Abstract:
A method provides a void creation device including an expandable structure adapted to undergo expansion in the cancellous bone volume of a bone selected for treatment. The expandable structure has at least one dimension so that the expandable structure will assume a predetermined shape and size when substantially expanded that compacts only a first volume of the cancellous bone volume to form a void, leaving a second volume of the cancellous bone volume substantially uncompacted by the expandable structure. A filling material is placed within the void through the percutaneous access path.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/884,365, filed Jun. 19, 2001 now U.S. Pat. No. 7,044,954, entitled “Method for Treating a Vertebral Body,” which is a continuation of U.S. patent application Ser. No. 08/911,805, filed Aug. 15, 1997 (now abandoned), which is a continuation-in-part of U.S. patent application Ser. No. 08/871,114, filed Jun. 9, 1997 (now U.S. Pat. No. 6,248,110), which is a continuation-in-part of U.S. patent application Ser. No. 08/659,678, filed Jun. 5, 1996 (now U.S. Pat. No. 5,827,289), which is a continuation-in-part of U.S. patent application Ser. No. 08/485,394, filed Jun. 7, 1995 (now abandoned), which is a continuation-in-part of U.S. patent application Ser. No. 08/188,224, filed Jan. 26, 1994 (now abandoned), entitled, “Improved Inflatable Device For Use In Surgical Protocol Relating To Fixation Of Bone.” 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the treatment of bone conditions in humans and other animals. 
     BACKGROUND OF THE INVENTION 
     When cancellous bone becomes diseased, for example, because of osteoporosis, avascular necrosis, or cancer, the surrounding cortical bone becomes more prone to compression fracture or collapse. This is because the cancellous bone no longer provides interior support for the surrounding cortical bone. 
     There are 2 million fractures each year in the United States, of which about 1.3 million are caused by osteoporosis alone. There are also other bone disease involving infected bone, poorly healing bone, or bone fractured by severe trauma. These conditions, if not successfully treated, can result in deformities, chronic complications, and an overall adverse impact upon the quality of life. 
     U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose apparatus and methods for the fixation of fractures or other conditions of human and other animal bone systems, both osteoporotic and non-osteoporotic. The apparatus and methods employ an expandable body to compress cancellous bone and provide an interior cavity. The cavity receives a filling material, which hardens and provides renewed interior structural support for cortical bone. 
     The better and more efficacious treatment of bone disease that these Patents promise can be more fully realized with improved systems and methods for making and deploying expandable bodies in bone. 
     SUMMARY OF THE INVENTION 
     The invention provides a method that provides a void creation device including an expandable structure adapted to undergo expansion in the cancellous bone volume of a bone selected for treatment. The expandable structure has at least one dimension so that the expandable structure will assume a predetermined shape and size when substantially expanded that compacts only a first volume of the cancellous bone volume to form a void, leaving a second volume of the cancellous bone volume substantially uncompacted by the expandable structure. A filling material is placed within the void through the percutaneous access path. 
     Features and advantages of the invention are set forth in the following Description and Drawings, as well as in the appended Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a probe that carries an expandable structure that embodies features of the invention; 
         FIG. 2  is a lateral view, partially broken away and in section, of a lumbar vertebra; 
         FIG. 3  is a coronal view of the lumbar vertebra, partially cut away and in section, shown in  FIG. 2 ; 
         FIG. 4  is a lateral view of the lumbar vertebra shown in  FIGS. 2 and 3 , partially cut away and in section, with the expandable structure shown in  FIG. 1  deployed by transpedicular access when in a substantially collapsed condition; 
         FIG. 5  is a coronal view of the transpedicular access shown in  FIG. 4 , partially cut away and in section; 
         FIG. 6  is a lateral view of the lumbar vertebra shown in  FIG. 4 , after expansion of the expandable structure shown in  FIG. 1  to form a cavity; 
         FIG. 7  is a perspective view of one representative embodiment of an expandable structure having a stacked doughnut-shaped geometry; 
         FIG. 8  is a view of another representative embodiment of an expandable structure having an oblong-shaped geometry; 
         FIG. 9  is an elevation view of another representative embodiment of an expandable structure showing three stacked structures and string-like restraints for limiting the expansion of the bodies during inflation; 
         FIG. 10  is a perspective view of another representative embodiment of an expandable structure having a kidney bean-shaped geometry; 
         FIG. 11  is a top view of another representative embodiment of an expandable structure having a kidney bean-shaped geometry with several compartments formed by a heating element or branding tool; 
         FIG. 12  is a cross-sectional view taken along line  12 - 12  of  FIG. 11 ; 
         FIG. 13  is a perspective, lateral view of a vertebral body, partially broken away to show the presence of an expandable structure, and also showing the major reference dimensions for the expandable structure; 
         FIG. 14  is a dorsal view of a representative expandable structure having a humpback banana-shaped geometry in use in a right distal radius; 
         FIG. 15  is a cross sectional view of the expandable structure shown in  FIG. 14 , taken generally along line  15 - 15  of  FIG. 14 ; 
         FIG. 16  is a side view, with parts broken away and in section, of an expandable structure having an enclosed stiffening member, to straighten the structure during passage through a guide sheath into an interior body region; 
         FIG. 17  is a side view of the expandable structure shown in  FIG. 16 , after deployment beyond the guide sheath and into the interior body region, in which the stiffening member includes a distal region having a preformed bend, which deflects the structure relative to the axis of the guide sheath; 
         FIG. 18  is a plan view of a sterile kit to store a single use probe, which carries an expandable structure of the type previously shown; and 
         FIG. 19  is an exploded perspective view of the sterile kit shown in  FIG. 18 . 
     
    
    
     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 
     The preferred embodiment describes improved systems and methods that embody features of the invention in the context of treating bones. This is because the new systems and methods are advantageous when used for this purpose. It should be appreciated that the systems and methods as described are not limited to use in the treatment of bones. 
     I. The Expandable Structure 
       FIG. 1  shows a tool  10 , which includes a catheter tube  12  having a proximal and a distal end, respectively  14  and  16 . The catheter tube  12  includes a handle  18  near its proximal end  14  to facilitate gripping and maneuvering the tube  12 . The handle  18  is preferably made of a foam material secured about the catheter tube  12 . 
     The distal end  16  carries an expandable structure  20 . The structure  20  is shown in  FIG. 1  in a substantially collapsed geometry. When substantially collapsed, the structure  20  can be inserted into the interior of a bone, as will be described in greater detail later. 
     Generally speaking (and as will be demonstrated in greater detail later), an animal bone includes an exterior formed from compact cortical bone, which encloses an interior volume of reticulated cancellous, or spongy, bone (also called medullary bone or trabecular bone). When collapsed, the structure  20  is deployed in the cancellous bone. 
     As will also be described in greater detail later, the structure  20 , when expanded, compresses the cancellous bone and thereby creates an interior cavity. The cavity is intended to receive a filling material, e.g., bone cement, which hardens and provides renewed interior structural support for surrounding cortical bone. The compaction of cancellous bone also exerts 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. 
     U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose the use of expandable structures for the fixation of fractures or other conditions of human and other animal bone systems, both osteoporotic and non-osteoporotic. These Patents are incorporated herein by reference. 
     A. Material Selection for the Expandable Structure 
     The material of the expandable structure  20  can be selected according to the therapeutic objectives surrounding its use. For example, materials including vinyl, nylon, polyethylenes, ionomer, polyurethane, and polyethylene tetraphthalate (PET) can be used. The thickness of the structure is typically in the range of 2/1000ths to 25/1000ths of an inch, or other thicknesses that can withstand pressures of up to, for example, 250-500 psi. 
     If desired, the material for the structure  20  can be selected to exhibit generally elastic properties, like latex. Alternatively, the material can be selected to exhibit less elastic properties, like silicone. Using expandable bodies with generally elastic or generally semi-elastic properties, the physician monitors the expansion to assure that over-expansion and wall failure do not occur. Furthermore, expandable bodies with generally elastic or generally semi-elastic properties may require some form of external or internal restraints to assure proper deployment in bone. The use of internal or external restraints in association with expandable bodies used to treat bone is discussed in greater detail in co-pending U.S. patent application Ser. No. 08/485,394, filed Jun. 7, 1995, which is incorporated herein by reference. 
     Generally speaking, for use in treating bone, providing relatively inelastic properties for the expandable structure  20 , while not always required, is nevertheless preferred, when maintaining a desired shape and size within the bone is important, for example, in a vertebral structure, where the spinal cord is nearby. Using relatively inelastic bodies, the shape and size can be better predefined, taking into account the normal dimensions of the outside edge of the cancellous bone. Use of relatively inelastic materials also more readily permits the application of pressures equally in a defined geometry to compress cancellous bone. 
     When treating bone, the choice of the shape and size of a expandable structure  20  takes 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 materials and geometry desired for the structure  20  based upon prior analysis of the morphology of the targeted bone using, for example, plain films, spinous process percussion, or MRI or CRT scanning. The materials and geometry of the structure  20  are selected to optimize the formation of a cavity that, when filled with bone cement, provide support across the middle region of the bone being treated. 
     In some instances, it is desirable, when creating a cavity, to also move or displace the cortical bone to achieve the desired therapeutic result. Such movement is not per se harmful, as that term is used in this Specification, because it is indicated to achieve the desired therapeutic result. By definition, harm results when expansion of the structure  20  results in a worsening of the overall condition of the bone and surrounding anatomic structures, for example, by injury to surrounding tissue or causing a permanent adverse change in bone biomechanics. 
     As one general guideline, the selection of the geometry of the expandable structure  20  should take into account that at least 40% of the cancellous bone volume needs to be compacted in cases where the bone disease causing fracture (or the risk of fracture) is the loss of cancellous bone mass (as in osteoporosis). The preferred range is about 30% to 90% of the cancellous bone volume. Compacting less of the cancellous bone volume can leave too much of the diseased cancellous bone at the treated site. The diseased cancellous bone remains weak and can later collapse, causing fracture, despite treatment. 
     Another general guideline for the selection of the geometry of the expandable structure  20  is the amount that the targeted fractured bone region has been displaced or depressed. The expansion of the structure  20  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. 
     However, there are times when a lesser amount of cancellous bone compaction is indicated. For example, when the bone disease being treated is localized, such as in avascular necrosis, or where local loss of blood supply is killing bone in a limited area, the expandable structure  20  can compact a smaller volume of total bone. This is because the diseased area requiring treatment is smaller. 
     Another exception lies in the use of an expandable structure  20  to improve insertion of solid materials in defined shapes, like hydroxyapatite and components in total joint replacement. In these cases, the structure  20  shape and size is defined by the shape and size of the material being inserted. 
     Yet another exception lays the use of expandable bodies in bones to create cavities to aid in the delivery of therapeutic substances, as disclosed in copending U.S. patent application Ser. No. 08/485,394, previously mentioned. In this case, the cancellous bone may or may not be diseased or adversely affected. Healthy cancellous bone can be sacrificed by significant compaction to improve the delivery of a drug or growth factor which has an important therapeutic purpose. In this application, the size of the expandable structure  20  is chosen by the desired amount of therapeutic substance sought to be delivered. In this case, the bone with the drug inside is supported while the drug works, and the bone heals through exterior casting or current interior or exterior fixation devices. 
     The materials for the catheter tube are selected to facilitate advancement of the expandable structure  20  into cancellous bone. The catheter tube 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 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 (Nitinol™ material), and other metal alloys. 
     B. Selection of Shape and Size for the Expandable Structure 
     As will also be demonstrated later, when relatively inelastic materials are used for the structure  20 , or when the structure  20  is otherwise externally restrained to limit its expansion prior to failure, a predetermined shape and size can be imparted to the structure  20 , when it is substantially expanded. The shape and size can be predetermined according to the shape and size of the surrounding cortical bone  28  and adjacent internal structures, or by the size and shape of the cavity desired to be formed in the cancellous bone  32 . 
     In one embodiment, which is generally applicable for treating bones experiencing or prone to fracture, the shape and size of the structure  20 , when substantially expanded, can be designed to occupy at least about 30% of the volume of cancellous bone  32  in the interior volume  30 . A structure  20  having a substantially expanded size and shape in the range of about 40% to about 99% of the cancellous bone volume is preferred. 
     In another embodiment, which is applicable for treating bones having more localized regions of fracture or collapse caused, for example, by avascular necrosis, the shape and size of the structure  20  can be designed to occupy as little as about 10% of the cancellous bone volume. In this embodiment, the structure  20  is deployed directly at the localized site of injury. 
     The shape of the cancellous bone  32  to be compressed, and the presence of surrounding local anatomic structures that could be harmed if cortical 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 materials and geometry desired for the structure  20  based upon prior analysis of the morphology of the targeted bone using, for example, plain films, spinous process percussion, or MRI or CRT scanning. The materials and geometry of the structure  20  are selected to create a cavity of desired size and shape in cancellous bone without applying harmful pressure to the outer cortical bone or surrounding anatomic structures. 
     In some instances, it is desirable, when creating the cavity, to move or displace the cortical bone to achieve the desired therapeutic result. Such movement is not per se harmful, as that term is used in this Specification, because it is indicated to achieve the desired therapeutic result. By definition, harm results when expansion of the structure  20  results in a worsening of the overall condition of the bone and surrounding anatomic structures, for example, by injury to surrounding tissue or causing a permanent adverse change in bone biomechanics. 
     II. Treatment of Vertebral Bodies 
       FIG. 2  shows a lateral (side) view of a human lumbar vertebra  22 .  FIG. 3  shows a coronal (top) view of the vertebra  22 . The vertebra  22  includes a vertebral body  26 , which extends on the anterior (i.e., front or chest) side of the vertebra  22 . The vertebral body  26  is in the shape of an oval disk. 
     As  FIGS. 2 and 3  show, the vertebral body  26  includes an exterior formed from compact cortical bone  28 . The cortical bone  28  encloses an interior volume  30  of reticulated cancellous, or spongy, bone  32  (also called medullary bone or trabecular bone). 
     The spinal canal  36  (see  FIG. 2 ), is located on the posterior (i.e., back) side of each vertebra  22 . The spinal cord  37  passes through the spinal canal  36 . The vertebral arch  40  surrounds the spinal canal  36 . Left and right pedicles  42  of the vertebral arch  40  adjoin the vertebral body  26 . The spinous process  44  extends from the posterior of the vertebral arch  40 , as do the left and right transverse processes  46 . 
     A selected expandable structure  20  can be inserted into bone in accordance with the teachings of the above described U.S. Pat. Nos. 4,969,888 and 5,108,404. For a given vertebral body  26 , access into the interior volume  30  can be accomplished, for example, by drilling an access portal  43  through either or both pedicles  42 .  FIG. 4  shows a single transpedicular approach in lateral view, and  FIG. 5  shows a single transpedicular approach in coronal view. As  FIG. 4  shows, the access portal  43  for a transpedicular approach enters at the top of the vertebral body  26 , where the pedicle  42  is relatively thin, and extends at an angle downward toward the bottom of the vertebral structure  26  to enter the interior volume  30 . The catheter tube  12  carrying the expandable structure  20  is guided into the interior volume  30  through an outer guide sheath  24 , which passes through the portal  43 . 
     As  FIG. 6 , expansion of the structure  20  in the interior volume  30  compresses the cancellous bone  32  and creates an interior cavity  34 . The cavity  34  remains after collapse and removal of the structure  20  from the interior volume  30 . The cavity  34  is intended to receive a filling material, like bone cement, to provide renewed interior structural support for surrounding cortical bone  28 . The compaction of cancellous bone also exerts interior force upon cortical bone  28 , making it possible to elevate or push broken and compressed bone back to or near its original prefracture, or other desired, condition. 
     Access to the interior volume  30  of a given vertebral body  26  can be achieved through the sides of the body, shown in phantom lines  45  in  FIG. 5 . This approach is called a postero-lateral approach. 
     The above described access can be carried out in a minimally invasive manner. It can also be carried out using an open surgical procedure. Using open surgery, the physician can approach the bone to be treated as if the procedure is percutaneous, except that there is no skin and other tissues between the surgeon and the bone being treated. This keeps the cortical bone as intact as possible, and can provide more freedom in accessing the interior volume  30  of the vertebral body. 
     A. Representative Embodiments of Expandable Structures to Treat Vertebrae 
     i. Constrained Donut-Shaped Geometries 
       FIG. 7  shows a representative embodiment of an expandable structure, which is broadly denoted by the numeral  210 . The structure  210  comprises a pair of hollow, inflatable, non-expandable parts  212  and  214  of flexible material, such as PET or Kevlar. Parts  212  and  214  have a suction tube  216  therebetween for drawing fats and other debris by suction into tube  216  for transfer to a remote disposal location. The suction tube  216  has one or more suction holes so that suction may be applied to the open end of tube  216  from a suction source (not shown). 
     The parts  212  and  214  are connected together by an adhesive which can be of any suitable type. Parts  212  and  214  are doughnut-shaped, as shown in  FIG. 7 , and have tubes  218  and  220  which communicate with and extend away from the parts  212  and  214 , respectively, to a source of inflating liquid under pressure (not shown). The liquid expands the structure  210 . 
       FIG. 8  shows a modified doughnut shape structure  280  of the type shown in  FIG. 7 , except the doughnut shapes of structure  280  are not stitched onto one another. In  FIG. 8 , structure  280  has a pear-shaped outer convex surface  282  which is made up of a first hollow part  284  and a second hollow part  285 . A tube  288  is provided for directing liquid into the two parts along branches  290  and  292  to inflate the parts after the parts have been inserted into the interior volume of a bone. A catheter tube  216  may or may not be inserted into the space  296  between two parts of the balloon  280  to provide irrigation or suction. An adhesive bonds the two parts  284  and  285  together. 
       FIG. 9  shows another representative embodiment of an expandable structure, designated  309 . The structure  309  has a generally round geometry and three expandable structure units  310 ,  312  and  314 . The structure units  310 ,  312 , and  314  include string-like external restraints  317 , which limit the expansion of the structure units  310 ,  312 , and  314  in a direction transverse to the longitudinal axes of the structure units  310 ,  312 , and  314 . The restraints  317  are made of the same or similar material as that of the structure units  310 ,  312 , and  314 , so that they have some resilience but substantially no expansion capability. 
     A tubes  315  direct liquid under pressure into the structure units  310 ,  312  and  314  to expand the units and cause compaction of cancellous bone. The restraints  317  limit expansion of the structure units prior to failure, keeping the opposed sides  377  and  379  substantially flat and parallel with each other. 
     ii. Constrained Kidney-Shaped Geometries 
       FIG. 10  shows another representative embodiment of an expandable structure  230 , which has a kidney-shaped geometry. The structure  230  has a pair of opposed kidney-shaped side walls  232  and a continuous end wall  234 . A tube  238  directs liquid into the structure to expand it within the vertebral structure. 
       FIG. 11  shows another representative embodiment of an expandable structure  242 , which also has a kidney-shaped geometry. The structure  242  is initially a single chamber bladder, but the bladder is branded along curved lines or strips  241  to form attachment lines  244  which take the shape of side-by-side compartments  246 , as shown in  FIG. 12 . A similar pattern of strips as in  242 , but in straight lines would be applied to a structure that is square or rectangular. The branding causes a welding of the two sides of the bladder to occur. 
     The details of these and other expandable structures usable to treat vertebral bodies are described in U.S. patent application Ser. No. 08/188,224, filed Jan. 26, 1994, and U.S. patent application Ser. No. 08/871,114, filed Jun. 9, 1997, which are incorporated herein by reference. 
     B. Selection of Desired Geometry 
     The eventual selection of the size and shape of a particular expandable structure  20  or structures to treat a targeted vertebral structure  26  is based upon several factors. When multiple expandable bodies are used, the total combined dimensions of all expandable bodies deployed, when substantially expanded, should be taken into account. 
     The anterior-posterior (A-P) dimension (see  FIG. 13 ) for the expandable structure or bodies is selected from the CT scan or plain film or x-ray views of the targeted vertebral structure  26 . The A-P dimension is measured from the internal cortical wall of the anterior cortex to the internal cortical wall of the posterior cortex of the vertebral structure. In general, the appropriate A-P dimension for the expandable structure or bodies is less than this anatomic measurement. 
     The appropriate side to side dimension L (see  FIG. 13 ) for an expandable structure or bodies is also selected from the CT scan, or from a plain film or x-ray view of the targeted vertebral structure. The side to side distance is measured between the internal cortical walls laterally across the targeted vertebral structure. In general, the appropriate side to side dimension L for the expandable structure is less than this anatomic measurement. 
     The lumbar vertebral structure tends to be much wider in side to side dimension L then in A-P dimension. In thoracic vertebral bodies, the side to side dimension and the A-P dimensions are almost equal. 
     The height dimensions H of the expandable structure or bodies (see  FIG. 13 ) is chosen by the CT scan or x-ray views of the vertebral bodies above and below the vertebral structure to be treated. The height of the vertebral bodies above and below the vertebral structure to be treated are measured and averaged. This average is used to determine the appropriate height dimension of the chosen expandable structure. 
     The dimensions of expandable structure or bodies for use in vertebrae are patient specific and will vary across a broad range, as summarized in the following table: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                 Posterior 
                   
               
               
                   
                   
                 Height (H) 
                 (A–P) 
                 Side to Side 
               
               
                   
                   
                 Dimension 
                 Dimension 
                 Dimension (L) 
               
               
                   
                   
                 of Typical 
                 of Typical 
                 of Typical 
               
               
                   
                   
                 Expandable 
                 Expandable 
                 Expandable 
               
               
                   
                 Vertebra 
                 structure 
                 Structure 
                 Structure 
               
               
                   
                 Type 
                 or Bodies 
                 or Bodies 
                 or Bodies 
               
               
                   
                   
               
             
             
               
                   
                 Lumbar 
                 0.5 cm to 
                 0.5 cm to 
                 0.5 cm to 
               
               
                   
                   
                 4.0 cm 
                 4.0 cm 
                 5.0 cm 
               
               
                   
                 Thoracic 
                 0.5 cm to 
                 0.5 cm to 
                 0.5 cm to 
               
               
                   
                   
                 3.5 cm 
                 3.5 cm 
                 4.0 cm 
               
               
                   
                   
               
             
          
         
       
     
     A preferred expandable structure for use in a vertebral structure is stacked with two or more expandable members of unequal height (designated  20 A and  20 B in  FIG. 13 ), where each member can be separately inflated through independent tube systems. The total height of the stack when fully inflated should be within the height ranges specified above. Such a design allows the fractured vertebral structure to be returned to its original height in steps, which can be easier on the surrounding tissue, and it also allows the same balloon to be used in a wider range of vertebral structure sizes. 
     III. Treatment of Other Bones 
     Like vertebrae, the interior regions of other bones in the appendicular skeleton are substantially occupied by cancellous bone, and thus can be treated with the use of one or more expandable structures. Regions in the appendicular skeleton which can be treated using expandable structures include the distal radius, the proximal tibial plateau, the proximal humerus, the proximal femoral head, and the calcaneus. 
     As for vertebral bodies, expandable structures possess the important attribute of being able, in the course of forming cavities by compressing cancellous bone, to also elevate or push broken or compressed cortical bone back to or near its normal anatomic position. This is a particularly important attribute for the successful treatment of compression fractures or cancellous bone fractures in the appendicular skeleton, such as the distal radius, the proximal humerus, the tibial plateau, the femoral head, hip, and calcaneus. 
     One representative example of an expandable structure for the treatment of cancellous bone regions of a long bone (distal radius) will be described. 
     A. Expandable Structure for the Distal Radius 
     The selection of an appropriate expandable to treat a fracture of the distal radius will depend on the radiological size of the distal radius and the location of the fracture. 
       FIGS. 14 and 15  show a representative expandable structure  260  for use in the distal radius. The structure  260 , which is shown deployed in the distal radius  252 , has a shape which approximates a pyramid but more closely can be considered the shape of a humpbacked banana. The geometry of the structure  260  substantially fills the interior of the space of the distal radius to compact cancellous bone  254  against the inner surface  256  of cortical bone  258 . 
     The structure  260  has a lower, conical portion  259  which extends downwardly into the hollow space of the distal radius  252 . This conical portion  259  increases in cross section as a central distal portion  261  is approached. The cross section of the structure  260  is shown at a central location ( FIG. 14 ), which is near the widest location of the structure  260 . The upper end of the structure  260 , denoted by the numeral  262 , converges to the catheter tube  288  for directing a liquid into the structure  260  to expand it and force the cancellous bone against the inner surface of the cortical bone. 
     The shape of the structure  260  is determined and restrained by tufts formed by string restraints  265 . These restraints are optional and provide additional strength to the structure  260 , but are not required to achieve the desired configuration. 
     The structure  260  is placed into and taken out of the distal radius in the same manner as that described above with respect to the vertebral bone. 
     Typical dimensions of the distal radius structure vary as follows: 
     The proximal end of the structure  260  (i.e. the part nearest the elbow) is cylindrical in shape and will vary from 0.4×0.4 cm to 1.8×1.8 cm. 
     The length of the distal radius structure will vary from 1.0 cm to 12.0 cm. 
     The widest medial to lateral dimension of the distal radius structure, which occurs at or near the distal radio-ulnar joint, will measure from 0.5 cm to 2.5 cm. 
     The distal anterior-posterior dimension of the distal radius structure will vary from 0.4 to 3.0 cm. 
     The details of these and other expandable structures usable to treat vertebral bodies are described in U.S. patent application Ser. No. 08/188,224, filed Jan. 26, 1994, and U.S. patent application Ser. No. 08/871,114, filed Jun. 9, 1997, which are incorporated herein by reference. 
     IV. Deflection of an Expandable Structure 
     As  FIG. 16  shows, a selected expandable structure  604  can include an enclosed tube  600 , which provides an interior lumen  602  passing within the expandable structure  604 . The lumen  602  accommodates the passage of a stiffening member or stylet  606  made, e.g., from stainless steel or molded plastic material. 
     The presence of the stylet  606  serves to keep the structure  604  in the desired distally straightened condition during passage through an associated guide sheath  608  toward the targeted body region  610 , as  FIG. 16  shows. As before explained, access to the targeted body region  610  through the guide sheath  608  can be accomplished using a closed, minimally invasive procedure or with an open procedure. 
     As shown in  FIG. 17 , the stylet  606  can have a preformed memory, to normally bend the distal region  612  of the stylet  606 . The memory is overcome to straighten the stylet  606  when confined within the guide sheath  608 , as  FIG. 16  shows. However, as the structure  604  and stylet  606  advance free of the guide sheath  608  and pass into the targeted region  610 , the preformed memory bends the distal stylet region  612 . The bend of the distal stylet region  612  bends the tube  600  and thereby shifts the axis  614  of the attached expandable structure  604  relative to the axis  616  of the access path (i.e., the guide sheath  608 ). The prebent stylet  606 , positioned within the interior of the structure  604 , aids in altering the geometry of the structure  604  in accordance with the orientation desired when the structure  604  is deployed for use in the targeted region  610 . 
     V. Single Use 
     Expansion of any one of the expandable structures described herein during first use in a targeted structure region generates stress on the material or materials which make up the structure. The material stress created by operational loads during first use in a targeted structure region can significantly alter the molded morphology of the structure, making future performance of the structure unpredictable. 
     For example, expansion within bone during a single use creates contact with surrounding cortical and cancellous bone. This contact can damage the structure, creating localized regions of weakness, which may escape detection. The existence of localized regions of weakness can unpredictably cause overall structural failure during a subsequent use. 
     In addition, exposure to blood and tissue during a single use can entrap biological components on or within the structure or the associated catheter tube. Despite cleaning and subsequent sterilization, the presence of entrapped biological components can lead to unacceptable pyrogenic reactions. 
     As a result, following first use, the structure can not be relied upon to reach its desired configuration during subsequent use and may not otherwise meet established performance and sterilization specifications. The effects of material stress and damage caused during a single use, coupled with the possibility of pyrogen reactions even after resterilization, reasonably justify imposing a single use restriction upon devices which carry these expandable structures for deployment in bone. 
     To protect patients from the potential adverse consequences occasioned by multiple use, which include disease transmission, or material stress and instability, or decreased or unpredictable performance, the invention also provides a kit  500  (see  FIGS. 18 and 19 ) for storing a single use probe  502 , which carries an expandable structure  504  described herein prior to deployment in bone. 
     In the illustrated embodiment (see  FIGS. 18 and 19 ), the kit  500  includes an interior tray  508 . The tray  508  holds the probe  502  in a lay-flat, straightened condition during sterilization and storage prior to its first use. The tray  508  can be formed from die cut cardboard or thermoformed plastic material. The tray  508  includes one or more spaced apart tabs  510 , which hold the catheter tube  503  and expandable structure  504  in the desired lay-flat, straightened condition. As shown, the facing ends of the tabs  510  present a nesting, serpentine geometry, which engages the catheter tube  503  essentially across its entire width, to securely retain the catheter tube  503  on the tray  508 . 
     The kit  500  includes an inner wrap  512 , which is peripherally sealed by heat or the like, to enclose the tray  508  from contact with the outside environment. One end of the inner wrap  512  includes a conventional peal-away seal  514  (see  FIG. 19 ), to provide quick access to the tray  508  upon instance of use, which preferably occurs in a sterile environment, such as within an operating room. 
     The kit  500  also includes an outer wrap  516 , which is also peripherally sealed by heat or the like, to enclosed the inner wrap  512 . One end of the outer wrap  516  includes a conventional peal-away seal  518  (see  FIG. 19 ), to provide access to the inner wrap  512 , which can be removed from the outer wrap  516  in anticipation of imminent use of the probe  502 , without compromising sterility of the probe  502  itself. 
     Both inner and outer wraps  512  and  516  (see  FIG. 19 ) each includes a peripherally sealed top sheet  520  and bottom sheet  522 . In the illustrated embodiment, the top sheet  520  is made of transparent plastic film, like polyethylene or MYLAR™ material, to allow visual identification of the contents of the kit  500 . The bottom sheet  522  is made from a material that is permeable to EtO sterilization gas, e.g., TYVEC™ plastic material (available from DuPont). 
     The sterile kit  500  also carries a label or insert  506 , which includes the statement “For Single Patient Use Only” (or comparable language) to affirmatively caution against reuse of the contents of the kit  500 . The label  506  also preferably affirmatively instructs against resterilization of the probe  502 . The label  506  also preferably instructs the physician or user to dispose of the probe  502  and the entire contents of the kit  500  upon use in accordance with applicable biological waste procedures. 
     The presence of the probe  502  packaged in the kit  500  verifies to the physician or user that probe  502  is sterile and has not be subjected to prior use. The physician or user is thereby assured that the expandable structure  504  meets established performance and sterility specifications, and will have the desired configuration when expanded for use. 
     The features of the invention are set forth in the following claims.