A fastener for bone fixation

Abstract

A fastener 100 for bone fixation, the fastener comprising: a tubular body 101 comprising a proximal end, a distal end and an intermediate portion 102 disposed therebetween, the tubular body having a l

Description

The present invention relates to a fastener for bone fixation, for example for use in orthopaedics. Particularly, but not exclusively, the present invention related to an expandable fastener that acts a substitute for a pedicle (spinal) screw. Expandable fasteners that are used in orthopaedics have been developed to provide improved bone fixation strength with the aim of reducing failures related to the implant. The operation of many existing expandable fasteners require the fastener to be screwed into a bore hole in the bone. Once in position a mechanism that runs through the centre of the fastener extends multiple elements in a radial direction at the distal end of the fastener. To remove the expandable fastener the extended elements must be retracted. Bone ingrowth can prevent this process from happening. Additionally, expandable fasteners as well as regular fasteners take a long time to insert. After preparing the bore in the bone, time consuming steps such as creating a thread, screwing in the fastener, and mixing and inserting bone cement prolong the length of surgery. Any reduction in surgery time is beneficial to the patient, the surgical team, and the healthcare provider in terms of cost and risk reduction. Many fasteners also present a difficulty to remove either during surgery or later during a revision procedure. If removal is needed during surgery the process to remove the fastener may damage the patient’s bone, subsequently provide an inferior fixation strength in this region. During a revision procedure, cemented screws are difficult to remove due to cerement leaching through the bone. Expandable screws are also hard to remove during a revision procedure due to partial bone ingrowth through the expansion mechanism. It would be desirable to provide an expandable fastener for bone fixation that mitigates or overcomes these disadvantages.. According to a first aspect of the invention, there is provided a fastener for bone fixation, the fastener comprising: a tubular body comprising a proximal end, a distal end and an intermediate portion disposed therebetween, the tubular body having a longitudinal axis extending from the proximal end to the distal end, wherein the intermediate portion comprises one or more transformable zones configured to transition from a first state to a second state in response to the distal end being moved towards the proximal end to form a raised profile in the outer surface of the tubular body for gripping bone. Advantageously, providing a fastener according to the first aspect of the invention can improve bone fixation by transitioning between two states. The first state allows the fastener to be inserted at the bone insertion site quickly and also removed quickly (if needed). The second state is the deployed state of the first state where an expanded structure has been deployed to provide strong bone fixation that is comparable in strength to screws that are cemented in patients. The one or more transformable zones may be in the form of one or more protrusions on the outer surface of the tubular body when the one or more transformable zones are in the second state. The raised profile may extend around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body. The one or more protrusions may extend around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body. The one or more transformable zones may comprise a plurality of transformable zones along the longitudinal axis of the tubular body. The plurality of transformable zones may be spaced apart along the longitudinal axis of the tubular body such that non-transformable regions of the tubular body reside between transformable zones. Alternatively, the plurality of transformable zones may be spaced along the longitudinal axis of the tubular body such that one end of a transformable zone is disposed adjacent to an end of a neighbouring transformable zone. The transformable zones may comprise a first portion and a second portion, and wherein the first portion and the second portion of each transformable zone together form a protruding edge when the one or more transformable zones are in the second state. The first portion and the second portion of each transformable zone connect at an internal angle at their respective protruding edge. The protruding edge of each transformable zone may expand radially when the one or more transformable zones transition from the first state to the second state. The length of the first and second portions of each transformable zone may be designed so as to influence the extent of radial expansion of the respective protruding edge of each transformable zone. The length of the first and second portions of each transformable zone may be a length as measured along the direction of the longitudinal axis of the tubular body. The one or more transformable zones may comprise a first transformable zone and a second transformable zone. The first transformable zone may be positioned between the proximal end of the tubular body and the second transformable zone. The length of the first and second portions of the first transformable zone may be different to the length of the first and second portions of the second transformable zone. This can result in the radial expansion of the protruding edge at the first transformable zone being different to the radial expansion of the protruding edge at the second transformable zone. In some embodiments, the length of the first and second portions of the first transformable zone may be less than the length of the first and second portions of the second transformable zone. For example, the length of the first and second portions of the first transformable zone may be at least 10 percent less than the length of the first and second portions of the second transformable zone. This can result in the radial expansion of the protruding edge at the first transformable zone being less than the radial expansion of the protruding edge at the second transformable zone. When the intermediate portion comprises the first and second transformable zones, with the first transformable zone being positioned between the proximal end of the tubular body and the second transformable zone, the fastener may further comprise a first stopper for the first transformable zone and a second stopper for the second transformable zone. The first stopper may be configured to engage with a respective engaging surface of the fastener to inhibit further radial expansion of the first transformable zone after the first transformable zone has transitioned from its first state to its second state. The respective engaging surface of the fastener may be an internal surface of the tubular body. The second stopper may be configured to engage with a respective engaging surface of the fastener to inhibit further radial expansion of the second transformable zone after the second transformable zone has transitioned from its first state to its second state. The respective engaging surface of the fastener may be an internal surface of the tubular body. The length of the first and second stoppers may be designed so as to influence the extent of radial expansion of the respective protruding edge of each transformable zone. The length of the first and second stoppers may be a length as measured along the direction of the longitudinal axis of the tubular body. The length of the first stopper may be different to the length of the second stopper. For example, the length of the first stopper may be greater than the length of the second stopper, for example, at least 10 percent greater than the length of the second stopper. This can result in the radial expansion of the first transformable zone being less than the radial expansion of the second transformable zone. The distance between the first stopper and its respective engaging surface of the fastener when the first transformable zone is in its first state may be different from the distance between the second stopper and its respective engaging surface of the fastener when the second transformable zone is in its first state. This difference in distance can result in the extent of radial expansion of the first transformable zone being different to the extent of radial expansion of the second transformable zone, because the first stopper needs to travel a different distance to reach its engaging surface than the second stopper. In this way, the first stopper can engage its engaging surface after a different extent of radial expansion of its transformable zone has happened when compared to the second stopper and the second transformable zone. For example, in some preferred embodiments, the distance between the first stopper and its respective engaging surface of the fastener when the first transformable zone is in its first state is less than the distance between the second stopper and its respective engaging surface of the fastener when the second transformable zone is in its first state. This can result in a greater radial expansion occurring at the second transformable zone when compared to the first transformable zone as the first and second transformable zones transition from their first to second states. In some embodiments, the one or more transformable zones comprise at least three transformable zones, the at least three transformable zones comprising: a transformable zone positioned closest to the proximal end of the tubular body; and a transformable zone positioned closest to the distal end of the tubular body. Preferably, the extent of radial expansion of the at least three transformable zones when in their second states progressively increases when moving from the transformable zone positioned closest to the proximal end of the tubular body to the transformable zone positioned closest to the distal end of the tubular body. In this way, the at least three transformable zones can provide a generally tapered profile to the tubular body when in their second state, the generally tapered profile increasing in size when moving from the proximal end of the tubular body to the distal end of the tubular body. The internal angle at each protruding edge may decrease as the protruding edge expands radially. The protruding edge of each of the one or more transformable zones may extend around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body. The one or more transformable zones may further comprise one or more openings in the tubular body which facilitate the transition of the one or more transformable zones from the first state to the second state. The one or more openings may be in the tubular wall of the tubular body. The one or more openings may be the only openings in the tubular wall of the tubular body. The one or more openings may comprise one or more slits, wherein each slit extends longitudinally in the direction of the longitudinal axis of the tubular body. The fastener may comprise one or more transformable zones comprising a first opening at a first end of the transformable zone and a second opening at a second end of the transformable zone. The first opening may correspond to a first end of a protrusion formed by its respective transformable zone and the second opening may correspond to a second end of said protrusion when the one or more transformable zones are in the second state. The raised profile in the outer surface of the tubular body is a threaded profile. Each of the one or more protruding edges may extend helically along the tubular body, such that one or more protruding edges are configured to expand radially when the one or more transformable zones transition from the first state to the second state to form one or more helical threads along the longitudinal axis of the tubular body. The outer surface of the tubular body may be substantially uninterrupted when the one or more transformable zones are in the first state. The outer surface of the tubular body may comprises one or more undulations formed by the one or more transformable zones being in the first state, the one or more undulations being configured to change as the one or more transformable zones transition from the first state to the second state to form the raised profile in the outer surface of the tubular body. The fastener, wherein the tubular body may be substantially cylindrical. The tubular body may comprises a tubular wall comprising the one or more transformable zones, and wherein the tubular wall may further comprise an outer surface defining the outer surface of the tubular body and an inner surface defining a lumen of the tubular body. The tubular wall may have a thickness of around at least 0.5 mm, preferably around at least 1.0 mm, more preferably around at least 1.5 mm, even more preferably around at least 2.0 mm, even more preferably around at least 3.0 mm, preferably around at least 4.0mm, preferably around at least 5.0 mm. The portion of the tubular wall forming at least one of the one or more transformable zones may have a thickness which is less than a thickness of a portion of the tubular wall which is adjacent to said at least one transformable zone. The fastener, wherein the distal end of the tubular body resides in a first position when the one or more transformable zones are in the first state and wherein the distal end of the tubular body resides in a second position when the one or more transformable zones are in the second state, and wherein the fastener may further comprise one or more stoppers configured to inhibit movement of the distal end towards the proximal end when the distal end resides in the second position. The one or more stoppers may be configured to engage with a respective internal edge of the tubular body to inhibit movement of the distal end towards the proximal end when the distal end resides in the second position. The one or more stoppers may form part of the inner surface of the tubular wall, and wherein each of the one or more stoppers may underlie at least a portion of a respective one of the one or more transformable zones. The combined thickness of a stopper and its respective transformable zone may be equal to or less than a thickness of a portion of the tubular wall which is adjacent to said transformable zone. The combined thickness of a stopper and its respective transformable zone is around at least 0.3 mm, preferably around at least 0.5 mm, preferably around at least 1.0 mm, more preferably around at least 1.5 mm, even more preferably around at least 2.0 mm, even more preferably around at least 3.0 mm The length of the stopper may contributes to controlling the extent of radial expansion of its corresponding protruding edge. The fastener may further comprise a fastener head coupled with the proximal end of the tubular body. The fastener head may comprise a cavity, wherein the cavity comprises an internal thread at a first end of the cavity for receiving an external tool. The proximal end of the tubular body may be positioned within the cavity at a second end of the fastener head. The fastener head may be configured to rotate about the proximal end of the tubular body. The tubular body may comprise a lumen. The lumen may extend from the distal end of the tubular body to the proximal end of the tubular body. The fastener may be part of a fastener system. The fastener system may comprise a fastener according to any preceding example, and an actuating element configured to be inserted into the tubular body of the fastener, wherein the actuating element is configured to move the distal end of the tubular body towards the proximal end of the tubular body to cause the one or more transformable zones to transition from the first state to the second state. The actuating element may be configured to anchor to an anchor portion of the tubular body, and wherein the intermediate portion of the tubular body is positioned between the anchor portion and the proximal end of the tubular body. The anchor portion may be at or adjacent to the distal end of the tubular body. The anchor portion may comprise an engaging element configured to engage with a corresponding engaging element on the actuating element to allow the actuating element to anchor to the tubular body. The engaging element on the actuating element may be at least partially located at or adjacent to a distal end of the actuating element. The engaging element of the anchor portion may be threaded and the engaging element of the actuating element may also be threaded. The actuating element may be removably connectable to the tubular body. The actuating element may have a length greater than the length of the tubular body. The actuating element may have a length which is equal to or less than the length of the fastener. The actuating element may comprise an elongate rod. The proximal end of the actuating element may have a coupling interface for coupling the actuating element to an external device. The actuating element may further comprise a collar coupled to the proximal end of the elongate rod. The collar may be integrally formed with the elongate rod. The collar may be coupled to the actuating element by a threaded engagement. The collar provides the coupling interface for coupling the actuating element to the external device. The collar may be configured to engage with an abutment surface of the proximal end of the tubular body when the actuating element is within the fastener to inhibit the actuating element from moving distally beyond a set position. The fastener system may be part of a system. The system may comprise the fastener system and a device configured to connect to the actuating element. The activation of the device may be configured to cause the actuating element to move the distal end of the tubular body towards the proximal end of the tubular body to cause the one or more transformable zones to transition from the first state to the second state. Below, there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another examples, embodiment, or aspect described herein. Example 1: A fastener for bone fixation, the fastener comprising: a tubular body comprising a proximal end, a distal end and an intermediate portion disposed therebetween, the tubular body having a longitudinal axis extending from the proximal end to the distal end, wherein the intermediate portion comprises one or more transformable zones configured to transition from a first state to a second state in response to the distal end being moved towards the proximal end to form a raised profile in the outer surface of the tubular body for gripping bone. Example 2: The fastener according to example 1, wherein the one or more transformable zones are in the form of one or more protrusions on the outer surface of the tubular body when the one or more transformable zones are in the second state. Example 3: The fastener according to example 1 or example 2, wherein the raised profile extends around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body. Example 4: The fastener according to example 2, wherein at least one of the one or more protrusions extend around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body. Example 5: The fastener according to any preceding example, wherein the one or more transformable zones comprise a plurality of transformable zones along the longitudinal axis of the tubular body. Example 6: The fastener according to any preceding example, wherein each of the transformable zones comprise a first portion and a second portion, and wherein the first portion and the second portion of each transformable zone together form a protruding edge when the one or more transformable zones are in the second state. Example 7: The fastener according to example 6, wherein the first portion and the second portion of each transformable zone connect at an internal angle at their respective protruding edge. Example 8: The fastener according to example 7, wherein the protruding edge of each transformable zone expands radially when the one or more transformable zones transition from the first state to the second state. Example 9: The fastener according to example 6, wherein one or more transformable zones comprise a first transformable zone and a second transformable zone, the first transformable zone preferably being positioned between the proximal end of the tubular body and the second transformable zone. Example 10: The fastener according to example 9 wherein the length of the first and second portions of the first transformable zone is different to the length of the first and second portions of the second transformable zone, and preferably wherein the length of the first and second portions of the first transformable zone is less than the length of the first and second portions of the second transformable zone. Example 11: The fastener according to example 9 or example 10 wherein the fastener further comprises a first stopper for the first transformable zone and a second stopper for the second transformable zone, the first stopper preferably being configured to engage with a respective engaging surface of the fastener to inhibit further radial expansion of the first transformable zone after the first transformable zone has transitioned from its first state to its second state, and the second stopper preferably being configured to engage with a respective engaging surface of the fastener to inhibit further radial expansion of the second transformable zone after the second transformable zone has transitioned from its first state to its second state. Example 12: The fastener according to example 11, wherein the length of the first stopper is different to the length of the second stopper, and preferably the length of the first stopper is greater than the length of the second stopper, for example, at least 10 percent greater than the length of the second stopper. Example 13: The fastener according to example 11 or example 12, wherein the distance between the first stopper and its respective engaging surface of the fastener when the first transformable zone is in its first state is different from the distance between the second stopper and its respective engaging surface of the fastener when the second transformable zone is in its first state Example 14: The fastener according to example 13, wherein the distance between the first stopper and its respective engaging surface of the fastener when the first transformable zone is in its first state is less than the distance between the second stopper and its respective engaging surface of the fastener when the second transformable zone is in its first state. Example 15: The fastener according to any preceding example, wherein the one or more transformable zones comprise at least three transformable zones, the at least three transformable zones comprising: a transformable zone positioned closest to the proximal end of the tubular body; and a transformable zone positioned closest to the distal end of the tubular body, and wherein optionally the extent of radial expansion of the at least three transformable zones when in their second states progressively increases when moving from the transformable zone positioned closest to the proximal end of the tubular body to the transformable zone positioned closest to the distal end of the tubular body. Example 16: The fastener according to any preceding example, wherein the internal angle at each protruding edge decreases as the protruding edge expands radially. Example 17: The fastener according to any preceding example, wherein the protruding edge of each of the one or more transformable zones extends around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body. Example 18: The fastener according to any preceding example, wherein the one or more transformable zones further comprise one or more openings in the tubular body which facilitate the transition of the one or more transformable zones from the first state to the second state. Example 19: The fastener according to example 18, wherein the one or more openings are one or more slits, each slit extending longitudinally in the direction of the longitudinal axis of the tubular body. Example 20: The fastener according to example 19, wherein each of the one or more transformable zones comprises a first opening at a first end of the transformable zone and a second opening at a second end of the transformable zone. Example 21 :The fastener according to example 20, wherein the first opening corresponds to a first end of a protrusion formed by its respective transformable zone and the second opening corresponds to a second end of said protrusion when the one or more transformable zones are in the second state. Example 22:The fastener according to examples 18 to 21, wherein the one or more openings in the one or more transformable zones are the only openings in the tubular wall of the tubular body. Example 23: The fastener according to any preceding example, wherein the raised profile in the outer surface of the tubular body is a threaded profile. Example 24: The fastener according to any of examples 6 to 22, wherein each of the one or more protruding edges extend helically along the tubular body, such that one or more protruding edges are configured to expand radially when the one or more transformable zones transition from the first state to the second state to form one or more helical threads along the longitudinal axis of the tubular body. Example 25: The fastener according to any preceding example, wherein the outer surface of the tubular body is substantially uninterrupted when the one or more transformable zones are in the first state. Example 26: The fastener according to any of examples 1 to 25, wherein the outer surface of the tubular body comprises one or more undulations formed by the one or more transformable zones being in the first state, the one or more undulations being configured to change as the one or more transformable zones transition from the first state to the second state to form the raised profile in the outer surface of the tubular body. Example 27: The fastener according to any preceding example, wherein the tubular body is substantially cylindrical. Example 28: The fastener according to any preceding example, wherein the tubular body comprises a tubular wall comprising the one or more transformable zones, and wherein the tubular wall further comprises an outer surface defining the outer surface of the tubular body and an inner surface defining a lumen of the tubular body. Example 29: The fastener according to example 28, wherein the tubular wall has a thickness of around at least 0.5 mm, preferably around at least 1.0 mm, more preferably around at least 1.5 mm, even more preferably around at least 2.0 mm, most preferably around at least 2.5 mm, preferably 3.0 mm, preferably 4.0mm, preferably 5.0mm. Example 30: The fastener according to example any of examples 28 to 29, wherein the portion of the tubular wall forming at least one of the one or more transformable zones has a thickness which is less than a thickness of a portion of the tubular wall which is adjacent to said at least one transformable zone. Example 31 :The fastener according to any preceding example, wherein the distal end of the tubular body resides in a first position when the one or more transformable zones are in the first state and wherein the distal end of the tubular body resides in a second position when the one or more transformable zones are in the second state, and wherein the fastener further comprises one or more stoppers configured to inhibit movement of the distal end towards the proximal end when the distal end resides in the second position. Example 32: The fastener according to example 31, wherein the one or more stoppers are configured to engage with a respective internal edge of the tubular body to inhibit movement of the distal end towards the proximal end when the distal end resides in the second position. Example 33: The fastener according to examples 31 or 32, wherein the one or more stoppers form part of the inner surface of the tubular wall, and wherein each of the one or more stoppers underlies at least a portion of a respective one of the one or more transformable zones. Example 34: The fastener according to example 33, wherein the combined thickness of a stopper and its respective transformable zone is equal to or less than a thickness of a portion of the tubular wall which is adjacent to said transformable zone. Example 35: The fastener according to example 33 or 34, wherein the combined thickness of a stopper and its respective transformable zone is around at least 0.5 mm, preferably around at least 1.0 mm, more preferably around at least 1.5 mm, even more preferably around at least 2.0 mm, most preferably around at least 2.5 mm, preferably 3.0 mm, preferably 4.0mm, preferably 5.0mm. Example 36: The fastener according to examples 31 to 35, wherein the length of the stopper contributes to controlling the extent of radial expansion of its corresponding protruding edge. Example 37: A fastener according to any preceding example, further comprising a fastener head coupled with the proximal end of the tubular body. Example 38: The fastener according to example 37, wherein the fastener head comprises a cavity, wherein the cavity comprises an internal thread at a first end of the cavity for receiving an external tool. Example 39: The fastener according to example 38, wherein the proximal end of the tubular body is positioned within the cavity at a second end of the fastener head. Example 40: The fastener according to examples 37 to 39, wherein the fastener head is configured to rotate about the proximal end of the tubular body. Example 41: The fastener according to any preceding example, wherein the tubular body comprises a lumen. Example 42: The fastener according to example 41, wherein the lumen extends from the distal end of the tubular body to the proximal end of the tubular body. Example 43: A fastener system comprising a fastener according to any preceding example, and an actuating element configured to be inserted into the tubular body of the fastener, wherein the actuating element is configured to move the distal end of the tubular body towards the proximal end of the tubular body to cause the one or more transformable zones to transition from the first state to the second state. Example 44: The fastener system according to example 43, wherein the actuating element is configured to anchor to an anchor portion of the tubular body, and wherein the intermediate portion of the tubular body is positioned between the anchor portion and the proximal end of the tubular body. Example 45: The fastener system according to example 44, wherein the anchor portion is at or adjacent to the distal end of the tubular body. Example 46: The fastener system according to example 44 or 45, wherein the anchor portion comprises an engaging element configured to engage with a corresponding engaging element on the actuating element to allow the actuating element to anchor to the tubular body. Example 47: The fastener system according to example 46, wherein the engaging element on the actuating element is at least partially located at or adjacent to a distal end of the actuating element. Example 48: The fastener system according to example 46 or 47, wherein the engaging element of the anchor portion is threaded and wherein the engaging element of the actuating element is threaded. Example 49: The fastener system according to any of examples 43 to 48, wherein the actuating element is removably connectable to the tubular body. Example 50: The fastener system according to any of examples 43 to 49, wherein the actuating element has a length which is equal to or less than the length of the fastener. Example 51: The fastener system according to any of examples 43 to 50, wherein the actuating element comprises an elongate rod. Example 52: The fastener system according to any of examples 43 to 51, wherein the proximal end of the actuating element has a coupling interface for coupling the actuating element to an external device. Example 53: The fastener system according to example 51 or 52, wherein the actuating element further comprises a collar coupled to the proximal end of the elongate rod. Example 54: The fastener system according to example 53, wherein the collar is integrally formed with the elongate rod. Example 55: The fastener system according to example 53, wherein the collar is coupled to the actuating element by a threaded engagement. Example 56: The fastener system according to any of examples 53 to 55 when dependent on example 46, wherein the collar provides the coupling interface for coupling the actuating element to the external device. Example 57: The fastener system according to any of examples 53 to 56, wherein the collar is configured to engage with an abutment surface of the proximal end of the tubular body when the actuating element is within the fastener to inhibit the actuating element from moving distally beyond a set position. Example 58: A system comprising the fastener system of examples 42 to 57, and a device configured to connect to the actuating element. Example 59: The system according to example 58, wherein activation of the device is configured to cause the actuating element to move the distal end of the tubular body towards the proximal end of the tubular body to cause the one or more transformable zones to transition from the first state to the second state. The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of the fastener in a first state according to a first embodiment of the disclosure; Figure 2 is a perspective view of the fastener in a second state according to the first embodiment of the disclosure; Figures 3A to 3C show enlarged cross sectional views of the fastener of Figures 1 and 2, depicting how a transformable zone transitions from the first state to the second state; Figures 4A to 4D show cross sectional views of the fastener of Figures 1 and 2, depicting how transformable zones of the fastener transition from the first state to the second state; Figure 5 shows a cross sectional view of the fastener of Figure 4D but where the actuating element has been moved beyond the distal end of the fastener; Figure 6 is a cross sectional view of the fastener head and the tubular body according to the first embodiment of the disclosure; Figure 7 is a perspective view of a portion of a fastener according to a second embodiment of the disclosure; Figure 8 is a cross sectional view of the portion of the fastener shown in Figure 7; Figure 9 shows a cross sectional view and a perspective view of a portion of a fastener according to a third embodiment of the disclosure when a transformable zone of the fastener is in a first position; Figure 10 shows a cross sectional view and a perspective view of the portion of the fastener of Figure 9, when the transformable zone of the fastener is in a second position; and Figure 11 shows a perspective view of the fastener of Figure 10. Figure 1 shows the fastener in its first state, pre-expansion, and Figure 2 shows the fastener in its second state, expanded. The design shown illustrates the fastener used for bone fixation in a cylindrical configuration for use inside a prepared bore in the bone. There are multiple elements in the fastener. In particular, the fastener has a tubular body 101 having a proximal end and a distal end and an intermediate portion 102 disposed between the proximal end and the distal end. The intermediate portion comprises a plurality of transformable zones 103 that expand, and a plurality of corresponding openings 104 in the transformable zones 103. The fastener also includes a fastener head 401, and an actuating element 501. The actuating element consists of an elongate rod and a collar 505 threadedly coupled to a proximal end of the elongate rod. The fastener 100 illustrated in Figure 1 expands helically resembling a thread. The pitch of the helical expansion, the extent of the expansion and the number of expansion elements are all controllable and can be adapted to the use of the fastener. Figure 3A to 3C shows a cross-section through a transformable zone of the fastener. Figure 3A shows how the fastener expands and how the extent of the expansion is controlled. Figure 3A shows the transformable zones of the fastener in its first state, pre-expansion. Figure 3B shows the cross section of a partial expansion of the transformable zones, and Figure 3C shows the transformable zones in the second state, a complete expansion. Figures 3A and 3B shows “r1” and “r2” that are radii from the centre axis (“A”) with values that do not change during the expansion process. Figure 3A highlights an outside diameter (“d1”) representing that diameter of the fastener pre-expansion and Figure 3C highlights a diameter (“d2”) representing the diameter of the fastener expanded. The extent to how much larger “d2” is compared to “d1” depends on the dimensions of the following elements in Figures 3A to 3C. The extent of the expansion is controlled by the length (“h”) of stopper 301. In Figure 3C stopper 301 can be seen in contact with the wall above it, preventing any further expansion of the transformable zones 103. Other elements that are controlled in the design of the fastener are the lengths of first portion 302 and second portion 303 in Figure 3C, denoted on element 302 as “w”. In addition, the thickness of first portion 302 and second portion 303 denoted in Figure 3C as “t” control the extent of expansion and the length of the expansion region denoted as “x” in Figure 3A controls the extent of expansion. Figures 4A to 4D shows the sequence of expansion for the fastener, with a cross-section showing the internal elements of the fastener. Figure 4A shows the fastener in its first state, preexpansion. Figures 4B and 4C show the sequence where there are expansion levels. Over the course of expansion, the length of the fastener changes from its initial length denoted as “L1” in Figure 4A to the fasteners final sequence hight denoted as “L2” in Figure 4D. The expansion is controlled by the actuation of the actuating element 501, along the longitudinal axis (axis “A”). The actuating element can be seen to be secured to the distal end of the fastener. The actuating element is secured by an anchor portion 115, in the form of a thread on the external surface of the distal end of the actuating element. This allows the actuating element to anchor to a corresponding thread on the distal end of the fastener. During the actuation, the actuating element rises through the fastener and can be seen to pass through the head of the fastener, also referred to as the proximal end of the fastener. The fastener 100 has a central lumen extending along its longitudinal axis. Throughout the structure in its first state there are undulation on the outside wall of the fastener that engage with the bone wall during insertion. The undulations define the regions (i.e. transformable zones 103) that will expand radially, and the shape of these undulations can vary depending on the application of the fastener. An actuating element 501 runs through the central lumen and is connected to the distal end of the fastener. The actuating element 501 also connects to an external actuating device beyond the proximal end of the fastener. Once the fastener is in position in the bone, the actuating element 501 can be forced (e.g. by the external actuating device) towards the proximal end of the fastener. This motion causes the distal end of the fastener to move proximally and in doing so the protruding edges concertina outwardly penetrating the bone to form the second state that is the expanded fastener. The degree of expansion is controlled by an internal geometry that follows the pattern of the protrusions. This internal geometry is crucial to control the shape of the concertinaed regions that penetrate the bone wall. The thickness of the internal geometry and the thickness of the protruding regions are controlled and can be adapted depending on the application of the fastener. The preparation of the bore or cavity in the bone could be prepared using a drill, or tool used to create a space in the bone. The size of the prepared bore or cavity will depend on the application of the fastener, where the force required to push the fastener into position does not require mechanical advantage. The fastener 100 is supplied in its first state and may have the actuating element 501 preattached. As noted above, an external actuating device separate to this fastener 100 will connect to the actuating element 501 that is beyond the proximal end of the fastener. Such a connection can be achieved by way of the threaded surface of the collar 505. Figure 6 shows the proximal region of the fastener. This illustrates the interaction between the fastener head 401 and the tubular body 101. The design is of a ‘ball and socket’ joint where the ‘ball’ or the main shaft is manufactured within the ‘socket’ or head. The clearance between the head and the main shaft is controlled to ensure the head can rotate freely. The fastener head 401 comprises a cavity 402 with an internal thread for receiving an external positioning device. The external positioning device may be the same as the external actuating device, or part of the same overall device as the external actuating device. This external positioning device will be used to position the fastener inside the bore or cavity in the bone. When the position of the fastener is correct, the external actuating device will force the actuating element 501 proximally. During the actuating process the proximal end of the fastener, that may be outside of the bone region, will remain static. Figure 4D shows the fastener when the transformable zones are in the second state, that is complete expansion respectively. Figure 5 shows the final stage of activation of the fastener. This step shows the actuating element being secured into a recess in the proximal region of the fastener. In doing so the actuating element, 501, projects through the distal end of the fastener. The actuating element (and in particular its elongate rod) can remain in the fastener throughout and thus can be an important component to the overall system by providing rigidity and strength to the fastener. The fastener 100 is designed to be pressed into position within a prepared bore or cavity in bone. Once the fastener is in position within a prepared bore or cavity in bone, the transformable zones in the fastener can be changed from the first state, with a cylindrical configuration, to its second state, a helical configuration. The second state has an outer diameter larger than the first state. The protruding edges at the transformable zones penetrate the bone walls when the transformable zones of the fastener are in the second state. Once the fastener has fully transitioned from its first state to its second state, the external actuating device can be disconnected from the proximal region of the fastener, and the actuating element 501 may be secured to the proximal region of the fastener. Keeping the actuating element 501 inside the fastener provides additional overall strength to the fastener. With the device removed and the fastener now secured in position, other elements can now be connected to the fastener that may be required to perform the surgical intervention. If the fastener 100 needs to be removed before transitioning to the second state, this can happen with minimal damage to the prepared bore or cavity in the bone. Once the fastener has fully transitioned to the second state, the fastener can be removed through a rotational movement in the case of a helical configuration. The helical configuration may require mechanical advantage to remove the fastener as the concatenated regions that have expanded and penetrated the bone wall need to create a thread during the rotational movement. Following complete expansion as a helical structure, the unique ability the device has is that it can be removed through rotation similar to a screw. If necessary, the fastener can also be returned to its first state by reversing the expansion process shown in figure 9 and figure 10. Figure 7 is a perspective view of a portion of a fastener according to a second embodiment of the disclosure. The portion shown in Figure 7 is a portion of the intermediate portion of the tubular body of the fastener. In the second embodiment, the intermediate portion of the tubular body therefore comprises at least a first transformable zone 2031 and a second transformable zone 2032. In the second embodiment, each of the first transformable zone 2031 and the second transformable zone 2032 are shown in their respective second states. Thus, each zone 2031, 2032 forms a raised profile on the outer surface of the tubular body for gripping bone. The first transformable zone 2031 is positioned between second transformable zone 2032 and the proximal end of the tubular body. The first transformable zone 2031 has a first portion 2031a and a second portion 2031b which have moved when the first transformable zone has transitioned from its first state to its second state to create the raised profile on the outer surface of the tubular body, the raised profile being in the form of a helical protrusion. The helical protrusion of the first transformable zone 2031 has a flattened protruding edge as shown in Figure 7. The second transformable zone 2032 has a first portion 2032a and a second portion 2032b which have moved when the second transformable zone has transitioned from its first state to its second state to create the raised profile on the outer surface of the tubular body, the raised profile being in the form of a helical protrusion. However, in contrast to the helical protrusion of the first transformable zone 2031, the helical protrusion of the second transformable zone 2032 has a sharper more point-like protruding edge as shown in Figure 7. Furthermore, as can be seen from Figure 7, the lengths of the first portion 2031a and the second portion 2031b of the first transformable zone 2031 are less than the lengths of the first portion 2032a and the second portion 2032b of the second transformable zone 2032. Consequently, the extent of radial expansion of the first transformable zone 2031 is less than extent of radial expansion of the second transformable zone 2032. Figure 8 is a cross sectional view of the portion of the fastener shown in figure 7 that is according to the second embodiment of the disclosure. Each of the first transformable zone 2031 and second transformable zone 2032 are in their second state where they have formed a raised profile on the outer surface of the tubular body for gripping bone. The cross-sectional view of Figure 8 highlights the first transformable zone 2031 has a flattened protruding edge and the second transformable zone 2032 has a sharper protruding edge, when each of the transformable zones are in their second state. Furthermore, as can be seen from Figure 8, the first transformable zone 2031 has a stopper 2033, and the second transformable zone 2032 has a stopper 2034, which prevents further expansion of each of the transformable zones 2031 and 2032 respectively, when each of the transformable zones are in their second state. Figure 9 shows a cross sectional view and a perspective view of a portion of a fastener according to a third embodiment of the disclosure when a transformable zone 3030 of the fastener is in a first position. In the embodiment of Figure 9, the depicted transformable zone 3030 is not configured to form a helical protrusion on the outer surface of the tubular body, when said transformable zone 3030 is in its second state. Instead, the transformable zone 3030 forms a substantially circular or ring-like protrusion which extends around the entire circumference of the tubular body. This can be best appreciated from viewing Figure 9 in conjunction with Figure 10 and Figure 11.

Claims

1. A fastener for bone fixation, the fastener comprising:a tubular body comprising a proximal end, a distal end and an intermediate portion disposed therebetween, the tubular body having a longitudinal axis extending from the proximal end to the distal end,wherein the intermediate portion comprises one or more transformable zones configured to transition from a first state to a second state in response to the distal end being moved towards the proximal end to form a raised profile in the outer surface of the tubular body for gripping bone, andwherein the raised profile in the outer surface of the tubular body is a threaded profile.

2. The fastener according to claim 1, wherein each of the transformable zones comprise a first portion and a second portion, and wherein the first portion and the second portion of each transformable zone together form a protruding edge when the one or more transformable zones are in the second state.

3. A fastener for bone fixation, the fastener comprising:a tubular body comprising a proximal end, a distal end and an intermediate portion disposed therebetween, the tubular body having a longitudinal axis extending from the proximal end to the distal end,wherein the intermediate portion comprises one or more transformable zones configured to transition from a first state to a second state in response to the distal end being moved towards the proximal end to form a raised profile in the outer surface of the tubular body for gripping bone,wherein each of the transformable zones comprise a first portion and a second portion, and wherein the first portion and the second portion of each transformable zone together form a protruding edge when the one or more transformable zones are in the second state, andwherein each of the one or more protruding edges extend helically along the tubular body, such that one or more protruding edges are configured to expand radially when the one or more transformable zones transition from the first state to the second state to form one or more helical threads along the longitudinal axis of the tubular body.

4. The fastener according to claim 2, wherein the protruding edge of each transformable zone expands radially when the one or more transformable zones transition from the first state to the second state.20 08 255. The fastener according to any of claims claim 2 to 4, wherein the first portion and the second portion of each transformable zone connect at an internal angle at their respective protruding edge, and wherein the internal angle at each protruding edge decreases as the protruding edge expands radially.

6. The fastener according to any of claims 2 to 5, wherein the protruding edge of each of the one or more transformable zones extends around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body.

7. The fastener according to any of claims 2 to 6, wherein one or more transformable zones comprise a first transformable zone and a second transformable zone, the first transformable zone being positioned between the proximal end of the tubular body and the second transformable zone.

8. The fastener according to claim 7, wherein the length of the first and second portions of the first transformable zone is less than the length of the first and second portions of the second transformable zone.

9. The fastener according to claim 7 or claim 8, wherein the fastener further comprises a first stopper for the first transformable zone and a second stopper for the second transformable zone,the first stopper being configured to engage with a respective engaging surface of the fastener to inhibit further radial expansion of the first transformable zone after the first transformable zone has transitioned from its first state to its second state, andthe second stopper being configured to engage with a respective engaging surface of the fastener to inhibit further radial expansion of the second transformable zone after the second transformable zone has transitioned from its first state to its second state.

10. The fastener according to claim 11, wherein the length of the first stopper is greater than the length of the second stopper; and / orwherein the distance between the first stopper and its respective engaging surface of the fastener when the first transformable zone is in its first state is less than the distance between the second stopper and its respective engaging surface of the fastener when the second transformable zone is in its first state.20 08 2511. The fastener according to any preceding claim, wherein the one or more transformable zones are in the form of one or more protrusions on the outer surface of the tubular body when the one or more transformable zones are in the second state.

12. The fastener according to claim 11, wherein at least one of the one or more protrusions extend around at least 50 percent of the circumference of the tubular body, more preferably around at least 75 percent of the circumference of the tubular body, even more preferably around at least 100 percent of the circumference of the tubular body.

13. The fastener according to any preceding claim, wherein the outer surface of the tubular body comprises one or more undulations formed by the one or more transformable zones being in the first state, the one or more undulations being configured to change as the one or more transformable zones transition from the first state to the second state to form the raised profile in the outer surface of the tubular body.

14. The fastener according to any preceding claim, wherein the tubular body comprises a tubular wall comprising the one or more transformable zones, and wherein the tubular wall further comprises an outer surface defining the outer surface of the tubular body and an inner surface defining a lumen of the tubular body.

15. The fastener according to claim 14, wherein the tubular wall has a thickness of around at least 0.5 mm, preferably around at least 1.0 mm, more preferably around at least 1.5 mm, even more preferably around at least 2.0 mm, most preferably around at least 2.5 mm, preferably 3.0 mm, preferably 4.0mm, preferably 5.0mm.

16. The fastener according to any of claims 14 to 15, wherein the portion of the tubular wall forming at least one of the one or more transformable zones has a thickness which is less than a thickness of a portion of the tubular wall which is adjacent to said at least one transformable zone.

17. The fastener according to any preceding claim, wherein the one or more transformable zones comprise at least three transformable zones, the at least three transformable zones comprising: a transformable zone positioned closest to the proximal end of the tubular body; and a transformable zone positioned closest to the distal end of the tubular body, and wherein the extent of radial expansion of the at least three transformable zones when in their second states progressively increases when moving from the transformable zone positioned closest to the20 08 25proximal end of the tubular body to the transformable zone positioned closest to the distal end of the tubular body.

18. A fastener system comprising a fastener according to any preceding claim, and an actuating element configured to be inserted into the tubular body of the fastener,wherein the actuating element is configured to move the distal end of the tubular body towards the proximal end of the tubular body to cause the one or more transformable zones to transition from the first state to the second state.

19. The fastener system according to claim 18, wherein the actuating element is configured to anchor to an anchor portion of the tubular body, and wherein the intermediate portion of the tubular body is positioned between the anchor portion and the proximal end of the tubular body.

20. The fastener system according to claim 19, wherein the anchor portion is at or adjacent to the distal end of the tubular body.

21. The fastener system according to any of claims 18 to 20, wherein the actuating element is removably connectable to the tubular body.

22. The fastener system according to any of claims 18 to 21, wherein the actuating element has a length which is equal to or less than the length of the fastener.

23. The fastener system according to any of claims 18 to 22, wherein the proximal end of the actuating element has a coupling interface for coupling the actuating element to an external device.

24. A system comprising the fastener system of claims 18 to 23, and a device configured to connect to the actuating element.

25. The system according to claim 24, wherein activation of the device is configured to cause the actuating element to move the distal end of the tubular body towards the proximal end of the tubular body to cause the one or more transformable zones to transition from the first state to the second state.

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