US20100318087A1 - Systems and methods for forming a cavity in cancellous bone - Google Patents

Abstract

A cavity creating device having a cavity creating axis is introduced through a percutaneous access path into a cancellous bone volume, e.g., within a vertebral body. The cavity creating device is manipulated to form a cavity in the cancellous bone volume. The manipulation includes deflecting the cavity creating device along the cavity creating axis relative to the axis of the access path. A material, such as bone cement, can be conveyed into the cavity.

Description

RELATED APPLICATIONS
• This application is divisional of co-pending U.S. patent application Ser. No. 10/436,551, filed May 13, 2003, which is a divisional of U.S. patent application Ser. No. 09/918,942, filed Jul. 31, 2001 (now U.S. Pat. No. 6,623,505), which is a divisional of U.S. patent application Ser. No. 09/404,662, filed Sep. 23, 1999, now U.S. Pat. No. 6,280,456, which is a divisional of U.S. patent application Ser. No. 08/911,827, filed Aug. 15, 1997, now U.S. Pat. No. 5,972,015, each of which is incorporated herein by reference.
FIELD OP THE INVENTION
• The invention, relates to expandable structures, which, in use, are deployed in interior body regions of humans and other animals.
BACKGROUND OF THE INVENTION
• The deployment of expandable structures into interior body regions is well known. For example, expandable structures, generically called “balloons,” are deployed during angioplasty to open occluded blood vessels. As another example, U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose apparatus and methods the use of expandable structures for the fixation of fractures or other osteoporotic and non-osteoporotic conditions of human and animal bones.
• Many interior regions of the body, such as the vasculature and interior bone, possess complex, asymmetric geometries. Even if an interior body region is somewhat more symmetric, it may still be difficult to gain access along the natural axis of symmetry.
• For example, deployment of an expandable structure in the region of branched arteries or veins can place the axis of an expandable structure off-alignment with the axis of the blood vessel which the structure is intended to occupy. As another example, insertion of an expandable structure into bone can require forming an access portal that is not aligned with the natural symmetry of the bone. In these instances, expansion of the structure is not symmetric with respect to the natural axis of the region targeted for treatment. As a result, expansion of the body is not symmetric with respect to the natural axis of the targeted region.
• It can also be important to maximize the size and surface area of an expandable structure when deployed in an interior body region. Current medical balloons manufactured by molding techniques are designed to be guided into a narrow channel, such as a blood vessel or the fallopian tube, where they are then inflated. In this environment, the diameter of the balloon is critical to its success, but the length is less so. Such balloons only need to be long enough to cross the area of intended use, with few constraints past the effective portion of the inflated balloon. This allows conventional balloons to be constructed in three molded pieces, comprising a cylindrical middle section and two conical ends, bonded to a catheter shaft. As a practical matter, neither the length of the conical end, nor the length of the bond of the balloon to the catheter shaft, affect the function of conventional balloons, and these regions on conventional balloons are often 1 cm in length or more. Indeed, the larger the balloon diameter, the longer the end cone, which creates a tradeoff between maximum effective length and maximum effective diameter. This tradeoff makes optimization of conventional structures problematic in interior structures with defined lengths, such as bone.
SUMMARY OF THE INVENTION
• One aspect of the invention provides a device comprising a shaft having an elongated shaft axis and a proximal end portion and a distal end portion. The elongated shaft is sized and configured for passage through a percutaneous access path into a cancellous bone region. The device also includes a cavity forming structure carried on the distal end of the shaft. The cavity forming device is sized and configured to be manipulated to form a cavity in the cancellous bone region. The cavity forming structure has an elongated cavity forming axis. The device further includes a mechanism for deflecting the cavity forming structure along the elongated cavity forming axis, to shift the elongated cavity forming axis relative to the elongated shaft axis.
• Another aspect of the invention provides a method that provides a percutaneous access path having an axis into bone having an interior volume occupied, at least in part, by cancellous bone. The method introduces a cavity creating device having a cavity creating axis through the access path into the cancellous bone volume. The method manipulates the cavity creating device to form a cavity in the cancellous bone volume. The manipulation includes deflecting the cavity creating device along the cavity creating axis relative to the axis of the access path.
• In one embodiment, a material, e.g., bone cement, is introduced into the cavity.
• In one embodiment, the cavity creating device is also expanded to form the cavity.
• In one embodiment, bone comprises a vertebral body.
• Features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a lateral view, partially broken away and in section, of a lumbar vertebra taken generally along line1-1 inFIG. 2;
• FIG. 2 is a coronal view of the lumbar vertebra, partially cut away and in section, shown inFIG. 1;
• FIG. 3 is a top view of a probe including a catheter tube carrying a tubular expandable structure of conventional construction, shown in a substantially collapsed condition;
• FIG. 4 is an enlarged side view of the tubular expandable structure carried by the probe shown inFIG. 3, shown in a substantially expanded condition;
• FIG. 5 is a lateral view of the lumbar vertebra shown inFIGS. 1 and 2, partially cut away and in section, with the expandable structure shown inFIGS. 3 and 4 deployed by transpedicular access when in a substantially collapsed condition;
• FIG. 6 is a coronal view of the transpedicular access shown inFIG. 5, partially cut away and in section;
• FIG. 7 is a lateral view of the transpedicular access shown inFIG. 5, with the expandable structure shown inFIGS. 3 and 4 in a substantially expanded condition, forming a cavity that is not centered with respect to the middle region of the vertebral body;
• FIG. 8 is a coronal view of the transpedicular access shown inFIG. 7, partially cut away and in section;
• FIG. 9 is a coronal view of the lumbar vertebra shown inFIGS. 1 and 2, partially cut away and in section, with the expandable structure shown inFIGS. 3 and 4 deployed by postero-lateral access when in a substantially collapsed condition;
• FIG. 10 is a coronal view of the postero-lateral access shown inFIG. 9, with the expandable structure shown in a substantially expanded condition, forming a cavity that is not centered with respect to the middle region of the vertebral body;
• FIGS. 11A and 11B are side views of improved expandable structures, each having an axis of expansion that is offset by an acute angle and not aligned with the axis of the supporting catheter tube;
• FIG. 12 is a lateral view of the lumbar vertebra shown inFIGS. 1 and 2, partially cut away and in section, with the offset expandable structure shown inFIG. 11A deployed by transpedicular access and being in a substantially expanded condition, forming a cavity that is substantially centered with respect to the middle region of the vertebral body;
• FIG. 13 is a coronal view of the lumbar vertebra shown inFIGS. 1 and 2, partially cut away and in section, with the offset expandable structure shown inFIG. 11 deployed by postero-lateral access and being in a substantially expanded condition, forming a cavity that is substantially centered with respect to the middle region of the vertebral body;
• FIGS. 14A and 14B are side views of other embodiments of improved expandable structures, each having an axis of expansion that is offset by a distance from the axis of the supporting catheter tube;
• FIG. 15 is a side view of a conventional expandable structure shown inFIG. 4, enlarged to show further details of its geometry when substantially expanded;
• FIG. 16 is a side view of an improved expandable structure, when in a substantially expanded condition, which includes end regions having compound curvatures that reduce the end region length and thereby provide the capability of maximum bone compaction substantially along the entire length of the structure;
• FIG. 17 is a side view of an improved expandable structure, when in a substantially expanded condition, which includes end regions having compound curvatures that invert the end regions about the terminal regions, where the structure is bonded to the supporting catheter tube, to provide the capability of maximum bone compaction substantially along the entire length of the structure;
• FIG. 18 is a side section view of an improved expandable structure, when in a substantially expanded condition, which includes end regions that have been tucked or folded about the terminal regions, where the structure is bonded to the supporting catheter tube, to provide the capability of maximum bone compaction substantially along the entire length of the structure;
• FIG. 19 is a side section view of a tubular expandable structure having a distal end bonded to an inner catheter tube and a proximal end bonded to an outer catheter tube, the inner catheter tube being slidable within the outer catheter tube;
• FIG. 20 is a side section view of the tubular expandable structure shown inFIG. 19, after sliding the inner catheter tube within the outer catheter tube to invert the end regions of the structure about the distal and proximal bonds, to thereby provide the capability of maximum bone compaction substantially along the entire length of the structure;
• FIG. 21 is a side section view of a tubular expandable structure having a distal end bonded to an inner catheter tube and a proximal end bonded to an outer catheter tube, the inner catheter tube and structure being made of a more compliant material than the outer catheter tube to provide proportional length and diameter expansion characteristics;
• FIG. 22 is an enlarged plan view of a branched blood vasculature region, in which an occlusion exists;
• FIG. 23 is a further enlarged view of the branched blood vasculature region shown inFIG. 22, in which an asymmetric expandable structure of the type shown inFIG. 11 is deployed to open the occlusion;
• FIG. 24 is a plan view of a sterile kit to store a single use probe, which carries an expandable structure as previously shown;
• FIG. 25 is an exploded perspective view of the sterile kit shown inFIG. 24;
• FIG. 26 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; and
• FIG. 27 is a side view of the expandable structure shown inFIG. 27, 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.
• 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 first 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.
• Another preferred embodiment describes the improved systems and methods in the context of relieving constrictions or blockages within branched blood vessels. This is because the vasculature also presents an environment well suited to receive the benefits of the invention.
• The two environments are described for the purpose of illustration. However, it should be appreciated that the systems and methods as described are not limited to use in the treatment of bones or the vasculature. The systems and methods embodying the invention can be used virtually in any interior body region that presents an asymmetric geometry, or otherwise requires an access path that is not aligned with the natural axis of the region.
I. Deployment in Bones
• The new systems and methods will be first described in the context of the treatment of human vertebra. Of course, other human or animal bone types, e.g., long bones, can be treated in the same or equivalent fashion.
• FIG. 1 shows a lateral (side) view of a human lumbar vertebra12.FIG. 2 shows a coronal (top) view of the vertebra. The vertebra12 includes avertebral body26, which extends on the anterior (i.e., front or chest) side of the vertebra12. Thevertebral body26 is in the shape of an oval disk. The geometry of thevertebral body26 is generally symmetric arranged about its natural mid-anterior-posterior axis66, naturalmid-lateral axis67, and natural mid-top-to-bottom axis69. Theaxes66,67, and69 intersect in the middle region or geometric center of thebody26, which is designated MR in the drawings.
• AsFIGS. 1 and 2 show, thevertebral body26 includes an exterior formed from compactcortical bone28. Thecortical bone28 encloses aninterior volume30 of reticulated cancellous, or spongy, bone32 (also called medullary bone or trabecular bone).
• The spinal canal36 (seeFIG. 2), is located on the posterior (i.e., back) side of each vertebra12. The spinal cord (not shown) passes through the spinal canal36. The vertebral arch40 surrounds the spinal canal36. Left and right pedicles42 of the vertebral arch40 adjoin thevertebral body26. Thespinous process44 extends from the posterior of the vertebral arch40, as do the left and right transverse processes46.
• 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 structure to compress cancellous bone and provide an interior cavity. The cavity receives a filling material, e.g., bone cement, which hardens and provides renewed interior structural support for 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.
• FIG. 3 shows a tool48, which includes a catheter tube50 having a proximal and a distal end, respectively52 and54. The catheter tube50 includes a handle51 to facilitate gripping and maneuvering the tube50. The handle51 is preferably made of a foam material secured about the catheter tube50.
• The distal end54 carries anexpandable structure56, whichFIG. 3 shows to be of conventional construction. Thestructure56 is shown inFIG. 3 in a substantially collapsed geometry. Thestructure56 conventionally comprises an elongated tube, formed, for example, by standard polymer extrusion and molding processes. Thetubular structure56 is bonded at its opposite ends58 to the catheter tube50, using, for example, an adhesive. When substantially collapsed, thestructure56 can be inserted into an interior body region.
• Tubular bodies of the type shown inFIG. 3 are made from polymer materials and are commonly deployed in veins and arteries, e.g., in angioplasty applications.FIG. 4 shows an enlarged view of thestructure56 when in a substantially expanded geometry. AsFIG. 4 shows, the middle region64 of thetubular structure56, when substantially expanded, assumes a generally cylindrical shape, which is symmetric about the main axis60 of the catheter tube50. Expansion stretches the polymer material of thestructure56 near its bonded ends58 to form generallyconical end portions62.
• Thestructure56 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 avertebral body26, access into theinterior volume30 can be accomplished, for example, by drilling an access portal43 through either pedicle42. This is called a transpedicular approach, whichFIG. 5 shows in lateral view andFIG. 6 shows in coronal view. AsFIG. 5 shows, the access portal43 for a transpedicular approach enters at the top of thevertebral body26, where the pedicle42 is relatively thin, and extends at an angle downward toward the bottom of thevertebral body26 to enter theinterior volume30. AsFIGS. 5 and 6 show, in a typical transpedicular approach, the access portal43 aligns the catheter tube axis60 obliquely with respect to allnatural axes66,67, or69 of thevertebral body26.
• As theconventional structure56 expands within the interior volume30 (asFIGS. 7 and 8 show, respectively, in lateral and coronal views for the transpedicular approach), thestructure56 symmetrically expands about the catheter tube axis60, compressingcancellous bone32 to form a cavity68. However, since the catheter tube axis60 is oriented obliquely relative to allnatural axes66,67, or69, the formed cavity is not centered with respect to the middle region MR. Instead, the cavity68 is offset on one lateral side of the middle region MR (asFIG. 8 shows) and also extends from top to bottom at oblique angle through the middle region MR (asFIG. 7 shows).
• Due to these, asymmetries, the cavity68 will not provide optimal support to the middle region MR when filled with bone cement. Since the bone cement volume is not centered about the middle region MR, the capability of thevertebral body26 to withstand loads is diminished. The asymmetric compaction ofcancellous bone32 in theinterior volume30 may also exert unequal or nonuniform interior forces uponcortical bone32, making it difficult to elevate or push broken and compressed bone.
• AsFIG. 9 shows, access to theinterior volume30 of thevertebral body26 also can be achieved by drilling anaccess portal45 through a side of thevertebral body26, which is called a postero-lateral approach. The portal45 for the postero-lateral approach enters at a posterior side of thebody26 and extends at angle forwardly toward the anterior of thebody26.
• AsFIG. 9 shows, the orientation of the portal45 in a typical postero-lateral approach does not permit parallel or perpendicular alignment of the catheter tube axis60 with either themid-lateral axis67 or the mid-anterior-posterior axis66 of the vertebral26. As a result, symmetric expansion of theconventional structure56 about the catheter tube axis60 forms an off-centered cavity68′, which extends obliquely across the middle region MR of thebody26, asFIG. 10 view shows. As with the cavity68 formed by thestructure56 using transpedicular access, the off-centered cavity68′ formed by thestructure56 using postero-lateral access also fails to provide optimal support to the middle region MR when filled with bone cement.
• A. Optimal Orientation for Cancellous Bone Compaction
• FIG. 11A shows an improvedbone treating tool14, which includes a catheter tube16 carrying at itsdistal end18 anexpandable structure20. The catheter tube16 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• FIG. 11A shows thestructure20 in a substantially expanded condition, in which the structure comprises acylinder21 with generally conical portions34, each having a top25 and abase27. The tops25 of conical portions34 are secured about the catheter tube16 and, in this respect, are generally aligned with the catheter tube axis24. However, unlike theexpandable structure56 shown inFIG. 4, the main axis22 of thecylinder21 and the axis24 of the catheter tube16 are not aligned. Instead, the cylinder axis22 is offset at an angle A from the catheter tube axis24. As a result, thestructure20, when substantially expanded (asFIG. 11A shows), is not symmetric with respect to the catheter tube axis24.
• InFIG. 11A, thebases27 of the conical portions34 extend generally perpendicularly to the cylinder axis22. In this orientation, the tops25 and thebases27 are not parallel to each other. Other orientations are possible. For example, inFIG. 11B, thebases27 of the conical portions34 extend generally perpendicularly to the catheter tube axis24. In this orientation, the tops25 and thebases27 are generally parallel to each other.
• FIG. 12 shows in lateral view, the offsetstructure20 shown inFIG. 11A deployed by a transpedicular approach in theinterior volume30 of avertebral body26. As before shown inFIGS. 7 and 8, the transpedicular approach inFIG. 12 does not align the catheter tube axis24 with any of thenatural axes66,67, and69 of thebody26. However, asFIG. 12 shows, the expansion of the offsetcylinder21 of thestructure20 about its axis22 is not symmetric with respect to the catheter tube axis24. Instead, expansion of the offsetstructure20 is generally aligned with thenatural axes66 and69 of thevertebral body26. AsFIG. 12 shows, a single offsetstructure20 introduced by transpedicular access, forms a cavity38 that, while still laterally offset to one side of the middle region MR (as shown inFIG. 8), is nevertheless symmetric in a top-to-bottom respect with the middle region MR. A matching, adjacent cavity can be formed by transpedicular deployment of a second offsetstructure20 on the opposite lateral side of thevertebral body26. The composite cavity, formed by the two offsetbodies20, introduced simultaneously or in succession by dual transpedicular access, is substantially centered in all respects about the middle region MR.
• FIG. 13 shows the offsetexpandable structure20 deployed by a postero-lateral approach in theinterior volume30 of avertebral body26. As before shown inFIG. 9, the postero-lateral approach inFIG. 13 does not align the catheter tube axis24 with thenatural axes66 and67 of thebody26. The expansion of the offsetstructure20, which is asymmetric about the catheter tube axis24, is nevertheless generally symmetric with respect to allnatural axes66,67, and69 of thevertebral body26. A single offsetstructure20, deployed by postero-lateral access, forms a cavity38′, which is substantially centered about the middle region MR.
• A cavity centered with respect to the middle region MR provides support uniformly across the middle region MR when filled with bone cement. The capability of thevertebral body26 to withstand loads is thereby enhanced. The symmetric compaction ofcancellous bone32 in theinterior volume30 that a centered cavity provides also exerts more equal and uniform interior forces uponcortical bone32, to elevate or push broken and compressed bone.
• FIGS. 14A and 14B show an expandable structure200 having an offset, asymmetric geometry different than the geometry of the offsetexpandable structure20 shown inFIGS. 11A and 11B. InFIGS. 11A and 11B, the offset angle A between the cylinder axis22 and the catheter tube axis24 is an acute angle. As a result, the axis22 of thestructure20 is offset in a nonparallel dimension or plane relative to the catheter tube axis24. InFIGS. 14A and 14B, the offset angle A between the cylinder axis220 and thecatheter tube axis240 is zero, as the axis220 of the cylinder210 is offset at a distance from and in a generally parallel dimension or plane relative to thecatheter tube axis240. The catheter tube160 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• As inFIGS. 11A and 11B, thetops250 ofconical portions340 are secured about the catheter tube160 and, in this respect, are generally aligned with thecatheter tube axis240. InFIGS. 14A and 14B, the orientation of the bases270 of theconical portions340 differ. InFIG. 14A, the bases270 of theconical portions340 extend generally perpendicularly to thecatheter tube axis240, and are therefore generally parallel to the tops250 (comparable to the orientation shown inFIG. 11B). InFIG. 14B, the bases270 of theconical portions340 extend at an angle B to thecatheter tube axis240. In this orientation, the tops250 and the bases270 are not parallel to each other.
• FIGS. 11A and 11B and14A and14B show that it is possible, by adjustment of the offset angle A, as well as adjustment of the orientation of the conical end bases, to achieve virtually any desired offset geometry, and thereby tailor the orientation of the expandable structure to the particular geometry of the point of use.
• B. Maximizing Cancellous Bone Compaction
• Referring back toFIG. 4, when the conventionaltubular structure56 shown inFIG. 4 is substantially expanded, material of the structure is stretched intoconical sections62 near the ends58, which are bonded to the catheter tube50.FIG. 15 shows the geometry of expandedtubular structure56 in greater detail. Theconical portions62 extend at a cone angle α from the bonded ends58. The expandedstructure56 therefore presents the generally cylindrical middle region64, where the maximum diameter of the structure56 (BODY_DIA) exists, and theconical portions62, which comprise regions of diameter that decreases with distance from the middle region64 until reaching the diameter of the catheter tube (TUBE_DIA).
• Due to the geometry shown inFIG. 15, maximum cancellous bone compaction does not occur along the entire length (L2) of theconventional structure56, as measured between the bonded ends58. Instead, maximum cancellous bone compaction occurs only along the effective length (L1) of the cylindrical middle region64 of thestructure56, where thestructure56 presents its maximum diameter BODY_DIA. Cancellous bone compaction diminishes along the length of theconical portions62, where the structure's diameter progressively diminishes. At the bonded ends58, and portions of the catheter tube50 extending beyond the bonded ends58, no bone compaction occurs. The catheter tube50 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• The lengths (Lc) of theconical regions62 and bonded ends58 relative to the entire length of the structure56 (L2) are important indications of the overall effectiveness of thestructure56 for compacting cancellous bone. The effective bone compaction length (L1) of any expandable structure having conical end regions, such asstructure56 shown inFIG. 15, can be expressed as follows:
• 
  L1=L2−2(Lc)
• where the length of a given conical region (Lc) can be expressed as follows:
• $\mathrm{Lc}=\frac{h}{\tan \frac{\alpha }{2}}$
• where:
• $h=\frac{{\mathrm{BODY}}_{\mathrm{DIA}}-{\mathrm{TUBE}}_{\mathrm{DIA}}}{2}$
• where (seeFIG. 15):
• • BODY_DIAis the maximum diameter of the middle region64, when substantially expanded,
  • TUBE_DIAis the diameter of the catheter tube50, and
  • α is the angle of the conical portion.
• As the foregoing expressions demonstrate, for a given conical angle α, the length Lc of theconical portions62 will increase with increasing maximum diameter BODY_DIAof the middle region64. Thus, as BODY_DIAis increased, to maximize the diameter of the formed cavity, the lengths Lc of theconical portions62 also increase, thereby reducing the effective length L1 of maximum cancellous bone compaction.
• The bone compaction effectiveness of an expandable structure of a given maximum diameter increases as L1 and L2 become more equal. The geometry of a conventionaltubular structure56 shown inFIG. 15 poses a tradeoff between maximum compaction diameter and effective compaction length. This inherent tradeoff makes optimization of thestructure56 for bone compaction application difficult.
• FIG. 16 shows an improved structure70 having a geometry, when substantially expanded, which mitigates the tradeoff between maximum compaction diameter and effective compaction length. The structure70 includes a middle region72, where BODY_DIAoccurs. The structure70 also includesend regions74, which extend from the middle region72 to the regions76, where the material of the structure is bonded to the catheter tube78, at TUBE_DIA. The catheter tube78 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• In the embodiment shown inFIG. 16, the end regions are molded or stressed to provide a non-conical diameter transformation between BODY_DIAand TUBE_DIA. The diameter changes over two predefined radial sections r1 and r2, forming a compound curve in theend regions74, instead of a cone. The non-conical diameter transformation of radial sections r1 and r2 between BODY_DIAand TUBE_DIAreduces the differential between the effective bone compaction length L1 of the structure70 and the overall length L2 of the structure70, measured between the bond regions76.
• FIG. 17 shows another improved expandable structure80 having a geometry mitigating the tradeoff between maximum compaction diameter and effective compaction length. Like the structure70 shown inFIG. 16, the structure80 inFIG. 16 includes a middle region82 of BODY_DIAand end regions84 extending from the middle region to the bonded regions86, at TUBE_DIA. As the structure70 inFIG. 16, the end regions84 of the structure80 make a non-conical diameter transformation between BODY_DIAand TUBE_DIA. InFIG. 17, the predefined radial sections r1 and r2 are each reduced, compared to the radial section r1 and r2 inFIG. 16. As a result, the end regions84 take on an inverted profile. As a result, the entire length L2 between the bonded regions86 becomes actually less than the effective length L1 of maximum diameter BODY_DIA. The catheter tube can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• The structures70 and80, shown inFIGS. 16 and 17, when substantially inflated, present, for a given overall length L2, regions of increasingly greater proportional length L1, where maximum cancellous bone compaction occurs.
• Furthermore, as inFIG. 17, the end regions84 are inverted about the bonded regions86. Due to this inversion, bone compaction occurs in cancellous bone surrounding the bonded regions86. Inversion of the end regions84 about the bonded regions86 therefore makes it possible to compact cancellous bone along the entire length of the expandable structure80.
• FIG. 18 shows another embodiment of an improved expandable structure90. Like the structure80 shown inFIG. 17, the structure90 includes a middle region92 and fullyinverted end regions94 overlying thebond regions96. The structure80 comprises, when substantially collapsed, a simple tube. At least the distal end of the tubular structure80 is mechanically tucked or folded inward and placed into contact with the catheter tube98. As shown inFIG. 18, both proximal and distal ends of the tubular structure are folded over and placed into contact with the catheter tube98. The catheter tube98 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• The catheter tube98 is dipped or sprayed beforehand with a material102 that absorbs the selected welding energy, for example, laser energy. The folded-over ends94 are brought into abutment against the material102. The welding energy transmitted from an external source through the middle region92 is absorbed by the material102. A weld forms, joining the material102, the folded-over ends94, and the catheter tube50. The weld constitutes thebond regions96.
• Theinverted end regions94 of the structure90 achieve an abrupt termination of the structure90 adjacent thedistal end104 of the catheter tube98, such that theend regions94 and the distalcatheter tube end104 are coterminous. The structure90 possesses a region of maximum structure diameter, for maximum cancellous bone compaction, essentially along its entire length. The structure90 presents no portion along its length where bone compaction is substantially lessened or no cancellous bone compaction occurs.
• FIGS. 19 and 20 show another embodiment of anexpandable structure110. AsFIG. 20 shows, thestructure110 includes amiddle region112 of maximum diameter BODY_DIAandinverted end regions114, which overlie the bondedregions116.
• FIG. 19 shows thestructure110 before theend regions114 have been inverted in the manufacturing process. AsFIG. 19 shows, thestructure110 comprises, when substantially collapsed, a simple tube. To facilitate formation of theinverted end regions114 and bondedregions116, a two-piece catheter tube is provided, comprising anouter catheter tube118 and aninner catheter tube120. Theinner catheter tube120 slides within theouter catheter tube118. Thecatheter tube118 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• AsFIG. 19 shows, during the manufacturing process, theinner catheter tube120 is moved a first distance d1 beyond theouter catheter tube118. In this condition, the proximal anddistal ends122 and124 of thetubular structure110 are bonded, without folding over or tucking in, about theinner catheter tube118 and theouter catheter tube120, respectively. The unfolded ends122 and124 of thetubular structure110 can then be directly exposed to conventional adhesive or melt bonding processes, to form the bondedregions116.
• Once the bondedregions116 are formed, theinner catheter tube120 is moved (see arrow130 inFIG. 20) to a distance d2 (shorter than d1) from the end of theouter catheter tube118. The shortening of theinner tube120 relative to theouter tube120 inverts theends122 and124. The inversion creates doublejointed end regions116 shown inFIG. 20, which overlie the bondedregions116. The relative position of the outer andinner catheter tubes118 and120 shown inFIG. 20 is secured against further movement, e.g., by adhesive, completing the assemblage of thestructure110.
• The double jointed inverted ends114 of thestructure110 inFIG. 20, like single jointed inverted ends94 of the structure90 inFIG. 18, assure that no portion of the catheter tube protrudes beyond the expandable structure. Thus, there is no region along eitherstructure94 or114 where cancellous bone compaction does not occur. Like the structure90 shown inFIG. 18, thestructure110 inFIG. 20 presents a maximum diameter for maximum cancellous bone compaction essentially along its entire length.
• FIG. 21 shows another embodiment of an improved expandable structure300 well suited for deployment in an interior body region. Like thestructure110 shown inFIGS. 19 and 20, the structure300 inFIG. 21 includes an inner catheter tube304 secured within anouter catheter tube302. Like thestructure110 shown inFIGS. 19 and 20, the distal end310 of the inner catheter tube304 inFIG. 21 extends beyond the distal end308 of theouter catheter tube302.
• The outer diameter of the inner catheter tube304 is likewise smaller than the inner diameter of theouter catheter tube302. A flow passage312 is defined by the space between the twocatheter tubes302 and304.
• Theproximal end314 of an expandable body306 is bonded to the distal end308 of theouter catheter tube302. The distal end316 of the expandable body306 is bonded to the distal end310 of the inner catheter tube304. An inflation medium318 is conveyed into the body306 through the flow passage312, causing expansion of the body306.
• InFIG. 21, the physical properties of the structure300 at theproximal body end314 differ from the physical properties of the structure300 at the distal body end316. The different physical properties are created by material selection. More particularly, materials selected for the inner catheter tube304 and the expandable body306 are more compliant (i.e., more elastic) than the materials selected for theouter catheter tube302. In a preferred embodiment, materials selected for the expandable body306 and the inner catheter tube304 possess hardness properties of less than about 90 Shore A and ultimate elongation of greater than about 450%, e.g., more compliant polyurethanes. In a preferred embodiment, materials selected for theouter catheter tube302 possess hardness properties of greater than about 45 Shore D and ultimate elongation of less than about 450%, e.g., less compliant polyurethanes or polyethylenes.
• Due to the differential selection of materials, the lack of compliance of theouter catheter tube302 at theproximal body end314 is counterpoised during expansion of the body306 against the compliance of the inner catheter tube304 at the distal, body end316. The different compliance characteristics causes the body306, during expansion, to increase in length in proportion to its increase in diameter during expansion. By virtue of the more compliant body306 and inner catheter tube304, the structure300 shown inFIG. 21 is elastic enough to conform to an interior body region, like inside a bone. Nevertheless, the structure300 is constrained from over-expansion by attachment of theproximal end314 of the body306 to the less elasticouter catheter tube302.
• The bond between a given expandable structure and its associated catheter tube can be strengthened by using a CO2 or NdYAG laser to weld the structure and tube materials together. Factors influencing joint strength include energy wave length, energy pulse width, pulse period, head voltage, spot size, rate of rotation, working distance, angle of attack, and material selection.
• Thecatheter tube302 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
II. Deployment in the Vasculature
• FIG. 22 shows ablood vasculature region400. Theregion400 includes afirst blood vessel402, which extends along a first axis404. Theregion400 also includes a second blood vessel406, which branches from thefirst blood vessel402 along a second axis408 offset from the first axis404.
• FIG. 22 also shows the presence of anocclusion410 adjacent the second blood vessel406. Theocclusion410 can comprise, e.g., plaque buildup along the interior wall of the second blood vessel406.
• FIG. 23 shows the distal end of atool412, which has been introduced into thevascular region400 for the purpose of opening theocclusion410. Thetool412 comprises acatheter tube416, which carries at its distal end anexpandable structure420 of the type shown inFIG. 11. Thecatheter tube416 can, at its proximal end, be configured like the tube50 shown inFIG. 3, with a handle51 made of, e.g., a foam material.
• Thecatheter tube416 is introduced by conventional vascular introducer and, with fluoroscopic monitoring, steered to the targetedregion400 along a guidewire430 deployed within the first andsecond vessels402 and406. Thestructure420 is expanded using a sterile fluid, like saline or a radio-contrast medium.FIG. 23 shows thestructure420 in a substantially expanded condition.
• Like theexpandable structure20 shown inFIG. 11, the main axis422 of thestructure420 shown inFIG. 23 and the axis424 of thecatheter tube416 are not aligned. Instead, the structure axis422 is offset at a selected acute angle A from the catheter tube axis424. Due to the offset angle A, thestructure420, when substantially expanded (asFIG. 23 shows), is not symmetric with respect to the catheter tube axis424.
• AsFIG. 23 shows, the asymmetric expansion of thestructure420 allows the physician to maintain thecatheter tube416 in axial alignment with thefirst blood vessel402, while maintaining theexpandable structure420 in axial alignment with the second blood vessel406. In this orientation, expansion of thestructure420 within the second blood vessel406 opens theocclusion410. The asymmetry of thestructure420 relative to thecatheter tube416 thereby permits access to branched blood vessels without complex manipulation and steering.
III. Deflection of the Structure
• In all of the foregoing embodiments, a length of the associated catheter tube extends within the expandable structure. In the embodiments shown inFIGS. 4,11A/B,14A/B, and15 to18, the enclosed catheter tube comprises an extension of the main catheter tube. In the embodiments shown inFIGS. 19 to 21, the enclosed catheter tube comprises a separate catheter tube carried by the main catheter tube.
• Regardless of the particular construction (seeFIG. 26), the enclosed length ofcatheter tube600 provides an interior lumen602 passing within theexpandable structure604. The lumen602 accommodates the passage of a stiffening member or stylet606 made, e.g., from stainless steel or molded plastic material.
• The presence of the stylet606 serves to keep thestructure604 in the desired distally straightened condition during passage through an associated guide sheath608 toward the targeted body region610, asFIG. 26 shows. Access to the target body region610 through the guide sheath608 can be accomplished using a closed, minimally invasive procedure or with an open procedure.
• As shown inFIG. 27, the stylet606 can have a preformed memory, to normally bend the distal region612 of the stylet606. The memory is overcome to straighten the stylet606 when confined within the guide sheath608, asFIG. 26 shows. However, as thestructure604 and stylet606 advance free of the guide sheath608 and pass into the targeted region610, the preformed memory bends the distal stylet region612. The bend of the distal stylet region612 bends thetube600 and thereby shifts the axis614 of the attachedexpandable structure604 relative to the axis616 of the access path (i.e., the guide sheath608). The prebent stylet606, positioned within the interior of thestructure604, further aids in altering the geometry of thestructure604 in accordance with the orientation desired when thestructure604 is deployed for use in the targeted region610.
IV. Material Selection
• In any of the foregoing embodiments, the material of the expandable structure 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 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 copending 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, while not always required, is nevertheless preferred, when maintaining a desired shape and size within the bone is important, for example, in a vertebral body, 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 an expandable structure 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 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 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 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 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 is the amount that the targeted fractured bone region has been displaced or depressed. The expansion of the structure 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 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 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 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 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 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.
V. Single Use
• Expansion of any one of the expandable structures described herein during first use in a targeted body 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 body 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 kit500 (seeFIGS. 24 and 25) for storing a single use probe502, which carries an expandable structure504 described herein prior to deployment in bone.
• In the illustrated embodiment (seeFIGS. 24 and 25), the kit500 includes aninterior tray508. Thetray508 holds the probe502 in a lay-flat, straightened condition during sterilization and storage prior to its first use. Thetray508 can be formed from die cut cardboard or thermoformed plastic material. Thetray508 includes one or more spaced aparttabs510, which hold the catheter tube503 and expandable structure504 in the desired lay-flat, straightened condition. As shown, the facing ends of thetabs510 present a nesting, serpentine geometry, which engages the catheter tube503 essentially across its entire width, to securely retain the catheter tube503 on thetray508.
• The kit500 includes aninner wrap512, which is peripherally sealed by heat or the like, to enclose thetray508 from contact with the outside environment. One end of theinner wrap512 includes a conventional peal-away seal514 (seeFIG. 25), to provide quick access to thetray508 upon instance of use, which preferably occurs in a sterile environment, such as within an operating room.
• The kit500 also includes an outer wrap516, which is also peripherally sealed by heat or the like, to enclosed theinner wrap512. One end of the outer wrap516 includes a conventional peal-away seal518 (seeFIG. 25), to provide access to theinner wrap512, which can be removed from the outer wrap516 in anticipation of imminent use of the probe502, without compromising sterility of the probe502 itself.
• Both inner andouter wraps512 and516 (seeFIG. 25) each includes a peripherally sealedtop sheet520 and bottom sheet522. In the illustrated embodiment, thetop sheet520 is made of transparent plastic film, like polyethylene or MYLAR™ material, to allow visual identification of the contents of the kit500. The bottom sheet522 is made from a material that is permeable to EtO sterilization gas, e.g., TYVEC™ plastic material (available from DuPont).
• The sterile kit500 also carries a label or insert506, which includes the statement “For Single Patient Use Only” (or comparable language) to affirmatively caution against reuse of the contents of the kit500. The label506 also preferably affirmatively instructs against resterilization of the probe502. The label506 also preferably instructs the physician or user to dispose of the probe502 and the entire contents of the kit500 upon use in accordance with applicable biological waste procedures. The presence of the probe502 packaged in the kit500 verifies to the physician or user that probe502 is sterile and has not be subjected to prior use. The physician or user is thereby assured that the expandable structure504 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.

Claims (13)

1-14. (canceled)

15. An instrument for forming a cavity in cancellous bone comprising:

a generally straight catheter tube having a proximal end, a distal end, a first lumen and a second lumen;

an expandable structure disposed at the distal end of the catheter tube, the expandable structure having a distal end and communicating with the first lumen of the catheter tube; and

a generally straight stiffening stylet inserted into the second lumen of the catheter tube;

wherein the second lumen extends through the first lumen of the catheter tube to the distal end of the expandable structure.

16. The instrument according to claim1, wherein the expandable structure is made from an elastic material.

17. The instrument according to claim1, wherein the stylet is removable from the second lumen.

18. The instrument according to claim1, wherein the stylet is formed from metal.

19. The instrument according to claim1, wherein the stylet is formed from plastic.

20. An instrument for forming a cavity in cancellous bone comprising:

a generally straight outer catheter tube including a distal end and a first lumen;

a generally straight inner catheter tube extending within the outer catheter tube and including a distal end and a second lumen, wherein the distal end of the inner catheter tube extends beyond the distal end of the outer catheter tube;

an expandable structure communicating with the first lumen; and

a generally straight stiffening stylet sized for insertion into the second lumen.

21. The instrument ofclaim 20 wherein the expandable structure includes a proximal end and distal end and wherein the distal end of the expandable structure is attached to the distal end of the inner catheter tube.

22. The instrument ofclaim 20 wherein the stylet is formed of metal.

23. The instrument ofclaim 20 wherein the stylet is formed of plastic.

24. The instrument ofclaim 20 wherein the stylet includes a region with a preformed memory.

25. The instrument ofclaim 20 further comprising a guide sheath sized for through passage of the stylet and catheter tubes.

26. The instrument ofclaim 20 wherein the inner catheter tube is formed from a material more compliant than the material from which the outer catheter tube is formed.

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