative embodiment, and now looking at Fig. 4, a headed distraction screw 100 is shown. Headed distraction screw has a head 160 that sits against the proximal bone, a proximal threaded region 110, a distal threaded region 120, and a central shaft 130.

[0030] In the field of orthopedics, it is common to utilize a nano-rough surface to enhance bone growth. Current methods of creating nano-rough surfaces are typically line-of-sight processes; thus, for cannulated screws, the outer surface will have nano-roughness features, but within the inner cannulation the surface remains unchanged.

[0031] Looking now at Fig. 5, electrochemical processing can be used to create a uniform surface covered by a thin nano-textured roughness that exhibited a “net-like” structure comprising thin nanometric sharp crests. This surface can be on all faces on the distraction screw. The crest-to-crest nano-texture roughness measures between 10 and 75nm in connection with a non-limiting representative implant. The nano-rough surface is on all surfaces of the screw, both on the outer surfaces, and within the internal regions of the cannulation.

[0032] Looking now at Fig. 6, an EDS spectrum of the surface of the non-limiting representative screw shows the oxide layer containing calcium and phosphorous. Unlike traditional methods for coating a screw with calcium and phosphorous (i.e., plasma spray) the calcium and phosphorous in the oxide layer of the screw is chemically bound to the screw and is not easily removed while inserting the screw. Traditional coatings on a screw can easily be removed by the stresses of inserting the screw. Additionally, traditional methods for adding biologically active agents (calcium and phosphorous) to the surface of implants is a line-of-sight process. Thus, the biologically active agent will coat the outer surface of the implant, but not coat the inner surfaces of the cannulation. The oxide layer of the screw in the present invention has an oxide layer on all surfaces (external and internal) of the screw that has calcium and phosphorous within the oxide.

[0033] Looking now at Fig. 7, the head of a representative screw of the present invention is shown. Screw head 200 has internal drive feature 140. Drive feature 140 may be a hex, a hexalobe, a flat head, a Phillips, or other drive feature geometry known in the art. In a preferred embodiment, drive feature 140 is a hexalobe. Inscribed in the inner diameter of the hexalobe is a left handed reverse thread 210. Looking now at Fig 8, reverse thread 210 is sized to accept a removal tool 220. Removal tool 220 has a left handed reverse thread screw engagement feature 480. Fig 9 shows the screw and removal tool engaged. A left handed reverse thread is used so that if the screw needs to be removed intra or post operatively, the action of unscrewing the screw will lock the screw to the removal tool. This allows the screw to be removed even if it becomes stripped in the bone.

[0034] Looking now at Fig. 10, the method of using the distraction screw is shown 300. Looking first at Fig. 10A, screw 100 is used to distract proximal bone 310 from distal bone 320. In some embodiments a k-wire or guide wire may be used to guide the placement of screw 100. A drill bit may be used to prepare a hole for screw 100. As shown in Fig. 10B, distraction screw 100 is shown so that the distal thread, and central region are fully inserted in the bone. Looking now at Fig 10C, distraction screw 100 is shown fully implanted. As proximal threads 110 enter proximal bone 310, they wish to advance further than distal threads 120 with each revolution of the screw. This creates distraction between the bones. As an example, is the distal thread pitch is 2.5mm and the proximal thread pitch is 3.5mm, with every full rotation of screw 100, 1mm of distraction will be generated.

[0035] It should be appreciated, that screw 100 may have one or more fenestrations distal to proximal threaded region 110. These fenestration may allow for a biologically active agent to be pumped into the distracted space created between the two bones. Alternatively, after fully inserting the screw and creating the distracted space a biologically active agent can be implanted into the distracted space from an alternative surgical incision.

[0036] Additionally, it should be appreciated that when bones 310 and 320 have cartilaginous surfaces, it may be beneficial to remove the layer of cartilage either before or after placement of distraction screw 100. Placement of a biologically active agent inside the distracted space may create a fusion between bone 310 and 320. Thus bridging bone can form to maintain the distraction.

[0037] Distraction screw 100 may be provided to a physician pre- sterilized and packaged in a sterile barrier. Additionally, sterile single use disposable instruments may be provided to the physician to create a sterile, single use kit. The instrument kit can include at least one of the following: screwdriver, drill bit, decorticator, guide wire, working cannula, and screw sizer. Modifications of the Preferred Embodiments

[0038] It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.

[0039] The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality” refers to two or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0040] Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Any feature described in any embodiment may be included in or substituted for any feature of any other embodiment. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

[0041] Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and / or configurations will depend on the specific application in which the disclosed methods and materials are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments disclosed.

Claims

What is claimed is:

1. A screw for securing a first bone fragment to a second bone fragment, said screw comprising: a proximal threaded region designed to grip bone; a distal threaded region designed to grip bone; a central unthreaded region; and a drive region. wherein said proximal threaded region has a thread pitch greater than said distal threaded region.

2. A screw according to claim 1 wherein said screw is cannulated.

3. A screw according to claim 1 wherein said screw has a nano-rough texture on all surfaces of the screw.

4. A nano-rough surface according to claim 3 wherein said crest-to-crest roughness measurements range from 10 to 75 nm.

5. A screw according to claim 1 wherein said screw has an oxide layer that includes calcium and phosphorous.

6. A screw according to claim 5 wherein said oxide layer that includes calcium and phosphorous is on all surfaces of the screw.

7. A screw according to claim 1 wherein when fully inserting the screw from a first bone fragment to a second bone fragment generates distraction between said first and second bone fragment wherein said gap ranges from 0.5 mm to 3.5 mm.

8. A screw according to claim 1 wherein when said screw is fully inserted across the facet joint to relieve pressure on nerves and alleviate pain.

9. A method for distracting two bones, the method including the use of a screw for securing a first bone fragment to a second bone fragment, said screw comprising: a proximal threaded region designed to grip bone; a distal threaded region designed to grip bone; a central unthreaded region; and a drive region. wherein said proximal threaded region has a thread pitch greater than said distal threaded region.

10. A method according to claim 9 wherein said screw is cannulated.

11. A method according to claim 9 wherein said screw has a nano-rough texture on all surfaces of the screw.

12. A nano-rough surface according to claim 11 wherein said crest-to-crest roughness measurements range from 10 to 75 nm.

13. A method according to claim 9 wherein said screw has an oxide layer that includes calcium and phosphorous.

14. A method according to claim 13 wherein said oxide layer that includes calcium and phosphorous is on all surfaces of the screw.

15. A method according to claim 9 wherein when fully inserting the screw from a first bone fragment to a second bone fragment generates distraction between said first and second bone fragment wherein said gap ranges from 0.5 mm to 3.5 mm.

16. A method according to claim 9 wherein when said screw is fully inserted across the facet joint to relieve pressure on nerves and alleviate pain.

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