Fastening devices, systems, and methods

Abstract

We provide fasteners with improved threads to resist multi-axial force and off-axial load scenarios. [Solution] The fastener may include a shaft and a plurality of helical threads arranged around the shaft. The plurality of helical threads may include a first helical thread and a second helical thread adjacent to the first helical thread. The first helical thread may include a first concave undercut surface and a first convex undercut surface. The second helical thread may include a second concave undercut surface and a second convex undercut surface. When the fastener is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, the first concave undercut surface and the second convex undercut surface may be oriented toward the proximal end of the shaft, and the first convex undercut surface and the second concave undercut surface may be oriented toward the distal end of the shaft.

Description

Technical Field

[0001] The present disclosure relates to fastening devices, systems, and methods. More specifically, the present disclosure relates to a fastening device having an improved screw design, a fastening system that utilizes a fastening device having an improved screw design, and a method of manufacturing a fastener having an improved screw design.

Background Art

[0002] Surgical procedures involving fasteners implanted within bone or other tissue can lose their effectiveness over time due to multi-axial forces and off-axis loading scenarios that can be applied to the fasteners during the healing process. Conventional screw designs of fasteners do not always provide sufficient fastener fixation to overcome these multi-axial forces and off-axis loading scenarios.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Therefore, there is a desire for a fastener with an improved screw design for improving bone fixation and load distribution between the bone / fastener interface that experiences multi-axial loading and unloading conditions, as well as an improved method for manufacturing such a fastener.

Means for Solving the Problems

[0004] Summary The various fastening devices, systems, and methods of the present disclosure have been developed in response to the problems and needs of the art that are not yet fully solved by current state-of-the-art, particularly current available fastening devices, systems, and methods. In some embodiments, the fastening devices, systems, and methods of the present disclosure can provide improved bone fixation and load distribution between the bone / fastener interface under multi-axial loading and unloading conditions.

[0005] In some embodiments, the implantable bone anchor may include a shaft, a first helical thread, and a second helical thread. The shaft may include a proximal end, a distal end, and a longitudinal axis. The first helical thread may be positioned around the shaft along the longitudinal axis between the proximal and distal ends of the shaft. The first helical thread may include a first undercut surface, a second undercut surface, a third undercut surface, and a fourth open surface. The second helical thread may be positioned around the shaft adjacent to the first helical thread. The second helical thread may include a fifth undercut surface, a sixth undercut surface, a seventh undercut surface, and an eighth open surface. The first undercut surface, the third undercut surface, the sixth undercut surface, and the eighth open surface may be angled toward the distal end of the shaft. The second undercut surface, the fourth open surface, the fifth undercut surface, and the seventh undercut surface may be angled toward the proximal end of the shaft.

[0006] In some embodiments of the implantable bone anchor, when the implantable bone anchor is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, the first helical thread may include at least one chevron shape oriented toward the distal end of the shaft, and the second helical thread may include at least one chevron shape oriented toward the proximal end of the shaft.

[0007] In some embodiments of the implantable bone anchor, the first helical thread may include a first plurality of chevron shapes oriented toward the distal end of the shaft, and the second helical thread may include a second plurality of chevron shapes oriented toward the proximal end of the shaft.

[0008] In some embodiments of the implantable bone anchor, a first plurality of chevron shapes and a second plurality of chevron shapes may be arranged alternately and continuously along the shaft of the implantable bone anchor.

[0009] In some embodiments of the implantable bone anchor, when viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, the first helical thread may include at least one partial crescent shape oriented toward the distal end of the shaft, and the second helical thread may include at least one partial crescent shape oriented toward the proximal end of the shaft.

[0010] In some embodiments of the implantable bone anchor, the first helical thread may include a first plurality of partial crescent shapes oriented toward the distal end of the shaft, and the second helical thread may include a second plurality of partial crescent shapes oriented toward the proximal end of the shaft.

[0011] In some embodiments of the implantable bone anchor, a first plurality of partial crescent shapes and a second plurality of partial crescent shapes may be arranged alternately and continuously along the shaft of the implantable bone anchor.

[0012] In some embodiments, the fastener may include a shaft and a plurality of helical threads. The shaft may include a proximal end, a distal end, and a longitudinal axis. The plurality of helical threads may be arranged around the shaft along the longitudinal axis between the proximal and distal ends of the shaft. The plurality of helical threads may include a first helical thread and a second helical thread. The first helical thread may include a first concave undercut surface and a first convex undercut surface. The second helical thread may include a second concave undercut surface and a second convex undercut surface. The first concave undercut surface and the second convex undercut surface may be oriented toward the proximal end of the shaft. The first convex undercut surface and the second concave undercut surface may be oriented toward the distal end of the shaft.

[0013] In some embodiments of the fastener, the multiple helical threads may include three helical threads.

[0014] In some embodiments of the fastener, the multiple helical screws may include four helical screws.

[0015] In some embodiments of the fastener, the multiple helical threads may include more than four helical threads.

[0016] In some embodiments of the fastener, at least one of the first concave undercut surface, the first convex undercut surface, the second concave undercut surface, and the second convex undercut surface may include at least one substantially flat surface.

[0017] In some embodiments of the fastener, at least one of the first concave undercut surface, the first convex undercut surface, the second concave undercut surface, and the second convex undercut surface may include at least one curved surface.

[0018] In some embodiments of the fastener, when the fastener is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, the first helical thread may include a first bend shape having a first intermediate portion oriented toward the distal end of the shaft, and the second helical thread may include a second bend shape having a second intermediate portion oriented toward the proximal end of the shaft.

[0019] In some embodiments of the fastener, when viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, a first bonding space may be formed midway between a first concave undercut surface and a second concave undercut surface, and a second bonding space may be formed midway between a first convex undercut surface and a second convex undercut surface. Each of the first and second bonding spaces may be configured to receive bone tissue therein, and each of the first and second bonding spaces may be shaped to bond with the bone tissue to enhance the fixation of the fastener within the bone tissue.

[0020] In some embodiments of the fastener, the first bonding space may be larger in size than the second bonding space.

[0021] In some embodiments, the implantable bone anchor may have a shaft having a proximal end, a distal end, and a longitudinal axis. The implantable bone anchor may also have a first helical thread positioned around the shaft along the longitudinal axis between the proximal and distal ends of the shaft. The first helical thread may have a first proximal-oriented surface facing the proximal end and a first distal-oriented surface facing the distal end. The implantable bone anchor may also have a second helical thread positioned around the shaft adjacent to the first helical thread. The second helical thread may have a second proximal-oriented surface facing the proximal end and a second distal-oriented surface facing the distal end. The first proximal-oriented surface and the first distal-oriented surface are not necessarily mirror-symmetry with respect to each other across any plane perpendicular to the longitudinal axis. The first proximal-oriented surface and the second distal-oriented surface may intersect a first plane perpendicular to the longitudinal axis and exhibit mirror symmetry with respect to each other.

[0022] The first proximal-oriented surface may be substantially concave. The second distal-oriented surface may be substantially convex.

[0023] The second proximal-oriented surface may be substantially convex. The first distal-oriented surface may be substantially concave.

[0024] The second proximal-oriented surface and the second distal-oriented surface do not necessarily have mirror symmetry with respect to each other across an arbitrary plane perpendicular to the longitudinal axis. The second proximal-oriented surface and the first distal-oriented surface may have mirror symmetry with respect to each other across a second plane perpendicular to the longitudinal axis.

[0025] In some embodiments, the process for forming a fastener includes disposing a first cutting head of a first milling tool at a first position along a substantially cylindrical substrate having a proximal end and a distal end, disposing a second cutting head of a second milling tool at a second position along the substantially cylindrical substrate, rotating the first cutting head about a first longitudinal axis of the first milling tool, rotating the second cutting head about a second longitudinal axis of the second milling tool, rotating the substantially cylindrical substrate about a third longitudinal axis of the substantially cylindrical substrate, and translating the first and second cutting heads along at least a portion of the length of the substantially cylindrical substrate to form a first concave undercut surface oriented toward the proximal end, a first convex undercut surface oriented toward the distal end, a second concave undercut surface oriented toward the distal end, and a second convex undercut surface oriented toward the proximal end.

[0026] In some embodiments of the process, translating the first and second cutting heads along at least a portion of the length of the substantially cylindrical substrate can form a first helical thread and a second helical thread. The first helical thread can include the first concave undercut surface and the first convex undercut surface. The second helical thread can include the second concave undercut surface and the second convex undercut surface.

[0027] In some embodiments, the process can also include disposing the first cutting head adjacent to the second cutting head along a side of the substantially cylindrical substrate such that the first longitudinal axis of the first milling tool is substantially parallel to the second longitudinal axis of the second milling tool.

[0028] In some embodiments of the process, the first cutting head can include at least one convex cutting surface and the second cutting head can include at least one concave cutting surface.

[0029] In some embodiments of the process, at least one convex cutting surface may include a first facet and a second facet, and at least one concave cutting surface may include a third facet and a fourth facet. The first and second facets may be angled relative to each other at a first angle which may be greater than 180 degrees to form at least one convex cutting surface, and the third and fourth facets may be angled relative to each other at a second angle which may be less than 180 degrees to form at least one concave cutting surface.

[0030] In some embodiments, the process may also include the steps of positioning a first cutting head on a first side of a substantially cylindrical substrate and positioning a second cutting head on a second side of a substantially cylindrical substrate. The first and second cutting heads may be separated by a selected degree of rotation around a third longitudinal axis of the substantially cylindrical substrate.

[0031] In some embodiments of the process, the first cutting head and the second cutting head may be separated by a 180-degree rotation around a third longitudinal axis of a substantially cylindrical substrate.

[0032] In some embodiments, the fastener may be formed by a process comprising the steps of: positioning a first cutting head of a first milling tool at a first position along the shaft of the fastener having a proximal end and a distal end; positioning a second milling tool at a second position along the shaft; rotating the first cutting head about a first longitudinal axis of the first milling tool; rotating the second cutting head about a second longitudinal axis of the second milling tool; rotating the shaft about a third longitudinal axis of the shaft; and translating the first and second cutting heads along at least a portion of the length of the shaft, thereby forming a first concave undercut surface oriented toward the proximal end, a first convex undercut surface oriented toward the distal end, a second concave undercut surface oriented toward the distal end, and a second convex undercut surface oriented toward the proximal end.

[0033] In some embodiments of the fastener formed by the process, the step of translating first and second cutting heads along at least a portion of the length of the shaft may form a first helical thread and a second helical thread. The first helical thread may include a first concave undercut surface and a first convex undercut surface. The second helical thread may include a second concave undercut surface and a second convex undercut surface.

[0034] Some embodiments of the fasteners formed by the process may also include the step of positioning a first cutting head adjacent to a second cutting head along the side of the shaft such that the first longitudinal axis of the first milling tool is substantially parallel to the second longitudinal axis of the second milling tool.

[0035] In some embodiments of the fastener formed by the process, the first cut head may include at least one convex cut surface, and the second cut head may include at least one concave cut surface.

[0036] In some embodiments of the fastener formed by the process, at least one convex cut surface may include a first facet and a second facet, and at least one concave cut surface may include a third facet and a fourth facet. The first and second facets may be angled relative to each other at a first angle which may be greater than 180 degrees, forming at least one convex cut surface, and the third and fourth facets may be angled relative to each other at a second angle which may be less than 180 degrees, forming at least one concave cut surface.

[0037] In some embodiments of the fastener formed by the process, the process may also include the steps of positioning a first cutting head on a first side of the shaft and positioning a second cutting head on a second side of the shaft. The first and second cutting heads may be separated by a selected degree of rotation around a third longitudinal axis of the shaft.

[0038] In some embodiments, an implantable bone anchor may be formed by a process comprising the steps of: positioning a first cutting head of a first milling tool at a first position along the shaft of the implantable bone anchor having a proximal end and a distal end; positioning a second cutting head of a second milling tool at a second position along the shaft; rotating the first cutting head about a first longitudinal axis of the first milling tool; rotating the second cutting head about a second longitudinal axis of the second milling tool; rotating the shaft about a third longitudinal axis of the shaft; and translating the first and second cutting heads along at least a portion of the length of the shaft, thereby forming a first proximal-oriented surface facing the proximal end of the shaft, a first distal-oriented surface facing the distal end of the shaft, a second proximal-oriented surface facing the proximal end of the shaft, and a second distal-oriented surface facing the distal end of the shaft.

[0039] In some embodiments of implantable bone anchors formed by the process, translating first and second cutting heads along at least a portion of the length of the shaft can form a first helical thread and a second helical thread. The first helical thread may include a first proximal-oriented surface facing the proximal end of the shaft and a first distal-oriented surface facing the distal end of the shaft. The second helical thread may include a second proximal-oriented surface facing the proximal end of the shaft and a second distal-oriented surface facing the distal end of the shaft. In some embodiments, the first proximal-oriented surface and the first distal-oriented surface do not necessarily have mirror symmetry with respect to each other by intersecting any plane perpendicular to the third longitudinal axis of the shaft. In some embodiments, the first proximal-oriented surface and the second distal-oriented surface may intersect a first plane perpendicular to the third longitudinal axis of the shaft and have mirror symmetry with respect to each other.

[0040] In some embodiments of the implantable bone anchor formed by the process, the process may also include the step of positioning the first cutting head adjacent to the second cutting head along the side of the shaft such that the first longitudinal axis of the first milling tool is substantially parallel to the second longitudinal axis of the second milling tool.

[0041] In some embodiments of the implantable bone anchor formed by the process, the first cutting head may include at least one convex cutting surface, and the second cutting head may include at least one concave cutting surface.

[0042] In some embodiments of the implantable bone anchor formed by the process, at least one convex cut surface may include a first facet and a second facet, and at least one concave cut surface may include a third facet and a fourth facet. The first and second facets may be angled relative to each other at a first angle which may be greater than 180 degrees, forming at least one convex cut surface, and the third and fourth facets may be angled relative to each other at a second angle which may be less than 180 degrees, forming at least one concave cut surface.

[0043] In some embodiments of the implantable bone anchor formed by the process, the process may also include the steps of positioning a first cutting head on a first side of the shaft and positioning a second cutting head on a second side of the shaft. The first and second cutting heads may be separated by a selected degree of rotation around a third longitudinal axis of the shaft.

[0044] These and other features and advantages of this disclosure will become more fully apparent from the following description and the attached claims, and can also be learned from the practice of the apparatus, systems, and methods described below.

[0045] The exemplary embodiments of this disclosure will become more fully apparent from the following description, which will be understood in conjunction with the accompanying drawings. Understanding that these drawings only illustrate exemplary embodiments and should not be considered to limit the scope of this disclosure, the exemplary embodiments of this disclosure will be described with additional specificity and detail through the use of the accompanying drawings. [Brief explanation of the drawing]

[0046] [Figure 1A] This is a front perspective view of a fastener according to one embodiment of the present disclosure. [Figure 1B] Figure 1A is a rear perspective view of the fastener. [Figure 1C] Figure 1A is a side view of the fastener. [Figure 1D] This is a side cross-sectional view of the fastener shown in Figure 1A, taken along line AA shown in Figure 1C. [Figure 2A] This is a front perspective view of a fastener according to another embodiment of the present disclosure. [Figure 2B] Figure 2A is a rear perspective view of the fastener. [Figure 2C] Figure 2A is a side view of the fastener. [Figure 2D] This is a side cross-sectional view of the fastener shown in Figure 2A, taken along line BB shown in Figure 2C. [Figure 3A] This is a front perspective view of a fastener according to another embodiment of the present disclosure. [Figure 3B] Figure 3A is a rear perspective view of the fastener. [Figure 3C] Figure 3A is a side view of the fastener. [Figure 3D] This is a side cross-sectional view of the fastener shown in Figure 3A, taken along line CC shown in Figure 3C. [Figure 4A] This is a front perspective view of a milling tool according to one embodiment of the present disclosure. [Figure 4B] Figure 4A is a rear perspective view of the milling tool. [Figure 4C] Figure 4A is a side view of the milling tool. [Figure 4D]Figure 4A is a front view of the milling tool. [Figure 5A] This is a front perspective view of a milling tool according to another embodiment of the present disclosure. [Figure 5B] Figure 5A is a rear perspective view of the milling tool. [Figure 5C] Figure 5A is a side view of the milling tool. [Figure 5D] Figure 5A is a front view of the milling tool. [Figure 6] Figure 5A is a perspective view of the milling tool used to perform milling operations on the fastener shown in Figure 1A. [Figure 7] Figure 5A shows the milling tool used to perform milling on the fastener shown in Figure 1A, and Figure 5B shows a side view of the milling tool. [Figure 8] Figure 5A shows a cross-sectional view of the milling tool and Figure 4A, which perform milling operations on the fastener shown in Figure 1A. [Figure 9] This is a flow diagram of a process for forming a thread on a fastener according to one embodiment of the present disclosure. [Figure 10] This is a partial side cross-sectional view of a fastener, including a crescent-shaped screw. [Modes for carrying out the invention]

[0047] It should be understood that the drawings are intended to illustrate the concepts of this disclosure and are not necessarily drawn to a specific scale. Furthermore, the drawings show exemplary embodiments and do not constitute a limitation on the scope of this disclosure.

[0048] The exemplary embodiments of this disclosure are best understood by reference to the drawings, and throughout, similar parts are indicated by similar figures. It will be readily apparent that the components of this disclosure may be arranged and designed in a wide variety of different configurations, as generally described and shown in the drawings. Accordingly, the following more detailed descriptions of the embodiments of implants, systems, and methods shown in the drawings are not intended to limit the scope of this disclosure, but merely represent exemplary embodiments of this disclosure.

[0049] The term “exemplary” is used herein to mean “provided as an example, case, or illustration.” Any embodiment described herein as “exemplary” should not necessarily be construed as being preferable or advantageous over other embodiments. Various aspects of the embodiments are shown in the drawings, but unless specifically indicated, the drawings are not necessarily drawn to a certain scale.

[0050] The following disclosures present a variety of fasteners for use as implantable devices in bone and other tissues (e.g., orthopedic implants, spinal implants, sports medicine implants, dental implants, trauma implants, reconstructive implants, limb implants, craniofacial (CMF) implants, veterinary implants, etc.) in order to streamline the present disclosure. However, it will be understood that the various fasteners and screw concepts presented herein may be used for any medium beyond bone / tissue and / or for any application beyond surgical procedures.

[0051] Exemplary applications / treatments in which any of the fasteners described or considered herein may be used in any configuration and in conjunction with any of the structures described herein include, but are not limited to, trauma treatment, spinal treatment (e.g., SI fixation, facet joint fixation), reconstructive treatment, sports-related treatment, ACL / Tenodes treatment, limb treatment, dental treatment, CMF treatment, veterinary treatment, fracture fixation plate treatment (distal femoral plate, proximal humeral plate, tibial plate, etc.), supplemental fixation for IBD treatment, intramedullary fixation treatment, nail fixation treatment, lower limb salvage and transfemoral treatment, limb amputation and splinting treatment, complete shoulder fixation, reverse glenoid fixation, small bone fixation (podiatry, hand / wrist, etc.), arthral fixation, single-tooth implant fixation, jaw / facial reconstruction, denture fixation, veterinary trauma, species-specific treatment (e.g., horse, dog, rabbit, etc.), TPLO, shear fixation, osteotomy, fixation, treatment with osteoporosis or damaged bone, etc.

[0052] Furthermore, the types of fasteners that may utilize any of the screw designs, forms, and / or features described herein may include, but are not limited to, cortical fasteners, soft tissue fasteners, elongated fasteners, intubation fasteners, plate fasteners, fixed / unfixed fasteners, dynamic hip fasteners, acetabular cup fasteners, schant pins, half pins, pedicle fasteners, cervical fasteners, threaded stems, threaded intramedullary stems, articular stems, modification fasteners, compression fasteners (e.g., headless / headed compression fasteners, hip compression fasteners, etc.), ACL fasteners, tendon fixation fasteners, bone-tendon-bone graft fasteners, suture anchors, dental fasteners, mandibular tenting fasteners, veterinary fasteners, and the like.

[0053] Figures 1A–1D show various diagrams of a fastener 100, an implantable bone anchor, or bone screw according to one embodiment of the present disclosure. Specifically, Figure 1A is a front perspective view of the fastener 100, Figure 1B is a rear perspective view of the fastener 100, Figure 1C is a side view of the fastener 100, and Figure 1D is a side cross-sectional view of the fastener 100 obtained along line AA in Figure 1C.

[0054] Generally, the fastener 100 may include a shaft 105 having a proximal end 101, a distal end 102, and a longitudinal axis 103. The fastener 100 may also include a head 104 located on the proximal end 101 of the shaft 105, a torque connection interface 106 (either male or female configuration) formed inside or on the head 104, and a self-tapping structure 107 formed on the distal end 102 of the shaft 105.

[0055] In some embodiments, the fastener 100 may include a first helical screw 110 arranged around the shaft 105 and a second helical screw 120 arranged around the shaft 105 adjacent to the first helical screw 110.

[0056] In some embodiments, the fastener 100 may include a “dual-start” or “dual-lead” screw configuration, which includes a first helical screw 110 and a second helical screw 120.

[0057] In some embodiments, the depth of the first helical thread 110 and / or the second helical thread 120 relative to the shaft 105 can define a larger diameter relative to a smaller diameter of the shaft 105 alone.

[0058] In some embodiments, the large and / or small diameters of the fastener 100 may be constant or substantially constant along the entire length of the fastener, or along most of the length of the fastener. In these embodiments, a constant small diameter may help avoid rupture of narrow / delicate bone (e.g., pedicle) when inserting the fastener into the bone. In some embodiments, a pilot hole may first be drilled in the narrow / delicate bone, and then a fastener having a similar small diameter to the diameter of the pilot hole may be selected to avoid rupture when inserting the fastener into the bone.

[0059] In some embodiments, the depth of the first helical thread 110 and / or the second helical thread 120 relative to the shaft 105 may vary along the length of the shaft 105, defining one or more large diameters of the fastener 100, and / or one or more regions along the fastener 100 may include one or more continuously varying large diameters.

[0060] In some embodiments, the thickness of the shaft 105 may vary along the length of the shaft 105, defining one or more small diameters of the fastener 100, and / or one or more regions along the fastener 100 may include one or more continuously varying small diameters. In some embodiments, the thickness / height / width / length / pitch / shape of the first helical thread 110 and / or the second helical thread 120 (or any additional helical threads) may vary along the length of the shaft 105. For example, the thickness / height / width / length / pitch / shape of the first helical thread 110 and / or the second helical thread 120 may become larger towards the tip of the fastener and smaller towards the head of the fastener (or vice versa) in a discrete or continuously varying manner.

[0061] In some embodiments, the larger and / or smaller diameters may increase towards the proximal end or head of the fastener to increase bone compression when the fastener is finally inserted into the bone / tissue.

[0062] In some embodiments, the pitch of the first helical thread 110 and / or the second helical thread 120 may vary along the length of the fastener 100.

[0063] In some embodiments, the fastener 100 may include multiple helical threads arranged around the shaft 105. However, it will also be understood that any fastener disclosed or discussed herein may include a single helical thread arranged around the shaft of the fastener. Furthermore, the fastener 100 may comprise multiple nested helical threads (not shown) having different lengths. In a non-limiting example, the fastener 100 may include a first helical thread 110 that is longer than a second helical thread 120, so that the fastener 100 has a double thread along the first portion of the shaft 105 and a single thread along the second portion of the shaft 105.

[0064] In some embodiments, the multiple helical screws may include three helical screws (not shown) with a “triple start” or “triple lead” screw configuration (not shown).

[0065] In some embodiments, the multiple helical screws may include four helical screws (not shown) including a "quadruple start" or "quadruple lead" screw configuration (not shown).

[0066] In some embodiments, the multiple helical screws may include more than four helical screws (not shown).

[0067] In some embodiments, the fastener 100 may include a first thread having one of the shapes disclosed herein, oriented toward one of the proximal and distal ends of the fastener 100, and positioned close to the distal end of the fastener 100, and a second thread having one of the shapes disclosed herein, oriented toward the other of the proximal and distal ends of the fastener 100, and positioned close to the head of the fastener 100 (not shown).

[0068] In some embodiments, the fastener 100 may include a plurality of threads having any of the shapes disclosed herein (e.g., double-started helical threads) positioned close to one of the proximal and distal ends of the fastener 100, and a second thread having any of the shapes disclosed herein (not shown), positioned close to the other of the proximal and distal ends of the fastener 100.

[0069] In some embodiments, the first helical screw 110 may include a plurality of first concave undercut surfaces 131 and a plurality of first convex undercut surfaces 141.

[0070] In some embodiments, the second helical thread 120 may include a plurality of second concave undercut surfaces 132 and a plurality of second convex undercut surfaces 142.

[0071] In some embodiments, when the fastener 100 is viewed in cross-section along a plane intersecting the longitudinal axis 103 of the shaft 105 (as shown in Figure 1D), the plurality of first concave undercut surfaces 131 and the plurality of second convex undercut surfaces 142 can be oriented toward (i.e., directed toward) the proximal end 101 of the shaft 105.

[0072] In some embodiments, the plurality of first convex undercut surfaces 141 and the plurality of second concave undercut surfaces 132 can be directed toward (i.e., oriented toward) the distal end 102 of the shaft 105.

[0073] In some embodiments, at least one of the plurality of first concave undercut surfaces 131, plurality of first convex undercut surfaces 141, plurality of second concave undercut surfaces 132, and plurality of second convex undercut surfaces 142 may include at least one substantially flat surface.

[0074] In some embodiments, when the fastener 100 is viewed in cross-section along a plane intersecting the longitudinal axis 103 of the shaft 105, the first helical thread 110 may include a plurality of first bend shapes (including at least one surface angled with respect to the longitudinal axis 103 of the shaft 105) having a plurality of first intermediate portions 151 that are oriented (i.e., directed) toward the distal end 102 of the shaft 105. This may be referred to as a “standard” thread with “standard” orientation.

[0075] In some embodiments, when the fastener 100 is viewed in cross-section along a plane intersecting the longitudinal axis 103 of the shaft 105, the second helical thread 120 may include a plurality of second bend shapes (including at least one surface angled with respect to the longitudinal axis 103 of the shaft 105) having a plurality of second intermediate portions 152 that are oriented (i.e., directed) toward the proximal end 101 of the shaft 105. This may be referred to as a “reverse” thread having “reverse” orientation.

[0076] In some embodiments, one or more helical threads may change / transition along the shaft of the fastener between a standard orientation and a reverse orientation.

[0077] In some embodiments, at least one of the plurality of first concave undercut surfaces 131, plurality of first convex undercut surfaces 141, plurality of second concave undercut surfaces 132, and plurality of second convex undercut surfaces 142 may include at least one curved surface.

[0078] As shown in Figure 1D, the proximal and distal surfaces of the first helical thread 110 (i.e., the first concave undercut surface 131 and the first convex undercut surface 141 in the fastener 100 in Figure 1D) do not necessarily have mirror symmetry with respect to any plane perpendicular to the longitudinal axis 103 of the fastener 100. Rather, the first concave undercut surface 131 and the first convex undercut surface 141 may be substantially parallel to each other. The same applies to the second helical thread 120, where the second concave undercut surface 132 and the second convex undercut surface 142 may be substantially parallel to each other, even though they do not have mirror symmetry with respect to each other.

[0079] Conversely, as shown in Figure 1D, the surface oriented proximal to the first helical screw 110 may have mirror symmetry with respect to the surface oriented distal to the second helical screw 120. Specifically, the first concave undercut surface 131 may have mirror symmetry with respect to the second convex undercut surface 142 with respect to a plane 170 that bisects the space between them and is located perpendicular to the longitudinal axis 103.

[0080] Similarly, the distally oriented surface of the first helical screw 110 may have mirror symmetry with respect to the proximal oriented surface of the second helical screw 120. Specifically, the second concave undercut surface 132 may have mirror symmetry with respect to the first convex undercut surface 141 with respect to a plane 172 that bisects the space between them and is located perpendicular to the longitudinal axis 103.

[0081] This mirror symmetry may exist along most of the lengths of the first and second helical screws 110 and 120, having symmetry across different planes, positioned between adjacent turns of the first and second helical screws 110 and 120 along the length of the longitudinal axis 103. Such mirror symmetry may help to more effectively capture bone between the first and second helical screws 110 and 120, as will be described in more detail below, and may also facilitate the manufacture of the fastener 100.

[0082] In some embodiments, along a plane intersecting the longitudinal axis 103 of the shaft 105, the fastener 100, when viewed in cross-section, may include at least one partial crescent shape, the first helical thread 110, which is oriented (i.e., directed) toward the distal end 102 and / or the proximal end 101 of the shaft 105. Figure 10 shows a partial cross-sectional view of the fastener 700 including the crescent shape as a non-limiting example of such an embodiment.

[0083] In some embodiments (not shown), when the fastener 100 is viewed in cross-section along a plane intersecting the longitudinal axis 103 of the shaft 105, the first helical thread 110 may include at least one partial crescent shape directed toward the distal end 102 of the shaft 105, and the second helical thread 120 may include at least one partial crescent shape directed toward the proximal end 101 of the shaft 105.

[0084] In some embodiments (not shown), the first helical thread 110 may include a first plurality of partial crescent shapes directed toward the distal end 102 of the shaft 105, and the second helical thread 120 may include a second plurality of partial crescent shapes directed toward the proximal end 101 of the shaft 105.

[0085] In some embodiments (not shown), the first plurality of partial crescent shapes and the second plurality of partial crescent shapes may be arranged alternately and continuously along the shaft 105 of the fastener 100.

[0086] In some embodiments, the fasteners may have only standard threads or only reverse threads. The preferred screw type may depend on the type and / or magnitude of the load applied to the fastener. For example, a screw that is axially loaded away from the bone into which it is embedded may have a standard screw, while a screw that is axially loaded towards the bone into which it is embedded may have a reverse screw. A screw that can experience multiaxial loading and / or unloading may have at least one standard screw and at least one reverse screw to enhance load distribution between bone fixation and the bone / fastener interface during multiaxial loading and / or unloading conditions, reducing severe bone strain and distributing the multiaxial forces applied to the bone in a load distribution configuration rather than load support. Shear loads and / or bending moments may also be optimally resisted by any selected combination of screws, screw forms, and / or screw deformations considered herein to optimally resist shear loads, bending moments, multiaxial loading, unloading conditions, etc.

[0087] In some embodiments, fasteners with standard threads may be used in combination with fasteners with reverse threads to accommodate different load patterns.

[0088] In some embodiments, a single fastener may have both a standard thread and a reverse thread, as in fastener 100. Such a combination of threads may help fastener 100 stay in place in unknown and / or changing load patterns.

[0089] In some embodiments, the shape of the threads of a fastener (having standard and / or reverse threads) may be modified to suit the fastener for a particular load scheme. For example, the number of threads, the number of thread starts, the thread pitch, the thread lead, the thread shape, any dimensions related to the thread (e.g., length / width / height related to the thread), large diameter, small diameter, the bending angle formation / angle related to the thread surface, the "winding direction" of the thread (e.g., right-handed and left-handed), etc., may be modified to suit a particular mounting medium, load pattern, application, treatment, etc., that may be involved.

[0090] In some embodiments, the material of any part of the fasteners described herein may include, but is not limited to, metals (e.g., titanium, cobalt, stainless steel), metal alloys, plastics, polymers, PEEK, UHMWPE, composite materials, additive particles, textured surfaces, biomass, biomaterials, bone, and the like.

[0091] In some embodiments, any of the fasteners described herein may include additional structures such as self-tapping structures, locking structures (e.g., locking screws formed on or near the head of the fastener, or other parts of the fastener), cannulations, fastener heads of any style (or no fastener head at all), or torque connection interfaces of any style (or no torque connection interface at all).

[0092] In some embodiments, a tap (not shown) may be used to pre-form a thread in a bone according to any thread shape disclosed herein. Thus, a tap having any suitable shape may be used with any fastener described or discussed herein to match or substantially match the thread shape of a given fastener.

[0093] In some embodiments, the diameter of the fastener may be chosen to match, or substantially match, the diameter of the pilot hole formed in the bone, in order to avoid bone rupture when the fastener is inserted into the pilot hole.

[0094] Additionally or alternatively, the type and / or shape of the screw may be modified based on the type of bone to which the fastener is anchored. For example, fasteners anchored to osteoporotic bone may function better with standard or reverse threads, or with increased or decreased pitch, large and / or small diameters, or with adjusted angle formation of the thread faces.

[0095] In some embodiments, the surgical kit may include multiple fasteners having any of the different screw options described or discussed herein. The surgeon may select the appropriate fastener from the kit based on the specific load being applied and / or the quality of the bone to which the fastener is to be fixed.

[0096] Continuing with respect to Figure 1D, in some embodiments, the first helical screw 110 may include a plurality of first undercut surfaces 111, a plurality of second undercut surfaces 112, a plurality of third undercut surfaces 113, and a plurality of fourth open surfaces 114.

[0097] In some embodiments, the second helical thread 120 may include a plurality of fifth undercut faces 125, a plurality of sixth undercut faces 126, a plurality of seventh undercut faces 127, and a plurality of eighth open faces 128.

[0098] In some embodiments, one or more of the plurality of first undercut surfaces 111, plurality of second undercut surfaces 112, plurality of third undercut surfaces 113, plurality of fourth open surfaces 114, plurality of fifth undercut surfaces 125, plurality of sixth undercut surfaces 126, plurality of seventh undercut surfaces 127, and plurality of eighth open surfaces 128 may include at least one flat or substantially flat surface.

[0099] In some embodiments, the plurality of first undercut surfaces 111, the plurality of third undercut surfaces 113, the plurality of sixth undercut surfaces 126, and the plurality of eighth open surfaces 128 may be angled toward the distal end 102 of the shaft 105.

[0100] In some embodiments, the plurality of second undercut surfaces 112, the plurality of fourth open surfaces 114, the plurality of fifth undercut surfaces 125, and the plurality of seventh undercut surfaces 127 may be angled toward the proximal end 101 of the shaft 105.

[0101] In some embodiments, when viewed in cross-section, the fastener 100, along a plane intersecting the longitudinal axis 103 of the shaft 105 (as shown in Figure 1D), may include at least one chevron shape directed toward (i.e., pointed toward) the distal end 102 of the shaft 105. Similarly, the second helical thread 120 may also include at least one chevron shape directed toward (i.e., pointed toward) the proximal end 101 of the shaft 105.

[0102] In some embodiments, when viewed in cross-section, the fastener 100 may have a first helical thread 110 that is oriented (i.e., directed) toward the distal end 102 of the shaft 105, as shown in Figure 1D. Similarly, the second helical thread 120 may have a second helical thread 120 that is oriented (i.e., directed) toward the proximal end 101 of the shaft 105.

[0103] In some embodiments, the first and second chevron shapes may be arranged alternately and continuously along the shaft 105 of the fastener 100 (see, for example, Figure 1D).

[0104] In some embodiments, a plurality of first coupling spaces 161 and a plurality of second coupling spaces 162 may be formed along the shaft 105 of the fastener 100 between the first helical thread 110 and the second helical thread 120.

[0105] In some embodiments, a plurality of first bonding spaces 161 may be formed between a first concave undercut surface 131 and a second concave undercut surface 132.

[0106] In some embodiments, a plurality of second bonding spaces 162 may be formed between the first convex undercut surface 141 and the second convex undercut surface 142.

[0107] In some embodiments, the plurality of first bond spaces 161 may be larger in size than the plurality of second bond spaces.

[0108] In some embodiments, a plurality of first bonding spaces 161 and a plurality of second bonding spaces 162 may be molded and / or configured to bond with bone / other tissues that receive therein, thereby reinforcing the fixation of the fastener 100 within the bone / other tissues and providing additional resistance to multiaxial forces that may be applied to the fastener 100 and / or bone / other tissues.

[0109] In some embodiments, the multiple second undercut surfaces 112 and the multiple sixth undercut surfaces 126 may be angled toward each other to capture bone / other tissue within the multiple first joint spaces 161 in order to increase fixation and resistance to multiaxial forces.

[0110] In some embodiments, the multiple third undercut surfaces 113 and the multiple seventh undercut surfaces 127 may be angled toward each other to capture bone / other tissue within the multiple second joint spaces 162 in order to increase fixation and resistance to multiaxial forces.

[0111] In some embodiments, the plurality of first undercut surfaces 111 and the plurality of fifth undercut surfaces 125 may each form an angle α with respect to the longitudinal axis 103 of the shaft 105, as shown in Figure 1D.

[0112] In some embodiments, the angle α may be greater than 90 degrees.

[0113] In some embodiments, the multiple second undercut surfaces 112 and the multiple sixth undercut surfaces 126 may each form an angle β with respect to the longitudinal axis 103 of the shaft 105.

[0114] In some embodiments, the angle β may be less than 90 degrees.

[0115] In some embodiments, the plurality of third undercut surfaces 113 and the plurality of seventh undercut surfaces 127 may each form an angle θ with respect to the longitudinal axis 103 of the shaft 105.

[0116] In some embodiments, the angle θ can be about 90 degrees.

[0117] In some embodiments, the angle θ may be greater than 90 degrees.

[0118] Figures 2A–2D show various diagrams of a multi-axis screw, or fastener 200, according to another embodiment of the present disclosure. Specifically, Figure 2A is a front perspective view of the fastener 200, Figure 2B is a rear perspective view of the fastener 200, Figure 2C is a side view of the fastener 200, and Figure 2D is a side cross-sectional view of the fastener 200 obtained along line BB in Figure 2C. The fastener 200 may include a shaft 205 having a proximal end 201, a distal end 202, and a longitudinal axis 203. The fastener 200 may also include a multi-axis head 204 positioned at the proximal end 201 of the shaft 205, a torque connection interface 206 formed within / on the multi-axis head 204, and a self-tapping structure 207 formed at the distal end 202 of the shaft 205. In some embodiments, the fastener 200 may include a first helical screw 210 positioned around the shaft 205 and a second helical screw 220 positioned around the shaft 205 adjacent to the first helical screw 210. In these embodiments, the fastener 200 may include a “dual-start” or “dual-lead” screw configuration. However, it will also be understood that the fastener 200 may include any screw configuration, features, or forms described or considered herein in order to achieve optimal fixation within a given bone / tissue.

[0119] Figures 3A–3D show various diagrams of a headless screw, or fastener 300, according to another embodiment of the present disclosure. Specifically, Figure 3A is a front perspective view of the fastener 300, Figure 3B is a rear perspective view of the fastener 300, Figure 3C is a side view of the fastener 300, and Figure 3D is a side cross-sectional view of the fastener 300 taken along line CC of Figure 3C. The fastener 300 may include a shaft 305 having a proximal end 301, a distal end 302, and a longitudinal axis 303. The fastener 300 may also include a torque connection interface 306 formed on the proximal end 301 of the shaft 305 and a self-tapping structure 307 formed on the distal end 302 of the shaft 305. In some embodiments, the fastener 300 may include a first helical screw 310 arranged around the shaft 305 and a second helical screw 320 arranged around the shaft 305 adjacent to the first helical screw 310. In these embodiments, the fastener 300 may include a “dual-start” or “dual-lead” screw design with alternating standard and reverse threads. However, it will also be understood that the fastener 300 may include any screw configuration, features, or forms described or considered herein in order to achieve optimal fixation within a given bone / tissue. Figures 4A-4D show various views of the first milling tool 400 according to one embodiment of the present disclosure.

[0120] Specifically, Figure 4A is a front perspective view of the first milling tool 400, Figure 4B is a rear perspective view of the first milling tool 400, Figure 4C is a side view of the first milling tool 400, and Figure 4D is a front view of the first milling tool 400. The first milling tool 400 may include a shaft 405 having a proximal end 401, a distal end 402, and a longitudinal axis 403.

[0121] In some embodiments, the first milling tool 400 may include a first cutting head 410 comprising one or more first cutting blades 420 positioned at the distal end 402 of a shaft 405.

[0122] In some embodiments, one or more first cutting blades 420 may include at least one convex cutting surface 430.

[0123] In some embodiments, at least one convex cutting surface 430 may include a first facet 431 and a second facet 432 (see, for example, Figures 4A and 4C, as a non-limiting example).

[0124] In some embodiments, the first facet 431 and / or the second facet 432 may include one or more flat surfaces.

[0125] In some embodiments, the first facet 431 and / or the second facet 432 may include one or more curved surfaces.

[0126] In some embodiments, the first facet 431 and the second facet 432 may be angled relative to each other to form at least one convex cutting surface 430.

[0127] In some embodiments, the first facet 431 and the second facet 432 may be angled relative to each other by a first angle 441, which may be greater than 180 degrees, in order to form at least one convex cutting surface 430.

[0128] Figures 5A–5D show various views of the second milling tool 500 according to another embodiment of the present disclosure. Specifically, Figure 5A is a front perspective view of the second milling tool 500, Figure 5B is a rear perspective view of the second milling tool 500, Figure 5C is a side view of the second milling tool 500, and Figure 5D is a front view of the second milling tool 500.

[0129] The second milling tool 500 may include a shaft 505 having a proximal end 501, a distal end 502, and a longitudinal axis 503.

[0130] In some embodiments, the second milling tool 500 may include a second cutting head 510 comprising one or more second cutting blades 520 positioned at the distal end 502 of the shaft 505.

[0131] In some embodiments, one or more second cutting blades 520 may include at least one concave cutting surface 530.

[0132] In some embodiments, at least one concave cutting surface 530 may comprise a third facet 533 and a fourth facet 534 (see, for example, Figures 5A and 5C as one non-limiting example).

[0133] In some embodiments, the third facet 533 and / or the fourth facet 534 may include one or more flat surfaces.

[0134] In some embodiments, the third facet 533 and / or the fourth facet 534 may include one or more curved surfaces.

[0135] In some embodiments, the third facet 533 and the fourth facet 534 may be angled relative to each other to form at least one concave cutting surface 530.

[0136] In some embodiments, the third facet 533 and the fourth facet 534 may be angled relative to each other by a second angle 542, which may be less than 180 degrees, in order to form at least one concave cutting surface 530.

[0137] Figures 6-8 show various diagrams of the first milling tool 400 and the second milling tool 500 performing a milling operation on the fastener 100 of Figure 1A to form a first helical thread 110 and a second helical thread 120. Specifically, Figure 6 is a perspective view of the second milling tool 500 performing a milling operation on the fastener 100, Figure 7 is a side view of both the first milling tool 400 and the second milling tool 500 performing a milling operation on the fastener 100 simultaneously, and Figure 8 is a side cross-sectional view of both the first milling tool 400 and the second milling tool 500 performing a milling operation on the fastener 100 simultaneously. Figure 8 shows how the first milling tool 400 and the second milling tool 500 can be used to form a plurality of first coupling spaces 161 and a plurality of second coupling spaces 162 between the first helical thread 110 and the second helical thread 120. Various milling techniques that can be used to form the helical threads described herein will be described in more detail here with reference to Figure 9.

[0138] Figure 9 shows a diagram of a process or method 600 for creating a threaded fastener or embedded bone anchor by forming threads on a shaft or substantially cylindrical substrate (not shown), according to some embodiments of the present disclosure.

[0139] In some embodiments, method 600 may begin in step 610, in which the first cutting head of a first milling tool may be positioned at a first location along a substantially cylindrical substrate.

[0140] In some embodiments of Method 600, the second cutting head of the second milling tool may, instead or in addition, be positioned in a second position along a substantially cylindrical substrate at the same time (or at another time) as the first cutting head is positioned in a first position in step 620. However, it will also be understood that in some embodiments, any number of cutting heads / milling tools may be used to form any number of helical threads around a substantially cylindrical substrate (as described above), either sequentially or simultaneously.

[0141] In some embodiments, the first cutting head may be positioned adjacent to the second cutting head along the side surface of a substantially cylindrical substrate.

[0142] In some embodiments, the first longitudinal axis of the first milling tool may be positioned substantially parallel to the second longitudinal axis of the second milling tool.

[0143] In some embodiments, the first cutting head may be spaced apart from the second cutting head along a substantially cylindrical substrate.

[0144] In some embodiments, the first cutting head may be positioned opposite the second cutting head along the opposing sides of a substantially cylindrical substrate.

[0145] In some embodiments, the first cutting head may be positioned on a first side of a substantially cylindrical substrate, and the second cutting head may be positioned on a second side of a substantially cylindrical substrate.

[0146] In some embodiments, the first cutting head can be separated from the second cutting head by an arbitrarily selected angle of rotation around the third longitudinal axis of a substantially cylindrical substrate.

[0147] In some embodiments, the first cutting head and the second cutting head may be positioned on opposing sides of a substantially cylindrical substrate and / or separated from each other by a rotation of about 180 degrees with respect to a third longitudinal axis of the substantially cylindrical substrate.

[0148] Once the first milling tool and / or the second milling tool are positioned along a substantially cylindrical substrate, the method 600 may proceed to one or more of steps 630, 640, and / or 650, wherein the first cutting head may be rotated around the first longitudinal axis of the first milling tool, the second cutting head may be rotated around the second longitudinal axis of the second milling tool, and the substantially cylindrical substrate may be rotated around the third longitudinal axis of the substantially cylindrical substrate.

[0149] As the first milling tool, the second milling tool, and the substantially cylindrical substrate all rotate around their respective axes, method 600 proceeds to step 660, in which the first and / or second cutting heads may be translated along the length of the substantially cylindrical substrate. Alternatively, or in addition to the above, the substantially cylindrical substrate may be translated relative to the first and / or second cutting heads.

[0150] When the first milling tool, the second milling tool, and / or a substantially cylindrical substrate are translated relative to each other during rotation, the cutting heads of the first and second milling tools may, in step 670, form a first helical thread on the substantially cylindrical substrate, and / or, in step 680, form a second helical thread on the substantially cylindrical substrate.

[0151] Method 600 can be completed when a plurality of desired helical threads are formed on a substantially cylindrical substrate.

[0152] Any procedure / method disclosed herein includes one or more steps or actions for performing the described method. The steps and / or actions of a method may be interchangeable with one another. In other words, the order and / or use of any particular steps and / or actions may be changed unless a particular order of steps or actions is required for the proper operation of the embodiment.

[0153] Any of the fasteners described herein may be configured to be removed and replaced during a change of procedure by simply loosening a screw and removing the fastener from the bone / tissue in which the fastener resides. Furthermore, the fasteners described herein may be advantageously removed from the bone during the removal process without removing any visible amount of bone, thus preserving bone. In this way, to provide an immediate and removable connection between the implant and the bone, the implant may be mechanically integrated with the bone, rather than being bonded to the bone or integrated through internal bone growth. Therefore, changes of procedure utilizing the fasteners described herein may result in less bone trauma and improved patient treatment outcomes.

[0154] Throughout this specification, any reference to “embodiments” or “their embodiments” means that certain features, structures, or characteristics described in relation to those embodiments are included in at least one embodiment. Therefore, not all terms or variations thereof quoted throughout this specification necessarily refer to the same embodiments.

[0155] Similarly, in the description of the embodiments above, it should be understood that, for the purpose of streamlining the disclosure, various features are often grouped together in a single embodiment, figure, or description thereof. However, this method of disclosure should not be interpreted as reflecting an intention that any embodiment requires more features than those explicitly enumerated in that embodiment. Rather, aspects of the invention lie in combinations of fewer features than all of the features of the single embodiments disclosed above.

[0156] The use of the term “first” in relation to a structure or element does not necessarily imply the existence of a second or additional such structure or element. Elements described in means-plus-function form are intended to be interpreted in accordance with § 112(f) of the U.S. Patent Act.

[0157] It will be apparent to those skilled in the art that modifications to the details of the embodiments described above can be made without departing from the fundamental principles described herein.

[0158] The terms “connected,” “joined,” and “communicating” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interactions. Two components may be functionally joined to each other even if they are not in direct contact with each other. The term “joined” may include components joined to each other by integral formation, as well as components joined to each other in a removable and / or non-removable manner. The term “contacting” refers to items that may be in direct physical contact with each other, even if they are not necessarily mounted together. The term “fluidally connected” refers to two or more structures connected such that fluid can move from one structure to another. Furthermore, as defined herein, the term “substantially” means within ±20% of a target value, measurement, or desired characteristic.

[0159] While specific embodiments and uses of this disclosure have been illustrated and described, it should be understood that the scope of this disclosure is not limited to the exact configurations and components disclosed herein. Various modifications, changes, and variations that will be apparent to those skilled in the art may be made to the arrangement, operation, and details of the devices, systems, and methods disclosed herein.

Claims

1. An implantable bone anchor, wherein the implantable bone anchor is A shaft, wherein the shaft is The proximal end and The distal end and The shaft includes a longitudinal axis, A first helical screw is arranged around the shaft along the longitudinal axis between the proximal and distal ends of the shaft, wherein the first helical screw is The first undercut surface, The second undercut surface, The third undercut surface, The first helical screw includes a fourth open surface, A second helical screw, positioned adjacent to the first helical screw and around the shaft, wherein the second helical screw is The fifth undercut surface, The sixth undercut surface, The seventh undercut surface, The second helical screw includes an eighth open surface, The first undercut surface, the third undercut surface, the sixth undercut surface, and the eighth open surface are angled toward the distal end of the shaft. An implantable bone anchor characterized in that the second undercut surface, the fourth open surface, the fifth undercut surface, and the seventh undercut surface are angled toward the proximal end of the shaft.

2. An implantable bone anchor according to claim 1, When the implantable bone anchor is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, The first helical screw includes at least one chevron shape oriented toward the distal end of the shaft, An implantable bone anchor characterized in that the second helical thread includes at least one chevron shape oriented toward the proximal end of the shaft.

3. An implantable bone anchor according to claim 2, The first helical thread includes a first plurality of chevron shapes oriented toward the distal end of the shaft, An implantable bone anchor characterized in that the second helical thread includes a second plurality of chevron shapes oriented toward the proximal end of the shaft.

4. An implantable bone anchor according to claim 3, characterized in that the first plurality of chevron shapes and the second plurality of chevron shapes are arranged alternately and continuously along the shaft of the implantable bone anchor.

5. An implantable bone anchor according to claim 1, When the implantable bone anchor is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, The first helical screw includes at least one partial crescent shape oriented toward the distal end of the shaft, An implantable bone anchor characterized in that the second helical thread includes at least one partial crescent shape oriented toward the proximal end of the shaft.

6. An implantable bone anchor according to claim 5, The first helical screw includes a first plurality of partial crescent shapes oriented toward the distal end of the shaft, An implantable bone anchor characterized in that the second helical thread includes a second plurality of partial crescent shapes oriented toward the proximal end of the shaft.

7. An implantable bone anchor according to claim 6, characterized in that the first plurality of partial crescent shapes and the second plurality of partial crescent shapes are arranged alternately and continuously along the shaft of the implantable bone anchor.

8. A fastener, wherein the fastener is A shaft, wherein the shaft is The proximal end and The distal end and The shaft includes a longitudinal axis, A plurality of helical screws are arranged around the shaft between the proximal and distal ends of the shaft, along the longitudinal axis, wherein the plurality of helical screws are A first helical screw, wherein the first helical screw is A first concave undercut surface, The first helical screw includes a first convex undercut surface, A second helical screw, wherein the second helical screw is A second concave undercut surface and The second helical screw includes a second convex undercut surface, The first concave undercut surface and the second convex undercut surface are oriented toward the proximal end of the shaft. A fastener characterized in that the first convex undercut surface and the second concave undercut surface include a plurality of helical screws oriented toward the distal end of the shaft.

9. A fastener according to claim 8, characterized in that the plurality of helical screws include three helical screws.

10. A fastener according to claim 8, characterized in that the plurality of helical screws include four helical screws.

11. A fastener according to claim 8, characterized in that the plurality of helical screws include more than four helical screws.

12. A fastener according to claim 8, characterized in that at least one of the first concave undercut surface, the first convex undercut surface, the second concave undercut surface, and the second convex undercut surface includes at least one substantially flat surface.

13. A fastener according to claim 8, characterized in that at least one of the first concave undercut surface, the first convex undercut surface, the second concave undercut surface, and the second convex undercut surface includes at least one curved surface.

14. A fastener according to claim 8, When the fastener is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, The first helical screw includes a first bent shape having a first intermediate portion oriented toward the distal end of the shaft, The fastener is characterized in that the second helical screw includes a second bent shape having a second intermediate portion oriented toward the proximal end of the shaft.

15. A fastener according to claim 8, When the fastener is viewed in cross-section along a plane intersecting the longitudinal axis of the shaft, The first bonding space is formed between the first concave undercut surface and the second concave undercut surface. A second bonding space is formed between the first convex undercut surface and the second convex undercut surface. Each of the first and second connection spaces is configured to receive bone tissue therein. A fastener characterized in that each of the first bonding space and the second bonding space is shaped to bond with the bone tissue in order to strengthen the fixation of the fastener within the bone tissue.

16. A fastener according to claim 15, characterized in that the first bonding space is larger in size than the second bonding space.

17. An implantable bone anchor, wherein the implantable bone anchor is A shaft, wherein the shaft is The proximal end and The distal end and The shaft includes a longitudinal axis, A first helical screw is arranged around the shaft between the proximal and distal ends of the shaft, along the longitudinal axis, wherein the first helical screw is A first proximal-facing surface facing the aforementioned proximal end, The first helical screw includes a first distally oriented surface facing the distal end, A second helical screw is arranged around the shaft adjacent to the first helical screw, wherein the second helical screw is A second proximal-facing surface facing the aforementioned proximal end, The second helical screw includes a second distally oriented surface facing the distal end, The first proximal-oriented plane and the first distal-oriented plane intersect an arbitrary plane perpendicular to the longitudinal axis and do not have mirror symmetry with respect to each other. An implantable bone anchor characterized in that the first proximal-oriented surface and the second distal-oriented surface intersect a first plane perpendicular to the longitudinal axis and have mirror symmetry with respect to each other.

18. An implantable bone anchor according to claim 17, The first proximal-facing surface is generally concave, An implantable bone anchor characterized in that the second distally oriented surface is generally convex.

19. An implantable bone anchor according to claim 18, The second proximal-facing surface is generally convex, An implantable bone anchor characterized in that the first distally oriented surface is generally concave.

20. An implantable bone anchor according to claim 17, The second proximal-oriented plane and the second distal-oriented plane intersect an arbitrary plane perpendicular to the longitudinal axis and do not have mirror symmetry with respect to each other. An implantable bone anchor characterized in that the second proximal-oriented surface and the first distal-oriented surface intersect a second plane perpendicular to the longitudinal axis and have mirror symmetry with respect to each other.

21. A method for forming a fastener, wherein the method is A step of positioning the first cutting head of a first milling tool at a first position along a substantially cylindrical base material having a proximal end and a distal end, The process involves positioning the second cutting head of the second milling tool at a second position along the substantially cylindrical base material, A step of rotating the first cutting head around the first longitudinal axis of the first milling tool, A step of rotating the second cutting head around the second longitudinal axis of the second milling tool, A step of rotating the substantially cylindrical substrate about a third longitudinal axis of the substantially cylindrical substrate, The process includes translating the first and second cutting heads along at least a portion of the length of the substantially cylindrical base material, A first concave undercut surface oriented toward the proximal end, A first convex undercut surface oriented toward the distal end, The second concave undercut surface oriented toward the distal end, A second convex undercut surface oriented toward the proximal end, A method characterized by forming

22. The method according to claim 21, wherein the step of translating the first and second cutting heads along at least a portion of the length of the substantially cylindrical base material is: A first helical screw, wherein the first helical screw is A first concave undercut surface, The first helical screw includes a first convex undercut surface, A second helical screw, wherein the second helical screw is A second concave undercut surface, A method for forming a second helical screw, which includes a second convex undercut surface.

23. The method according to claim 21, A method comprising the step of positioning the first cutting head adjacent to the second cutting head along the side of the substantially cylindrical base material, wherein the first longitudinal axis of the first milling tool is substantially parallel to the second longitudinal axis of the second milling tool.

24. The method according to claim 21, The first cutting head includes at least one convex cutting surface, The method is characterized in that the second cutting head includes at least one concave cutting surface.

25. The method according to claim 24, The at least one convex cutting surface is The first facet, Including the second facet, The at least one concave cutting surface is The third facet, Including the fourth facet, The first facet and the second facet are angled relative to each other at a first angle greater than 180 degrees to form the at least one convex cutting surface. The method is characterized in that the third facet and the fourth facet are angled relative to each other at a second angle of less than 180 degrees to form the at least one concave cutting surface.

26. The method according to claim 21, The steps include: positioning the first cutting head on the first side of the substantially cylindrical base material; The step includes arranging the second cutting head on the second side of the substantially cylindrical base material, A method characterized in that the first cutting head and the second cutting head are separated by a selected degree of rotation around a third longitudinal axis of the substantially cylindrical base material.

27. A method according to claim 26, characterized by comprising the step of positioning the first cutting head opposite the second cutting head along the opposing side of the substantially cylindrical base material.

28. A method according to claim 27, characterized in that the first cutting head and the second cutting head are separated by a 180-degree rotation around the third longitudinal axis of the substantially cylindrical base material.

29. A step of positioning the first cutting head of a first milling tool at a first position along the shaft of a fastener having a proximal end and a distal end, A step of positioning the second cutting head of the second mill tool at a second position along the shaft, A step of rotating the first cutting head of the first milling tool around the first longitudinal axis, A step of rotating the second cutting head of the second milling tool around the second longitudinal axis, The process of rotating the shaft around the third longitudinal axis of the shaft, The process includes translating the first and second cutting heads along at least a portion of the length of the shaft, A first concave undercut surface oriented toward the proximal end, A first convex undercut surface oriented toward the distal end, The second concave undercut surface oriented toward the distal end, A fastener characterized by being formed by a method of forming a second convex undercut surface oriented toward the proximal end.

30. The fastener according to claim 29, wherein the step of translating the first and second cutting heads along at least a portion of the length of the shaft is: A first helical screw, wherein the first helical screw is The first concave undercut surface, The first helical screw includes the first convex undercut surface, A second helical screw, wherein the second helical screw is The second concave undercut surface, A fastener characterized by forming the second convex undercut surface and the second helical screw including the second convex undercut surface.

31. The fastener according to claim 29, wherein the method further comprises: A fastener comprising the step of positioning the first cutting head along the side of the shaft adjacent to the second cutting head, wherein the first longitudinal axis of the first milling tool is substantially parallel to the second longitudinal axis of the second milling tool.

32. A fastener according to claim 29, The first cutting head includes at least one convex cutting surface, The fastener is characterized in that the second cutting head includes at least one concave cutting surface.

33. A fastener according to claim 32, The at least one convex cutting surface is The first facet, Including the second facet, The at least one concave cutting surface is The third facet, Including the fourth facet, The first facet and the second facet are angled relative to each other at a first angle greater than 180 degrees, forming the at least one convex cutting surface. The fastener is characterized in that the third facet and the fourth facet are angled relative to each other at a second angle of less than 180 degrees, thereby forming the at least one concave cut surface.

34. The fastener according to claim 29, wherein the method further comprises: The steps include: positioning the first cutting head on the first side of the shaft; The process includes the step of positioning the second cutting head on the second side of the shaft, A fastener characterized in that the first cutting head and the second cutting head are separated by a selected degree of rotation around the third longitudinal axis of the shaft.

35. The steps include positioning the first cutting head of a first milling tool at a first position along the shaft of an implantable bone anchor having a proximal end and a distal end, The process involves positioning the second cutting head of the second milling tool at a second position along the shaft, A step of rotating the first cutting head around the first longitudinal axis of the first milling tool, A step of rotating the second cutting head around the second longitudinal axis of the second milling tool, A step of rotating the shaft around a third longitudinal axis of the shaft, The process includes translating the first and second cutting heads along at least a portion of the length of the shaft, A first proximal-facing surface facing the proximal end of the shaft, A first distally oriented surface facing the distal end of the shaft, A second proximal-facing surface facing the proximal end of the shaft, An implantable bone anchor characterized by being formed by a method of forming a second distally oriented surface facing the distal end of the shaft.

36. The implantable bone anchor according to claim 35, wherein the step of translating the first and second cutting heads along at least a portion of the length of the shaft is: A first helical screw, wherein the first helical screw is A first proximal-oriented surface facing the proximal end of the shaft, The first helical screw includes a first distally oriented surface facing the distal end of the shaft, A second helical screw, wherein the second helical screw is A second proximal-oriented surface facing the proximal end of the shaft, The second helical thread includes a second distally oriented surface facing the distal end of the shaft, The first proximal-oriented surface and the first distal-oriented surface intersect with any plane perpendicular to the third longitudinal axis of the shaft and do not have mirror symmetry with respect to each other. An implantable bone anchor characterized in that the first proximal-oriented surface and the second distal-oriented surface intersect a first plane perpendicular to the third longitudinal axis of the shaft and have mirror symmetry with respect to each other.

37. An implantable bone anchor according to claim 35, wherein the method further comprises: An embeddable bone anchor comprising the step of positioning the first cutting head along the side of the shaft adjacent to the second cutting head, wherein the first longitudinal axis of the first milling tool is substantially parallel to the second longitudinal axis of the second milling tool.

38. An implantable bone anchor according to claim 35, The first cutting head includes at least one convex cutting surface, The implantable bone anchor is characterized in that the second cutting head includes at least one concave cutting surface.

39. An implantable bone anchor according to claim 38, The at least one convex cutting surface is The first facet, Including the second facet, The at least one concave cutting surface is The third facet, Including the fourth facet, The first facet and the second facet are angled relative to each other at a first angle greater than 180 degrees, forming the at least one convex cutting surface. An implantable bone anchor characterized in that the third facet and the fourth facet are angled relative to each other at a second angle of less than 180 degrees, forming the at least one concave cutting surface.

40. An implantable bone anchor according to claim 35, wherein the method further comprises: The steps include: positioning the first cutting head on the first side of the shaft; The process includes the step of positioning the second cutting head on the second side of the shaft, An implantable bone anchor characterized in that the first cutting head and the second cutting head are separated by a selected degree of rotation around the third longitudinal axis of the shaft.

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