A BI-stage expandable bone fastener

Abstract

The invention relates to a bi-stage expandable bone fastener. The bone fastener includes an expandable outer region and a cannulated threaded bolt. The expandable outer region includes a circular disc and a plurality of surfaces conjoined via a plurality of living hinges forming a hollow cylindrical structure. The surfaces are mounted on the circular disc such that one of the surface is rigidly attached to the circular disc. The expandable outer region is operably coupled to a centrally cannulated threaded bolt. The cannulated threaded bolt has a first threaded region proximal to a first end and a second threaded region proximal to a second end. A first conical projection and a second conical projection are mounted on the cannulated threaded bolt. A hammering head is provided with a detachable screw driver for enabling bi-stage expansion of the bone fastener due to a bi-directional movement of the first conical projection and the second conical projection.

Description

[0001] A BI-STAGE EXPANDABLE BONE FASTENER

[0002] FIELD OF THE INVENTION

[0003] The invention generally relates to an apparatus to facilitate arthroscopic surgery. In particular, the invention relates to a bi-stage expandable bone fastener.

[0004] BACKGROUND OF THE INVENTION

[0005] An interference screw is a widely used tendon-to-bone fixation device. The device relies on the screw threads to engage and compress the graft for fixation. The interference screw is most commonly used in Anterior Cruciate Ligament reconstruction. However, the bone-to-tendon fixation has been challenging for the orthopaedic surgeons. The nature of the bone with weak cancellous and hard cortical bone consistency makes it very difficult to achieve the required interference forces to hold the tendon and bone together during the healing period. The loss of tension happens mostly in the cancellous weak bone leading to failure and non-healing of the ligament-to-bone fixation. Thus, results in multiple failures of the fixation method. There is a need for a screw that allows fixation that is adaptable for different types of bone tissues.

[0006] One such expandable fixation assembly is disclosed in the Indian patent application 9979 / CHENP / 2011, titled “expandable fixation assemblies”, that provides a screw that can expand to ensure better bone engagement. However, a disadvantage of the assembly disclosed, is that the screw is expandable at only one end and hence adaptable for only one kind of bone tissue.

[0007] Another non patent document titled “Biomechanics of single-tunnel doublebundle anterior cruciate ligament reconstruction using fixation with a unique expandable interference screw”, by Hua-yang Huang et al, discloses an expandable interference screw that secures the graft and properly positions the two bundles of the graft when used for single-tunnel double-bundle reconstruction of the ACL. However, the document is silent on asynchronous or asymmetric expansion of the interference screw.

[0008] Another non-patent literature titled “Design and Development of a Novel Expanding Pedicle Screw for Use in the Osteoporotic Lumbar Spine”, by Parham Rasoulinejad, discloses helix expandable screw that is capable of changing the shape of the screw at the site. Another design of an expandable titanium interference screw is capable of bone-tendon attachment by ensuring perfect surface contact as long as the length of the screw. However, the prior art cited above does not focus on selective asynchronous expansion capable of expanding more in week cancellous bones and less in hard cortical bone to deliver steady force in holding the tendon-to-bone.

[0009] Therefore, there is a need in the art for an expandable interference screw capable of delivering uniform consistent forces to hold the tendon and the bone together, preventing the failure of the fixation.

[0010] SUMMARY

[0011] One aspect of the invention discloses a bi-stage expandable bone fastener. The bone fastener includes an expandable outer region and a cannulated threaded bolt. The expandable outer region comprising of a circular disc having an orifice, a plurality of surfaces conjoined to form a hollow cylindrical structure on the circular disc. The plurality of surfaces has a flat end and a projected end conjoined via a plurality of living hinges. The living hinges flexes during the expansion of the bone fastener. The plurality of surfaces are mounted on the circular disc such that one of the surface is rigidly attached to the circular disc. Each of the surfaces has an external region and an internal region. The external region is provided with ridges having at least two distinct sections of variable thickness. The internal region is provided with two expandable ramps of variable depth each corresponding to the section having variable thickness, on the external region. The expandable outer region is operably coupled to a centrally cannulated threaded bolt, positioned parallelly to the expandable outer region. The cannulated threaded bolt is provided with a first threaded region proximal to a first end and a second threaded region proximal to a second end. The second end is provided with a groove. A first conical projection and a second conical projection is mounted on the cannulated threaded bolt. A hammering head is provided with a detachable screw driver for enabling bi-stage expansion of the bone fastener due to a bidirectional movement of the first conical projection and second conical projection.

[0012] BRIEF DESCRIPTION OF DRAWINGS

[0013] So that the manner in which the recited features of the invention can be understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0014] FIG. 1 shows a cross sectional view of the bi-stage expandable bone fastener, according to an embodiment of the invention.

[0015] FIG. 2a shows an expandable outer region of the bone fastener during expanded state, according to an embodiment of the invention.

[0016] FIG. 2b shows a cannulated threaded bolt of the bone fastener, according to an embodiment of the invention.

[0017] FIG. 3a shows a perspective view from the closed end of the expandable outer region, according to an embodiment of the invention.

[0018] FIG. 3b shows a perspective view of the bi-stage expandable bone fastener, according to an embodiment of the invention

[0019] FIG. 4a shows a front view of unexpanded state of the bi-stage expandable bone fastener, according to an embodiment of the invention. FIG. 4b shows a front view of axial symmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention.

[0020] FIG. 4c shows a front view of axial asymmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention.

[0021] FIG. 5a shows a side view of unexpanded state of the bi-stage expandable bone fastener, according to an embodiment of the invention.

[0022] FIG. 5b shows a side view of axial symmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention.

[0023] FIG. 5c shows a side view of axial asymmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention.

[0024] DETALED DESCRIPTION OF THE INVENTION

[0025] The definitions, terms and terminology adopted in the disclosure have their usual meaning and interpretations, unless otherwise specified.

[0026] The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms a, an, etc. does not denote a limitation of quantity, but rather denotes the presence of at least one of the referenced items. It will be further understood that the terms “comprises” and / or “comprising,” or “includes” and / or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof. It will be further understood that for the purposes of this disclosure, “at least one of” will be interpreted to mean any combination of the enumerated elements following the respective language, including combination of multiples of the enumerated elements. Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals are understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.

[0027] Various embodiment of the invention discloses a bi-stage expandable bone fastener. The bi-stage expandable bone fastener is capable of undergoing symmetric and asymmetric expansion after insertion of the bone fastener into a region of interest while repairing a damaged bone during an arthroscopic surgery. Mostly during bone fracture, bone reconstruction, fixation of bone-to-bone, bone-to-tendon fixation. A tunnel is drilled at the site of repair before inserting the bone fastener. The expandable bone fastener delivers uniform consistent forces within the bones. The bone fastener is capable of expanding more in weak cancellous bones and less in hard cortical bone to deliver steady force in holding the tendon-to-bone, or bone-to-bone.

[0028] FIG. 1 shows the cross sectional-view of a bi-stage expandable bone fastener, according to an embodiment of the invention. The bone fastener (100) includes an expandable outer region (1) and a cannulated threaded bolt (3). The expandable outer region (1) comprising of a circular disc (8), a plurality of surfaces (2) conjoined to form a hollow cylindrical structure on the circular disc (8). The plurality of surfaces (2) having a flat end (1a) and a projected end (1b) are conjoined via a plurality of living hinges (not shown). Each of the surfaces (2) has an external region (2a) and an internal region (2b). The external region (2a) is provided with ridges having at least two pre-determined sections of variable thickness. The ridges of variable thickness include a first ridge (4a) and a plurality of second ridges (4b). The predetermined section for the first ridge (4a) and the plurality of second ridge (4b) allows ingrowth of bones by adhering to the expandable bone fastener. The internal region (2b) is provided with at least two opposingly positioned expandable ramps, a first expandable ramp (5a) and a second expandable ramp (5b) corresponding to the pre-determined sections of the external region (2a). The expandable outer region (1) is operably coupled to a centrally cannulated threaded bolt (3), positioned parallel to the expandable outer region (1). The cannulated threaded bolt (3) has a first end (3a) and a second end (3b). The first end (3a) complimentary fits with the flat end (1a) of the surfaces (2) of the expandable outer region (1). The second end (3b) complimentary fits with the projected end (1a) of the surfaces (2) of the expandable outer region (1). The cannulated threaded bolt (3) is provided with a plurality of conical projections. A first conical projection (9a) corresponds to the first expandable ramp (5a) and a second conical projection (9b) corresponds to the second expandable ramp (5b) of the internal region (2b). The predetermined section for the first ridge (4a) of a particular thickness enables accommodation of the first conical projection (9a) by means of the first expandable ramp (5a). The first conical projection (9a) and second conical projection (9b) are configured to move within the expandable outer region (1) to enable expansion of the bone fastener. The movement of the first conical projection (9a) and the second conical projection (9b) is enabled by the first expandable ramp (5a) and the second expandable ramp (5b) respectively. The first expandable ramp (5a) acts as a guide rail for movement of the first conical projection (9a) within the cannulated threaded bolts (3). The second expandable ramp (5b) acts as a guide rail for movement of the second conical projection (9b) within the cannulated threaded bolts (3). The second expandable ramp (5b) is slightly shorter to accommodate movement of the second conical projection (9b) during a first stage of expansion. The first stage of expansion allows axial symmetric expansion of the bi-stage expandable bone fastener. The first expandable ramp (5a) is slightly longer to accommodate movement of the first conical projection (9a) during the first stage of expansion as well as during a second stage of expansion. The second stage of expansion allows axial asymmetric expansion of the bi-stage expandable bone fastener. Each of the first conical projection (9a) and the second conical projection (9b) is capable of being operated in multiple modes. The multiple modes include clockwise mode, anticlockwise mode or a combination thereof. The first conical projection (9a) and the second conical projection (9b) subjects the cannulated threaded bolt (3) to undergo two distinct operations, each configured for a specific section of the bone. The specific section of the bone includes cortical bone and cancellous bone.

[0029] FIG. 2a shows the expandable outer region of the bone fastener during expanded state, according to an embodiment of the invention. The expandable outer region (1) comprises a circular disc (not shown) and a plurality of surfaces (2) conjoined via a plurality of living hinges (6) forming the hollow cylindrical structure. The living hinge (6) flexes during the expansion of the bone fastener. The plurality of surfaces (2) forming the expandable outer region (1) are mounted on the circular disc (not shown) such that one of the surface (2) is rigidly attached to the circular disc (not shown). The external region (2a) is provided with ridges having at least two pre-determined sections of variable thickness. The ridges of variable thickness include the first ridge (4a) and the plurality of second ridges (4b).

[0030] FIG. 2b shows the cannulated threaded bolt of the bone fastener, according to an embodiment of the invention. The cannulated threaded bolt (3) is provided with a first threaded region (11a) for movement of the first conical projection (9a) and a second threaded region (11b) for movement of the second conical projection (9b). The first threaded region (11a) is proximal to the first end (3a) of the cannulated threaded bolt (3) and the second threaded region (11b) is proximal to the second end (3b) of the cannulated threaded bolt (3). The movement of the first conical projection (9a) and the second conical projection (9b) around the first threaded region (11a) and the second threaded region (11b) respectively renders the expansion of the bone fastener. In one example, length of the first threaded region (11a) is longer than the length of the second threaded region (11b). The difference in the length of the first threaded region (11a) and the second threaded region (11b) enables bi-stage expansion of the bone fastener. The first conical projection (9a) and the second conical projection (9b) are opposingly threaded, rendering bi-directional movement of the first conical projection (9a) and the second conical projection (9b) on the cannulated threaded bolt (3). In one example, a pitch of first threaded region (11a) and the second threaded region (11b) are different. In another example of the invention, the axis and the pitch of the first threaded region (11a) and the second threaded region (11b) may vary to enable bidirectional expansion. In yet another example, the first conical projection (9a) is left threaded and the second conical projection (9b) is right threaded rendering bi-directional movement of the conical projections (9a and 9b), pushing the expandable outer region (not shown) outwards against a specific section of the bone. The specific sections of the bone are cortical bone and cancellous bone.

[0031] The invention further includes a hammering head provided with a detachable screw driver that complimentary fits into the slotted grooves (10) of the projected end (1b) of the expandable outer region (1) and the groove (7) of the cannulated threaded bolt (3). The operation of the screw driver enables engaging of the bone fastener in a bi-stage manner rendered by the bi-directional movement of the first conical projection (9a) and the second conical projection (9b).

[0032] FIG. 3a shows the perspective view of the expandable outer region of the bone fastener, according to an embodiment of the invention. The expandable outer region (1) is provided with the circular disc (8) having an orifice (12).

[0033] The orifice (12) enables passage of the guide wire within the cannulated threaded bolt (not shown) while positioning of the bone fastener. The plurality of surfaces (2) forming the expandable outer region (1) are mounted on the circular disc (8) such that one of the surface (2) is rigidly attached to the circular disc (8). The external region (2a) is provided with the plurality of ridges, the first ridge (4a) and the plurality of second ridge (4b) having at least two pre-determined sections of variable thickness. Once the bone fastener is positioned, the screw driver allows fastening of the bone fastener for bi-stage expansion. The bone fastener enables ingrowth of the bone once fixed at the region of repair.

[0034] FIG. 3b shows the perspective view of the bi-stage expandable bone fastener, according to an embodiment of the invention. The bi-stage expandable bone fastener includes the expandable outer region (1) and the cannulated threaded bolt (3). The expandable outer region (1) is formed by plurality of surfaces (2) having the flat end (1a) (not shown) and the projected end (1b) conjoined via plurality of living hinges (6) forming the hollow cylindrical structure. The external region (2a) of the plurality of surfaces (2) is provided with the first ridge (4a) and the plurality of second ridge (4b). The expandable outer region (1) is operably coupled to the cannulated threaded bolt (3). The cannulated threaded bolt (3) is positioned parallel to the expandable outer region (1). The projected end (1b) of the expandable outer region (1) is provided with a slotted groove (10). The projected end (1b) of the expandable outer region (1) aligns with the second end (3b) of the cannulated threaded bolt (3). The second end (3b) of the cannulated threaded bolt (3) is provided with a groove (7). The slotted groove (10) of the expandable outer region (1) and the groove (7) of the cannulated threaded bolt (3) have a complimentary fit with the detachable screw driver of the hammering head. The cannulated threaded bolt (3) accommodates a guide wire for visualization of the site of repair while inserting the bone fastener.

[0035] The movement of the screw driver enables engaging of the bone fastener in a bi-stage manner until the desired forces of torque is reached between the bone and the ligament for holding them together till the healing process is completed.

[0036] FIG. 4a shows the front view of unexpanded state of the bi-stage expandable bone fastener, according to an embodiment of the invention. The bone fastener in an unexpanded state, before being hammered and screwed inside the bone is depicted in the FIG. 4a.

[0037] FIG. 4b shows the front view of axial symmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention. The symmetric expansion of the bone fastener is represented in FIG. 4b. When the screw driver (not shown) drives the bone fastener inside the bone, the first conical projection (9a and second conical projection (9b) both undergo at least one movement within the expandable ramps (not shown) to enable axial symmetric expansion. The region of the bone fastener housing the first conical projection (9a) is close to the cancellous bone and the region of the bone fastener housing the second conical projection (9b) is close to the cortical bone. The symmetric expansion of the bone fastener in the cortical and cancellous bone is observed.

[0038] FIG. 4c shows the front view of axial asymmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention. The asymmetric expansion of the bone fastener is represented in FIG. 4c. When the bone fastener (not shown) is further driven after axial symmetric expansion (as shown in fig 4b), by the screw driver (not shown), the regions close to the cancellous bone expands more compared to the cortical bone. The expansion is rendered by the movement of the first conical projection (9a). The first expandable ramp (not shown) corresponding to the first conical projection (9a) is bigger than the second expandable ramp (not shown) corresponding to the second conical projection (9b), thereby, promoting asymmetric or asynchronous expansion. The asymmetric expansion of the bi-stage expandable bone fastener in the cortical and cancellous bone is observed.

[0039] FIG. 5a shows the side view of unexpanded state of the bi-stage expandable bone fastener, according to an embodiment of the invention. The bone fastener in an unexpanded state, before being hammered and screwed inside the bone is observed. The living hinge (6) is found to be in close proximity to each face of the expandable outer region (1).

[0040] FIG. 5b shows the side view of axial symmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention. The bone fastener during axial symmetric expansion is observed. The axial symmetric expansion is a first stage of expansion of the bi-stage expandable bone fastener. The living hinge (6) is found to be slightly flexed during symmetric expansion. The projected end (1b) of the expandable outer region (1) and the region proximal to the circular disc (8) of the expandable outer region (1) is partially expanded. The symmetric expansion allows expansion of the bone fastener equally on either ends.

[0041] FIG. 5c shows the side view of axial asymmetric expansion of the bi-stage expandable bone fastener, according to an embodiment of the invention. The bone fastener during axial asymmetric expansion is observed. The axial asymmetric expansion is a second stage of expansion of the bi-stage expandable bone fastener. The living hinge (6) is found to be completely flexed during the asymmetric expansion. The asymmetric expansion allows expansion of the bone fastener asymmetrically. The projected end (1b) of the expandable outer region (1) is partially expanded while the region proximal to the circular disc (8) of the expandable outer region (1) is fully expanded.

[0042] In one example, the bi-stage expandable bone fastener is used during Anterior Cruciate Ligament reconstruction. The repair involves identifying a damaged ligament. A small incision is made to insert an arthroscope. A tunnel is drilled in the femoral bone and tibia using a guide wire. A bone tendon bone graft or a hamstring graft consisting of tendon and bony attachment is inserted into the tunnel. The graft is secured using the bone fastener. The screw driver drives the bone fastener within the tunnel compressing the graft against the tunnel.

[0043] The first conical projection (9a) and the second conical projection (9b) move along the first expandable ramp (5a) and second expandable ramp (5b) respectively to enable bi-stage expansion of the bone fastener. The bone fastener is expanded more towards the weaker bone to enable better support and adherence. The bone fastener expands a little less at the rigid bone region. Once the bi-stage expansion is completed, the screw driver is retracted and removed from the damaged region. The incision on the skin is sutured.

[0044] The bi-stage expandable bone fastener is made of a non-radiopaque material. The material is expandable to allow flexibility to the living hinge. The size of the bi-stage expandable bone fastener varies based on the region the bone fastener is inserted to accommodate graft or sutures from size 1 to size 12. The bone fastener is rendered for a single usage. The bi- stage expandable bone fastener described herein is operable either manually or through robotics.

[0045] The invention thus provides a bi-stage expandable bone fastener. The bone fastener expands in both symmetric and asymmetric or asynchronous manner. The asynchronous manner of expansion renders expansion of the bone fastener more in the cancellous bone and less in the hard cortical bone. The bone fastener is expanded till the desired tension is reached between the bone and the ligament for holding the both together till the healing process is completed. The expansion leads to equal distribution of the forces and less graft failure. The bone fastener delivers uniform consistent forces to hold the graft to the bone, preventing the loosening of the graft before healing.

[0046] The bi-stage expansion mechanism will be a predecessor for robotic surgical screw in determining the fixation by achieving set torque forces for optimal healing.

[0047] The invention finds application in fixation of Anterior and Posterior cruciate ligament reconstruction as well as ligament repairs and reconstructions. The principle can be used to develop suture anchors for the humerus, talus and various other weaker bones where the need for bigger size of the anchor dimensions are required. The bone fastener is used for fixations such as bone to bone, ligament to bone, soft tissue or bony repair procedures.

[0048] The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the scope and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims

WE CLAIM:

1. A bi-stage expandable bone fastener, the fastener comprising of: an expandable outer region (1) comprising of a circular disc (8), a plurality of surfaces (2) conjoined to form a hollow cylindrical structure on the circular disc (8), each of the surface having an external region (2a), the external region (2a) provided with a plurality of ridges having at least two distinct sections of variable thickness, and an internal region (2b), the internal region (2b) having a first expandable ramp (5a) and a second expandable ramp (5b) opposingly positioned with respect to the first expandable ramp; and a centrally cannulated threaded bolt (3) provide with a first threaded region (11a) proximal to a first end (3a) and a second threaded region (11b) proximal to a second end (3b), a first conical projection (9a) corresponding to the first expandable ramp (5a) and a second conical projection (9b) corresponding to the second expandable ramp (5b), mounted on the cannulated threaded bolt (3), wherein the bi-stage expansion of the bone fastener is rendered due to the differential movement of the first conical projection (9a) and the second conical projection (9b) within the first expandable ramp (5a) and the second expandable ramp (5b).

2. The bone fastener as claimed in claim 1, wherein the multiple modes include clockwise mode, anticlockwise mode or a bi-direction movement including both clockwise mode and anticlockwise mode.

3. The bone fastener as claimed in claim 1, wherein the projected end (1b) of the expandable outer region (1) is provided with slotted grooves (10).

4. The bone fastener as claimed in claim 1, wherein the circular disc (8) is provided with an orifice (12) aligning with the cannulated threaded bolt (3) for passage of a guide wire.

5. The bone fastener as claimed in claim 1, wherein a hammering head is provided with a detachable screw driver capable of complimentary fit into the slotted groove (10) of the expandable outer region (1) and the groove (7) of the cannulated threaded bolt (3).

6. The bone fastener as claimed in claim 1, wherein the engaging of the screw driver enables bi-directional movement of the first conical projection (9a) and second conical projection (9b) for bi-stage expansion of the bone fastener.

7. The bone fastener as claimed in claim 1, wherein the first expandable ramp (5a) corresponding to first conical projection (9a) is bigger than the second expandable ramp (5b) corresponding to the second conical projection (9b) to enable bi-stage expansion of the bone fastener.

8. The bone fastener as claimed in claim 1, wherein the external region is provided with a first ridge (4a) and a plurality of second ridges (4b) having at least two pre-determined sections of variable thickness.

9. The bone fastener as claimed in claim 1, wherein the predetermined section for a first ridge (4a) of a particular thickness enables accommodation of the first conical projection (9a) by means of the first expandable ramp (5a).

10. The bone fastener as claimed in claim 1, wherein the predetermined section for a plurality of second ridge (4b) allows adhering of the expandable bone fastener to the bone.

11. The bone fastener as claimed in claim 1, wherein the cannulated threaded bolt (3) is operably coupled to the expandable outer region (1) and is configured to undergo two distinct operations.

12. The bone fastener as claimed in claim 1, wherein the first expandable ramp (5a) acts as a guide rail for movement of the first conical projection (9a) within the first threaded region (11a) of the cannulated threaded bolt (3).

13. The bone fastener as claimed in claim 1 , wherein the second expandable ramp (5b) acts as a guide rail for movement of the second conical projection (9b) within the cannulated threaded bolts (3).

14. The bone fastener as claimed in claim 1, wherein the two distinct operations include axial expansion and an asymmetric expansion rendered by the bi-directional movement of the first conical projection (9a) and the second conical projection (9b).

15. The bone fastener as claimed in claim 1 , wherein the first conical projection (9a) and the second conical projection (9b) are opposingly threaded, left and right threaded, rendering bi-directional movement of the conical projections, pushing the expandable outer region (1) outwards against a specific section of the bone.

16. The bone fastener as claimed in claim 1, wherein the specific sections of the bone are cortical bone and cancellous bone.

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