US20040010263A1 - Expandable preformed structures for deployment in interior body regions - Google Patents

Abstract

A tool for deploying an expandable structure into interior body regions provides a catheter body having an interior lumen. The catheter body carries an expandable structure. A stylet is sized configured for passage through the lumen and adapted to straighten the expandable structure during deployment into an interior body region.

Description

RELATED APPLICATIONS
• This application is a divisional of copending U.S. patent application Ser. No. 09/420,529, filed Oct. 19, 1999, which is a continuation-in-part of U.S. patent application Ser. No. 09/088,459, filed Jun. 1, 1998, and entitled “Expandable Preformed Structures for Deployment in Interior Body Regions,” now abandoned.[0001]
FIELD OF THE INVENTION
• The invention relates to expandable structures, which, in use, are deployed in interior body regions of humans and other animals.[0002]
BACKGROUND OF THE INVENTION
• The deployment of expandable structures, generically called “balloons,” into cancellous bone is known. For example, U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose apparatus and methods using expandable structures in cancellous bone for the fixation of fractures or other osteoporotic and non-osteoporotic conditions of human and animal bones.[0003]
SUMMARY OF THE INVENTION
• According to one aspect of the invention, a tool for deploying an expandable structure into bone comprises a catheter body defining an interior lumen and having a proximal end and a distal end. An expandable structure having a distal end is carried by the catheter body. A stylet having a proximal end is sized and configured for passage through the lumen and adapted to straighten the expandable structure during deployment into an interior body region.[0004]
• In one embodiment, the stylet is substantially rigid. In one embodiment, the stylet is made of stainless steel.[0005]
• According to another aspect of the invention, the proximal end of the stylet is coupleable to the catheter body after passage of the stylet through the lumen.[0006]
• According to yet another aspect of the invention, the stylet abuts against the distal end of the expandable structure after passage of the stylet through the lumen.[0007]
• Features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended claims.[0008]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a coronal view of a vertebral body;[0009]
• FIG. 2 is a lateral view of the vertebral body shown in FIG. 1;[0010]
• FIG. 3 is a plan view of a tool which carries at its distal end an expandable structure that embodies features of the invention;[0011]
• FIG. 4 is an enlarged view of the proximal end of the tool shown in FIG. 3, showing the handle and connected luer fittings;[0012]
• FIG. 5 is an enlarged view of the distal end of the tool shown in FIG. 3, showing the expandable structure;[0013]
• FIG. 6 is a plan view of the tool shown in FIG. 3, also showing a stylet that can be inserted into the tool to straighten the expandable structure during deployment in bone;[0014]
• FIG. 7 is an enlarged view of the distal end of the tool shown in FIG. 3, also showing an insertion sleeve that can be used to compact the expandable structure prior to insertion into a cannula;[0015]
• FIG. 8 is a top view of a mold forming the expandable structure shown in FIG. 5;[0016]
• FIG. 9 is a coronal view of the vertebral body shown in FIG. 1, with the tool shown in FIG. 3 deployed to compress cancellous bone as a result of inflating the expandable structure;[0017]
• FIG. 10 is a coronal view of the vertebral body shown in FIG. 9, upon removal of the tool, showing the cavity formed by the compression of cancellous bone by the expandable structure;[0018]
• FIG. 11 is an enlarged view of the expandable structure shown in FIG. 5, diagrammatically showing the expansion characteristics of the structure; and[0019]
• FIG. 12 is a graph which plots the effects of increasing pressure applied to the interior of the structure to the expanded volume of the structure.[0020]
• 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.[0021]
DESCRIPTION OF THE PREFERRED EMBODIMENT
• 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. However, aspects of the invention can be advantageously applied for diagnostic or therapeutic purposes in other areas of the body.[0022]
• The new systems and methods will be more specifically described in the context of the treatment of human vertebra. Of course, other human or animal bone types can be treated in the same or equivalent fashion.[0023]
• I. Anatomy of a Vertebral Body[0024]
• FIG. 1 shows a coronal (top) view of a[0025]human lumbar vertebra12. FIG. 2 shows a lateral (side) view of thevertebra12. Thevertebra12 includes avertebral body26, which extends on the anterior (i.e., front or chest) side of thevertebra12. Thevertebral body26 is shaped generally like a marshmallow.
• As FIGS. 1 and 2 show, the[0026]vertebral body26 includes an exterior formed from compactcortical bone28. Thecortical bone28 encloses an interior volume of reticulated cancellous, or spongy, bone32 (also called medullary bone or trabecular bone).
• The spinal canal[0027]36 (see FIG. 1), is located on the posterior (i.e., back) side of eachvertebra12. The spinal cord (not shown) passes through thespinal canal36. Thevertebral arch40 surrounds thespinal canal36. Left andright pedicles42 of thevertebral arch40 adjoin thevertebral body26. Thespinous process44 extends from the posterior of thevertebral arch40, as do the left and righttransverse processes46.
• It may be indicated, due to disease or trauma, to compress cancellous bone within the vertebral body. The compression, for example, can be used to form an interior cavity, which receives a filling material, e.g., a flowable material that sets to a hardened condition, like bone cement, allograft tissue, autograft tissue, hydroxyapatite, or synthetic bone substitute, as well as a medication, or combinations thereof, to provide improved interior support for cortical bone or other therapeutic functions, or both. 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.[0028]
• II. Tool for Treating Vertebral Bodies[0029]
• FIGS.[0030]3 to5 show atool48 for accessing bone for the purpose of compacting cancellous bone. Thetool48 includes acatheter tube assembly10. The distal end of thecatheter tube assembly10 carries anexpandable structure56. In use, the structure is deployed and expanded inside bone, e.g., in thevertebral body26 shown in FIGS. 1 and 2, tocompact cancellous bone32, as will be described later.
• As best shown in FIGS. 4 and 5, the[0031]catheter tube assembly10 includes anouter catheter body16 and aninner catheter body18, which extends through theouter catheter body16. The proximal ends of the outer andinner catheter bodies16 and18 are coupled to a y-shaped adaptor/handle14 (as FIG. 4 shows).
• As FIG. 5 shows, the[0032]expandable structure56 is coupled at its proximal end to the distal end of theouter catheter body16. Likewise, the expandable structure is coupled at its distal end to the distal end of theinner catheter body18.
• The[0033]outer catheter body16 defines an interior lumen20 (see FIGS. 4 and 5), through which theinner catheter body18 extends. In use, theinterior lumen20 conveys a pressurized liquid, e.g., sterile water, radiopaque fluid (such as CONRAY™ solution, from Mallinkrodt, Inc., or another fluid into thestructure56, to expand it.
• A first female-to-male luer fitting[0034]22 is secured to thehandle14 and serves, in use, to couple theinterior lumen20 to a source of pressured liquid.
• As FIGS. 4 and 5 also show, the[0035]inner catheter body18 defines aninterior lumen24, which passes concentrically through theinterior lumen20 of theouter catheter body16. In use, theinterior lumen24 can serve to convey a flushing liquid, e.g., sterile saline, for discharge through anopening30 at the distal end of theinner catheter body18.
• A second female-to-male luer fitting[0036]34, which is joined to theinner catheter body18, is also secured to thehandle14. If desired, the second female-to-male luer fitting34 can serve to couple theinterior lumen24 to a source of flushing liquid. In addition, theinterior lumen24 of theinner catheter body18 can accommodate passage of a stylet38 (see FIG. 6). The distal end of thestylet38 is preferably radiused, to prevent puncture of theinner catheter body18.
• As FIG. 6 shows, the[0037]stylet38 desirably carries ascrew cap50, which when attached to the second luer fitting34, holds thestylet38 in place within theinner catheter body18. In the illustrated embodiment, the proximal end of theinner catheter body18 includes a flared region52 (see FIG. 4) where it joins the second luer fitting34. The flaredregion52 allows smooth insertion of thestylet38, free of interference or contact with the peripheral edge of theinner catheter body18.
• When the[0038]cap50 is screwed into the second luer fitting34, thestylet38 desirably extends through the entireinterior lumen24 of theinner catheter body18. In the illustrated embodiment, theopening30 at the distal end of theinner catheter body18 is sized to block passage of thestylet38 beyond the distal end of theinner catheter body18. Thus, when inserted through theinterior lumen24 and locked to thehandle14 with thescrew cap50, thestylet38 desirably abuts against the distal end of thestructure56. The presence of thestylet38 desirably prevents thestructure56 from bunching or deflecting when thestructure56 is inserted into thecannula78 and/or bone.
• The[0039]tool48 also includes an insertion sleeve54 (see FIG. 7). Theinsertion sleeve54 is carried for sliding movement along theouter catheter body16. Theinsertion sleeve54 slides forward over the structure56 (shown in phantom lines in FIG. 7), to protect and compress thestructure56 during its insertion into thecannula78. Once thestructure56 is deployed into thecannula78, theinsertion sleeve54 slides aft away from the structure56 (shown in solid lines in FIG. 7), and can, if desired, engage thehandle14.
• Various materials can be selected for the component parts of the[0040]tool48. Furthermore, the dimensions of the component parts of thetool48 can also vary, according to its intended use. The following table lists preferred component materials and dimensions, which are well suited for atool48 that can be deployed for use in a vertebral body:

  	Component	Material	Dimension (Inches)
  	Outer	99% TEXIN ® 5270	Outside Diameter:
  	catheter	Polyurethane	0.102
  	body 16	1% Titanium	Inside Diameter:
  		Dioxide	0.078
  		(Colorant)
  	Inner	A Blend	Outside Diameter:
  	catheter	Comprising:	0.063
  	body 18	25% TEXIN ® 5286
  		Polyurethane	Inside Diameter:
  		75% TEXIN ® 5270	0.043
  		Polyurethane
  	Expandable	TEXIN ® 5286	As Formed:
  	Structure	Polyurethane
  			Axial Length (From
  			Distal End of Outer
  			Catheter Tube to
  			Distal end of Inner
  			Catheter Tube): 0.949
  			Compressed Diameter:
  			0.160″
  			Non - Expanded
  			Diameter: 0.270″
  	Tool		Total End to End
  			Length: 15.75
  	Stylet	Stainless Steel	Outside Diameter:
  			0.038
  	Insertion	PEBAX ® Tubing	Outside Diameter:
  	sleeve 54		0.195
  			Inside Diameter:
  			0.160
  			Length: 1.5

• The blend of polyurethane materials for the[0041]inner catheter body18 desirably enhances the strength of the distal bond between theinner catheter body18 and thestructure56, due to the presence in both components of the common TEXIN® 5286 Polyurethane material. This improved bond allows the length of the distal bond to be reduced without sacrificing bond integrity. In addition, because both theinner catheter body18 and thestructure56 are clear plastic, visual inspection of the distal bond area is simplified.
• The component parts of the[0042]tool48 can be formed and assembled in various ways. A preferred assembly will now be described.
• A. The Expandable Structure[0043]
• The material from which the[0044]structure56 is made should possess various physical and mechanical properties to optimize its functional capabilities to compact cancellous bone. The three most important properties are the ability to expand its volume; the ability to deform in a desired way when expanding and assume a desired shape inside bone; and the ability to withstand abrasion, tearing, and puncture when in contact with cancellous bone.
• 1. Expansion Property[0045]
• A first desired property for the structure material is the ability to expand or otherwise increase its volume without failure. This property enables the[0046]structure56 to be deployed in a collapsed, low profile condition subcutaneously, e.g., through a cannula, into the targeted bone region. This property also enables the expansion of thestructure56 inside the targeted bone region to press against and compress surrounding cancellous bone, or move cortical bone to a prefracture or other desired condition, or both.
• The desired expansion property for the structure material can be characterized by ultimate elongation properties, which indicate the degree of expansion that the material can accommodate prior to failure. Sufficient ultimate elongation permits the[0047]structure56 to compact cortical bone, as well as lift contiguous cortical bone, if necessary, prior to wall failure. Desirably, thestructure56 will comprise material able to undergo an ultimate elongation of at least 50%, prior to wall failure when expanded outside of bone. More desirably, the structure will comprise material able to undergo an ultimate elongation of at least 150%, prior to wall failure, when expanded outside of bone. Most desirably, the structure will comprise material able to undergo an ultimate elongation of at least 300%, prior to wall failure, when expanded outside of bone.
• 2. Shape Property[0048]
• A second desired property for the material of the[0049]structure56 is the ability to predictably deform during expansion, so that thestructure56 consistently achieves a desired shape inside bone.
• The shape of the[0050]structure56, when expanded in bone, is desirably 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, and also taking into account the teachings of U.S. patent application Ser. No. 08/788,786, filed Jan. 23, 1997, and entitled “Improved Inflatable Device for Use in Surgical Protocol Relating to Fixation of Bone,” which is incorporated herein by reference. The physician is also desirably able to select the desired expanded shape inside bone based upon prior analysis of the morphology of the targeted bone using, for example, plain film x-ray, fluoroscopic x-ray, or MRI or CT scanning. The expanded shape inside bone is selected to optimize the formation of a cavity that, when filled with a selected material, provides support across the region of the bone being treated. The selected expanded shape is made by evaluation of the predicted deformation that will occur with increased volume due to the shape and physiology of the targeted bone region.
• 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[0051]structure56 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 consideration, 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[0052]structure56 inside bone should take into account the cancellous bone volume which should be compacted to achieve the desired therapeutic result. An exemplary range is about 30% to 90% of the cancellous bone volume, but the range can vary depending upon the targeted bone region. Generally speaking, compacting less of the cancellous bone volume leaves more uncompacted, diseased cancellous bone at the treatment site.
• Another general guideline for the selection of the expanded shape of the[0053]structure56 inside bone is the amount that the targeted fractured bone region has been displaced or depressed. The controlled deformation diameter expansion of thestructure56 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. Generally speaking, inadequate compaction of cancellous bone results in less lifting of contiguous cortical bone.
• For practical reasons, it is desired that the expanded shape of the[0054]structure56 inside bone, when in contact with cancellous bone, substantially conforms to the shape of thestructure56 outside bone, when in an open air environment. This allows the physician to select in an open air environment a structure 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.
• An optimal degree of shaping can be achieved by material selection and by special manufacturing techniques, e.g., thermoforming or blow molding, as will be described in greater detail later.[0055]
• 3. Toughness Property[0056]
• A third desired property for the[0057]structure56 is the ability to resist surface abrasion, tearing, and puncture when in contact with cancellous bone. This property can be characterized in various ways.
• One way of measuring a material's resistance to abrasion, tearing and/or puncture is by a Taber Abrasion test. A Taber Abrasion test evaluates the resistance of a material to abrasive wear. For example, in a Taber Abrasion test configured with an H-18 abrasive wheel and a 1 kg load for 1000 cycles (ASTM Test Method D 3489), Texin® 5270 material exhibits a Taber Abrasion value of approximately 75 mg loss. As another example, under the same conditions Texin® 5286 material exhibits a Taber Abrasion value of approximately 30 mg loss. Typically, a lower Taber Abrasion value indicates a greater resistance to abrasion. Desirably, the structure will comprise material having a Taber Abrasion value under these conditions of less than approximately 200 mg loss. More desirably, the structure will comprise material having a Taber Abrasion value under these conditions of less than approximately 145 mg loss. Most desirably, the structure will comprise material having a Taber Abrasion value under these conditions of less than approximately 90 mg loss.[0058]
• Another way of measuring a material's resistance to abrasion, tearing and/or puncture is by Elmendorf Tear Strength. For example, under ASTM Test Method D 624, Texin® 5270 material exhibits a Tear Strength of 1,100 lb-ft/in. As another example, under the same conditions, Texin 5286 exhibits a Tear Strength of 500 lb-ft/in. Typically, a higher Tear Strength indicates a greater resistance to tearing. Desirably, the structure will comprise material having a Tear Strength under these conditions of at least approximately 150 lb-ft/in. More desirably, the structure will comprise material having a Tear Strength under these conditions of at least approximately 220 lb-ft/in. Most desirably, the structure will comprise material having a Tear Strength under these conditions of at least approximately 280 lb-ft/in.[0059]
• Another way of measuring a material's resistance to abrasion, tearing and/or puncture is by Shore Hardness. For example, under ASTM Test Method D 2240, Texin® 5270 material exhibits a Shore Hardness of 70D. As another example, under the same conditions, Texin® 5286 material exhibits a Shore Hardness of 86A. Typically, a lower Shore Hardness number on a given scale indicates a greater degree of elasticity, flexibility and ductility. Desirably, the structure will comprise material having a Shore Hardness under these conditions of less than approximately 75D. More desirably, the structure will comprise material having a Shore Hardness under these conditions of less than approximately 65D. Most desirably, the structure will comprise material having a Shore Hardness under these conditions of less than approximately 10A.[0060]
• It should be noted that a structure incorporating a plurality of materials, such as layered materials and/or composites, may possess significant resistance to surface abrasion, tearing and puncture. For example, a layered expandable structure incorporating an inner body formed of material having a Taber Abrasion value of greater than 200 mg loss and an outer body having a shore hardness of greater than 75D might possess significant resistance to surface abrasion, tearing and puncture. Similarly, other combinations of materials could possess the desired toughness to accomplish the desired goal of compressing cancellous bone and/or moving cortical bone prior to material failure.[0061]
• 4. Creating a Pre-Formed Structure[0062]
• The expansion and shape properties just described can be enhanced and further optimized for compacting cancellous bone by selecting an elastomer material, which also possess the capability of being preformed, i.e., to acquire a desired shape by exposure, e.g., to heat and pressure, e.g., through the use of conventional thermoforming or blow molding techniques. Candidate materials that meet this criteria include polyurethane, silicone, thermoplastic rubber, nylon, and thermoplastic elastomer materials.[0063]
• As described earlier, in the illustrated embodiment, TEXIN® 5286 polyurethane material is used. This material is commercially available from Bayer in pellet form.[0064]
• The pellets can be processed and extruded in a tubular shape using, e.g., a screw type (888 4:1) extrusion machine, with a GENCA™ head, with a single finger spider and a 80-100-200 screen. The following table summarizes representative process settings for the extrusion.[0065]

  	Extrusion Element	Nominal Setting
  	Die	0.338″
  	Mandrel	0.180″
  	Zone 1 Set/Actual	270 degrees F.
  	Zone 2 Set/Actual	370 degrees F.
  	Zone 3 Set/Actual	380 degrees F.
  	Melt Temperature	405 degrees F.
  	Clamp Set/Actual	370 degrees F.
  	Adaptor Set/Actual	380degrees F.
  	Die
  1 Set/Actual	380 degrees F.
  	Die 2 Set/Actual	380 degrees F.
  	Extruder	1600 RPM
  	Barrel	1600 PSI
  	Motor	5 Amps
  	Mandrel Air	2″ of water
  	Entry Hole Diameter	0.3″
  	Bath Dist. fromTooling	1″
  	Water Flow/Temperature	6 GPH/70 degrees F.
  	Air Wipe	20 PSI
  	Speed	21.5 FPM
  	Min Dryer Time/Temperature	Overnight/160 degrees F.

• The ultimate dimensions of the tubular extrusion can vary, according to the desired size and shape of the[0066]structure56. In a representative embodiment, the tubular extrusion has an outside diameter of 0.164″, and inner diameter of 0.092″, and a wall diameter of 0.36″. Reasonable processing tolerances can of course be established
• The tubular extrusion is cut into individual lengths for further processing. The tube length can vary, according to the desired configuration of the[0067]structure56. In a representative embodiment, each tube is cut to a length of about 48″ for further processing.
• The[0068]structure56 is formed by exposing acut tube length60 to heat and then enclosing theheated tube60 within amold58 while positive interior pressure is applied to thetube length60. Themold10 can be part of a conventional balloon forming machine, such as the Model No. 9608C made by Interface Associates.
• As FIG. 8 shows, the[0069]mold58 includes atube holding channel62, through which thetube length60 extends for processing. The holdingchannel62 includes a formedintermediate cavity64, which possesses a desired geometry. Thecavity64 defines the geometry intended for thestructure56.
• In the illustrated embodiment, the[0070]cavity64 possesses twoenlarged cavity spaces92 and94 with anintermediate channel96. The dimensions of thespaces92,94 andchannel96 can, of course, vary according to the desired dimensions of thestructure56.
• In a representative embodiment, each[0071]enlarged cavity space92 and94 extends 0.395″ on each side of thecenter line66. The maximum diameter of eachcavity space92 and94 is 0.314″, and the maximum diameter for thespacing channel96 is 0.174″. Desirably, all surfaces within themold58 are radiused to provide a smooth transition.
• Prior to heating, one end of the[0072]tube length60 is attached to a source of pressurized air, e.g., nitrogen. The other end of thetube length60 is gripped and closed. The tube is desirably subjected to a tensioning force (e.g., 16 oz).
• The[0073]tube length60 is then subjected to a heating cycle. During the heating cycle, thetube length60 is heated to a predetermined heated temperature for a set dwell time. The heated temperature and dwell time are selected to soften thetube length60 for subsequent stretching and pressure shaping.
• The range of heated temperatures in which softening occurs will depend upon the particular composition of the polymeric material used. For example, for the polyurethane tube of the dimensions described above, a heated temperature of 290 degrees F. and a dwell time of 220 seconds can be used. An operating range of softening temperatures for a given plastic material can be empirically determined. Suitable processing tolerances can also be empirically established.[0074]
• When the heating cycle ends, the heat-softened[0075]tube length60 is stretched by pulling it a set amount. The stretching desirably reduces the thickness of the tube walls. In a representative embodiment, the tube is stretched approximately 0.198″ to each side. The amount of stretching is selected to facilitate shaping without significantly reducing the resistance of the material, once shaped, to puncture.
• The[0076]mold58 then closes over the heated and stretchedtube length60. Pressurized air (typically, nitrogen) is introduced through the interior of thetube length60 for a set amount of dwell time at a set flow rate. The magnitude of pressure, dwell time, and flow rate will vary, depending upon the wall thickness and other physical characteristics of the material used. For the polyurethane tube of the dimensions described, a pressure of 100 PSI at a flow rate of 0.4 l/min for a dwell time of 45 seconds can be used.
• The introduction of pressurized air into[0077]tube length60 causes the tube region located within thecavity64 to expand or billow outward, forming thestructure56. Thecavity64 limits the extent to which thestructure56 expands. Thestructure56, upon expansion in thecavity64, will desirably conform to the geometry of thecavity64. During the pressurization phase, the flow of pressurized air can be used to help cool thetube length60.
• After the pressurization phase, the[0078]tube length60 is removed from the mold. The source of pressurized air is detached. Excess material on both sides of the formed structure region is discarded. Preferably, at least one inch of tube material is left on each side of the formed structure region to aid handling and identification during further processing.
• B. Assembly of the Tool[0079]
• 1. Assembling the Outer Catheter Body[0080]
• In a representative embodiment, the[0081]outer catheter body16 comprises an extruded tube, made from 99% TEXIN® 5270 Material and 1% Titanium Dioxide. The TEXIN® material can be purchased in pellet form from Bayer. The outer catheter body can be extruded in a tubular shape using, e.g., a screw type (888 4:1) extrusion machine, with a GENCA™ head, with a single finger spider and a C5WB23 screen. The following table summarizes representative process settings for the extrusion.

  	Extrusion Element	Nominal Setting
  	Die	0.203″
  	Mandrel	0.150″
  	Zone 1 Set/Actual	300 degrees F.
  	Zone 2 Set/Actual	340 degrees F.
  	Zone 3 Set/Actual	400 degrees F.
  	Clamp Set/Actual	24.6 degrees F.
  	Adaptor Set/Actual	400degrees F.
  	Die
  1 Set/Actual	400 degrees F.
  	Die 2 Set/Actual	400 degrees F.
  	Extruder	400 RPM
  	Motor	In. 2300 Auto/Dis. 2929
  	Mandrel Air	5.2 PSI
  	Entry Hole Diameter-	300-½″
  	Distribution
  	Water Flow/Temperature	20 ccm
  	Air Wipe	20 PSI
  	Speed	39 FPM
  	Min Dryer Time/Temperature	Overnight/l60 degrees F.

• The extrusion is initially cut to lengths of 16″ for assembly.[0082]
• Each tubing length comprising an[0083]outer catheter body16 preferably undergoes annealing, e.g., by oven curing at 60 to 70 degrees C. for 2 to 6 hours. Annealing reduces the incidence of shrinkage of theouter catheter body16 during sterilization and/or storage prior to use.
• The proximal end of the[0084]structure56 is heat bonded to the distal end of theouter catheter body16 in the presence of an overlying ring of silicone tubing68 (see FIG. 5), which compresses theouter catheter body16 and the proximal end of thestructure56 together during the heat bonding process. In one representative assembly technique, a support mandrel (e.g., having an outside diameter of 0.075″) is inserted within theouter catheter body16, and the proximal end of thestructure56 is slid over the distal end of theouter catheter body16. A length of the silicone tubing68 (having, e.g., an initial inside diameter of 0.104″) is subsequently slid over the proximal end of thestructure56 and thecatheter body16. Heat from the heat box is applied to the silicone tubing, and the structure andouter catheter body16 fuse together. The silicone tubing is then discarded.
• For the materials and dimensions described, representative settings for the heat box are a temperature of 545 degrees F., an air flow of 40 SCFH, and an air pressure of 20 to 30 PSI. At this setting, the[0085]silicone tubing68 and junction of thestructure56 and theouter catheter body16 are exposed to heat for 60 seconds, and are rotated 180 degrees after the first 30 seconds. The resulting heat bond is allowed to cool.
• The[0086]outer catheter body16 can then be cut to a desired final length, e.g., which in a representative embodiment is 350 mm measured from the center of thestructure56. In the illustrated embodiment (see FIG. 4), heat shrinktubing70, which bears appropriate identification information for thetool48, is bonded about theouter catheter body16, about 0.5″ from the proximal end of theouter catheter body16.
• A suitable UV adhesive (e.g., Dymax 204 CTH, available commercially from Dymax Corp) is applied to the proximal end of the[0087]outer catheter body16, and theouter catheter body16 is inserted into thehandle14. The adhesive joint is cured under UV light for an appropriate time period, e.g., 15 seconds. This secures theouter catheter body16 and attachedstructure56 to thehandle14.
• 2. Assembling The Inner Catheter Body[0088]
• In a representative embodiment, the[0089]inner catheter body18 comprises an extruded tube, made from 25% TEXIN® 5286 Material and 75% TEXIN® 5270 Material. The TEXIN® materials can be purchased in pellet form from Bayer.
• The[0090]inner catheter body18 can be extruded in a tubular shape using, e.g., a screw type (888 4:1) extrusion machine, with a GENCA™ head, with a 80-100-200 screen. The following table summarizes representative process settings for the extrusion.

  	Extrusion Element	Nominal Setting
  	Die	0.195″
  	Mandrel	0.135″
  	Zone 1 Set/Actual	360 degrees F.
  	Zone 2 Set/Actual	380 degrees F.
  	Zone 3 Set/Actual	490 degrees F.
  	Clamp Set/Actual	400 degrees F.
  	Adaptor Set/Actual	400degrees F.
  	Die
  1 Set/Actual	400 degrees F.
  	Die 2 Set/Actual	400 degrees F.
  	Extruder	30.7 RPM
  	Motor	In. 3300 Auto/Dis. 1772
  	Mandrel Air	1 PSI
  	Entry Hole Diameter -	300-1″
  	Distribution
  	Water Flow/Temperature	20 ccm
  	Air Wipe	20 PSI
  	Speed	87 FPM
  	Min Dryer Time/Temperature	Overnight/160 degrees F.

• The extrusion is initially cut to lengths of 16″ for assembly. Like the[0091]outer catheter body16, theinner catheter body18 is preferably subject to heat annealing.
• After annealing, the flared[0092]region52 is formed using a 0.099″ stylet heated by a heat gun. One possible setting of the heat gun is 200 degrees C. After cooling, UV adhesive is applied to secure the flaredregion52 to the second luer fitting34, which, at this stage of assembly, is not yet connected to thehandle14. The adhesive is cured under UV light for an appropriate time period.
• In the illustrated embodiment (see FIG. 5),[0093]fluoroscopic marker bands72 are secured on theinner catheter body18. Themarker bands72 facilitate fluoroscopic visualization of the proximal and distal ends of thestructure56 on the distal end of thetool48. In the illustrated embodiment, themarker bands72 are made from platinum/iridium material (commercially available from Johnson Matthey).
• In a representative embodiment, the[0094]marker bands72 are located on theinner catheter body18 about 1 mm beyond the distal end of theouter catheter body16 and also distally about 10.6 mm from the center of thestructure56. Prior to attaching themarker bands72, the inner catheter body18 (stiffened by an appropriate interior support mandrel) is inserted into theouter catheter body16, so that the desired relative positions of themarker bands72 can be determined using a reference tool, such as a ruler. Theinner catheter body18 is then removed fromouter catheter body16, and themarker bands72 are affixed at the indicated positions. The distal tip ofinner catheter body18 can be cut at a 45 degree angle to facilitate slipping themarker bands72 about thebody18. Themarker bands72 are secured to theinner catheter body18 using, e.g., a suitable adhesive primer (e.g., Loctite 7701 Primer, which is commercially available from Loctite), followed by use of a suitable adhesive (e.g. Cyanoacrylate 4061, which is commercially available from Loctite). After the adhesive cures, theinner catheter body18 is inserted into theouter catheter body16 and the second luer fitting34 is secured to thehandle14 using an UV adhesive (e.g., 204-CTH Adhesive, commercially available from Dymax). The adhesive is cured by exposure to UV light for an appropriate time period. This secures theinner catheter body18 to thehandle14.
• The distal end of the[0095]inner catheter body18 can now be secured to the distal end of thestructure56. During this operation, the dimension of theopening30 of theinner catheter body18 is also reduced, to block passage of thestylet38, as previously described.
• A first support mandrel (e.g., having an outer diameter of 0.041″) is placed within the[0096]inner catheter body18. A temporary ring of silicone tubing (e.g., having an inner diameter of 0.132″) is slid over the junction of the distal end of thestructure56 and the distal end of theinner catheter body18. Using a heat box, heat is applied to the silicone tubing, which causes the distal end of thestricture56 to shrink slightly about theinner catheter body18. This allows a smaller diameter silicone tubing to be used to form the final bond, as will be described later. Using the materials described, the heat box is set at a temperature of 525 degrees F., an air flow of 30 SCFH, and an air pressure of 20 to 30 psi. Exposure to heat desirably occurs for 16 seconds, with the assembly rotated 180 degrees after the first eight seconds.
• The first support mandrel is then removed, and a reduced diameter stylet (e.g., having an outside diameter of 0.008″) is inserted into the[0097]inner catheter body18. A smaller diameter silicone tubing74 (made, e.g., from silicone tubing having a initial inner diameter of 0.078″) (see FIG. 5) is slid over the junction for final bonding of thestructure56 to theinner catheter body18. Heat from the above-described heat box is then applied for 30 seconds to each side of the assembly. The structure-tubing interface is allowed to cool. The distal end of thestructure56 is trimmed, e.g., to a 3 mm length.
• As a result of these processing steps, the inside diameter of the[0098]opening30 is desirably reduced to a diameter that approximates the outside diameter of the reduced diameter stylet (e.g., 0.008″). This diameter is significantly smaller than the outside diameter of thestylet38, which in the representative embodiment is 0.038″. The reduced diameter of theopening 30 blocks passage of thestylet38. Still, the reduced diameter of theopening30 allows flushing liquid to be discharged.
• The[0099]stylet38 can now be inserted into theinner catheter body18, with the distal end flush against the distal bond. The proximal end of thestylet38 is secured by UV-cured adhesive (e.g., 198-M Adhesive, commercially available from Dymax) to thescrew cap50. Thecap50 can now be screwed upon the second luer fitting34 of thehandle14.
• A cut length of tubing made of Pebax™ material (e.g., 0.160 inch interior diameter) is flared at each end, using, e.g., a heat gun with a flare nozzle. This forms the[0100]insertion sleeve54. Theinsertion sleeve54 is slid over thestructure56 and onto theouter catheter body16.
• This completes the assembly of the[0101]tool48. Thetool48 can then be packaged for sterilization in a suitable kit. If desired, thestylet38 can be packaged next to thetool48 to facilitate ETO sterilization, and be inserted into theinner catheter body18 in the manner described at the time of use.
• III. Use of the Tool[0102]
• A. Deployment in a Vertebral Body[0103]
• The[0104]structure56 is well suited for insertion into bone in accordance with the teachings of U.S. Pat. Nos. 4,969,888 and 5,108,404, which are incorporated herein by reference.
• For example, as FIG. 9 shows, access can be accomplished, for example, by drilling an[0105]access portal76 through a side of thevertebral body26. This is called a lateral approach. Alternatively, the access portal can pass through eitherpedicle42, which called a transpedicular approach. A hand held tool can be used to facilitate formation of theaccess portal76, such as disclosed in copending U.S. patent application Ser. No. 09/421,635, filed Oct. 19, 1999, and entitled “Hand Held Instruments that Access Interior Body Regions.” Another hand held tool that can be used to form theaccess portal76 and gain access is disclosed in copending U.S. patent application Ser. No. 09/014,229 filed Jan. 27, 1998 and entitled “A Slip-Fit Handle for Hand-Held Instruments that Access Interior Body Regions.”
• A guide sheath or[0106]cannula78 is placed into communication with theaccess portal76, which can comprise a component part of the hand held tool just described. Thecatheter tube assembly10 is advanced through thecannula78 to deploy thestructure56 into contact withcancellous bone32. Access in this fashion can be accomplished using a closed, minimally invasive procedure or with an open procedure.
• The[0107]structure56 is passed into the bone in a normally collapsed and not inflated condition. The presence of thestylet38 in theinner catheter body18 serves to keep thestructure56 in the desired distally straightened condition during its passage through thecannula78. Theinsertion sleeve54 is desirably advanced over thestructure56 prior to insertion into thecannula78, to protect and compress thestructure56. Once deployed incancellous bone32, thestylet38 can be withdrawn.
• As FIG. 9 shows, expansion of the structure[0108]56 (indicated by arrows in FIG. 9) compressescancellous bone32 in thevertebral body26. The compression forms aninterior cavity80 in thecancellous bone32.
• As FIG. 10 shows, subsequent collapse and removal of the[0109]structure56 leaves thecavity80 in a condition to receive a fillingmaterial88, e.g., bone cement, allograft tissue, autograft tissue, hydroxyapatite, or synthetic bone substitute. Thematerial88 provides improved interior structural support forcortical bone32.
• The compaction of[0110]cancellous bone32, as shown in FIG. 9, can also exert an interior force upon the surroundingcortical bone28. The interior force can elevate or push broken and compressed bone back to or near its original prefracture, or other desired, condition. In the case of avertebral body26, deterioration ofcancellous bone32 can cause the top and bottom plates (designated TP and BP in FIG. 2), as well as the side walls (designated AW and PW in FIG. 2), to compress, crack, or move closer together, reducing the normal physiological distance between some or all of the plates. In this circumstance, the interior force exerted by thestructure56 as it compactscancellous bone32 moves some or all of the plates and/or walls farther apart, to thereby restore some or all of the spacing between them, which is at or close to the normal physiological distance.
• 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, an[0111]expandable structure56 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[0112]expandable structure56 to improve insertion of solid materials in defined shapes, like hydroxyapatite and components in total joint replacement. In these cases, the structure shape and size is defined by the shape and size of the material being inserted.
• Yet another exception lies in the use of expandable structures 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[0113]expandable structure56 is chosen by the desired amount of therapeutic substance sought to be delivered.
• It should be understood that the filling[0114]material88 itself could be used to expand thestructure56 within thevertebral body26, thereby causing compaction of thecancellous bone32 and/or movement of thecortical bone28 as previously described. If desired, the fillingmaterial88 within thestructure56 could be allowed to harden, and thestructure56 and hardened fillingmaterial88 could remain within thevertebral body26. This would significantly reduce the possibility ofnon-hardened filling material88 leaking outside of thevertebral body26. Alternatively, the pressurized fluid could be withdrawn from thestructure56 after formation of some or all of thecavity80, andfiller material88 could be injected into the structure to fill thecavity80 and/or complete expansion of thestructure56. As another alternative,filler material88 could be used to expand thestructure56, and thestructure56 could subsequently be removed from thevertebral body26 before the fillingmaterial88 within thevertebral body26 sets to a hardened condition.
• B. Expansion Characteristics of the Structure[0115]
• In the illustrated embodiment, the[0116]structure56 is created by extruding or molding atube60 of a selected polyurethane material. Thetube60 is heated, stretched, and subjected to internal pressure. After stretching and pressure forming, thetube60 has a normal wall thickness (T5) and a normal outside diameter (D5) (as shown in FIG. 11).
• The segmented shaped[0117]regions82 and84 of thestructure56 are created by exposing thetube86 to heat and positive interior pressure inside thecavity64. Once formed, thestructure56 possesses, in an open air environment, a normal expanded shape, having diameter D7 (shown in phantom lines in FIG. 11). The normal shape and diameter D7 for theregions82 and84 generally correspond with the shape and dimension of thecavity spaces92 and94, respectively. When an interior vacuum is drawn, removing air from thestructure56, thestructure56 desirably assumes a substantially collapsed, and not inflated geometry, shown in phantom lines D6 in FIG. 11.
• The[0118]regions82 and84 are separated by atubular waist86, which segments thestructure56 into twoexpandable regions82 and84. When substantially collapsed under vacuum or not inflated, thestructure56 desirably exhibits a low profile, ideal for insertion into the cannula and targeted cancellous bone region.
• The introduction of fluid volume back into the[0119]structure56 will cause eachregion82 and84 to return from the collapsed diameter D6 back to the normal, enlarged, but not distended geometry, having the shape and diameter shown in phantom lines D7 in FIG. 11.
• In the illustrated embodiment, the first and second shaped[0120]regions82 and84 have generally the same radius of expansion and thus the same non-distended shape and diameter D7. Alternatively, eachregion82 and84 can have a different radius of expansion, and thus a different non-distended shape and diameter. Moreover, theregions82 and84 can be shaped by heat and interior pressure within different cavities to assume different geometries, e.g., cylindrical or elliptical geometry, or a non-spherical, non-cylindrical, or non-elliptical geometry, with either uniform or complex curvature, and in either symmetric or asymmetric forms. Of course, more than twosegmented regions82 and84 can be formed.
• Each shaped[0121]region82 and84 possesses a wall thickness (designed T7 in FIG. 11) when in the normally enlarged but not distended geometry D7. Due to expansion of the wall during structure formation, the wall thickness is typically not uniform along the longitudinal axis of thestructure56, i.e., T7 is typically less than the normal wall thicknesses T5 and/or T9 of thetube60. The wall thickness T7 for theregions82 and84 can be the same or different.
• When in the enlarged, but not distended geometry, the[0122]waist region86 has an outside diameter (designated D9 in FIG. 11), which is desirably equal to or greater than the diameter D5 of thetube60. The size of thechannel96 in the fixture90 desirably determines the magnitude of the diameter D9. Due to expansion of the material during structure formation, thewaist region86 has a wall thickness (designated T9 in FIG. 11) which is less than or equal to the wall thickness T5 of thetube60. Desirably, the wall thickness T9 of thewaist region86 is greater than the wall thickness T7 of either fully shapedregion82 or84.
• The formed[0123]complex structure56 thus desirably possesses regions of non-uniform minimum wall thickness along its longitudinal length; that is, T5, T9>T7. The formedcomplex structure56 also provides multipleexpandable regions82 and84 of the same or different enlarged outside diameters (D7), segmented by awaist region86.
• By injecting additional fluid into the[0124]expandable structure56, the shapedregions82 and84 of thestructure56 will desirably continue to enlarge beyond diameter D7 to a distended shape and geometry, designated D8 in FIG. 11. Typically, the wall thickness T7 further decreases and approaches T8. As theregions82 and84 expand, thewaist region86 will likewise expand towards diameter D10, as FIG. 11 shows. However, because the wall thickness T9 of thewaist region86 is typically greater than the wall thickness T7 of theregions82 and84, thewaist region86 will typically expand more slowly than theregions82 and84, thereby expanding thestructure56 in a more cylindrical manner, providing more uniform, elongated surface contact with cancellous bone than would a sphericalexpandable structure56 of similar volume.
• Enlargement of the[0125]structure56 beyond diameter D7 desirably stretches the material in theregions82,84, and86 beyond their pre-formed geometries. Desirably, theseregions82 and84 will essentially maintain the preformed shape dictated by thecavities92 and94. Continued volume flow of pressurized fluid into thestructure56 continues to increase the interior volume of the structure56 (see FIG. 12). As their volume increase, the shapedregions82 and84 of thestructure56 continue to enlarge beyond the normal diameter D7 toward a distended shape and geometry D8.
• Of course, it should be understood that the[0126]waist region86 could be formed of a material having different expansion characteristics than the material of the shapedregions82 and84, wherein a more expansion-resistant material could constrain the expansion of the waist region in a manner similar to the thickness differentials described above.
• The degree of stretching and increases in volume can be tailored to achieve a desired, fully distended diameter D8. The final, fully distended diameter D8 can be selected by the treating physician, using real-time monitoring techniques, such as fluoroscopy or real-time MRI, to match the dimensions of the targeted cancellous bone region. The controlled stretching of the[0127]segmented regions82 and84 desirably provides compression of cancellous bone with a maximum diameter that is less than a single non-segmented region (i.e., one without the waist region86). Stated another way,segmented regions82 and84, when expanded to a given inflation volume, desirably have an outer diameter less than a sphere expanded to an equal inflation volume.
• While expanding in the region between D7 and D8, the[0128]structure56, when inside bone, desirably assumes an increasingly larger surface and volume, thereby compacting surrounding cancellous bone. Inflation in cancellous bone may occur at the same pressures as outside bone. However, an increase in the inflation pressures inside bone may be required, due to the density of the cancellous bone and resistance of the cancellous bone to compaction.
• For example, the configuration of the Pressure vs. Volume curve for a given material and[0129]structure56 remains essentially the same as shown in FIG. 12, except that the generally horizontal portion of the curve between D7 and D8 is shifted upward on the Y-axis, as shown in phantom lines in FIG. 12. As a general statement, the threshold pressure inside bone is determined by the material property of thestructure56 and any added resistance due to the presence of cancellous bone.
• The distance between D7 and D8, along the x-axis of FIG. 12, defines the degree to which the wall can elongate at a substantially constant pressure condition and with increasing material stress to compact cancellous bone, without failure. As volume increases at the substantially constant threshold pressure P(t), wall failure becomes more likely as the diameter of the structure enlarges significantly further beyond the distended diameter D8. There comes a point when the[0130]structure56 can no longer increase its volume as the material elasticity approaches ultimate elongation, or as material stress approaches ultimate tensile strength. When either of these ultimate values are reached, wall failure is likely. Accordingly, the distance between D7 and D8 in FIG. 12 during expansion inside bone is a simultaneous expression of the three physical and mechanical properties—expansion, shape, and toughness—as previously described.
• The features of the invention are set forth in the following claims.[0131]

Claims (5)

We claim:

1. A tool for deploying an expandable structure into interior body regions, the tool comprising

a catheter body defining an interior lumen,

an expandable structure having a distal end and carried by the catheter body, and

a stylet having a proximal end and being sized and configured for passage through the lumen and adapted to straighten the expandable structure during deployment into an interior body region.

2. A tool as inclaim 1

wherein the stylet is substantially rigid.

3. A tool as inclaim 1

wherein the stylet is made of stainless steel.

4. A tool as inclaim 1

wherein, after passage of the stylet through the lumen, the proximal end of the stylet is coupleable to the catheter body.

5. A tool as inclaim 1

wherein, after passage of the stylet through the lumen, the stylet abuts against the distal end of the expandable structure.

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