Abstract:
Methods and devices that displace bone or other hard tissue to create a cavity in the tissue. Where such methods and devices rely on a driving mechanism for providing moving of the device to form a profile that improves displacement of the tissue. These methods and devices also allow for creating a path or cavity in bone for insertion of bone cement or other filler to treat a fracture or other condition in the bone. The features relating to the methods and devices described herein can be applied in any region of bone or hard tissue where the tissue or bone is displaced to define a bore or cavity instead of being extracted from the body such as during a drilling or ablation procedure.

Description:
RELATED APPLICATION 
     This application is a non-provisional of Provisional application No. 61/416,042 filed Nov. 22, 2010 entitled SYSTEM FOR USE IN TREATMENT OF VERTEBRAL FRACTURES, the entirety of which is incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to medical instruments and systems for creating a path or cavity in vertebral bone to receive bone cement to treat a vertebral compression fracture. The features relating to the methods and devices described herein can be applied in any region of bone or hard tissue where the tissue or bone is displaced to define a bore or cavity instead of being extracted from the body such as during a drilling or ablation procedure. In addition, the present invention also discloses methods and devices for ablating or coagulating tissues, including but not limited to ablating tumor tissue in vertebral and/or cortical bone. 
     SUMMARY OF THE INVENTION 
     Methods and devices described herein relate to improved creation of a cavity within bone or other hard tissue where the cavity is created by displacement of the tissue. In a first example, a method according to the present disclosure includes treating a vertebral body or other bone structure. In one variation, the method includes providing an elongate tool having a sharp tip configured for penetration into vertebral bone, the tool having an axis extending from a proximal end to a working end thereof, where the working end comprises at least a first sleeve concentrically located within a second sleeve and a third sleeve located concentrically about the second sleeve, where each sleeve comprises a series of slots or notches to limit deflection of the working end to a first curved configuration in a single plane and where the respective series of slots or notches are radially offset in each sleeve; advancing the working end through vertebral bone; causing the working end to move from a linear configuration to a curved configuration by translating the first sleeve relative to the second sleeve in an axial direction; and moving the working end in the curved configuration within the bone to create a cavity therein. Translating of the first sleeve relative to the second sleeve can include moving either sleeve or both sleeves in an axial direction. Additional variations include moving one or both sleeves in a rotational direction to produce relative axial displacement between sleeves. 
     In an additional variation, the present devices include medical osteotome devices that can for treat a hard tissue (e.g., in a vertebral body) by mechanically displacing the hard tissue and/or applying therapeutic energy to ablate or coagulate tissue. For example, one such variation includes an osteotome type device that is coupled to a power supply and further includes a handle having an actuating portion and a connector for electrically coupling the osteotome device to the power supply; a shaft comprising a first sleeve located concentrically within a second sleeve, the shaft having a distal portion comprising a working end capable of moving between a linear configuration and an articulated configuration where the articulated configuration is limited to a single plane, and where each sleeve comprises a series of slots or notches to limit deflection of the working end to the articulated configuration, where the respective series of slots or notches are radially offset in adjacent sleeves, where a first conductive portion of the shaft is electrically coupleable to a first pole of the power supply; a sharp tip located at a distal tip of the first sleeve of the working end, the sharp tip adapted to penetrate bone within the vertebral body, where the distal tip is coupleable to a second pole of the power supply, such that when activated, current flows between a portion of the distal tip and the shaft; a non-conductive layer electrically isolating the first sleeve from the first conductive portion; and where the shaft and sharp tip have sufficient column strength such that application of an impact force on the handle causes the distal portion of the shaft and the distal tip to mechanically displace the hard tissue. The power supply can be coupled to the outer sleeve (either the second or third sleeve discussed herein.) 
     Another variations of the method disclosed herein can include the application of energy between electrodes on the device to ablate tissues (e.g., tumor) or to perform other electrosurgical or mapping procedures within the tissue. In one such example for treating a vertebral body, the method can include providing an elongate tool having a sharp tip configured for penetration into vertebral bone, the tool having an axis extending from a proximal end to a working end thereof, where the working end comprises at least a first sleeve concentrically located within a second sleeve, where each sleeve comprises a series of slots or notches to limit deflection of the working end to a first curved configuration in a single plane and where the respective series of slots or notches are radially offset in adjacent sleeves, where a first conductive portion of the first sleeve is electrically coupled to a first pole of a power supply; advancing the working end through vertebral bone; causing the working end to move from a linear configuration to a curved configuration by translating the first sleeve relative to the second sleeve in an axial direction; and applying energy between the first conductive portion and a return electrode electrically coupled to a second pole of the energy supply to ablate or coagulate a region within the vertebral body. 
     In variations of the method, moving the working end to from the linear configuration to the curved configuration can include moving the working end to move through a plurality of curved configurations. 
     In an additional variation, causing the working end to move from a linear configuration to the curved configuration comprises actuating a handle mechanism to move the working end from the linear configuration to the curved configuration. The handle mechanism can be moved axially and/or rotationally as described herein. 
     In one variation, actuating of the handle mechanism causes the working end to move to the first curved configuration without torquing the third sleeve. 
     In additional variations, the working end of the osteotome or tool is spring biased to assume the linear configuration. 
     The working end can move from the linear configuration to the curved configuration by applying a driving force or impact to the elongate tool wherein penetration in the cortical bone moves the working end from the linear configuration to the curved configuration. For example, as a hammering or impact force is applied to the working end, the interaction of the sharp tip against bone causes the working end to assume an articulated and/or curved configuration. Where further axial movement of the tool causes compression of the bone and creation of the cavity. 
     The method can further include the use of one or more cannulae to introduce the tool into the target region. Such a cannula can maintain the tool in a straight or linear configuration until the tool advances out of the cannula or until the cannula is withdrawn from over the tool. 
     As described herein, upon creation of the cavity, the method can further include the insertion of a filler material or other substance into the cavity. The filler material can be delivered through the tool or through a separate cannula or catheter. 
     This disclosure also includes variations of devices for creating a cavity within bone or hard tissue. Such variations include devices for treating a vertebral body or other such structure. In one variation a device includes a handle having an actuating portion; a shaft comprising a first sleeve located concentrically within a second sleeve and a third sleeve located concentrically about the second sleeve, the shaft having a distal portion comprising a working end capable of moving between a linear configuration and an articulated configuration where the second articulated configuration is limited to a single plane, and where each sleeve comprises a series of slots or notches to limit deflection of the working end to the articulated configuration, where the respective series of slots or notches are radially offset in each sleeve; and a sharp tip located at a distal tip of the working end, the sharp tip adapted to penetrate vertebral bone within the vertebral body. 
     In one variation, the devices described herein can include a configuration where the first sleeve is affixed to the second sleeve at the working end such that proximal movement of the first sleeve causes the working end to assume the articulated configuration. The sleeves can be affixed at any portion along their length via a mechanical fixation means (e.g., a pin or other fixation means), an adhesive, or one or more weld points. In some variations, fixation of the sleeves occurs at the working end so that movement of the inner or first sleeve causes the working end to assume the curved configuration. In some cases, the third sleeve can be affixed outside of the working end so long as when the first and second sleeves articulate, the third sleeve still articulates. 
     Devices described herein can optionally include a force-limiting assembly coupled between the actuating portion and the first sleeve such that upon reaching a threshold force, the actuating portion disengages the first sleeve. In one variation, the force-limiting mechanism is adapted to limit force applied to bone when moving the working end from the first configuration toward the second configuration. 
     In additional variations, devices for creating cavities in bone or hard tissue can include one or more spring elements that extending through the first sleeve, where the spring element is affixed to the shaft (within or about either the first, second, or third sleeve). Such spring elements cause the working end to assume a linear configuration in a relaxed state. 
     In additional variations, a device can include an outer or third sleeve where the slots or notches (that allow deflection) are located on an exterior surface of the third sleeve. The exterior surface is typically the surface that faces outward from a direction of the curved configuration. This configuration allows for an interior surface (the surface located on the interior of the curved portion) to be smooth. As a result, if the device is withdrawn through tissue or a cannula or other introducer, the smooth surface on the interior of the curve minimizes the chance that the device becomes caught on the opening of the cannula or any other structure. 
     Variations of the device can include one or more lumens that extend through the shaft and working end. These lumens can exit at a distal tip of the device or through a side opening in a wall of the device. The lumen can include a surface comprising a lubricious polymeric material. For example, the material can comprise any bio-compatible material having low frictional properties (e.g., TEFLON®, a polytetrafluroethylene (PTFE), FEP (Fluorinated ethylenepropylene), polyethylene, polyamide, ECTFE (Ethylenechlorotrifluoro-ethylene), ETFE, PVDF, polyvinyl chloride and silicone). 
     As described herein, the devices can include any number of configurations to prevent rotation between adjacent sleeves but allow axial movement between the sleeves. For example, the sleeves can be mechanically coupled via a pin/slot or key/keyway configuration. In an additional variation, the sleeves can be non-circular to prevent rotation. 
     In an additional variation, the disclosure includes various kits comprising the device described herein as well as a filler material (e.g., a bone cement or other bone filler material). 
     Variations of the access device and procedures described above include combinations of features of the various embodiments or combination of the embodiments themselves wherever possible. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of an osteotome of the invention. 
         FIG. 2  is a side view of the osteotome of  FIG. 1 . 
         FIG. 3  is a cross sectional view of the osteotome of  FIG. 1 . 
         FIG. 4  is an enlarged sectional view of the handle of the osteotome of  FIG. 1 . 
         FIG. 5  is an enlarged sectional view of the working end of the osteotome of  FIG. 1 . 
         FIG. 6A  is a sectional view of the working end of  FIG. 5  in a linear configuration. 
         FIG. 6B  is a sectional view of the working end of  FIG. 5  in a curved configuration. 
         FIGS. 7A-7C  are schematic sectional views of a method of use of the osteotome of  FIG. 1 . 
         FIG. 8  is another embodiment of an osteotome working end. 
         FIG. 9  is another embodiment of an osteotome working end. 
         FIG. 10  is another variation of an osteotome with an outer sleeve. 
         FIG. 11  is a cut-away view of the working end of the osteotome of  FIG. 10 . 
         FIG. 12A  is sectional view of another embodiment of working end, taken along line  12 A- 12 A of  FIG. 11 . 
         FIGS. 12B and 12C  illustrate additional variations of preventing rotation between adjacent sleeves. 
         FIG. 13  is sectional view of another working end embodiment similar to that of  FIG. 11 . 
         FIG. 14  is a cut-away perspective view of the working end of  FIG. 13 . 
         FIG. 15  illustrates another embodiment of an osteotome as described herein that has a distal working end that is configured for deformation resistance when used in very hard cancellous bone. 
         FIG. 16  illustrates an osteotome device as shown in  FIG. 15  with a torque-limiting mechanism built into a handle portion. 
         FIG. 17  illustrates a de-mated slotted sleeve of the device of  FIG. 15  wherein the slots are configured to resist radial deformation of the working end when articulated. 
         FIGS. 18A and 18B  illustrate first and second concentric slotted sleeves of the device of  FIG. 15  from different sides to illustrate the configuration of the slots. 
         FIG. 18C  illustrates a sleeve configuration with arcuate slots and a radial slot. 
         FIGS. 19A-19C  are enlarged schematic views the working end of the osteotome of  FIG. 15  illustrating the progressive application of force would be applied by the working end to cancellous bone, wherein the force application progresses over different axial portions of the working end as it articulates. 
         FIGS. 20A-20B  show the distal end of a prior art stylet with a hinged distal tip that is used to treat cancellous bone;  FIG. 19A  showing the working end in a linear shape for insertion into bone;  FIG. 19B  showing the working end in an articulated shape for creating a space in bone having a certain area. 
         FIG. 21  is a view of the working end of  FIGS. 15 and 19A-19C  illustrating the width and volume of displaced cancellous bone caused by articulation of the working end. 
         FIG. 22  is a view of the working end of  FIGS. 15 and 19A-19C  illustrating the volume of displaced cancellous bone caused by articulation and rotation of the working end. 
         FIG. 23  is a view of the prior art stylet working end of  FIGS. 20A-20B  depicting the limited volume of cancellous bone that can be displaced by articulation and rotation of the prior art device. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-5 , an apparatus or osteotome  100  is shown that is configured for accessing the interior of a vertebral body and for creating a pathway in vertebral cancellous bone to receive bone cement. In one embodiment, the apparatus is configured with an extension portion or member  105  for introducing through a pedicle and wherein a working end  110  of the extension member can be progressively actuated to curve a selected degree and/or rotated to create a curved pathway and cavity in the direction of the midline of the vertebral body. The apparatus can be withdrawn and bone fill material can be introduced through a bone cement injection cannula. Alternatively, the apparatus  100  itself can be used as a cement injector with the subsequent injection of cement through a lumen  112  of the apparatus. 
     In one embodiment, the apparatus  100  comprises a handle  115  that is coupled to a proximal end of the extension member  105 . The extension member  105  comprises an assembly of first (outer) sleeve  120  and a second (inner) sleeve  122 , with the first sleeve  120  having a proximal end  124  and distal end  126 . The second sleeve  122  has a proximal end  134  and distal end  136 . The extension member  105  is coupled to the handle  115 , as will be described below, to allow a physician to drive the extension member  105  into bone while contemporaneously actuating the working end  110  into an actuated or curved configuration (see  FIG. 6 ). The handle  115  can be fabricated of a polymer, metal or any other material suitable to withstand hammering or impact forces used to drive the assembly into bone (e.g., via use of a hammer or similar device on the handle  115 ). The inner and outer sleeves are fabricated of a suitable metal alloy, such as stainless steel or NiTi. The wall thicknesses of the inner and outer sleeves can range from about 0.005″ to 0.010″ with the outer diameter the outer sleeve ranging from about 2.5 mm to 5.0 mm. 
     Referring to  FIGS. 1, 3 and 4 , the handle  115  comprises both a first grip portion  140  and a second actuator portion indicated at  142 . The grip portion  140  is coupled to the first sleeve  120  as will be described below. The actuator portion  142  is operatively coupled to the second sleeve  122  as will be described below. The actuator portion  142  is rotatable relative to the grip portion  140  and one or more plastic flex tabs  145  of the grip portion  140  are configured to engage notches  146  in the rotatable actuator portion  142  to provide tactile indication and temporary locking of the handle portions  140  and  142  in a certain degree of rotation. The flex tabs  145  thus engage and disengage with the notches  146  to permit ratcheting (rotation and locking) of the handle portions and the respective sleeve coupled thereto. 
     The notches or slots in any of the sleeves can comprise a uniform width along the length of the working end or can comprise a varying width. Alternatively, the width can be selected in certain areas to effectuate a particular curved profile. In other variation, the width can increase or decrease along the working end to create a curve having a varying radius. Clearly, it is understood that any number of variations are within the scope of this disclosure. 
       FIG. 4  is a sectional view of the handle showing a mechanism for actuating the second inner sleeve  122  relative to the first outer sleeve  120 . The actuator portion  142  of the handle  115  is configured with a fast-lead helical groove indicated at  150  that cooperates with a protruding thread  149  of the grip portion  140  of the handle. Thus, it can be understood that rotation of the actuation portion  142  will move this portion to the position indicated at  150  (phantom view). In one embodiment, when the actuator portion  142  is rotated a selected amount from about 45° to 720°, or from about 90° to 360°, the inner sleeve  122  is lifted proximally relative to the grip portion  140  and outer sleeve  120  to actuate the working end  110 . As can be seen in  FIG. 4  the actuator portion  142  engages flange  152  that is welded to the proximal end  132  of inner sleeve  122 . The flange  152  is lifted by means of a ball bearing assembly  154  disposed between the flange  152  and metal bearing surface  155  inserted into the grip portion  140  of the handle. Thus, the rotation of actuator  142  can lift the inner sleeve  122  without creating torque on the inner sleeve. 
     Now turning to  FIGS. 5, 6A and 6B , it can be seen that the working end  110  of the extension member  105  is articulated by cooperating slotted portions of the distal portions of outer sleeve  120  and inner sleeve  122  that are both thus capable of bending in a substantially tight radius. The outer sleeve  120  has a plurality of slots or notches  162  therein that can be any slots that are perpendicular or angled relative to the axis of the sleeve. The inner sleeve  122  has a plurality of slots or notches indicated at  164  that can be on an opposite side of the assembly relative to the slots  162  in the outer sleeve  120 . The outer and inner sleeves are welded together at the distal region indicated at weld  160 . It thus can be understood that when inner sleeve  122  is translated in the proximal direction, the outer sleeve will be flexed as depicted in  FIG. 6B . It can be understood that by rotating the actuator handle portion  142  a selected amount, the working end can be articulated to a selected degree. 
       FIGS. 4, 5, 6A and 6B  further illustrate another element of the apparatus that comprises a flexible flat wire member  170  with a proximal end  171  and flange  172  that is engages the proximal side of flange  152  of the inner sleeve  122 . At least the distal portion  174  of the flat wire member  170  is welded to the inner sleeve at weld  175 . This flat wire member thus provides a safety feature to retain the working end in the event that the inner sleeve fails at one of the slots  164 . 
     Another safety feature of the apparatus comprises a torque limiter and release system that allows the entire handle assembly  115  to freely rotate—for example if the working end  110  is articulated, as in FIG,  6 B, when the physician rotates the handle and when the working end is engaged in strong cancellous bone. Referring to  FIG. 4 , the grip portion  142  of the handle  115  engages a collar  180  that is fixed to a proximal end  124  of the outer sleeve  120 . The collar  180  further comprises notches  185  that are radially spaced about the collar and are engaged by a ball member  186  that is pushed by a spring  188  into notches  185 . At a selected force, for example a torque ranging from greater than about 0.5 inch-lbs but less that about 7.5 inch-lbs, 5.0 inch-lbs or 2.5 inch-lbs, the rotation of the handle  115  overcomes the predetermined limit. When the torque limiter assembly is in its locked position, the ball bearing  186  is forced into one of the notches  185  in the collar  180 . When too much torque is provided to the handle and outer sleeve, the ball bearing  186  disengages the notch  185  allowing the collar  180  to turn, and then reengages at the next notch, releasing anywhere from 0.5 inch-lbs to 7.5 inch-lbs, of torque. 
     Referring to  FIGS. 6A and 6B , it can be understood that the inner sleeve  122  is weakened on one side at its distal portion so as to permit the inner sleeve  122  to bend in either direction but is limited by the location of the notches in the outer sleeve  120 . The curvature of any articulated configuration is controlled by the spacing of the notches as well as the distance between each notch peak. The inner sleeve  122  also has a beveled tip for entry through the cortical bone of a vertebral body. Either the inner sleeve or outer sleeve can form the distal tip. 
     Referring to  FIGS. 7A-7C , in one variation of use of the device, a physician taps or otherwise drives a stylet  200  and introducer sleeve  205  into a vertebral body  206  typically until the stylet tip  208  is within the anterior ⅓ of the vertebral body toward cortical bone  210  ( FIG. 7A ). Thereafter, the stylet  200  is removed and the sleeve  205  is moved proximally ( FIG. 7B ). As can be seen in  FIG. 7B , the tool or osteotome  100  is inserted through the introducer sleeve  205  and articulated in a series of steps as described above. The working end  110  can be articulated intermittently while applying driving forces and optionally rotational forces to the handle  115  to advance the working end through the cancellous bone  212  to create path or cavity  215 . The tool is then tapped to further drive the working end  110  to, toward or past the midline of the vertebra. The physician can alternatively articulate the working end  110 , and drive and rotate the working end further until imaging shows that the working end  100  has created a cavity  215  of an optimal configuration. Thereafter, as depicted in  FIG. 7C , the physician reverses the sequence and progressively straightens the working end  110  as the extension member is withdrawn from the vertebral body  206 . Thereafter, the physician can insert a bone cement injector  220  into the path or cavity  215  created by osteotome  100 .  FIG. 7C  illustrates a bone cement  222 , for example a PMMA cement, being injected from a bone cement source  225 . 
     In another embodiment (not shown), the apparatus  100  can have a handle  115  with a Luer fitting for coupling a bone cement syringe and the bone cement can be injected through the lumen  112  of the apparatus. In such an embodiment  FIG. 9 , the lumen can have a lubricious surface layer or polymeric lining  250  to insure least resistance to bone cement as it flows through the lumen. In one embodiment, the surface or lining  250  can be a fluorinated polymer such as TEFLON® or polytetrafluroethylene (PTFE). Other suitable fluoropolymer resins can be used such as FEP and PFA. Other materials also can be used such as FEP (Fluorinated ethylenepropylene), ECTFE (Ethylenechlorotrifluoro-ethylene), ETFE, Polyethylene, Polyamide, PVDF, Polyvinyl chloride and silicone. The scope of the invention can include providing a polymeric material having a static coefficient of friction of less than 0.5, less than 0.2 or less than 0.1. 
       FIG. 9  also shows the extension member or shaft  105  can be configured with an exterior flexible sleeve indicated at  255 . The flexible sleeve can be any commonly known biocompatible material, for example, the sleeve can comprise any of the materials described in the preceding paragraph. 
     As also can be seen in  FIG. 9 , in one variation of the device  100 , the working end  110  can be configured to deflect over a length indicated at  260  in a substantially smooth curve. The degree of articulation of the working end  100  can be at least 45°, 90°, 135° or at least 180° as indicated at  265  ( FIG. 9 ). In additional variations, the slots of the outer  120  and inner sleeves  120  can be varied to produce a device having a radius of curvature that varies among the length  260  of the device  100 . 
     In another embodiment of the invention, the inner sleeve can be spring loaded relative the outer sleeve, in such a way as to allow the working end to straighten under a selected level of force when pulled in a linear direction. This feature allows the physician to withdraw the assembly from the vertebral body partly or completely without further rotation the actuating portion  142  of handle  115 . In some variations, the force-limiter can be provided to allow less than about 10 inch-lbs of force to be applied to bone. 
     In another embodiment shown in  FIG. 8 , the working end  110  is configured with a tip  240  that deflects to the position indicated at  240 ′ when driven into bone. The tip  240  is coupled to the sleeve assembly by resilient member  242 , for example a flexible metal such as stainless steel or NiTi. It has been found that the flexing of the tip  240  causes its distal surface area to engage cancellous bone which can assist in deflecting the working end  110  as it is hammered into bone. 
     In another embodiment of the invention (not shown), the actuator handle can include a secondary (or optional) mechanism for actuating the working end. The mechanism would include a hammer-able member with a ratchet such that each tap of the hammer would advance assembly and progressively actuate the working end into a curved configuration. A ratchet mechanism as known in the art would maintain the assembly in each of a plurality of articulated configurations. A release would be provided to allow for release of the ratchet to provide for straightening the extension member  105  for withdrawal from the vertebral body. 
       FIGS. 10 and 11  illustrate another variation of a bone treatment device  400  with a handle  402  and extension member  405  extending to working end  410  having a similar construction to that  FIGS. 1 to 6B . The device  400  operates as described previously with notched first (outer) sleeve  120  and cooperating notched second (inner) sleeve  122 . However, the variation shown in  FIGS. 10 and 11  also includes a third concentric notched sleeve  420 , exterior to the first  120  and second  122  sleeves. The notches or slots in sleeve  420  at the working end  410  permit deflection of the sleeve as indicated at  265  in  FIG. 11 . 
       FIG. 10  also illustrates the treatment device  400  as including a luer fitting  412  that allows the device  402  to be coupled to a source of a filler material (e.g., a bone filler or bone cement material). The luer can be removable from the handle  402  to allow application of an impact force on the handle as described above. Moreover, the luer fitting  402  can be located on the actuating portion of the handle, the stationary part of the handle or even along the sleeve. In any case, variations of the device  400  permit coupling the filler material with a lumen extending through the sleeves (or between adjacent sleeves) to deposit filler material at the working end  410 . As shown by arrows  416 , filler material can be deposited through a distal end of the sleeves (where the sharp tip is solid) or can be deposited through openings in a side-wall of the sleeves. Clearly, variations of this configuration are within the scope of those familiar in the field. 
     In some variations, the third notched sleeve  420  is configured with its smooth (non-notched) surface  424  disposed to face inwardly on the articulated working end ( FIG. 11 ) such that a solid surface forms the interior of the curved portion of the working end  410 . The smooth surface  424  allows withdrawal of the device  110  into a cannula or introducer  205  without creating a risk that the slots or notches become caught on a cannula  205  (see e.g.,  FIG. 7B ). 
     As shown in  FIGS. 10-11 , the third (outermost) sleeve  420  can extend from an intermediate location on the extension member  405  to a distal end of the working end  410 . However, variations of the device include the third sleeve  420  extending to the handle  402 . However, the third sleeve  420  is typically not coupled to the handle  402  so that any rotational force or torque generated by the handle  402  is not directly transmitted to the third sleeve  420 . 
     In one variation, the third sleeve  420  is coupled to the second sleeve  120  at only one axial location. In the illustrated example shown in  FIG. 11 , the third sleeve  420  is affixed to second sleeve  420  by welds  428  at the distal end of the working end  410 . However, the welds or other attachment means (e.g., a pin, key/keyway, protrusion, etc.) can be located on a medial part of the sleeve  420 . The sleeve  420  can be fabricated of any bio-compatible material. For example, in one variation, the third sleeve is fabricated form a 3.00 mm diameter stainless steel material with a wall thickness of 0.007″. The first, second and third sleeves are sized to have dimensions to allow a sliding fit between the sleeves. 
       FIG. 12A  is a sectional view of extension member  405  of another variation, similar to that shown in  FIGS. 10-11 . However, the variation depicted by  FIG. 12A  comprises non-round configurations of concentric slidable sleeves (double or triple sleeve devices). This configuration limits or prevents rotation between the sleeves and allows the physician to apply greater forces to the bone to create a cavity. While  FIG. 12A  illustrates an oval configuration, any non-round shape is within the scope of this disclosure. For example, the cross-sectional shape can comprise a square, polygonal, or other radially keyed configuration as shown in  FIGS. 12B and 12C . As shown in  FIG. 12C  the sleeves can include a key  407  and a receiving keyway  409  to prevent rotation but allow relative or axial sliding of the sleeves. The key can comprise any protrusion or member that slides within a receiving keyway. Furthermore, the key can comprise a pin or any raised protrusion on an exterior or interior of a respective sleeve. In this illustration, only the first  122  and second  120  sleeves are illustrated. However, any of the sleeves can be configured with the key/keyway. Preventing rotation between sleeves improves the ability to apply force to bone at the articulated working end. 
       FIGS. 13-14  illustrate another variation of a working end  410  of an osteotome device. In this variation, the working end  410  includes one or more flat spring elements  450 ,  460   a ,  460   b ,  460   c ,  460   d , that prevent relative rotation of the sleeves of the assembly thus allowing greater rotational forces to be applied to cancellous bone from an articulated working end. The spring elements further urge the working end assembly into a linear configuration. To articulate the sleeves, a rotational force is applied to the handle as described above, once this rotational force is removed, the spring elements urge the working end into a linear configuration. As shown in  FIG. 13 , one or more of the spring elements can extend through the sleeves for affixing to a handle to prevent rotation. Furthermore, the distal end  454  of flat spring element  450  is fixed to sleeve assembly by weld  455 . Thus, the spring element is fixed at each end to prevent its rotation. Alternate variations include one or more spring elements being affixed to the inner sleeve assembly at a medial section of the sleeve. 
     As shown in  FIGS. 13-14 , variations of the osteotome can include any number of spring elements  460   a - 460   d . These additional spring elements  460   a - 460   d  can be welded at either a proximal or distal end thereof to an adjacent element or a sleeve to allow the element to function as a leaf spring. 
       FIGS. 15-16  illustrate another embodiment of an osteotome  500  with shaft assembly  505  having an articulating working end  510  that is designed to provide especially high strength and thus is adapted for use in dense, hard cancellous bone. In one aspect, the working end  510  exhibits high strength in applying high forces capable of displacing dense cancellous bone as the working end is moved from a linear insertion shape towards an articulated, non-linear shape. In a second aspect, the working end  510  exhibits high strength in resisting radial deformation when the articulated working end articulates to displace dense cancellous bone. 
     In  FIG. 15 , it can be seen that handle  512  is coupled to the shaft assembly  505  that extends about an indicated at  515 . The first handle portion or body  516  and the rotatable actuator or second handle body  518  function as described in previous embodiments to articulate the working end  510  and axis  515  from a linear configuration to a curved configuration.  FIGS. 15 and 16  show that the first handle body  516  is coupled to outer sleeve  520  of the shaft assembly  505  and the second handle body  518  is coupled to inner sleeve  522 . 
       FIG. 16  is a sectional view of handle  512  again showing the mechanism for actuating the second inner sleeve  522 . relative to the first outer sleeve  520 , wherein the first and second handle bodies  516  and  518  are mated along a fast-lead helical thread  526 . Thus, rotation of handle body  518  from about 45° to 90° will lift or translate the inner sleeve  522  axially relative to the outer sleeve  520  to articulate the working end  510 , As can be seen in FIG,  16  the second handle body  518  engages flange  528  that is welded or otherwise joined to the proximal end  532  of inner sleeve  522 , In this embodiment, a torque limiting mechanism is provided in handle  512  which comprises a ball  535  that is urged by spring  536  into a detent  538  in metal collar  540  that is fixedly coupled to handle body  516 . A set screw  542  is provided to adjust the force at which the torque-release mechanism will release under rotation of the handle. The reset torque release mechanism is set to release at a minimum of 8 inch-lbs torque. In one embodiment, the release is set at 8 inch-lbs of torque, 10 inch-lbs of torque, 12 inch-lbs of torque, or 15 inch-lbs of torque. 
     In  FIG. 15 , it can be seen that the working end  510  is configured with a series of slots  550  in the first and second sleeves  520  and  522  that allow for articulation of the assembly. The slots  550  are provided in both sleeves and can range in number from about 5 to 20. However, additional variations of the device can include any number of slots in either sleeve. This variation also illustrates slots that have an arcuate configuration rather than being a simple radial slot is shown in previous embodiments. In one variation, the slots  550  each have a first radial slot portion  552  that extends substantially radially about a sleeve  520  or  522  and a second axial slot portion  555  that extends substantially axially in a sleeve  520  or  522 . 
       FIG. 17  shows an outer sleeve  520  de-mated from the shaft assembly  505  to more particularly depict the dimensions and features of arcuate slots  550 . In this variation, the arcuate slots  550  are also configured as a ‘keyed’ or interlocking features wherein one slot edge comprises a projecting ‘key’ element  560  that slides into and engages a key-receiving shape  562  of the opposing slot edge when the sleeve is articulated. Thus, the interlocking projecting and receiving features  560  and  562  provide the shaft assembly  505  with significantly increased strength in resisting deformation when the working end is rotated in dense cancellous bone. The arcuate slots  550  as depicted in  FIG. 17  can be provided in either the outer sleeve  520 , the inner sleeve  522  or both sleeves. Also, either or both sleeves can include any combination of arcuate and radial slots in the same sleeve. Alternatively, a cooperating sleeve without the arcuate slots  550  of  FIG. 17  can have radially-oriented slots as described in earlier embodiments. The radial oriented slots, as shown previously, comprise slots that extend about a portion of the circumference of the sleeve. Where each radial oriented slot is typically within a plane is perpendicular to an axis of the sleeve (when straight). An arcuate slot, also is located about a portion of the circumference of the sleeve but is not limited to within a plane that is perpendicular to an axis of the sleeve. As shown in  FIG. 18B , the arcuate slots are angled when viewed from a side of the device. In certain additional variations, a sleeve can include both arcuate slots and radial slots as shown in  FIG. 18C . The arcuate shaped slots can also be referred to as axial oriented slots as the direction of the slot is parallel or angled from an axis of the sleeve while a radial oriented slot is perpendicular to an axis of the sleeve. Such a combination of slots can be provided on any sleeve (an inner sleeve, an outer sleeve, or both sleeves). 
       FIG. 18A  is a plan view of inner sleeve  522  de-mated from shaft assembly  505  and again shows the arcuate slots  550  with interlocking projecting and receiving features  560  and  562 . In  FIG. 18B , it can be seen that on shaft assembly  505  includes arcuate slots  550  in both sleeves. The slot can be aligned or non-aligned when the working end is in a linear position. The distal ends of the shafts can be coupled together by a press-fit pins inserted into holes  566  in the sleeves ( FIG. 17 ) or by any other suitable fastening means such as welding. 
     In another aspect of the invention best seen in  FIGS. 17 and 18A , the arcuate slots  550  have a varied width, again for providing greater resistance to torsional, twisting or radial deformation when in use. In one embodiment, the slot width A on the axially-extending slot portions  555  along the sides  570   a  and  570   b  of the projecting feature  560  is less than the slot width R on the radial-extending slot portion  552  adjacent the end surface  572  of projecting feature  560 . Referring to  FIGS. 18A, 18B and 20 , it can be understood how the keyed featured  560  and  562  will mesh and interlock when the working end is articulated and thus resist deformation under twisting loads. In one embodiment, the axial slot portions  555  have a width A of less than 0.010″, 008″ or 0.006″. In such an embodiment, the said radial slot portions  552  have a width R that greater than 0.006″, 008″ or 0.010″. Such slot can be cut by a laser cutter as is known in the art. 
     Referring back to  FIG. 15 , the working end  510  is adapted for providing a sharp, tight radius curvature which is desirable in an osteotome  500  used in a vertebral body. In one embodiment, the transverse dimension TD of the working end  510  in the fully articulated position is at least 10 mm. Further, the working end  510  is capable of articulation such that the linear axis  515  is deflected at least 90° to axis  515 ′ as depicted in  FIG. 15 . In one embodiment, the deflectable shaft portion has a length dimension LD of 12 mm or less in its linear shape ( FIG. 15 ) and is capable of articulation to provide a maximum transverse dimension TD of at least 10 mm and further articulate the axis  515  at least 90°. In general, the working end has a deflectable shaft portion that provides a ratio of at least 0.8:1 of the maximum transverse dimension TD relative to the length dimension LD of the deflecting shaft portion. 
     Now referring to  FIGS. 19A-19C , another aspect of the invention relates to the level of forces that can be applied to bone when articulating the working end  510 , without regard to rotation of the articulated working end. In one embodiment as depicted in  FIGS. 15-19C , movement of the working end toward the articulated configuration can apply at least 30 lbs. force to cancellous bone, or at least 50 lbs. force to bone or at least 70 lbs. force to bone. Still referring to  FIGS. 19A-19C , another aspect of the invention relates to the manner is which forces are applied to bone when the working end is progressively articulated and in which there is not single hinge point around which the working end pivots. As the plurality of slots close together, they do so in a sequential manner to progressively articulate the working end.  FIGS. 19A-19C  illustrate that maximum forces are applied at the distal tip of the device in a progressive manner as first the most distal portion of the shaft articulates, then an adjacent proximal portion of the shaft articulated an so forth. This aspect of the working end differs greatly from the prior art stylet device and working end  580  of  FIGS. 20A-20B , wherein the stylet tip  582  is actuated by pull rod  584  which caused the tip  582  to swing around a single pivot point  585  which thus loads the entire elongated surface  588  of the stylet tip  582 . It can be understood that device of  FIGS. 19A-19C  which provide a progressive, sequential application of force over discrete articulating portions can displace cancellous bone far more effectively with a small diameter tool than hinge-type device as in  FIG. 20B  which cannot apply forces progressively and sequentially over the articulating surface. 
       FIG. 21  depicts another aspect of the invention wherein it can be seen that working end  510  can be progressively articulated to displace a path in cancellous bone having a width W. In other words, the width W is equal to the diameter of the working end  510 . In contrast, the prior art device of  FIG. 20B  can typically only displace a path in cancellous bone having a width X, which is less that the diameter of the tool. 
       FIGS. 22 and 23  illustrate another aspect of the invention wherein the working end when rotated can displace a much greater volume of cancellous bone that the prior art device of  FIGS. 20A-20B . In  FIG. 22 , it can be seen that rotation of working  510  as it is articulated can great a very large displaced volume Y of cancellous bone compared to the volume Z that could potentially be displaced by the working end  580  of  FIGS. 20A-20B . 
     Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration and the above description of the invention is not exhaustive. Specific features of the invention are shown in some drawings and not in others, and this is for convenience only and any feature may be combined with another in accordance with the invention. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims.