FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to orthopedic implants and, in particular, it concerns an implant, for example a screw, for insertion into hard tissue such as bone.

5 There are numerous surgical treatments requiring the insertion of a screw into human tissue (and preferably bone). Examples relevant to the present invention include, but are not limited, to use of an implant: as an anchor, to connect two parts of a broken bone, to connect between two or more bones, to build a construct for fixation (with plates, rods or the like), or to fixate an implant to bone. In some cases, two or more 10 screws are implanted to prevent rotation between the parts being connected (as with fractured hips and sacroiliac joint fixation).

In all such applications, it is critical to achieve effective, long-term immobilization of the screw(s). Complications due to loosening and/or pulling out of bone screws are well documented, occurring particularly in cases where bone quality 15 has deteriorated. There is also a risk of unthreading of the screw and 'backing out' of the bone.

SUMMARY OF THE INVENTION

The present invention is an implant for insertion into hard tissue such as bone. According to the teachings of an embodiment of the present invention there is

20 provided, an implant comprising: (a) a body providing a substantially cylindrical bone- contact surface for insertion into a bone, the body comprising a first body portion and a second body portion, each of the first and second body portions providing a part of the substantially cylindrical bone-contact surface, the body having a central axis; and (b) an internal actuator deployed within the body and displaceable axially within the body, the

25 internal actuator having at least one wedge surface obliquely angled to the axis, wherein the second body portion is formed with abutment features cooperating with the at least one wedge surface such that, when the internal actuator is displaced axially, the at least one wedge surface bears on the abutment features to displace the second body portion

1 relative to the first body portion, thereby displacing the part of the bone contact surface provided by the second body portion away from the axis.

According to a further feature of an embodiment of the present invention, there is also provided a threaded drive configuration associated with the first body portion and with the internal actuator, the threaded drive configuration being operative to displace the internal actuator axially relative to the first body portion.

According to a further feature of an embodiment of the present invention, the second body portion is displaced relative to the first body portion in a linear displacement perpendicular to the axis.

According to a further feature of an embodiment of the present invention, the substantially cylindrical bone-contact surface features at least one helical projecting ridge defining an effective screw thread.

According to a further feature of an embodiment of the present invention, the at least one helical projecting ridge comprises at least one ridge portion formed on the first body portion and at least one ridge portion formed on the second body portion.

According to a further feature of an embodiment of the present invention, the first body portion and the second body portion are coextensive along a majority of a length of the implant.

According to a further feature of an embodiment of the present invention, the part of the substantially cylindrical bone-contact surface provided by the first body portion is a first half cylinder, and wherein the part of the substantially cylindrical bone-contact surface provided by the second body portion is a second half cylinder.

According to a further feature of an embodiment of the present invention, the at least one wedge surface of the internal actuator is implemented as at least two wedge surfaces obliquely angled on opposite sides of the central axis, and wherein the first body portion is formed with abutment features cooperating with one of the at least two wedge surface such that, when the internal actuator is displaced axially, the first and second body portions move apart symmetrically from the axis. According to a further feature of an embodiment of the present invention, the at least one wedge surface of the internal actuator is implemented as at least two wedge surfaces spaced along the length of the implant.

According to a further feature of an embodiment of the present invention, the first body portion and the second body portion are each formed with an internal radial groove, and wherein the implant further comprises a radial flange engaged with the radial grooves so as to prevent or limit relative axial movement between the first body portion and the second body portion.

According to a further feature of an embodiment of the present invention, the radial flange is integrated with a threaded element in threaded engagement with a threaded part of the internal actuator so as to define a drive configuration such that, when the threaded element is turned about a drive configuration axis, the internal actuator is displaced axially relative to the first and second body portions.

According to a further feature of an embodiment of the present invention, the first body portion provides a part of the substantially cylindrical bone-contact surface encompassing the central axis, and wherein the second body portion is circumscribed by the first body portion.

According to a further feature of an embodiment of the present invention, the at least one wedge surface of the internal actuator is implemented as at least two wedge surfaces, and wherein the body comprises a third body portion providing a part of the substantially cylindrical bone-contact surface, the second body portion being formed with abutment features cooperating with one of the at least two wedge surfaces such that, when the internal actuator is displaced axially, a part of the bone contact surface provided by the third body portion is displaced away from the axis.

According to a further feature of an embodiment of the present invention, the second and third body portions are located on opposite sides of the central axis and are displaced in opposing directions.

There is also provided according to the teachings of the present invention, a method comprising: (a) providing the aforementioned implant; and (b) inserting the implant bridging between an ilium and a sacrum of a human and axially displacing the internal actuator as part of a procedure for fixating a sacroiliac joint.

There is also provided according to the teachings of the present invention, a method comprising: (a) providing the aforementioned implant; and (b) inserting the implant so as to intersect two bones of a human and axially displacing the internal actuator as part of a procedure for fixating a joint between the two bones.

There is also provided according to the teachings of the present invention, a method comprising: (a) providing the aforementioned implant; and (b) inserting the implant bridging between two parts of a fractured bone and axially displacing the internal actuator as part of a procedure for treating a fracture.

There is also provided according to the teachings of the present invention, a method comprising: (a) providing the aforementioned implant; and (b) iaserting the implant into a bone and axiaily displacing the internal actuator to provide an anchoring structure in the bone. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 A is an exploded isometric view of an implant, constructed and operative according to an embodiment of the present invention, for insertion into hard tissue;

FIG. I B is a view similar to FIG. 1 A showing the implant modified by addition of fenestration;

FIGS. 2A and 2B are axial cross-sectional views through the assembled implant of FIG. 1 A showing the implant in a closed insertion state and an expanded clamping state, respectively;

FIGS. 3A and 3B are proximal and distal isometric views, respectively, of the implant of FIG. 1 A in the closed insertion state;

FIGS. 3C and 3D are proximal and distal isometric views, respectively, of the implant of FIG. 1 A in the expanded clamping state; FIGS. 4A and 4B are isometric views of an implant, constructed and operative according to a farther embodiment of the present invention, for insertion into hard tissue, the implant shown in a closed insertion state and an expanded clamping state, respectively;

FIGS. 5A and 5B are upright and inverted exploded views, respectively, of the implant of FIG. 4A;

FIGS. 6A and 6B are axial cross-sectional views through the assembled implant of FIG. 4A showing the implant in a closed insertion state and an expanded clamping state, respectively;

FIGS. 7A and 7B are isometric views of an implant, constructed and operative according to a further embodiment of the present invention, for insertion into hard tissue, the implant shown in a closed insertion state and an expanded clamping state, respectively;

FIGS. 8A and 8B are upright and rotated exploded views, respectively, of the implant of FIG. 7 A;

FIGS. 9A and 9B are axial cross-sectional views through the assembled implant of FIG. 7A showing the implant in a closed insertion state and an expanded clamping state, respectively;

FIG. 10A is a view similar to FIG. 1 A illustrating a variant implementation of an implant in which displacement of an internal actuator is driven by an externally applied linear force;

FIGS. 11-17 are schematic representations of the deployment of implants of the present invention during various surgical procedures, corresponding to methods according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an implant for insertion into hard tissue such as bone, and corresponding methods. The principles and operation of implants and methods according to the present invention may be better understood with reference to the drawings and the accompanying description.

By way of introduction, the present invention provides a number of different implementations of an implant for insertion into hard tissue, such as into bone or between adjacent bones, all of which share a number of generic features. A first implementation, generally designated 10, is illustrated in FIGS. 1A-3D. A second implementation, generally designated 100, is illustrated in FIGS. 4A-6B. A third implementation, generally designated 200. is illustrated in FIGS. 7A-9B. An implementation 10' similar to implementation 10 but illustrating an alternative actuation arrangement is illustrated in FJGS. 10A and JOB. A number of applications of the invention are then illustrated in FIGS. 1 1-17.

Generic Description

For conciseness of presentation, this document will begin with a description of the features that are generic to a number of the illustrated embodiments, referring generically to the different embodiments with features of implant 10 numbered as referenced in the text and the corresponding features of implants 100 and 200 referenced with the same numeral incremented by 100 or 200, respectively. The following description should be understood to refer generically to each of the embodiments below. except where subsequently explicitly stated or clearly self-evident otherwise.

Referring now generically to the drawings (with correspondingly adjusted reference numerals for implants 100 and 200), in general terms, the present invention provides an implant 10, 100 and 200, constructed and operative according to the teachings of various embodiments of the present invention. The implant includes a body, providing a substantially cylindrical bone-contact surface 12 and having a central axis 14, for insertion into a bone. The body includes a first body portion 16 and a second body portion 18, each of which provide a part of the substantially cylindrical bone- contact surface 12. An internal actuator 20, deployed so as to be axially within the body, has at least one wedge surface 22 obliquely angled to axis 14. Second body portion 18 is formed with abutment features 24 cooperating with wedge surface 22 such that, when internal actuator 20 is displaced axiaily, wedge surface 22 bears on abutment features 24 to displace second body portion 18 relative to first body portion 16, thereby displacing the part of bone contact surface 12 provided by second body portion 18 away from axis 14.

Most preferably, second body portion 18 is displaced relative to first body portion 16 in a linear displacement perpendicular to the axis. The term ''linear displacement' ^' as used in this context refers to a motion in which the contact surface provided by second body portion 18 undergoes motion with little or no rotational component, and which most preferably occurs in a direction perpendicular to part of the contact surface. In contrast to pivotal opening motions or various undefined flexing motions, such a linear motion tends to provide a well distributed outward loading on a relatively large region of adjacent tissue, thereby clamping the implant in place against a relatively large region of tissue. This enhances the gripping effect of the implant and helps to avoid highly localized loading which could compromise the integrity of the tissue.

The implants of the present invention may be used in a wide range of applications, primarily but not exclusively for insertion into and/or between bone surfaces as part of an orthopedic procedure. Examples of applications include, but are not limited to: use as an anchor, to connect two parts of a broken bone, to connect between two or more bones, to build a construct for fixation (with plates, rods or the like), or to fixate an implant to bone. In some cases, two or more screws are implanted to prevent rotation between the parts being connected (as with fractured hips and sacroiliac joint fixation). For these application, in many cases, it is preferred to implement substantially cylindrical bone contact surface 12 with at least one helical projecting ridge 26 defining an effective screw thread, thereby providing a device that is inserted as a bone screw. In this context, the phrase "effective screw thread" is used to refer to any thread-like arrangement of ridges, even where interrupted or otherwise non- continuous, so long as the overall form operates as a screw thread when advanced into bone. In most preferred cases, the at least one helical projecting ridge 26 includes at least one ridge portion formed on first body portion 16 and at least one ridge portion formed on second body portion 18.

Although configurations in which projecting ridge 26 forms a helical thread are believe to be particularly advantageous, it should be noted that alternative embodiments without threading may be preferred for certain applications. For example, a non- threaded element, with or without circumferential ridges or other bone-purchasing features, may be tapped into a prepared bore formed in one or more bone and men actuated to achieve effective gripping within the bone(s).

In certain particularly preferred implementations of the present invention, a threaded drive configuration is provided for displacing internal actuator 20 axially relative to first and second body portioas 16 and 18. The threaded drive configuration typically includes a threaded drive element 28 which has a threaded portion 30 for engaging one or other of first body portion 16 and internal actuator 20 so that rotation of threaded drive element 28 about its own axis, typically corresponding to central axis 14, is operative to displace internal actuator 20 axially relative to first body portion 16. Various abutment surfaces typically prevent axial movement of drive element 28 relative to the other elements, as seen in each implementation. Actuation of the implant is thus achieved by engaging a suitable tool, such as a screwdriver or hex key with drive element 28 and rotating it, thereby displacing internal actuator 20 relative to first and second body portions 16 and 18 so that wedge surfaces 22 bear on abutment features 24, thereby pushing outwards regions of bone contact surface 12.

It should be noted that the threaded drive configuration illustrated here is only one of a number of arrangements which can be used to effect the axial displacement of internal actuator 20. By way of one further non-limiting example, applicable to the various implementations described herein, FIGS. 10A and 10B illustrate a further option according to which axial displacement of internal actuator 20 is actuated by axial force applied, typically manually, by a surgeon. The force may be applied using suitable detachable gripping elements (not shown) that extend outwards from implant 10', either by direct manual force or by use of a simple tool (not shown), such as a pistol-grip lever, to provide force amplification. A locking arrangement is preferably provided to retain internal actuator 20 in its displaced position after deployment so as to retain an expanded gripping state of the implant. In the arrangement shown, internal actuator 20 is provided with one or more leaf springs or otherwise implemented resilient teeth 32 which are deployed to snap into complementary recesses 34 in first and second body portions 16 and 18, thereby locking internal actuator near the end of its motion. Clearly, a range of other snap-locking or other locking arrangement may be provided. Optionally, the snap-locking configuration may be configured to facilitate nondestructive unlocking, for example, by forming complementary recesses 34 with release channels (not shown) which allow release of resilient teeth 32 on rotation of a proximal portion of internal actuator 20.

In various applications of the present invention, it may be desirable to promote fusion between two bones or between two sides of a fracture and/or osteo-integration of the implant with surrounding bone. To this end, the various implementations of the present invention may be formed with fenestration implemented as bone windows 36 formed in one or both of first and second body portions 16 and 18, as illustrated in FIG. IB. Most preferably, bone windows 36 are complemented by corresponding channels 38 in internal actuator 20 deployed such that, in the displaced/expanded state of the implant, windows 36 and channels 38 align to provide a contiguous, and preferably direct, path for formation of bone through the implant. This process may be further enhanced by providing an internal hollow channel through the implant along which bone or other bone growth-promoting material may be introduced prior to, during and/or after deployment of the implant. Although illustrated primarily in FIG. IB, it should be appreciated that the fenestration features are applicable to all implementations of the invention.

In applications for which the implant of the present invention serves as an anchor or platform for supporting a device or structure, one or more elements of the implant are typically implemented so as to project externally from the bone. In one implementation, an implant according to one of the implementations illustrated here may be mounted partially inserted into bone and partially projecting therefrom to provide an anchoring post. The proximal end of such a post may be adapted for attachment of an additional structure, for example, as is known in the field of pedicle screws or other bone screws for externa! fixation. Alternatively, the entire expanding implant structure as illustrated herein may be inserted into die bone, and a distinct anchoring post (not shown), typically integrated with one or both of body portions 16 and 18, may extend outwards from the bone.

The implants of the present invention may be formed with sharpened or self- tapping tips to facilitate their insertion into tissue without prior preparation of a bore, or so as to expand a previously existing natural or pre-formed channel. Additionally or alternatively, they may be implemented as over-the-wire devices which advance along a previously inserted orthopedic guide wire. Examples of both of these options will be discussed further below.

First Implementation

Turning now to the remaining features of implant 10 as illustrated in FIGS. 1 A- 3D, first and second body portions 16 and 18 as implemented here are coextensive along a majority of a length of the implant, with each providing a part of the substantially cylindrical bone-contact surface approximating to first and second halves of a cylinder split parallel to its axis. As a result of this structure, expansion of implant 10 occurs as moving apart of the two half-cylinders so as to open a small gap 40 between the two halves, as seen in FIGS. 2B, 3C and 3D. This results in a slightly non-circular cross- sectional profile of implant 10 along substantially its entire embedded length, such that any risk of "backing out" of the implant by an unscrewing motion is typically eliminated. At the same time, the expansion occurs over a large surface area, thereby avoiding localized stress and damage to the hard tissue. The large area of gripping allows highly effective gripping of the tissue by use of small expansions. In many cases, an expansion of between 5% and 30% of the diameter of the device in its insertion (circular cross-section) state is employed, with a particularly preferred range for certain applications being 10%-25%.

As best seen in FIGS. 1A-2B. the structure of implant 10 is configured to open symmetrically, with both first body portion 16 and second body portion 18 being displaced symmetrically away from central axis 14. Thus the at least one wedge surface 22 of internal actuator 20 is here implemented as at least two wedge surfaces 22 obliquely angled on opposite sides of central axis 14, and first body portion 16 is also formed with abutment features 24 cooperating with the corresponding wedge surfaces 22. As a result of this structure, displacement of internal actuator 20 axially results in symmetrical moving apart of first and second body portions 16 and 18 symmetrically from axis 14. The opposing wedge surfaces may be in pairs at the same longitudinal positions along the implant (as shown here), or may be staggered longitudinally if preferred.

In order to provide additional support and stability to the elongated body portions, internal actuator 20 as illustrated here provides at least two, and in this case three, wedge surfaces 22, spaced along the length of implant 10, for displacing each elongated body portion 16 and 18. Clearly, each elongated body portion is provided with correspondingly positioned and oriented abutment features 24.

As noted earlier, the body portions of implants of the present invention most preferably undergo linear relative displacement in a direction perpendicular to the central axis. Various features of implant 10 contribute to maintaining the desired direction of relative motion while preventing lateral and longitudinal drift and angular rocking between the body portions. Specifically, in the embodiment shown here, flat lateral surfaces 42 of internal actuator 20 are in sliding engagement with corresponding bearing surfaces 44 of first and second body portions 16 and 18 (see FIG. I A) which, together with the contact of the flat wedge/abutment surfaces, maintain alignment of body portions 16 and 18 one above the other through the range of opening motion. Over-separation of body portions 16 and 18 is prevented by retaining bolts 46 which engage corresponding holes 48 in internal actuator 20, and which slide within obliquely angled slots 50, thereby following motion of the body portions as they move along wedge surfaces 22.

In order to prevent axial drift between first and second body portions 16 and 18, each of first body portion 16 and second body portion 18 is preferably formed with an internal radial groove 34, meaning a groove with at least one "radial" surface roughly perpendicular to central axis 14. A radial flange 52, meaning a flange with at least one "radiar surface roughly perpendicular to central axis 14, is engaged with radial grooves 34 so as to prevent or limit relative axial movement between first body portion 16 and second body portion 18 during insertion and expansion/deployment of the implant. In the example illustrated here, the flange-groove combination is implemented at two locations, one near each end of the implant, which contributes to the rigidity and load- bearing properties of the implant. The size of flange 52 and the corresponding depth of grooves 34 are chosen such that reliable engagement is preserved even when the two body portions reach their maximally-separated state after displacement of internal actuator 20.

In the particularly preferred implementation of implant 10 as shown, the radial flange 52 at the proximal end of implant 10 is integrated with threaded drive element 28, thereby providing engagement to prevent axial displacement between drive element 28 and first and second body portions 16 and 18. The threaded surface 30 of drive element 28 is here in threaded engagement with a threaded part 54 of internal actuator 20 (see FIG. 2B), thereby defining a drive configuration such that, when threaded drive element 28 is turned about its axis, internal actuator 20 is displaced axially relative to first and second body portions 16 and 18.

Implant 10 also exemplifies an "over-the-wire" implementation in which a central bore 56 extends throughout the length of the implant, allowing the implant to be mounted on and advanced along a pre-positioned orthopedic guidewire or rail, during deployment to its final desired position. Where relevant, the central bore 56 may also serve as a channel for introduction of bone or other bone growth-inducing material.

Second Implementation

Turning now to implant 100 as illustrated in FIGS. 4A-6B, the main features of this implant have already been described in considerable detail above in the generic description, where reference numerals refer also to this implementation with addition of 100 to each numeral. The remaining features of implant 100 are generally similar to implant 10 in that first and second body portions 116 and 118 are coextensive along a majority of a length of the implant, with each providing a part of the substantially cylindrical bone-contact surface approximating to first and second halves of a cylinder split parallel to its axis. As a result of this structure, expansion of implant !OO occurs as moving apart of the two half-cylinders so as to open a small gap 140 between the two halves, as seen in FIGS. 4B and 6B. The use of two half cylinders provides the same functionality and advantages as described above in the context of implant 10.

Implant 100 differs from implant 10 in that it employs asymmetric opening.

Internal actuator 120 is here implemented with only one set of wedge surfaces 122 which displace second body portion 118, while internal actuator 120 slides axial ly in relation to first body portion 116. Internal actuator 120 is here implemented with a T- shaped rail 142 which slides along in engagement with a complementary T-shaped slot 144 in first body portion 116. Wedge surfaces 122 are implemented as lateral oblique ridges while the abutment features 124 of second body portion 118 are correspondingly angled slots. These forms of engagement help to prevent unintended separation of the two body portions.

A further distinction between implant 100 and implant 10 is that threaded drive element 128 is here in threaded engagement with first body portion 116 so as to move together with internal actuator 120. Specifically, threaded surface 130 is here an external surface which engages an internally-threaded cylindrical guide 146 (FIGS. 5A-6B) that is integrated with a proximal part of first body portion 116. Rotation of drive element 128 advances it along cylindrical guide 146, thereby forcing forward internal actuator 120 between the two body portions and causing expansion.

Implant 100 as illustrated here is shown without a central channel for over-the- wire deployment, and is shown as having an outwardly flared head. It will be appreciated however that all of the implementations described herein may be implemented as either implant with a head or as a "headless" implementation, and can be with or without a central channel, all according to the intended application.

Third Implementation

Turning now to implant 200 as illustrated in FIGS. 7A-9B, the main features of this implant have already been described in considerable detail above in the generic description, where reference numerals refer also to this implementation with addition of 200 to each numeral. Implant 200 differs from implants 10 and 100 described above primarily in that first body portion 216 here provides a part of the substantially cylindrical bone-contact surface 212 encompassing the central axis, and typically making up the majority of the bone contact surface, while second body portion 218 is circumscribed by the first body portion. In other words, first body portion 216 in this case approximates to a full cylindrical structure (e.g., pin or screw) from which one or more sub-regions of the surface are provided by smaller displaceable body portions 218. In the example illustrated here, two "second" body portions (or second and third body portions) 218 are provided. The displaceable body portions may be spaced along the length of implant 200 and/or, as illustrated here, arranged bilaterally on opposite sides of central axis 214 so as to be displaced in opposing directions. The deployment mechanism for each second body portion 218 remains as described above, with wedge surfaces 222 of an internal actuator 220 bearing on abutment features 224 of each second body portion 218.

The implementation of threaded drive element 228 illustrated here is similar to that of implant 100 described above, with the drive element in threaded engagement so as to advance along a threaded internal guide 242 (FIG. 8B) within first body portion 216. Drive element 228 is trapped within a slot 244 of internal actuator 220 so that turning of drive element 228 using an internal hex key advances internal actuator, thereby forcing wedge surfaces 222 against abutment features 224 to generate bilateral outward displacement of the parts of bone contact surface 212 provided by second body portions 218.

Although the parts of the contact surface that are displaced according to this implementation are smaller than in the half-cylinder implementations, expansion still occurs over a relatively large area, and the circular symmetry of the screw or pin is disrupted over a significant proportion (preferably at least 20%, and in certain preferred cases at least 30%) of the length of the bone contact surface, thereby providing highly effective resistance against backing-out of the implant. At the same time, the use of a first body portion 216 which provides a unitary structure around the entire periphery of the body for much (typically at least 50%) of the length, provides a particularly structurally strong and effective implant structure for a wide range of applications. Applications

The present invention may be used to advantage in a wide range of applications, primarily but not exclusively for insertion into and/or between bone surfaces as part of an orthopedic procedure. Examples of applications include, but are not limited to: joint fixation applications, treatment of bone fractures, and bone anchoring applications in which the implant forms at least part of an anchoring arrangement for supporting another device or structure. A number of non-limiting illustrative applications will now be discussed with reference to FIGS. 11-17. The implant in these figures is designated 10, but it will be appreciated that these applications may be implemented using an implant according to any implementation described herein or variant thereof.

FIG. I I illustrates schematically an application of the present invention to sacroiliac joint fixation and fusion. In this case, implant 10 is inserted so as to bridge between an ilium and a sacrum of a human. The internal actuator is then displaced so as to fix the implant within each bone as part of a procedure for fixating a sacroiliac joint. In this case (and various other application, as will be clear to one ordinarily skilled in the art), there is significance to the orientation of implant 10, and specifically gap 40, so as to expand the device in a clinically relevant direction. The implant may be one of a number of similar implants, or differently sized implants, inserted in spaced-apart relation, in order to complete the procedure. The implant is illustrated here as being inserted roughly perpendicular to bone surfaces making up the joint. However, the implants of the present invention may be used to advantage in techniques for sacroiliac joint fixation, and any other joint fixation or fusion, in which the implant is inserted to as to intersect two or more bones making up the joint, whether inserted parallel to surfaces of the bones making up the joint, perpendicular thereto, or at any other angle at which they intersect with both bones,

FIG. 12 illustrates positioning of an implant of the present invention as part of a process for fixation and/or fusion of various joints in the ankle, where the direction of insertion is generally parallel to the surfaces of bones making up the various joints. The invention can be used for any one or combination of the joints shown, or any other desired joint. FIG. 13 illustrates the use of the implant of the present invention in a jaw bone as an anchor for a dental prosthesis. The implant may be a stand-alone anchor, or may be part of an anchoring arrangement using two or more implants to support a bridge or other prosthetic structure.

FIGS. 14 and 15 illustrate applications of the present invention in the treatment of bone fractures, where the implant is inserted to as to bridge between two parts of a fractured bone and the internal actuator is axially displaced as part of a procedure for treating a fracture. FIG. 14 illustrates treatment of a fracture in the region of the femoral head or neck, while FIG. 15 illustrates treatment of a fracture in an intermediate position along a long bone segment. In these cases gap orientation is not particularly clinically relevant.

FIGS. 16 and 17 illustrates use of the implant of the present invention as a pedicle screw, which may form a basis for an interbody fusion procedure or any other corrective or therapeutic treatment based on pedicle screw anchoring.

Other possible applications of the implants of the present invention include, but are not limited to: fixation and/or fusion of facet joins, where the screws are generally inserted roughly parallel to bone surfaces of the joint; and fixation of a tibial component in total knee replacements, where the implant is generally inserted along the central canal of a single bone it will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.