Patent Publication Number: US-2015088139-A1

Title: Devices for introduction into a body via a substantially  straight conduit to form a predefined curved  configuration, and methods employing such devices

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to devices for introduction into a body via a substantially straight conduit to form a predefined curved configuration, and methods employing such devices. 
     It is known to insert straight elements into various types of bodies. In the general field of mechanical engineering, this includes insertion of drills, nails, screws and rods of various kinds into structures such as walls, articles such as furnishings, other inanimate bodies, plant bodies such as wood, and animal or human bodies. In certain cases, the straight elements have structures or mechanisms for securing the elements against withdrawal from the body. 
     It is also known in certain contexts to insert elements with a fixed degree of curvature into a body. Examples of this kind include curved needles such as are used for sewing leather, and arcuate drills for medical applications, such as described in U.S. Pat. No. 4,312,337 to Donohue and U.S. Pat. No. 4,941,466 to Romano. Such structures are limited to a very superficial depth of penetration into the body, and generally channel through an arc of less than 180° within the body. 
     In a third group of applications, primarily limited to the field of medical endoscopy, steerable flexible elements are introduced into a body. Steerable flexible elements can be introduced through straight conduits and can then be deflected within the body in order to steer them to a desired location, thereby allowing the elements to reach a location at an arbitrary desired depth within a body. These elements, however, do not generally assume a well defined curved configuration within the body, and typically do not turn through angles of more than about 180°. In many cases, steerable elements are specifically kept away from their mechanical limit of flexing in order to avoid structural damage through over-flexing. 
     None of the above provide a structure or method through which a curved structure can be introduced into a body via a straight conduit and then assumes a deployed position in a predefined curved configuration within the body, and particularly where the predefined curved structure turns through more than 180°, has a variable curvature and/or assumes a three dimensional (non-planar) geometry. 
     There is therefore a need for devices for introduction into a body via a substantially straight conduit to form a predefined curved configuration, and methods employing such devices. 
     SUMMARY OF THE INVENTION 
     The present invention is a device for introduction along a guide into a body and assuming within the body a predefined curved configuration. 
     According to an embodiment of the present invention there is provided, a device for introduction along a guide into a body, the device assuming within the body a curved configuration, the device comprising: an elongated element formed primarily from a plurality of sequentially flexibly interconnected segments, the elongated element being configured such that: (a) when the elongated element is confined by the guide to an insertion configuration, the elongated element can be pushed so as to advance along the guide; and (b) when the elongated element is not confined by the guide to the insertion configuration, each segment is deflectable relative to adjacent segments until at least one abutment surface of each of the segments comes into abutment with at least one corresponding abutment surface of each adjacent segment, thereby defining a flexed state of the elongated element, the flexed state corresponding to a curved configuration of the elongated element; and wherein the at least one abutment surface of each of the segments includes at least one surface of a recess, and wherein the at least one corresponding abutment surface of each adjacent one of the segments includes at least one surface of a projection configured for engaging the recess. 
     According to a further feature of an embodiment of the present invention, the recess of each segment is formed as a surface with a concave form in at least one direction. 
     According to a further feature of an embodiment of the present invention, the recess of each segment forms a channel extending along a majority of a dimension of the segment. 
     According to a further feature of an embodiment of the present invention, the channel is a stepped recess formed with a channel base and two channel walls. 
     According to a further feature of an embodiment of the present invention, the recess and the projection are configured such that, in the flexed state, engagement of the projection with the recess helps resist torsional deformation of the elongated element 
     According to a further feature of an embodiment of the present invention, the segments are sequentially flexibly interconnected by a flat connecting portion of flexible material interconnecting between adjacent of the segments. 
     According to a further feature of an embodiment of the present invention, each of the flat connecting portions is integrally formed with adjacent of the segments. 
     According to a further feature of an embodiment of the present invention, all of the segments and the flat connecting portions are integrally formed. 
     According to a further feature of an embodiment of the present invention, the flat connecting portions are resiliently biased to deflect the segments so that the elongated element tends to assume the flexed state. 
     According to a further feature of an embodiment of the present invention, each of the segments is formed as a non-hollow block of material. 
     According to a further feature of an embodiment of the present invention, each of the segments is formed as a hollow block of material. 
     According to a further feature of an embodiment of the present invention, the elongated element has a beveled distal tip angled so as to tend to deflect the elongated element into the flexed state as the elongated element advances through a medium. 
     According to a further feature of an embodiment of the present invention, there is also provided a tensile element deployed along a length of the elongated element. 
     According to a further feature of an embodiment of the present invention, the guide is a conduit with a substantially rectangular cross-section. 
     According to a further feature of an embodiment of the present invention, there is also provided at least one fixation arrangement for fixing a part of the elongated element relative to the body such that the elongated element forms at least part of an implant. 
     According to a further feature of an embodiment of the present invention, there is also provided a drilling element associated with a distal end of the elongated element. 
     According to a further feature of an embodiment of the present invention, a length of the elongated element is at least ten times greater than each transverse dimension of the elongated element. 
     According to a further feature of an embodiment of the present invention, the curved configuration includes a conical spiral. 
     According to a further feature of an embodiment of the present invention, the curved configuration includes a helix. 
     According to a further feature of an embodiment of the present invention, lateral surfaces of the segments are formed with complementary stepped or interlocking features so as to inhibit lateral displacement of successive coils of the helix. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIG. 1  is an isometric view of a first implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration; 
         FIG. 2  is a side view of the device of  FIG. 1  during insertion along a straight conduit, the conduit being cut-away for clarity of presentation; 
         FIG. 3  is a view similar to  FIG. 2  showing the device extending beyond the straight conduit and assuming a predefined curved configuration; 
         FIG. 4  is an isometric view of a second implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration, the device having a hollow central channel; 
         FIG. 5  is a side view of the device of  FIG. 4  during insertion along a straight conduit, the conduit being cut-away for clarity of presentation; 
         FIG. 6  is a view similar to  FIG. 5  showing the device extending beyond the straight conduit and assuming a predefined curved configuration; 
         FIG. 7  is an isometric view of a third implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration, the device having a circular cross-sectional shape; 
         FIG. 8  is an isometric view of a fourth implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration, the device having a semicircular cross-sectional shape; 
         FIG. 9A  is a front view of a fifth implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration, the device having oblique effective hinges between adjacent segments; 
         FIG. 9B  is an isometric view of the device of  FIG. 9A ; 
         FIG. 10  is a view similar to  FIG. 9A  showing the device in its predefined curved configuration; 
         FIG. 11  is a side view of a sixth implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration, the device having a first region configured to produce a predefined curved configuration with a first radius of curvature and a second region configured to produce a predefined curved configuration with a second radius of curvature; 
         FIGS. 12A ,  12 B and  12 C are side views of the device of  FIG. 11  at three stages during insertion along a straight conduit, the conduit being cut-away for clarity of presentation; 
         FIG. 13  is an isometric view of a seventh implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to faint a predefined curved configuration, the device having a predefined shape corresponding to a conical helix; 
         FIG. 14  is a front view of an eighth implementation of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit to form a predefined curved configuration, the device having a predefined curved shape including both a flat spiral with a closed cylindrical helix; 
         FIGS. 15A and 15B  are a partial schematic isometric view, and a partial schematic side view, of part of a device according to the present invention showing an arrangement for interlocking between adjacent segments of the device, the device being shown in its straight and curved states, respectively; 
         FIGS. 16A and 16B  are a partial schematic isometric views of part of a device according to the present invention showing an alternative arrangement for interlocking between adjacent segments of the device, for a solid and hollow device, respectively; 
         FIGS. 17A and 17B  are isometric cut-away views of a device according to the present invention showing an arrangement for interlocking between adjacent coils of a predefined curved shape corresponding to a closed helix; 
         FIGS. 18A and 18B  are schematic partial side views of a device according to the present invention in its predefined curved shape and its straightened shape, respectively, showing an implementation of hinged interconnection for an arbitrarily curved shape; 
         FIGS. 19A-19C  are schematic isometric, longitudinal cross-sectional and end views, respectively, of an individual segment for use in a further implementation of a device according to the teachings of the present invention; 
         FIGS. 19D and 19E  are schematic longitudinal cross-sectional views of a device formed from a plurality of the segments of  FIGS. 19A-19C , the device being shown in its straightened state and predefined curved shape, respectively; 
         FIG. 20A  is a schematic side view of components of a drill assembly, constructed and operative according to the teachings of the present invention; 
         FIG. 20B  is a schematic side view of the drill assembly of  FIG. 20A  assembled; 
         FIG. 20C  is a schematic cross-sectional view through the drill assembly of  FIG. 20B ; 
         FIGS. 21A and 21B  are schematic side views, taken at orthogonal angles, illustrating the operation of the drill assembly of  FIG. 20A ; 
         FIGS. 22A-22C  are schematic illustrations of an implementation of the present invention for posterior cervical bone anchoring using quadru-cortical bone engagement; 
         FIGS. 23A-23C  are schematic illustrations of an implementation of the present invention for anterior cervical bone anchoring using quadru-cortical bone engagement; 
         FIG. 24  is a schematic illustration of an implementation of the present invention for inter-vertebral disc reinforcement; 
         FIGS. 25A-25C  are schematic lateral, anterior and axial views, respectively, showing an implementation of the present invention for inter-vertebral disc replacement; 
         FIG. 26A  is a schematic lateral view showing an implementation of the present invention for inter-vertebral disc replacement with adjustable height restoration; 
         FIGS. 26B and 26C  are axial cross-sectional views taken along lines B-B and C-C, respectively, in  FIG. 26A ; 
         FIGS. 27A-27C  are schematic posterior views of two adjacent vertebrae during progressive correction of scoliosis as a minimally invasive procedure according to the present invention; 
         FIGS. 28A-28C  are schematic sagittal cross-sectional views illustrating three variant implementations of multiple-segment vertebral body reinforcement according to the present invention; 
         FIG. 29A  is a sagittal cross-sectional view illustrating a spinal column with healthy vertebrae; 
         FIG. 29B  is a view similar to  FIG. 29A  illustrating a collapsed vertebra; and 
         FIG. 29C  is a view of the spinal column of  FIG. 29B  illustrating schematically the restoration of vertebral height according to the teachings of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is a device for introduction into a body via a substantially straight conduit to form a predefined curved configuration, and methods employing such a device. 
     The principles and operation of devices 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 family of devices all based on a common inventive concept but varying in their specific implementations, and most notably, in the specific predefined curved form which the devices are configured to assume when they are inserted into a body. The devices are defined geometrically by their structure, and mechanically by their properties, but are not limited to use in any specific field of technology or any specific application. These devices will be described below with reference to  FIGS. 1-19E . Then, with reference to  FIGS. 20A-29C , a small number of exemplary applications employing these devices will be presented, primarily in the field of medical treatment of the human body. 
     Referring now to the drawings,  FIGS. 1-3  show a first basic illustration of a device, constructed and operative according to the teachings of the present invention, for introduction into a body via a substantially straight conduit  20 , and assuming within the body a predefined curved configuration. 
     In general terms, the device of each embodiment of the present invention includes an elongated element  10  formed primarily from a plurality of segments  12  sequentially interconnected so as to form an effective hinge  14  between adjacent segments  12 . Segments  12  and effective hinges  14  are configured such that: (a) when the elongated element  10  is confined to a substantially straight state, effective hinges  14  transfer compressive forces from each segment  12  to the next so that the elongated element  10  can be pushed so as to advance through substantially straight conduit  20 ; and (b) when elongated element  10  is not confined to a substantially straight state, effective hinges  14  allow deflection of each segment  12  relative to adjacent segments  12  until at least one abutment surface  16  of each segments comes into abutment with at least one corresponding abutment surface  18  of each adjacent segment, thereby defining a fully flexed state of elongated element  10  corresponding to a predefined curved configuration of the elongated element. 
     It will immediately be clear that the device of the present invention thus defined is capable of insertion into a body to any desired depth, since it initially follows a substantially straight path, and then deploys within the body to form a predefined curved structure in which adjacent segments are interconnected at an effective hinge and abut via at least one additional surface, thereby providing considerable mechanical stability. Thus, a wide range of curved or convoluted structures can be introduced temporarily or permanently via an insertion opening which has dimensions corresponding to the cross-sectional dimensions of the elongated element making up the final shape. 
     The devices of the present invention may thus be used for a wide range of applications including, but not limited to: forming a curved channel through a body; cutting-out a sample of material from a body; providing a curved anchoring structure within a body; joining together two parts of a body; aligning two parts of a body; forming a reinforcing structure within a body; filling a region of a body; and expanding a spacing between parts of a body. 
     The transition from the substantially straight configuration of the device to the predefined curved configuration can be achieved in a number of ways. According to a first set of implementations, elongated element  10  is resiliently biased so as to tend to deflect towards its predefined curved state. This may be achieved through pre-biasing of effective hinges  14  or by addition of supplementary springs or other resilient elements (not shown). In an alternative set of implementations, the geometry of elongated element  10  is chosen such that mechanical resistance during insertion of element  10  into a body causes deflection of the device to its curved state. According to either of the above options, flexing of the device is progressive, occurring continuously as the device is extended beyond the delivery conduit  20 . According to a further alternative, a selectively operable mechanism (not shown), such as one or more drawstring, may be provided for allowing a user to selectively induce deflection to the predefined curved configuration. 
     As already mentioned, the present invention can be used in a wide range of fields of application including, but not limited to, building, mining, industrial applications, carpentry, and medicine. Accordingly, the “body” within which the device is deployed may be any body, including but not limited to: a human body; an animal body; wood; other biological materials; walls; furniture; minerals; and other inanimate objects. Clearly, the dimensions, materials and other design parameters for the device of the present invention must be selected to render it suited to the intended application, as will be clear to one ordinarily skilled in the field of applications for which it is to be used. 
     Turning now to structural features of specific implementations of the device of the present invention, elongated element  10  as illustrated in  FIG. 1  is preferably formed from a single elongated rod of rectangular cross-section from which, a series of transverse slots are cut to subdivide the elongated element into segments  12 . The relatively thin connecting bridge of material left beneath the slots renders the interconnections flexible, thereby providing effective hinges  14 . The slots are shown here as V-shape slots, corresponding to sloped end surfaces of segments  12 . Other slot shapes, such as U-shaped slots, rectangular slots, and more complex shaped slots, may also be used. 
     It will be appreciated that the structure shown provides all the structural features of the device of the present invention in a very straightforward and easily manufactured manner, simply by forming appropriately shaped and positioned slots in a rectangular rod. Effective hinges  14  are thus integrally formed as flat connecting portions of flexible material interconnecting between adjacent segments. The term “flat” is used in this context to refer to the cross-sectional shape, namely, that in cross-section along the effective axis of the hinge, the thickness of the integral hinge is significantly less than its width, thereby providing a well-defined direction of flexing. The integral hinge may have significant length extending between segments  12  (as illustrated in certain examples below) or may have minimal length (such, as illustrated here). Effective hinges  14  preferably provide resistance to relative motion of adjacent segments  12  other than the intended hinged motion, thereby avoiding unwanted torsional deformation of elongated element  10 . 
     Clearly, if the device is constructed by cutting slots in an initially straight rod of material, and unless the elongated element is further treated to change its properties, the unstressed state of the elongated element will be in the straightened configuration. According to a particularly preferred option illustrated here, elongated element  10  terminates in a beveled distal tip  22  angled so as to tend to deflect the elongated element into the fully flexed state as the elongated element advances through a medium. Specifically, the beveled distal tip  22  preferably has a leading edge on the side from which the slots are cut and a bevel surface facing away from the side of slots. This shape, when advanced into a compressible or displaceable medium, tends to be deflected so as to follow a curved path, thereby bending elongated element  10  progressively towards its fully flexed curved form as it advances beyond delivery conduit  20 , as shown in  FIG. 3 . 
     The dimensions of the device of the present invention are chosen according to the intended application and the required predefined curved shape which is to be formed. Thus, at one extreme, for use in hollowing out a subterranean tunnel or an underwater tunnel, an element with a width and height of one meter or more may be used. At the other extreme, certain delicate medical applications may use an elongated element with a width and height of 5 millimeters or less. For a wide range of domestic and medical applications, lateral dimensions of 1-30 mm are suitable. 
     In terms of relative dimensions, elongated element  10  is termed “elongated” in the sense that its length is significantly longer than both its width and its height. Most preferably, a length of elongated element  10  is at least ten times greater than each transverse dimension (height and width) of the elongated element. Preferably, the device is configured to form a predefined curved configuration including an arc turning through an angle of at least 180°, and in many cases, passing through one or more complete revolutions as will be illustrated in a number of examples below. 
     The materials for the device of the present invention are also chosen according to the intended application and the mechanical and other properties which are required, and may be any suitable materials. For many applications, various metals and metal alloys (referred to collectively as metallic materials) are suitable. For some applications, various plastics and other polymer materials are suitable. Other possibilities include, but are not limited to, composite materials and ceramic materials. For medical applications, biocompatible are used, typically either metallic materials or polymers such as PEEK. 
     It will be noted that the terms “two-dimensional” and “planar” are used to refer to the geometry of the predefined curved configuration of certain embodiments such as those of  FIGS. 1-8  and  11 - 12 C, whereas the terms “three-dimensional” and “non-planar” are used to refer to the geometry of the predefined curved configuration of embodiments such as those of  FIGS. 9A-10 ,  13  and  14 . These terms are used to classify the nature of the curvature exhibited, i.e., that a circle or flat spiral is a “planar” geometry whereas a helix or cone is a “non-planar” geometry. Clearly, even the “planar” geometry implementations also occupy space in three dimensions due to the width of the elements. 
     In the example of  FIGS. 1-3 , elongated element  10  is cut from a solid rod such that each segment  12  is formed as a non-hollow block of material. Although the unitary construction with the effective hinges  14  integrally formed with the segments  12  is believed to be advantageous, it should be noted that alternative implementations of effective hinges  14  also fall within the scope of the present invention. By way of example, a first alternative implementation employs a flexible strip as a backbone for the device to which segments  12  (separate blocks) are attached by any suitable attachment technique. An example of this kind is illustrated below with reference to  FIGS. 19   a - 19 E. A second alternative implementation employs a pivotal interlocking hinge arrangement, of a type either with or without a hinge pin, for connecting between initially separate segments  12 . 
     Substantially straight conduit  20  may be any suitable conduit, preferably close-fitting to the external shape of elongated element  10  in its substantially straight configuration. Conduit  20  may be made of similar materials to elongated element  10 , or may be made from any other materials which are compatible with the intended application. Furthermore, although conduit  20  is the preferred example of a structure for restricting elongated element to a substantially straight configuration during a first part of insertion into a body, it should be noted that other alternatives also fall within the general scope of the present invention. Thus, for example, in hollow implementations (such as will be described below with reference to  FIGS. 4-6 ), an equivalent effect may be achieved using a centrally deployed rail passing at least partially within elongated element  10  which restricts a part of elongated element  10  to its straight configuration. 
     Turning now to  FIGS. 4-6 , these show a second implementation of the device of the present invention. This implementation is generally similar to that of  FIGS. 1-3 , differing in two respects, as will now be detailed. 
     Firstly, in this implementation, the slots are formed as rectangular slots, so that the abutment surfaces  16  and  18  are only along the upper edges of the adjacent segments. This form has certain advantages of simplicity of manufacture, and is also less sensitive to the presence of foreign matter between the abutment surfaces interfering with the curved configuration. On the other hand, the curved structure has triangular lateral openings between adjacent segments which may be undesirable for certain applications. 
     Secondly, this implementation is formed from a hollow rod, resulting in an elongated element  10  in which each segment  12  is a hollow block of material. The resulting central channel through elongated element  10  may be useful for a wide range of functions, including but not limited to: cutting out a sample of material from a body; excavating a volume of material from a body; insertion of a flexible tool through elongated element  10  to reach a target location within a body; delivering a quantity of fluid or other material to a target location within a body; providing a drive shaft for a drilling tool or other tool located at the distal end of elongated element  10 ; relaying illumination and/or images to/from a target location within a body; filling with cement to fix a deployed configuration of elongated element  10 ; and filling elongated element  10  with other materials for imparting desired properties to elongated element  10  or surrounding regions of a body. 
     In all other respects, the structure and function of the implementation of  FIGS. 4-6  can be fully understood by analogy with the structure and function of the implementation of  FIGS. 1-3  described above. 
     Turning now to  FIGS. 7 and 8 , it should be noted that elongated element  10  may be implemented with a wide range of different cross-sectional shapes. Thus, by way of examples,  FIG. 7  shows an implementation in which elongated element  10  is substantially circular in cross-section. In this case, effective hinges  14  are preferably formed as integral hinges by leaving a portion corresponding to a chord of the circle bridging between adjacent segments  12 .  FIG. 8  shows an implementation in which elongated element  10  is substantially semi-circular. Effective hinges  14  interconnecting segments  12  are preferably formed at the flat side of the elongated element. 
     Turning now to  FIGS. 9A ,  9 B and  10 , these illustrate an implementation of the device of the present invention generally similar to that of  FIGS. 1-3  but wherein the predefined curved configuration is a helix. To achieve this result, the slots between adjacent segments  12 , and therefore the axes of effective hinges  14 , are at an oblique angle relative to a direction of elongation of elongated element  10 . This is seen most clearly in the plan view of  FIG. 9A  where angle α denotes the inclination of the effective hinge axes relative to a line perpendicular to the direction of extension of elongated element  10 . The result of this oblique angle of the effective hinges  14  is that the predefined curved configuration includes a lateral component of curvature, thereby forming a helix as shown in  FIG. 10 . Varying angle of inclination a varies the pitch of the helix, so that the helix can be designed to be either open as shown (i.e., with space between adjacent coils of the helix) or closed (i.e., where adjacent coils touch each other). 
     Turning now to FIGS.  11  and  12 A- 12 C, it should be noted that the predefined curved configuration of the devices of the present invention does not have to be a uniform configuration with constant curvature along the length of elongated element  10 . Thus, by way of example,  FIG. 11  illustrates an elongated element  10  which produces a predefined curved configuration (visible in  FIG. 12C ) including a first region  24  having a first radius of curvature R 1  and a second region  26  having a second radius of curvature R 2  greater than R 1 . To achieve this result, the size of segments  12  and their spacing are varied between regions  24  and  26  so that a greater degree of deflection occurs between adjacent segments  12  and/or the segments are more closely spaced in region  24 . 
       FIGS. 12A-12C  illustrate the sequence of deployment of the device of  FIG. 11  as it is advanced from conduit  20 . As the distal tip of elongated element  10  first advances beyond conduit  20 , it occupies a height dimension h 1  corresponding substantially to the corresponding dimension of the device in its substantially straight configuration. (The up-down dimension as illustrated is referred to here for convenience as “height” although the device can clearly be used in any orientation.) As it advances, region  24  starts to assume its predefined curved configuration, thereby defining a part of a substantially circular form of diameter (and hence height) h 2  which is twice the smaller radius of curvature R 1 . Then, as elongated element  10  is advanced further, region  26  progressively extends beyond conduit  20  to form an arc of radius R 2 , and hence raising the overall height to h 3  (twice R 2 ). The overall effect is gradual opening of a shape which is referred to herein as a spiral. Clearly, this effect could be continued, for example by forming a third region of elongated element  10  with more closely spaced segments configured to provide a yet larger radius of curvature. 
     It will be noted that the gradual increase in the effective height of the device, and in particular, during the transition from h 2  of  FIG. 12B  to h 3  of  FIG. 12C , renders the device useful as a mechanism for lifting a part of a body, or for separating between two parts of a body. An example of such an application will be illustrated below. 
     It will be noted that the term “spiral” is used herein in its colloquial sense to refer to any shape which spirals inwards/outwards, and is not limited to a geometric spiral which is referred to herein as a “perfect spiral”. The spiral formed from a stepped increase in radius of curvature as described here may be preferred due to its simplicity of manufacture. Nevertheless, it will be appreciated that it is possible to vary segment size and/or inter-segment spacing in a continuous manner to achieve a close approximation to a perfect spiral, or any other varying curvature profile desired. 
     Turning now to  FIGS. 13 and 14 , it should be noted that the principles of lateral progression described above with reference to  FIGS. 9A-10  and of variable curvature described above with reference to  FIGS. 11-12C  can be combined to achieve an effectively unlimited range of convoluted three-dimensional structures in which radius of curvature and axial progression are arbitrarily chosen according to a specific desired application.  FIGS. 13 and 14  illustrate two examples of particular importance which combine these principles. 
     Specifically,  FIG. 13  illustrates schematically a predefined curved configuration of an elongated element  10  which is formed as a conical spiral, i.e., a series of coils with sequentially increasing radius of curvature combined with axial progression. As before, the variation of the radius of curvature may be either continuous (i.e., varying between each adjacent pair of segments) or may be varied in steps, such as every few segments, or every 90° or 180° of a coil. 
       FIG. 14  shows a further preferred example in which a distal part of elongated element  10  is configured to form a planar spiral  30  (similar to  FIG. 12C ) and a second portion of elongated element  10  forms a helix  32 . In this case, helix  32  is preferably a closed helix, i.e., where each coil sits in contact with the adjacent coils (referred to as “stacked coils”). This contact between coils renders the shape structurally strong so that the device can be used for lifting part of a body or separating between two parts of a body, even where considerable forces are involved. At the same time, the presence of the planar spiral at the distal end ensures that a flat surface contacts the body to be lifted, thereby avoiding heavy abrasion of the lifted body by the leading end of the elongated element. An application of this implementation of the device will be described below. 
     Turning now to  FIGS. 15A-17B , it will be noted that various modifications of the shape of segments  12  may be made in order to provide various forms of interlocking, thereby improving mechanical stability of the predefined curved configurations of the present invention. Thus,  FIGS. 15A and 15B  show one possible modification in which abutment surfaces  16  and corresponding abutment surfaces  18  are configured with interlocking features such that, in the fully flexed state of  FIG. 15B , the interlocking features help resist torsional deformation of the elongated element. In the example shown here, abutment surfaces  16  are formed with slots  34  while complementary abutment surfaces  18  are formed with projecting ridges  36  configured for engaging slots  34 . 
       FIGS. 16A and 16B  illustrate the same concept implemented without sharp ridges and slots, but rather with concavely and convexly curved abutment surfaces  16  and  18 .  FIG. 16B  illustrates the same structure as  FIG. 16A  implemented in a hollow embodiment. 
     Turning now to  FIGS. 17A and 17B , these illustrate an additional option specifically for closed helical forms such as helix  32  of  FIG. 14  in order to further stabilize the resulting stack of coils. According to this feature, lateral surfaces of segments  12  are formed with complementary interlocking features so as to inhibit lateral displacement of successive coils of the helix. In the example of  FIG. 17A , these complementary interlocking features are implemented as such as ridges  38  and slots  40 . In the example of  FIG. 178 , a single step or shoulder  42  is provided. This second option is also useful for stabilizing a closed conical spiral where the difference in radial dimensions between adjacent coils is equal to the width of the single step. 
     Turning now to  FIGS. 18A and 18B , these illustrate schematically an alternative approach to implementing the device of the present invention which facilitates forming elongated elements with arbitrarily shaped predefined curved configurations in two or three dimensions, and which are biased to their curved configurations. Specifically, according to this approach, an elongated element, typically having a uniform cross-section, is first formed into the desired predefined curved configuration by known techniques. These may include wire or bar shaping techniques for metallic material, and molding or extrusion for polymer materials. For three-dimensional shapes, a round cross-section is typically preferred. The elongated element is then cut to form a plurality of slits  44  from the inside of the local curvature of the element outwards and, in the case of a round cross-section, a corresponding clearance channel  46  from the opposite side of the element. Most preferably, a round bore  48  is formed at the base of each slit  44  to spread stresses within the material. This structure thus defines an elongated element  10  with a plurality of segments  12  formed between slits  44  and effective hinges  14  formed between bores  48  and clearance channels  46 , allowing the element to be opened up to a substantially straight configuration as shown in  FIG. 18B . Although the example shown here for simplicity of visual representation is a two-dimensional form with curvature reversal, it will be appreciated that the curvature, and the corresponding hinge axis directions defined by slits  44  and clearance channels  46 , can be rotated, at arbitrarily chosen angles, allowing substantially any three-dimensional curved shape to be produced. The resulting structures can be opened up to a substantially straight configuration as required, but are naturally pre-biased to return to their predefined curved configuration. 
     Turning now to  FIGS. 19A-19E , as mentioned earlier, the devices of the present invention may be implemented using a wide variety of structures for segments  12  and effective hinges  14 . By way of a further non-limiting example preferred for certain applications,  FIGS. 19A-19C  show an implementation of a segment  12  formed as a separate block, and  FIGS. 19D and 19E  show an elongated element  10  formed from a series of such blocks positioned in abutment along a sheet-spring element  60 . The sheet spring  60  passes through channels  62  formed in each segment  12 , thereby aligning the segments. The sheet spring is preferably pre-biased to a curved form so that it returns resiliently to the curved form of  FIG. 19E  and can be straightened to the form of  FIG. 19D . In the example shown here, each segment  10  further features a substantially cylindrical central opening  64 , openings  64  being aligned in the elongated element to form a “hollow” element in the sense used above. This round central channel is particularly suited to applications such as the flexible drill shaft described below with reference to  FIGS. 20A-21B . 
     Turning now to applications for the devices of the present invention, it should be noted that the invention may be used in any situation where it is useful to provide a structure with a predefined curved shape which can be straightened into an elongated structure for convenient delivery, such as along a conduit. Examples of types of application for which the present invention is useful include, but are not limited to: tunneling or drilling to form a channel; extracting material; anchoring to a body; clamping together two bodies; providing a reinforcing structure; as a filler structure; as an expander; and as a medical implant. 
     Depending upon the physical properties of the body into which the device is introduced, the device may form its own channel by one or more process including compacting material, displacing material, or, in the case of hollow embodiments such as in  FIGS. 4-6 , cutting out a core of material which enters the hollow of the device. Optionally, a mechanism (not shown) may be provided for mechanically advancing the device into the material. In other cases, it may be necessary or preferable to provide the device with active drilling capabilities. One configuration suitable for implementing the present invention in combination with a drill is illustrated schematically in  FIGS. 20A-21B . 
     Thus, turning to  FIGS. 20A-20C , these show a curve-drilling attachment, implemented according to the teachings of the present invention, for use with a conventional or slightly modified drill. The attachment includes a rotating drill element  50  formed from a rotatable drive shaft of which at least a portion  52  is flexible and which terminates in a drilling burr  54 . The flexible portion  52  of the shaft may be implemented as a helical spring as shown, or as various other flexible drive element effective for transferring rotational power to the drilling burr. The drill element  50  is located within a hollow implementation of elongated element  10  which is anchored around flexible portion  52  but does not rotate. Around elongated element  10  is an outer conduit  56  which is urged by a spring  58  towards drilling burr  54 . As visible in  FIG. 20C , the elongated element  10  and outer conduit  56  of the preferred embodiment shown here are implemented with rectangular cross-sections. 
       FIGS. 21A and 21B  illustrate the operation of the drill attachment. As the drill is advanced into a body, outer conduit  56  is held back, either by being too large to follow the drill element into the hole or due to a flange (not shown) located to define a straight-drilling depth. Once outer conduit  56  stops advancing, subsequent advancing of the drill element  50  allows the portion of elongated element  10  beyond the conduit to assume its predefined curved configuration, in this case an arc of a circle, thereby bending the flexible portion  52  so that drilling burr  54  follows an arcuate path as seen in  FIG. 21B . It should be noted that a drill attachment and corresponding drilling method according to these principles may be used in a wide variety of applications. For example, in household applications, arcuate drilled channels may be used for anchoring to a wall or other object. Similarly, in dental applications, this form of drilling may be important for anchoring implants within bone. Other non-limiting examples of applications will be discussed below. 
     Parenthetically, it will be noted that this drilling technique can be used for drilling more complex three-dimensional structures. For example, if a helical hollow elongated element is used, it is possible to drill a helical bore through solid material. Such a bore may be valuable for various applications, including but not limited to, forming a helical cooling channel for pumping a coolant within a cylindrical wall of a cylinder. 
     Turning now to  FIGS. 22A-22C  and  23 A- 23 C, these illustrate a further medical application of the arcuate drilling technique of the present invention for providing bone anchoring. Particularly, the examples illustrated in these figures relate to anchoring in the cervical vertebrae, which are considered highly problematic due to the lack of cancellous bone volume. In contrast to conventional approaches, this preferred example of the present invention achieves effective anchoring by using four non-collinear regions of engagement which pass through cortical bone (surfaces). This mode of anchoring is referred to herein as “quadru-cortical bone engagement”. The four regions of engagement are illustrated by numbered lines in  FIGS. 22A and 23A . In the case of  FIGS. 22A-22C , posterior access cervical bone anchoring is shown, whereas in the case of  FIGS. 23A-23C  anterior approach cervical bone anchoring is shown. In both cases, the anchoring element may be the elongated element  10  inserted during drilling. Alternatively, the entire drill assembly may be withdrawn and a separate anchoring element inserted in the channel. 
     Turning now to  FIG. 24 , this illustrates a related technique and corresponding structure for inter-vertebral disc reinforcement. Specifically, there is shown an elongated element  10  according to the present invention passing vertically in a semicircular arc between pedicle screws  66  in vertically adjacent vertebrae. The properties of elongated element  10 , and specifically the capability of opening up toward a lower-curvature state, allow significant relative movement between vertebrae for flexion or translation. At the same time, the opposition of the element against bending tighter than its predefined curved form provides significant vertical load-bearing ability, thereby maintaining spacing between the vertebrae and relieving pressure from the inter-vertebral disc (not shown). Optionally, additional resilient material  68  may be incorporated into elongated element  10  so as to provide an additional cushioning effect. 
     Turning now to  FIGS. 25A-25C , these illustrate an application of a helical elongated element of the present invention as an inter-vertebral disc replacement. In this case, the element  10  is preferably inserted via a single pedicle screw  66  to which it is fixated after insertion. The external footprint of the helical implant is approximately cylindrical, and is positioned with its axis directed laterally, thereby providing support between adjacent vertebrae while allowing flexion motion. 
     Turning now to  FIGS. 26A-26C , these illustrate a further preferred implementation of the present invention employing the structure of  FIG. 14  for inter-vertebral disc replacement with adjustable height restoration. In this case, the device is introduced directly between the pedicles into the inter-vertebral volume, preferably previously evacuated by a discectomy. As the elongated element it is introduced, the distal part of the elongated element first forms a flat spiral, thereby providing a non-abrasive contact surface for the upper (or lower) vertebra. Then, as the element is advanced further, the closed helix begins to accumulate, gradually lifting the upper vertebra away from the lower one until the desired height restoration is achieved. The elongated element is then anchored to a single pedicle screw  66  and severed to provide an anchored disc replacement. 
     Turning now to  FIGS. 27A-27C , these show schematically a minimally invasive procedure according to the present invention for progressive correction of scoliosis. In the implementation illustrated here, a spiral implementation of an elongated element is introduced through a pedicle delivery screw on the side of the spinal column where vertebral separation is required. As successive coils of the spiral form, the increasing diameter of the structure progressively lifts the side of the upper vertebra away from the lower vertebra. This process can be performed in parallel for a number of vertebrae. If the procedure is performed using only local anesthetic, the patient can be asked to stand between adjustments of the vertebral correction, and the adjustments can be performed iteratively until optimal correction is achieved. Here too, once the required correction has been achieved, the elements are fixated to the pedicle screw and severed, remaining as implants. 
     Turning now to  FIGS. 28A-28C , these illustrate the use of elongated helical implementations of the present invention as multiple-segment vertebral body reinforcements. Specifically, by employing an elongated element  10  with a tight helical form, it is possible to introduce a reinforcing element via a single pedicle screw which will then extend vertically through the vertebral bodies and discs of multiple adjacent vertebrae. This provides reinforcement and support for the spinal column while preserving flexibility. The element may extend upwards as shown in  FIG. 28A  or downwards as shown in  FIG. 28B . Since only one pedicle is needed for introduction of each element, it is further possible to introduce one element via a first pedicle extending upwards and second via the other pedicle extending downwards, as illustrated in  FIG. 28C . 
     Turning now to  FIGS. 29A-29C , an implementation of the present invention for vertebral height restoration will now be described. Like in the height restoration for an intervertebral disc described above with reference to  FIGS. 26A-26C , this aspect of the present invention is also advantageously implemented using the form of elongated element described above with reference to  FIG. 14 , and in a manner analogous to that described in  FIGS. 26A-26C . 
       FIGS. 29A and 29B  contrast a spinal column with healthy vertebrae against another with a collapsed vertebra.  FIG. 29C  illustrates the spinal column of  FIG. 29B  after introduction of an elongated element  10  according to the teachings of the present invention. The black lines overlaid over the vertebrae adjacent to the collapsed vertebra of  FIGS. 29B and 29C  show clearly the vertebral height restoration achieved. Optionally, the internal volume within the deployed element may be filled with suitable biocompatible material to impart additional structural or therapeutic properties. Examples of structural filling materials include, but are not limited to, bone cement, flexible biocompatible fillers and osteo-inductive agents for promoting bone growth, including bone grafts and bone marrow. Examples of therapeutic materials which can be introduced into the internal volume include, but are not limited to, antibiotics, anti-neoplastic agents and anti-mitotic agents. 
     Although only a very limited, set of examples of applications of the present invention have been presented, it will be clear that it may be used in numerous other procedures and treatments in the medical field, as well as in other fields. For example, the various hollow implementations of the elongated element may optionally be used for sampling tissue, such as for a biopsy, or for removing tissue, such as for a discectomy. 
     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.