Abstract:
A cannula establishes a subcutaneous path into bone. The cannula includes at least one predetermined marking. A tamping instrument is advanced through the cannula to deliver material into the bone by grasping an enlarged handle portion formed on the tamping instrument. The advancement is visually gauged by observing at least one predetermined marking on the tamping instrument to determine a position of a terminus of the tamping instrument relative to a distal end of the cannula.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a divisional of co-pending U.S. patent application Ser. No. 11/599,943, filed Nov. 15, 2006, and entitled “Systems and Methods for Placing Materials into Bone,” which is a divisional of U.S. patent application Ser. No. 10/617,976, filed Jul. 11, 2003 (now U.S. Pat. No. 7,153,307), which is a divisional of U.S. patent application Ser. No. 09/804,107, filed Mar. 12, 2001 (now U.S. Pat. No. 6,613,054), which is a divisional of U.S. patent application Ser. No. 09/134,323, filed Aug. 14, 1998 (now U.S. Pat. No. 6,241,734). 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention generally relates to the treatment of bone conditions in humans and other animals.  
       BACKGROUND OF THE INVENTION  
       [0003]     Injection devices similar to a household caulking gun are used to inject bone cement into bone. A typical bone cement injection device has a pistol shaped body, which supports a cartridge containing bone cement. A trigger actuates a spring-loaded ram, which forces a volume of bone cement in a viscous condition through a suitable nozzle and into the interior of a bone targeted for treatment. According to the teachings of U.S. Pat. Nos. 4,969,888 and 5,108,404, a cavity can be first formed by compacting cancellous bone inside the bone, into which the bone cement is injected. Conventional cement injection devices provide no opportunity to override the spring action and quickly terminate the flow of cement, should the cavity fill before the spring-actuated load cycle is completed. Furthermore, once the spring-actuated mechanism is triggered, conventional cement injection devices do not permit the injection volume or inject rate to be adjusted or controlled in real time, in reaction to cancellous bone volume and density conditions encountered inside bone.  
         [0004]     In a clinical procedure called vertebroplasty, bone cement is injected at high pressure (typically, about 700 psi) into the interior of a vertebral body, without the prior formation of a cavity. Because high pressure is used, there is little opportunity to quickly and accurately adjust cement flow in reaction to bone volume and density conditions encountered. Momentum generated by high pressure-induced cement flow continues to propel cement into the targeted bone site even after termination of the high pressure.  
         [0005]     As a result of the relatively high pressure that conventional procedures rely upon, coupled with the effective lack of a short response time, the targeted bone interior can suddenly overfill. Excess filling material can be forced outside the bone interior, and into adjoining tissue regions, where the presence of filling material is not required or desired.  
         [0006]     For these and other reasons, there is a need for new systems and methods for placing material into bones, with greater rate and volume control, a faster response time, and without requiring the use of high pressure.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention provides instruments, systems, and methods, which, in use, enable greater control over the placement of materials into bone.  
         [0008]     One aspect of the invention provides apparatus including a cannula for establishing a subcutaneous path into bone and including at least one radiopaque marker. The apparatus includes a tamping instrument for advancement through the cannula comprising a body portion and a handle portion. The handle portion has a cross-sectional area greater than the cross-sectional area of the body portion to facilitate manipulation by a user. Another aspect of the invention provides a method for using the apparatus as described.  
         [0009]     Another aspect of the invention provides apparatus including a cannula for establishing a subcutaneous path into bone. The apparatus includes a tamping instrument for advancement through the cannula. The tamping instrument includes at least one marking to visually gauge the advancement of the terminus relative to the distal end of the cannula. The tamping instrument comprises a body portion and a handle portion having a cross-sectional area greater than the cross-sectional area of the body portion to facilitate manipulation by a user. Another aspect of the invention provides a method for using the apparatus as described.  
         [0010]     Another aspect of the invention provides a method. the method includes deploying an expandable device through a percutaneous path into a vertebral body having cancellous bone volume to create a cavity in the cancellous bone volume. The method includes advancing a tamping instrument through a percutaneous cannula to deliver material into the cavity by manipulating an enlarged handle portion formed on the tamping instrument.  
         [0011]     The method includes gauging the advancement by observing at least one predetermined marking on the tamping instrument or the cannula to determine a position of a terminus of the tamping instrument relative to a distal end of the cannula.  
         [0012]     Features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended Claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a plane view of a kit housing a system of functional instruments, which, in use, gain subcutaneous access to the inside of a bone to compact cancellous bone and form a cavity for therapeutic purposes;  
         [0014]      FIG. 2  is an exploded perspective view of the kit shown in  FIG. 1 ;  
         [0015]      FIG. 3  is a perspective view of the subcutaneous access instrument group that forms a part of the system shown in  FIG. 1 ;  
         [0016]      FIG. 4A  is a perspective view of the cavity forming instrument that forms a part of the system shown in  FIG. 1 ;  
         [0017]      FIG. 4B  is a section view of the catheter tube of the cavity forming instrument, taken generally along line  4 B- 4 B in  FIG. 1 ;  
         [0018]      FIG. 4C  is an end view of an alternative embodiment of the cavity forming instrument shown in  FIG. 4A , having a prebent stylet;  
         [0019]      FIG. 5  is a perspective view of the material introducing instrument group that forms a part of the system shown in  FIG. 1 ;  
         [0020]      FIGS. 6 and 7  are, respectively, top and side views of a human vertebral body;  
         [0021]      FIG. 8  is a top view of a vertebral body during insertion of a spinal needle instrument to begin a bone access procedure;  
         [0022]     FIGS.  9  to  11  are top views showing subsequent steps, after insertion of the spinal needle instrument shown in  FIG. 8 , of inserting a guide pin instrument into the vertebral body;  
         [0023]      FIG. 12  is a perspective view showing a subsequent step, after insertion of the guide pin instrument shown in FIGS.  9  to  11 , which deploys an obturator instrument deployed over the guide pin instrument with aid of a handle;  
         [0024]      FIG. 13  is a top view of the vertebral body, with the obturator instrument shown in  FIG. 12  deployed;  
         [0025]      FIG. 14  is a perspective view showing a subsequent step, after insertion of the obturator instrument shown in  FIG. 12 , which uses the handle shown in  FIG. 12  to aid in the deployment of a cannula instrument over the obturator instrument;  
         [0026]      FIG. 15  is a top view of the vertebral body, with the cannula instrument shown in  FIG. 14  deployed;  
         [0027]      FIG. 16  is a perspective view showing a subsequent step, after insertion of the cannula instrument shown in  FIG. 14 , which removes the obturator instrument from the cannula instrument, to leave the cannula instrument and guide pin instrument in place;  
         [0028]      FIG. 17  is a top view of the vertebral body, after the obturator removal step shown in  FIG. 16 , leaving the cannula instrument and guide pin instrument in place;  
         [0029]      FIG. 18  is a perspective view showing a subsequent step, after removal of the obturator instrument shown in  FIG. 16 , which uses the handle shown in  FIG. 14  to aid in the deployment of a drill bit instrument through the cannula instrument along the guide pin instrument;  
         [0030]      FIG. 19  is a top view of the vertebral body, as the drill bit instrument shown in  FIG. 18  is deployed with aid of the handle to open a passage into the interior volume of the vertebral body;  
         [0031]      FIG. 20  is a perspective view showing a subsequent step, after removal of the drill bit instrument and guide pin instrument shown in  FIG. 18 , of deploying the cavity forming instrument into the vertebral body;  
         [0032]      FIG. 21  is a top view of the vertebral body, as the expandable structure carried by the cavity forming instrument shown in  FIG. 20  is deployed into the interior volume of the vertebral body;  
         [0033]      FIG. 22  is a top view of the vertebral body, as the expandable structure shown in a collapsed condition in  FIG. 21  is expanded to compact cancellous bone and form a cavity;  
         [0034]      FIG. 23  is a top view of the vertebral body, after removal of the expandable structure, showing the cavity formed by compacting cancellous bone;  
         [0035]      FIG. 24  is a perspective view of the syringe of the material introducing instrument group, shown in  FIG. 5 , being filled with a material selected for introduction into the cavity shown in  FIG. 23 ;  
         [0036]      FIG. 25  is a perspective view of the syringe shown in  FIG. 24  being joined to a nozzle, which also forms a part of the material introducing instrument group shown in  FIG. 5 ;  
         [0037]      FIG. 26  is a perspective view showing the syringe and attached nozzle shown in  FIG. 25  being deployed through the cannula instrument in preparation of introducing material into the cavity;  
         [0038]      FIGS. 27 and 28  are perspective and top views, respectively, showing the syringe and attached nozzle shown in  FIG. 26  in use to inject material into the cannula instrument for passage into the cavity;  
         [0039]      FIG. 29  is a top view of the vertebral body after a measured volume of material has been injected and the syringe and attached nozzle withdrawn from the cannula instrument;  
         [0040]      FIG. 30  is a top view showing the deployment of a tamping instrument, which forms a part of the material introducing instrument group shown in  FIG. 5 , being deployed in the cannula instrument;  
         [0041]      FIG. 31  is a top view showing advancement of the tamping instrument in the cannula instrument to displace and distribute material from the cannula instrument into the cavity;  
         [0042]      FIG. 32  is a top view of the vertebral body after removal of the tamping instrument and cannula instrument, showing the cavity, now filled with the material;  
         [0043]      FIG. 33  is a perspective view of a reduced diameter cannula instrument and associated reduced diameter material introducing instruments, which embody features of the invention;  
         [0044]      FIG. 34  is a perspective view of a cavity forming instrument having an expandable cavity forming structure, which, in use, is deployed using the reduced diameter cannula instrument shown in  FIG. 33 , the cavity forming instrument having a sliding introducer sleeve shown in its rearward position;  
         [0045]      FIG. 35  is a perspective view of the cavity forming instrument shown in  FIG. 34 , with the introducer sleeve moved forward to overlie and compress the expandable cavity forming structure;  
         [0046]      FIG. 36  is a perspective view of the cavity forming structure shown in  FIG. 35 , with the introducer sleeve (shown partially in section) coupled to the proximal end of the cannula instrument, to guide the expandable structure compressed within the sleeve into the reduced diameter cannula instrument without damage; and;  
         [0047]      FIG. 37  is a perspective view of the cavity forming structure shown in  FIG. 36 , after the expandable structure has been guided by the introducer sleeve into the cannula instrument and is being advanced through the cannula instrument for deployment in bone. 
     
    
       [0048]     The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0049]      FIGS. 1 and 2  show a system  10  of functional instruments. In use, certain instruments of the system  10  are deployed in a purposeful manner to penetrate tissue and gain subcutaneous access to the inside of a bone. Inside bone, other instruments of the system  10  are deployed to form a cavity in cancellous bone, into which a material is placed for therapeutic purposes.  
         [0050]     In the illustrated embodiment, the system  10  is arranged as a prepackage kit  12  in three functional instrument groups  14 ,  16 , and  18 . The first group  14  (which  FIG. 3  shows outside the kit  12 ) comprises instruments whose purpose is to gain subcutaneous access to a bone interior. The second group  16  (which  FIG. 4  shows outside the kit  12 ) comprises an instrument whose function is to create a cavity in cancellous bone. The third group  18  (which  FIG. 5  shows outside the kit  12 ) comprises instruments whose function is to introduce a material into the cavity.  
         [0051]     The kit  12  can take various forms. In the illustrated embodiment, the kit  12  comprises a sterile, wrapped assembly.  
         [0052]     Further details of each functional instrument group  14 ,  16 , and  18  and the kit  12  follow.  
       I. The Subcutaneous Access Instrument Group  
       [0053]     The number and type of instruments in the group  14  can vary.  FIG. 3  shows five representative instruments, each having a different size and function.  
         [0054]     A. The Spinal Needle and Guide Pin  
         [0055]     As  FIG. 3  shows, one instrument comprises a conventional spinal needle assembly  20  and a guide pin instrument  26 .  
         [0056]     In use, the spinal needle assembly  20  establishes the initial subcutaneous path leading to the targeted treatment site. The guide pin instrument  26  is deployed through this path, followed by progressively larger instruments, as will be described later.  
         [0057]     The spinal needle assembly  20  comprises a stylet  22 , which is slidably deployed within a stylus  24 . The stylus  24  typically has, for example, about an eleven gauge diameter. Other gauge diameters can be used, according to the gauge of the guide pin instrument  26  used.  
         [0058]     In use, the guide pin instrument  26  is deployed through the subcutaneous path established by the spinal needle assembly  20 , by exchange with the needle stylet  22 . The guide pin instrument  26  serves to guide the establishment of the main operative pathway to the targeted treatment site.  
         [0059]     The remaining instruments  28 ,  30 , and  32  in the group  14  share some common features, although they are intended, in use, to perform different functions. These instruments  28 ,  30 , and  32  are each made of a rigid, surgical grade plastic or metal material. These instruments  28 ,  30 , and  32  each comprises an elongated, cylindrical body having a proximal end  34  and a distal end  36 .  
         [0060]     B. The Obturator Instrument  
         [0061]     The instrument  28  functions as an obturator. Its distal end  36  is tapered to present a penetrating surface  38 . In use, the surface  38  is intended to penetrate soft tissue in response to pushing or twisting forces applied by the physician at the proximal end  34 .  
         [0062]     The proximal end  34  of the obturator instrument  28  presents a flanged surface  40 , which tapers from a larger outer diameter to a smaller outer diameter in the direction of the proximal end  34 . The flanged surface  40  includes an array of circumferentially spaced teeth  42 .  
         [0063]     An interior lumen  44  extends through the obturator instrument  28  from the distal end  36  to the proximal end  34 . The interior lumen  44  is sized to accommodate the guide pin instrument  26 , as will be described in greater detail later.  
         [0064]     C. The Cannula Instrument  
         [0065]     The instrument  30  functions as a cannula or guide sheath. The cannula instrument  30  is somewhat larger in diameter than and not as long as the obturator instrument  28 . The cannula instrument  30  includes an interior lumen  46  that extends from its distal end  36  to its proximal end  34 . The interior lumen  46  is sized to accept the obturator instrument  28 . The size of the interior lumen  46  permits a physician to slide and rotate the cannula instrument  30  relative to the obturator instrument  28 , and vice versa, as will be described in greater detail later.  
         [0066]     The distal end  36  of the cannula instrument  30  presents an end surface  48 . In use, the end surface  48  of the cannula instrument  30  is intended to penetrate soft tissue surrounding the obturator instrument  28  in response to pushing or twisting forces applied at the proximal end  34 .  
         [0067]     The proximal end  34  carries an enlarged fitting  50 . The fitting  50  tapers from a larger diameter to a smaller diameter in the direction of the proximal end  34 . Like the tapered flange  40  on the obturator instrument  28 , the tapered fitting  50  has an array of circumferentially spaced teeth  52 . The tapered fitting  50  of the cannula instrument  30  possesses a larger maximum outer diameter than the maximum outer diameter of the tapered flange  40  of the obturator instrument  28 .  
         [0068]     The cannula instrument  30  includes measured markings  118  along its length (see  FIG. 3 ). The measured markings  118  gauge the depth of insertion. The markings  118  can be placed, for example, at one centimeter intervals. As  FIG. 3  shows, the markings  118  can be consecutively numbered, beginning at the distal end  36 , so that the physician can ascertain the insertion depth at a glance.  
         [0069]     D. The Drill Bit Instrument  
         [0070]     The instrument  32  functions as a drill bit. The drill bit instrument  32  has generally the same physical dimensions as the obturator instrument  28 . Like the obturator instrument  28 , the drill bit instrument  32  is intended, in use, to fit for sliding and rotational movement within the interior lumen  46  of the cannula instrument  30 .  
         [0071]     The distal end  36  of the drill bit instrument  32  includes machined cutting edges  54 . In use, the cutting edges  54  are intended to penetrate hard tissue in response to rotation and longitudinal load forces applied at the proximal end  34  of the drill bit instrument  32 .  
         [0072]     The proximal end  34  presents a tapered flange  56 , which is substantially identical to the flange  40  on the obturator instrument  28 . Like the obturator instrument  28 , the tapered flange  56  changes from a larger diameter to a smaller diameter in the direction of the proximal end  34 . The tapered flange  56  of the drill bit instrument  32  also includes an array of circumferentially spaced teeth  58 . The form and orientation of the teeth  58  on the drill bit instrument  32  correspond to the form and orientation of the teeth  42  on the obturator instrument  28 .  
         [0073]     E. The Handle  
         [0074]     The group includes a handle  60 . The handle  60  engages the functional instruments  28 ,  30 , and  32  in a removable, slip fit fashion to aid a physician in manipulating the instruments during use.  
         [0075]     The handle  60  is made from a molded or cast rigid plastic or metal material. The handle  60  is shaped to be comfortably and securely grasped by a normal human hand. The shape and size to accommodate this function can, of course, vary. In the illustrated embodiment, the handle  60  is elongated along a main axis to fit comfortably across the palm of the hand.  
         [0076]     The handle  60  includes a center post  62 , which is integrally molded to the handle  60  about its geometric center. The center post  62  extends downward to give the handle  60  a general T-shape.  
         [0077]     The handle  60  includes two interior cavities or sockets  64  and  66  in the center post  62 . The sockets guide the attachment between the handle  60  and the instruments  28 ,  30 , and  32 . The first and second sockets  64  and  66  are sized to present unique attachment sites for different functional instruments.  
         [0078]     The first socket  64  includes an array of circumferentially spaced grooves  68 , which, in form and orientation, match the teeth  42  and  58  at the proximal ends  34  of the obturator instrument  28  and the drill bit instrument  32 . The first socket  64  accepts the tapered flange  40  or  56  of either the obturator instrument  28  or the drill bit instrument  32 . The teeth  42  and  58  of either tapered flange  40  or  56  mesh in a slip-fit with the grooves  68  of the first socket  64 . The running slip-fit allows longitudinal force to be applied to either instrument  28  or  32  through the handle  60 . The running slip-fit also prevents relative rotation between either instrument  28  or  32  and the first socket  64 , thereby permitting torsional or twisting forces to be applied to either instrument  28  or  32  by the handle  60 , with an increased mechanical advantage.  
         [0079]     The second socket  66  is larger than the first socket  64  and is sized to accept the larger tapered fitting  50  of the cannula instrument  30 . The second socket  66  includes an array of circumferentially spaced grooves  70 , which, in form and orientation, match the teeth  52  on the tapered fitting  50 . The teeth  52  of the tapered fitting  50  mesh in a slip-fit with the grooves  70  of the second socket  66 . The running slip-fit allows both longitudinal and torsional forces to be applied to the cannula instrument  30  through the handle  60 , with increased mechanical advantage.  
         [0080]     As shown in phantom lines in  FIG. 3 , a first passage  72  extends through the top of the handle  60 , through the center post  62 , and into the first socket  64 . The passage  72  is generally aligned with the center of the first socket  64  and is sized to pass the guide pin instrument  26  (see  FIG. 12 ).  
         [0081]     Likewise, as also shown in phantom lines in  FIG. 3 ) a second passage  74  extends through the top of the handle  60 , through the center post  62 , and into the second socket  66 . The passage  74  is generally aligned with the center of the second socket  66  and is sized to pass the either obturator instrument  28  or the drill bit instrument  32  (see  FIG. 14 ).  
         [0082]     Further details of the handle  60  can be found in co-pending U.S. patent application Ser. No. 09/014,229, filed Jan. 27, 1998, and entitled AA Slip-Fit Handle for Hand-Held Instruments that Access Interior Body Regions.  
         [0083]     Further details regarding the use of the handle  60  and the associated instruments  26 ,  28 , and  30  will be provided later.  
       II. The Cavity Forming Instrument  
       [0084]     As  FIG. 4A  shows, the group  16  includes an instrument  76 , which is deployed through the cannula instrument  30  to a location inside bone (see  FIG. 20 ). When so deployed, the instrument  76  serves to form a cavity in cancellous bone.  
         [0085]     The instrument  76  can be constructed in various ways. In the illustrated embodiment, the instrument  76  includes a flexible catheter tube  78  having a proximal end  80  and a distal end  82 . The proximal end  80  carries a handle grip  84  to facilitate gripping and maneuvering the catheter tube  78 . The materials for the catheter tube  78  are selected to facilitate its advancement through the cannula instrument  30 . The catheter tube  78  can be constructed, for example, using standard flexible, medical grade plastic materials, like vinyl, nylon, polyethylenes, ionomer, polyurethane, and polyethylene tetraphthalate (PET). The catheter tube  78  can also include more rigid materials to impart greater stiffness and thereby aid in its manipulation. More rigid materials that can be used for this purpose include stainless steel, nickel-titanium alloys (Nitinolj material), and other metal alloys.  
         [0086]     The distal end  82  of the instrument  76  carries an expandable structure  86 . In the illustrated embodiment, the expandable structure  86  is made from a polyurethane or an elastomer (e.g., silicone or nylon) material. The structure  86  has been preformed to possess a desired shape by exposure to heat and pressure, e.g., through the use of conventional thermoforming techniques.  
         [0087]     As  FIG. 4B  shows, the catheter body  78  includes an interior lumen  88 , which communicates with the interior of the structure  86 . A fitting  90  on the proximal end  80  of the catheter tube  78  (see  FIG. 4B ) communicates with the lumen  88 . The fitting  90  couples the lumen  88  to a source  92  of fluid, e.g., sterile saline (see  FIG. 21 ), or a radiopaque contrast medium.  
         [0088]     The fluid is introduced from the source  92  into the structure  86  under positive pressure, causing the structure  86  to expand. During expansion inside bone, the material selected for the structure  86  preferably resists deformation, so that the expanded shape inside bone essentially corresponds to its expanded shape outside bone, i.e., when in an open air environment. This allows the physician to select in an open air environment a structure  86  having an expanded shape desired to meet the targeted therapeutic result, with the confidence that the expanded shape inside bone will be similar in important respects. In addition to being able to expand its volume while resisting deformation inside bone, the material of the structure  86  preferable withstands abrasion, tearing, and puncture when in contact with cancellous bone.  
         [0089]     The shape of the structure  86 , when expanded inside bone, is selected by the physician, taking into account the morphology and geometry of the site to be treated. The shape of the cancellous bone to be compressed, and the local structures that could be harmed if bone were moved inappropriately, are generally understood by medical professionals using textbooks of human skeletal anatomy along with their knowledge of the site and its disease or injury. The physician is also able to select the expanded shape inside bone based upon prior analysis of the morphology of the targeted bone using, for example, plain film x-ray, fluroscopic x-ray, or MRI or CT scanning. The expanded shape inside bone is selected to optimize the formation of a cavity that, e.g., when filled with a suitable material, provides support across the region of the bone being treated.  
         [0090]     As one general guideline, in cases where the bone disease causing fracture (or the risk of fracture) is the loss of cancellous bone mass (as in osteoporosis), the selection of the expanded shape of the structure  86  inside bone should take into account that from 30% to 90% of the cancellous bone volume should be compacted. Another general guideline is the amount that the targeted fractured bone region has been displaced or depressed. The expansion of the structure  86  within the cancellous bone region inside a bone can elevate or push the fractured cortical wall back to or near its anatomic position occupied before fracture occurred.  
         [0091]     In the illustrated embodiment (see  FIG. 4A ), the structure  86  possesses a preformed hour-glass or peanut shape. This shape is selected in contemplation of deploying the structure  86  in a vertebral body, as will be described in greater detail later.  
         [0092]     To facilitate deployment of the structure  86  through the cannula instrument  30 , the catheter tube  78  includes a second interior lumen  94 . The lumen  94  extends from a second fitting  98  on the proximal end  80  of the catheter tube  78 , through the body of the cannula tube  78 , and through the interior of the structure  86  to the tip end  172  of the structure  86 . The lumen  94  receives a generally stiff stylet  96 , which can be made from a molded plastic or stainless steel material. The stylet  96  is inserted through the fitting  98  into the lumen  94 , and includes a threaded coupling  100  to secure the stylet  96  against movement. The presence of the stylet  96  serves to keep the structure  86  in the desired distally straightened condition during passage through the cannula instrument  30  into the targeted tissue region. Once the structure  86  is free of the cannula instrument  30  and inside bone, the stylet  96  can be withdrawn (shown by arrow  174  in  FIG. 4A ). This returns normal flexibility to the catheter tube  78  and facilitates manipulation of the structure  86  inside bone. With the stylet  96  withdrawn, the lumen  94  can also serve as a pathway for introducing rinsing liquid or to aspirate debris from the bone.  
         [0093]     In the illustrated embodiment, the stylet  96  is biased toward a generally straight condition. In an alternative embodiment (see  FIG. 4C ), a stylet  102  can have a preformed memory, to normally bend its distal region. The memory is overcome to straighten the stylet  102  when confined within the cannula instrument  30 . However, as the structure  86  and distal region of the preformed stylet  102  advance free of the cannula instrument  30 , to pass into the targeted region, the preformed memory bends the distal region of the stylet  102  and thereby shifts the main axis of the expandable structure  86 . The prebent stylet  102 , positioned within the interior of the structure  86 , aids in altering the orientation of the structure  86 , bringing it into better anatomic alignment with the targeted region.  
         [0094]     Other types of instruments that can form cavities in cancellous bone and other interior body regions are described in copending U.S. patent application Ser. No. 09/055,805, entitled A Structures and Methods for Creating Cavities in Interior Body Regions,@ filed Apr. 6, 1998.  
       III. The Material Introducing Instrument Group  
       [0095]     The group  18  includes instruments  104 ,  106 , and  108  which serve to convey and compact a selected material inside the cavity formed by the structure  86 . The material in the cavity provides a desired therapeutic result, e.g., replacement of tissue mass, or renewed interior support for the bone, or the delivery of medication, or combinations thereof. Accordingly, the material to perform this function can be selected from among, e.g., a material that sets to a hardened condition, including bone cement, autograft tissue, allograft tissue, synthetic bone substitute, as well as a medication, or combinations thereof.  
         [0096]     In the illustrated embodiment, the group  18  comprises material injection instruments  104  and  106  and a material tamping instrument  108 , which deliver material at a low delivery pressure, i.e., a pressure no greater than about 360 psi.  
         [0097]     A. Low Pressure Material Injection Instruments  
         [0098]     In the illustrated embodiment, the material is injected by use of a conventional syringe  104 , to which a specially designed injection nozzle  106  is coupled. A manual actuated syringe with a push plunger can be used. Alternatively, a LeVeen Inflation Syringe with threaded plunger can be used, which can be actuated manually or by use of a mechanical actuator.  
         [0099]     In the illustrated embodiment, the syringe  104  is made from a clear plastic material. The syringe  104  includes a chamber  110 , which receives the material to be injected. The material is expressed from the chamber  100  by a manually advanced syringe piston  112  (see also  FIG. 25 ).  
         [0100]     The injection nozzle  106  connects by a threaded connector  114  to the end of the syringe  104   9  (see also  FIG. 25 ). In the illustrated embodiment, the nozzle  106  is made from a generally flexible, inert plastic material, such as such as polyethylene or another suitable polymer. Alternatively, the nozzle  106  can be made from a generally rigid plastic or metal material.  
         [0101]     The injection nozzle  106  is sized to be advanced through the cannula instrument  30  (see  FIG. 26 ). The nozzle  106  includes measured markings  116  along its length. The markings  116  can be placed, for example, at one centimeter intervals, to correspond with the markings  118  on the cannula instrument  30 , so that the relative position of the nozzle  106  within the cannula instrument  30  can be gauged. The markings  118  can, e.g., include a set point  176 . Alignment of the set point  176  at the proximal end  34  of the cannula instrument  30 , indicates that the distal end of the nozzle  106  is located in an aligned relationship with the distal end  36  of the cannula instrument  30 . In this arrangement, the markings  118  are consecutively numbered with positive numbers proximally of the set point  176  and with negative numbers distally of the set point  176 . The physician is thereby able to tell at a glance the location of the distal end of the nozzle  106 , in terms of how far beyond or short of the distal end  36  of the cannula instrument  30  it is.  
         [0102]     In use, the distal end of the nozzle  106  is located beyond the distal end  36  of the cannula instrument  30  within the cavity formed in the targeted tissue region. As  FIG. 5  shows, the distal end of the nozzle  106 , when made from a plastic material, can carry at least one radiopaque marker  208 , to enable remote visualization of the nozzle position within the body. The syringe  104  ejects a predetermined volume of material into the nozzle  106  in a low pressure stream into the cavity. As the material fills the cavity, the nozzle (still ejecting material) is retracted from the cavity and into the cannula instrument  30  itself. Further details of this function and result will be provided later.  
         [0103]     B. The Material Tamping Instrument  
         [0104]     The group  18  also includes a material tamping instrument  108 . The tamping instrument  108  is made from generally rigid, inert plastic or metal material. The tamping instrument  108  is also sized to be advanced into the cannula instrument  30  (see  FIG. 30 ). The free end  124  of the tamping instrument  108  is ribbed or contoured to facilitate gripping the instrument  108  during use.  
         [0105]     The tamping instrument  108  includes measured markings  122  along its length. The markings  116  can be placed, for example, at one centimeter intervals, to correspond with the markings  118  on the cannula instrument  30 , so that the relative position of the tamping instrument  108  within the cannula instrument  30  can be gauged. Like the nozzle  106 , the markings  122  on the tamping instrument  108  includes a set point  178 , which indicates when the distal end of the tamping instrument  108  aligns with the distal end  36  of the cannula instrument  30 . Also like the nozzle  106 , the markings  122  on the tamping instrument  108  are consecutively numbered with positive numbers proximally of the set point  178  and with negative numbers distally of the set point  178 . The physician is thereby able to tell at a glance the location of the end of the tamping instrument  108 , in terms of how far beyond or short of the distal end  36  of the cannula instrument  30  it is. As  FIG. 5  also shows, the end of the tamping instrument  108 , when made from a plastic material, can carry at least one radiopaque marker  210 , so that its position can be visualized from outside the body.  
         [0106]     After withdrawal of the nozzle  106  from the cannula instrument  30 , residual material is left in the cannula instrument  30 . The purpose of the tamping instrument  108  is to displace the residual material out the distal end  36  of the cannula instrument  30  and into the cavity, to thereby fill the cavity without exerting undue pressure within the bone. The tamping instrument  108  thereby serves to clear residual material from the cannula instrument  30 , to assure that the desired volume of material is delivered into the cavity. The removal of residual material from the cannula instrument  30  by the tamping instrument  108  also prevents seepage of material into surrounding tissue regions upon removal of the cannula instrument  30 . The tamping instrument  108  also compacts the material uniformly within the cavity, again without undue pressure. Further details of these functions and results will be discussed later.  
       IV. The Kit  
       [0107]     As  FIGS. 1 and 2  show, in the illustrated embodiment, the kit  12  includes an interior tray  126  made, e.g., from die cut cardboard, plastic sheet, or thermo-formed plastic material. The tray  126  includes spaced apart tabs  128 , which hold the various instruments in a secure position during sterilization and storage prior to use.  
         [0108]     When packaged as a sterile assembly, the kit  12  includes an inner wrap  130 , which is peripherally sealed by heat or the like, to enclose the tray  126  from contact with the outside environment. One end of the inner wrap includes a conventional peal-away seal  132 , to provide quick access to the tray  126  at the instant of use, which preferably occurs in a sterile environment, such as within an operating room.  
         [0109]     When packaged as a sterile assembly, the kit  12  also includes an outer wrap  134 , which is also peripherally sealed by heat or the like, to enclose the inner wrap  130 . One end of the outer wrap includes a conventional peal-away seal  136 , to provide access to the inner wrap  130  and its contents. The outer wrap  134  can be removed from the inner wrap in anticipation of imminent use, without compromising sterility of the contents of the kit  12 .  
         [0110]     As  FIG. 2  shows, each inner and outer wrap  130  and  134  includes a peripherally sealed top sheet  138  and bottom sheet  140 . In the illustrated embodiment, the top sheet  138  is made of transparent plastic film, like polyethylene or MYLAR7 material, to allow visual identification of the contents of the kit  12 . The bottom sheet  140  is made from a material that is permeable to ETO sterilization gas, e.g., TYVEK7 plastic material (available from DuPont).  
         [0111]     In the illustrated embodiment, the tray  126  presents the instruments groups  14 ,  16 , and  18  in an ordered, organized layout, which is arranged to aid the physician in carrying out the intended procedure. For example, the layout of the tray  126  can present the instruments groups  14 ,  16 , and  18  in top-to-bottom order, according to sequence of intended use. For example, in a typical bone access procedure (as will be demonstrated in greater detail later), the stylet  22  and stylus  24  of the spinal needle assembly  20  are deployed first, followed by the guide pin instrument  26 , followed by the obturator instrument  28 , then the cannula instrument  30 , then the drill bit instrument  32 , then the cavity forming instrument  76 , then the syringe  104  and nozzle  106  instruments, and lastly the tamping instrument  108 . Accordingly, the tray  126  packages these instruments and components in a top-to-bottom order, with the spinal needle assembly  20  topmost, the guide pin instrument  26  next, the obturator instrument  28  next, and so on, with the tamping instrument  108  lowermost on the tray  126 .  
         [0112]     In this layout, the handle  60  is packaged to the side of the access instrument group  14 . The tray  126  can include written labels (not shown) identifying the components contained in the kit  12 .  
         [0113]     The kit  12  also preferably includes in the tray  126  directions  144  for using the contents of the kit  12  to carry out a desired procedure. An exemplary procedure which the directions  144  can describe will be explained later.  
         [0114]     When packaged as a sterile assembly, the directions  144  can also include the statement “For Single Patient Use Only” (or comparable language) to affirmatively caution against reuse of the contents of the kit  12  whose performance characteristics and efficacy degrade after a single use. The spinal needle assembly  20 , the cavity forming instrument  76 , and the material introducing instruments  104 ,  106 , and  108  should, for these reasons, be used but a single time and then discarded. The directions  144  also preferably affirmatively instruct against resterilization of at least these contents of kit  12 , and also instructs the physician to dispose of at least these contents of the kit  12  upon use in accordance with applicable biological waste procedures.  
         [0115]     The presence of the instrument groups  14 ,  16 , and  18  packaged in the sterile kit  12  verifies to the physician that the contents are sterile and have not been subjected to prior use. The physician is thereby assured that the instrument groups meet established performance and sterility specifications.  
         [0116]     It should be appreciated that the various instruments contained in the kit  12  can be packaged into several, smaller functional kits. For example, a first kit can package the access instrument group  14 , a second kit can package the cavity forming instrument group  16 , and a third kit can package the material introduction instrument group  18 .  FIGS. 1 and 2  illustrate one of many different possible embodiments.  
       V. Illustrative Use of the System  
       [0117]     The following describes use of the instrument groups  14 ,  16 , and  18  packaged in the kit  12  in the context of treating bones. This is because the instruments of the groups  14 ,  16 , and  18  can be advantageously used for this purpose. Still, it should be appreciated that one or more of the instrument groups, used alone or in association with other instruments, can perform other diagnostic or therapeutic functions in other interior regions of the body.  
         [0118]     In particular, the instrument groups  14 ,  16 , and  18  will described with regard to the treatment of human vertebra. It should be appreciated, however, their use is not limited to human vertebrae. The instrument groups  14 ,  16 , and  18  can be used in association with hand-held instruments in the treatment of diverse human or animal bone types.  
         [0119]     A. The Vertebral Body  
         [0120]     As  FIGS. 6 and 7  show, a typical vertebra  146  includes a vertebral body  148 , which extends on the anterior (i.e., front or chest) side of the vertebra  146 . The vertebral body  148  has the shape of an oval disk. The vertebral body  148  includes an exterior formed from compact cortical bone  150 . The cortical bone  150  encloses an interior volume of reticulated cancellous, or spongy, bone  152  (also called medullary bone or trabecular bone).  
         [0121]     The spinal cord  154  passes through the spinal canal  156  of the vertebra  146 . The vertebral arch  158  surrounds the spinal canal  156 . The pedicles  160  of the vertebral arch  158  adjoin the vertebral body  148 . The spinous process  162  extends from the posterior of the vertebral arch  158 , as do the left and right transverse processes  164 .  
         [0122]     B. Treatment of a Vertebral Body  
         [0123]     During a typical procedure, a patient lies on an operating table. The patient can lie face down on the table, or on either side, or at an oblique angle, depending upon the physician&#39;s preference.  
         [0124]     The physician or surgical assistant removes the outer and inner wraps  130  and  134  of the kit  12 , exposing the tray  126  for use. The physician acquires the spinal needle assembly  20  from the tray  126 . As  FIG. 8  shows, the physician introduces the spinal needle assembly  20  into soft tissue ST in the patient&#39;s back. Under radiologic or CT monitoring, the physician advances the spinal needle assembly  20  through soft tissue down to and into the targeted vertebra  146 . The physician will typically administer a local anesthetic, for example, lidocaine, through assembly  20 . In some cases, the physician may prefer other forms of anesthesia.  
         [0125]     The physician directs the spinal needle assembly  20  to penetrate the cortical bone  150  and the cancellous bone  152  of the targeted vertebral body  148 . Preferably the depth of penetration is about 60% to 95% of the vertebral body  148 .  
         [0126]      FIG. 8  shows gaining access to cancellous bone through the side of the vertebral body  148 , which is called postero-lateral access. However, access may be indicated through a pedicle  160 , which is called transpedicular access. The type of access is based upon the objectives of the treatment or for other reasons, based upon the preference of the physician.  
         [0127]     As  FIG. 9  shows, after positioning the spinal needle assembly  20  in cancellous bone  152 , the physician holds the stylus  24  and withdraws the stylet  22 . The physician acquires the guide pin instrument  26  from the tray  126 . As  FIG. 10  shows, while still holding the stylus  24 , the physician slides the guide pin instrument  26  through the stylus  24  and into the cancellous bone  152 . The physician now removes the stylus  24  (see FIG.  11 ), leaving the guide pin instrument  26  deployed within the cancellous bone  152 .  
         [0128]     The physician next acquires the obturator instrument  28  and the handle  60  from the tray  126 . The physician slides the obturator instrument  28  over the guide pin instrument  26 , distal end first. The physician slides the guide pin instrument  26  through the first passage  72  and the first socket  64  of the handle  60 . As  FIG. 12  shows, the physician slides the handle  60  along the guide pin instrument  26  toward the tapered flange  40  of the obturator instrument  28 , until achieving a running slip-fit between the first socket  64  and the tapered flange  40 , in the manner previously described. The obturator instrument  28  is now ready for use.  
         [0129]     As  FIG. 12  shows, the physician makes a small incision I in the patient&#39;s back. The physician twists the handle  60  while applying longitudinal force to the handle  60 . In response, the surface  38  of the obturator instrument  28  rotates and penetrates soft tissue ST through the incision I. The physician may also gently tap the handle  60 , or otherwise apply appropriate additional longitudinal force to the handle  60 , to advance the obturator instrument  28  through the soft tissue along the guide pin instrument  26  down to the entry site (see  FIG. 13 ). The physician can also tap the handle  60  with an appropriate striking tool to advance the surface  30  of the obturator instrument  28  into the side of the vertebral body  148  to secure its position (as  FIG. 13  shows).  
         [0130]     The physician next slides the handle  60  along the guide pin instrument  26  away from the obturator instrument  28  to disengage the tapered flange  40  from the first socket  64 . The physician then proceeds to slide the handle  60  completely off the guide pin instrument  26 .  
         [0131]     The physician acquires the cannula instrument  30  from the tray  126 . As  FIG. 14  shows, the physician slides the cannula instrument  30  over the guide pin instrument  26 , distal end first, and, further, over the obturator instrument  28 , until contact between the end surface  48  and soft tissue tissue ST. The physician now slides the guide pin instrument  26  and obturator instrument  26  through the second passage  74  and second socket  66  of the handle  60 . The physician slides the handle  60  toward the tapered fitting  50  of the cannula instrument  30  until a running slip-fit occurs between the second socket  66  and the tapered fitting  50 , as previously described. The cannula instrument  30  is now ready for use.  
         [0132]     As  FIG. 14  shows, the physician applies appropriate twisting and longitudinal forces to the handle  60 , to rotate and advance the cannula instrument  30  through soft tissue ST along the obturator instrument  28 . As  FIG. 15  shows, when the end surface  48  of the cannula instrument  30  contacts cortical bone, the physician can appropriately tap the handle  60  with a striking tool to advance the end surface into the side of the vertebral body  148  to secure its position.  
         [0133]     As  FIG. 16  shows, the physician now withdraws the obturator instrument  28 , sliding it off the guide pin instrument  26 . This leaves the guide pin instrument  26  and the cannula instrument  30  in place, as  FIG. 17  shows. The physician next slides the handle  60  along the guide pin instrument  26  away from the cannula instrument  30  to disengage the tapered fitting  50  from the second socket  66 . The physician then slides the handle  60  completely off the guide pin instrument  26 .  
         [0134]     The physician now acquires the drill bit instrument  32  from the tray  126 . As  FIG. 18  shows, the physician slides the drill bit instrument  32  over the guide pin instrument  26 , distal end first, through the cannula instrument  30  until contact between the machined surface  54  and bone tissue occurs. As  FIG. 18  also shows, the physician next leads the guide pin instrument  26  through the first passage  72  and first socket  64  of the handle  60 . The physician slides the handle  60  along the guide pin instrument  26  toward the tapered flange  56  of the drill bit instrument  32 , until a running slip-fit occurs between the first socket  64  and the tapered flange  56 , as previously described. The drill bit instrument  32  is now ready for use.  
         [0135]     As shown by  FIG. 18 , guided by X-ray (or another external visualizing system), the physician applies appropriate twisting and longitudinal forces to the handle  60 , to rotate and advance the cutting edge  54  of the drill bit instrument  32  to open a passage  166  (see  FIG. 19 ) through the bone tissue and completely into the cancellous bone  152 . The drilled passage  166  preferable extends no more than 95% across the vertebral body  148 .  
         [0136]     The physician now slides the handle  60  along the guide pin instrument  26  away from the drill bit instrument  32  to disengage the tapered flange  56  from the first socket  64 . The physician, further, slides the handle  60  completely off the guide pin instrument  26 . The physician can now remove the drill bit instrument  32  and the guide pin instrument  26 , leaving only the cannula instrument  30  in place. The passage  166  made by the drill bit instrument  32  remains. Subcutaneous access to the cancellous bone  152  has been accomplished.  
         [0137]     The physician can now acquire the cavity forming instrument from the tray  126 . As  FIG. 20  shows, the physician can advance the expandable structure  86  through the cannula instrument  30  and passage  166  into the interior volume of the vertebral body  148 , as  FIG. 21  also shows. The structure  86  is in its normally collapsed and not expanded condition during deployment. The stylet  96  or  102  is inserted in the lumen  94  of the catheter tube  78  to provide added stiffness to the structure  86  while being passed through the cannula instrument  30 .  
         [0138]     As shown in phantom lines in  FIG. 20 , the physician can, if desired, reconnect the handle  60  to the cannula instrument  30 , to help stabilize the cannula instrument  30  while deploying the structure  86 . The second passage  74  of the handle accommodates the catheter tube  78  and the structure  86 , when collapsed.  
         [0139]     As  FIG. 21  shows, the structure  86  is oriented in the desired way in the passage  166 . As before explained, the bent stylet  102  can aid in this task. Before, during, or after the orientation process, the stylet  96  or  102  can be withdrawn (as  FIG. 21  shows), to open the lumen  94  for use to pass a rinsing liquid or negative aspiration pressure.  
         [0140]     Sterile liquid is conveyed under pressure from the source  92  through the lumen  88  into the structure  86 . As  FIG. 22  shows, the structure  86  expands inside bone. Expansion of the structure  86  compresses cancellous bone  152  in the vertebral body  148 .  
         [0141]     The compression forms an interior cavity  168  in the cancellous bone  152 . As  FIG. 23  shows, subsequent collapse and removal of the structure  86  leaves the cavity  168  in a condition to receive a filling material.  
         [0142]     The compaction of cancellous bone  152  can also exert interior force upon cortical bone, making it possible to elevate or push broken and compressed bone back to or near its original prefracture, or other desired condition.  
         [0143]     Upon formation of the cavity  168 , the physician acquires the syringe  104  and injection nozzle  106  from the kit  12 . As  FIG. 24  shows, the physician fills the syringe chamber  110  with the desired volume of filling material  170 . As  FIG. 25  shows, the physician attaches the nozzle  106  to the filled syringe  104 . As  FIG. 26  shows, the physician inserts the nozzle  106  a selected distance beyond the distal end  36  of the cannula instrument  30  and into the cavity, guided by the markings  116 .  
         [0144]     As shown in phantom lines in  FIG. 26 , the handle  60  can remain attached to the cannula instrument  30  to provide stability, as the second passage  74  of the handle accommodates the nozzle  106 .  
         [0145]     As  FIG. 27  shows, the physician manually advances the piston  112  to cause the material  170  to flow through and out of the nozzle  106  and into the cavity. As material  170  fills the cavity, the physician withdraws the nozzle from the cavity and into the cannula instrument  30 . The cannula instrument  30  channels the material  170  flow toward the cavity  168 . As  FIG. 28  shows, the cement material  170  flows in a stream into the cavity  168 .  
         [0146]     If the selected material  170  is bone cement, the cement material  170  is placed into the syringe chamber  110  shortly after it is mixed from two materials (e.g., in an external mixing device), while it is in a low viscosity, relatively free flowing liquid state, like a thin pancake batter. In time (e.g., about two minutes after mixing), the consistency of the cement material  170  will change to a substantially putty-like character.  
         [0147]     The physician operates the syringe  104  to expel the cement material  170  from the chamber, through the nozzle  106 , first into the cavity and then into the cannula instrument  30 . Typically, at the end of the syringe injection process, material  170  should extend from the cavity and occupy about 40% to 50% of the cannula instrument  30 .  
         [0148]     When a desired volume of cement is expelled from the syringe  104 , the physician withdraws the nozzle  106  from the cannula instrument  30 , as  FIG. 29  shows. The physician may first rotate the syringe  104  and nozzle  106 , to break loose the material  170  in the nozzle  106  from the ejected bolus of material  170  occupying the cannula instrument  30 .  
         [0149]     The physician acquires the tamping instrument  108  from the kit  12 . As  FIG. 30  shows, the physician advances the tamping instrument  108  through the cannula instrument  30 . As phantom lines in  FIG. 30  show, the handle  60  can remain attached to the cannula instrument  30  to provide stability, as the second passage  74  of the handle accommodates the tamping instrument  108 .  
         [0150]     The distal end of the tamping instrument  108  contacts the residual volume of cement material  170  in the cannula instrument  30 . As  FIGS. 30 and 31  show, advancement of the tamping instrument  108  displaces progressively more of the residual material  170  from the cannula instrument  30 , forcing it into the cavity  168 . The flow of material  170  into the cavity  168 , propelled by the advancement of the tamping instrument  108  in the cannula instrument  30 , serves to uniformly distribute and compact the material  170  inside the cavity  168 , without the application of undue pressure.  
         [0151]     The use of the syringe  104 , nozzle  106 , and the tamping instrument  108  allows the physician to exert precise control when filling the cavity with material  170 . The physician can immediately adjust the volume and rate of delivery according to the particular local physiological conditions encountered. The application of low pressure (i.e., no greater than 360 psi), which is uniformly applied by the syringe  104  and the tamping instrument  108 , allows the physician to respond to fill volume and flow resistance conditions in a virtually instantaneous fashion. The chance of overfilling and leakage of material  170  outside the cavity is significantly reduced.  
         [0152]     When the physician is satisfied that the material  170  has been amply distributed inside the cavity  168 , the physician withdraws the tamping instrument  108  from the cannula instrument  30 . The physician preferably first twists the tamping instrument  108  to cleanly break contact with the material  170 . The handle  60  can now be removed and the cannula instrument  30  withdrawn, as  FIG. 32  shows. The incision site is sutured closed. The bone treatment procedure is concluded.  
         [0153]     Eventually the material  170 , if cement, will harden a rigid state within the cavity  168 . The capability of the vertebral body  148  to withstand loads is thereby improved.  
         [0154]     The selected material  170  can be an autograft or allograft bone graft tissue collected in conventional ways. For example, the graft material can be in paste form, as described by Dick, A Use of the Acetabular Reamer to Harvest Autogenic Bone Graft Material: A Simple Method for Producing Bone Paste,@ Archives of Orthopaedic and Traumatic Surgery (1986), 105: 235-238, or in pellet form, as described by Bhan et al, A Percutaneous Bone Grafting for Nonunion and Delayed Union of Fractures of the Tibial Shaft,@ International Orthopaedics (SICOT) (1993) 17: 310-312, both of which are incorporated herein by reference. Alternatively, the bone graft tissue can be obtained using a Bone Graft Harvester, which is commercially available from SpineTech. Using a funnel, the paste or pellet graft tissue material is loaded into the cannula instrument  30 . The tamping instrument  108  is then advanced into the cannula instrument  30  in the manner previously described, to displace the paste or pellet graft tissue material out of the cannula instrument  30  and into the cavity.  
         [0155]     The selected material  170  can also comprise a granular bone material harvested from coral, e.g., ProOsteonJ calcium carbonate granules, available from Interpore. The granules are loaded into the cannula instrument  30  using a funnel and advanced into the cavity using the tamping instrument  108 .  
         [0156]     The selected material  170  can also comprise demineralized bone matrix suspended in glycerol (e.g., GraftonJ allograft material available from Osteotech), or SRSJ calcium phosphate cement available from Novian. These viscous materials, like the bone cement previously described, can be loaded into the syringe  104  and injected into the cavity using the nozzle  106 , which is inserted through the cannula instrument  30  into the cavity. The tamping instrument  108  is used to displace residual material from the cannula instrument  30  into the cavity, as before described.  
         [0157]     The selected material  170  can also be in sheet form, e.g. CollagraftJ material made from calcium carbonate powder and collagen from bovine bone. The sheet can be rolled into a tube and loaded by hand into the cannula instrument  30 . The tamping instrument  108  is then advanced through the cannula instrument, to push and compact the material in the cavity.  
       VI. Alternative Embodiments  
       [0158]     The use of low pressure delivery of material  170  frees the system  10  from the need to accommodate relatively large diameter, high pressure delivery devices. The interior diameter of the cannula instrument  30  can be downsized accordingly, thereby minimizing the dimensions of the subcutaneous pathway to gain access to the targeted bone region.  
         [0159]     Typically, when low pressure material injection instruments are used, the largest tool that the reduced-diameter cannula instrument must accommodate is the expandable cavity-forming structure  82 . The structure  82  presents a minimal profile during deployment, as it can be collapsed and, if desired, a lubricous coating may also be applied to the exterior of the structure  82  to facilitate its passage through the reduced-diameter cannula instrument.  
         [0160]     A. Low Pressure Material Injection Instruments  
         [0161]      FIG. 33  exemplifies low pressure material injection instruments  180  and  182  that function in association with a cannula instrument  184  having a reduced interior diameter, e.g. only about 3.4 mm or less.  
         [0162]     One instrument  180  comprises a reduced-diameter nozzle. As  FIG. 33  shows, the nozzle  180  is sized to pass through the reduced-diameter cannula instrument  184 , to thereby pass into bone in the manner previously shown in  FIG. 26 . The reduced-diameter nozzle  180  connects by a threaded connector  186  to the syringe  104 . For material strength, despite its reduced dimension, the nozzle  180  is preferably formed from a rigid metal material, e.g., stainless steel.  
         [0163]     As  FIG. 33  shows, the reduced-diameter nozzle  180  also includes measured markings  188  along its length, as previously described. The markings  188  include a set point  190 , as previously described, which aligns with the proximal end of the cannula instrument  184  when the distal ends of the cannula instrument  184  and the nozzle  180  align.  
         [0164]     The other reduced diameter instrument  182  comprises a stylet, which is sized to pass through the interior bore of the nozzle  180 . The stylet  182  includes a handle  192 , which rests on the proximal connector  186  of the nozzle  180  when the stylet  182  is fully inserted into the nozzle  180 . When the handle  192  is rested, the distal ends of the stylet  182  and nozzle  180  align. The presence of the stylet  182  inside the nozzle  180  closes the interior nozzle bore.  
         [0165]     In use, the nozzle  180  is coupled to the syringe  104  and inserted through the cannula instrument  184  into the material-receiving cavity  168  formed in cancellous bone, in the same manner shown in  FIG. 26 . Material in the syringe  104  is injected at low pressure through the nozzle  180  into the cavity  168 . As before explained, as the cavity  168  progressively fills with material, the nozzle  180  is withdrawn back into the cannula instrument  184 . Typically, when the injection of material is completed, material extends from the cavity  168  and occupies about 40% to 50% of the cannula instrument  184 .  
         [0166]     At this point, the nozzle  180  can be fully withdrawn from the cannula instrument  184  and unthreaded from the syringe  104 . The stylet  182  can be advanced into the nozzle  180 , to bring the handle  192  at rest against the connector  186 , thereby clearing residual material from the nozzle  180 . The nozzle  180  and stylet can then be inserted as a nested unit into the cannula instrument  184 . Nested together, the nozzle  180  and stylet  182  form a tamping instrument. Upon advancement through the cannula instrument  184 , the nested nozzle  180  and stylet  182  displace residual material from the cannula instrument  184  into the cavity  168 , in generally the same manner as previously shown in  FIGS. 30 and 31 , thereby uniformly compacting material within the cavity  168  in a controlled fashion and without undue pressure.  
         [0167]     Alternatively, a single-piece tamping instrument, separate from the nozzle  180 , can be provided, downsized to fit through the reduced-diameter cannula instrument  184 . In this embodiment, the stylet  182  is not necessary, unless it is desired to reclaim material from the nozzle.  
         [0168]     B. Cavity Forming Instrument  
         [0169]      FIG. 34  shows a cavity forming instrument  194  intended to be deployed through the reduced-diameter cannula instrument  184 , shown in  FIG. 33 . In many respects, the instrument  194  is like the instrument  76 , previously described and shown in  FIG. 4A , and common reference numerals will be assigned to common structural elements. The instrument  184  includes a flexible catheter tube  78  having a proximal end  80  and a distal end  82 . The proximal end  80  carries a handle grip  84 , and the distal end  82  carries an expandable structure  86 , which, when deployed in bone, compacts cancellous bone and forms the cavity  168 .  
         [0170]     Unlike the previously-described instrument  76 , the instrument  194  carries an introducer sleeve  196 . The introducer sleeve  196  slides along the catheter tube  78  between the handle grip  84  and the expandable structure  86 . The introducer sleeve  196  includes a tubular main body  198  with a forward collar  200  and a rear collar  202 .  
         [0171]     The introducer sleeve  196  normally occupies an advanced position on the instrument  194 , as shown in  FIG. 35 . In this position, the main body  198  overlies and surrounds the expandable structure  86 . The main body  198  is sized to compress the structure  86  to an outside diameter that is slightly less than the interior diameter of the reduced-diameter cannula instrument  184 .  
         [0172]     As  FIG. 35  shows, when the introducer sleeve  196  occupies the advanced position, the forward collar  200  extends beyond the distal end of the compressed expandable structure  82 . As  FIG. 36  shows, in this position, the forward collar  200  presents itself for engagement with the proximal end  204  of the cannula instrument  184 . The forward collar  200  is sized to have an interior diameter that makes friction-fit engagement about the proximal end  204  of the cannula instrument  184 .  
         [0173]     As  FIG. 36  shows, when it is time to deploy the expandable structure  86  through the cannula instrument  184 , the physician engages the forward collar  200  of the introducer sleeve  196  in a friction fit about the proximal end  204  of the cannula instrument  184 . As  FIG. 37  shows, advancing the catheter tube  78  moves the compressed structure  86  through the main body  198  of the sleeve  196  and into the bore of the cannula instrument  184 . The engagement of the forward collar  200  about the proximal cannula end  204  aligns the axis of the structure  86  with the axis of the cannula instrument  184 , while compressing the structure  86  to a diameter smaller than the interior of the cannula instrument  184 . Upon advancement of the catheter tube  78 , the introducer sleeve  196  guides the structure  86  into the cannula instrument  194  without tearing or other damage.  
         [0174]     Once the expandable structure  86  is advanced through the cannula instrument  184  and into bone, the physician can slide the introducer sleeve  196  rearward away from the proximal cannula end  204 , to break the friction fit between the end  204  and the forward sleeve. As  FIG. 34  shows, the rear collar  202  of the sleeve  196  is sized to make a snap fit engagement about a stem  206 , which surrounds the catheter tube  78  near the handle  84 . The snap fit engagement stabilizes the position of the sleeve  196  during subsequent use and manipulation of the cavity-forming instrument  194 .  
         [0175]     The features of the invention are set forth in the following claims.