WO2012064473A1

WO2012064473A1 - Covered stent devices for use in treatment of fracture

Info

Publication number: WO2012064473A1
Application number: PCT/US2011/056840
Authority: WO
Inventors: Steven Charlebois
Original assignee: Med Institute, Inc.
Priority date: 2010-11-09
Filing date: 2011-10-19
Publication date: 2012-05-18

Abstract

Among other things, there is shown and described a stent for use in orthopedic procedures for support of tissues. In particular embodiments, the stent includes a frame of a series of interconnected struts with a polymer covering on its inside and/or its outside and covering its open ends, to form a sealed internal chamber. A filler material, such as a hydrogel, is passed through the covering into the chamber for support and to approximate natural tissue biomechanical characteristics. The stent may be self-expanding, or expanded by filling with the filler material or other substance.

Description

COVERED STENT DEVICES FOR USE IN TREATMENT OF FRACTURE

This disclosure concerns devices and methods for orthopedic implantation that are easily implantable and expandable, and may be used to support tissue in a variety of therapies involving implantation, e.g. to preserve substantial mobility, encourage fusion, or a combination.

BACKGROUND

In a number of orthopedic procedures, it has become known to implant support devices after excising tissue. For example, in cases of vertebral or intervertebral disk trauma, malformation, disease, and injury, implants have been proposed for insertion between vertebral bodies as replacements for disk material and/or as aids in fusing vertebrae to shore up support for the spinal column.

Corrective orthopedic surgery can leave the patient substantially immobile for a substantial period of time, or a body joint fused permanently. For instance, in correction of valgus knee malalignments a wedge osteotomy is taken from the tibia, and the bones of the knee joint are fixed using an external fixator apparatus. Such procedures have not only the immobility and pain associated with external fixators, but also a significant risk of infection arising from the external fixator extending through the skin, as well as potential for non-union.

Thus, existing implants for orthopedic repair or augmentation can produce significant negative side effects, such as those noted above. Some cases result in implants that may migrate within and/or out of the implant space, in some situations dislocating from the space, causing severe pain and necessitating surgery to remove the replacement and perform additional correction. In the case of intervertebral disk replacement, devices that anchor solidly in the vertebral end plates or other tissue may not provide for certain types or ranges of motion that a natural intervertebral disk allows. Many devices do not have mechanical properties that approximate the behavior of natural tissue. Further, many devices must be implanted by invasive open surgical approaches, which generally require a much longer recuperation time and immobility (or drastic reduction of mobility) for the patient with much greater discomfort due to the necessity of cutting through and retracting a variety of tissues.

SUMMARY

Among other things, there are disclosed devices and methods for orthopedic repair or augmentation that are easier to use and provide an easier recuperation for the patient. For example, there is disclosed a stent for use in orthopedic

applications, that includes in certain embodiments a frame formed of a set of struts having openings between them. The frame has a generally cylindrical shape with first and second open ends, and a polymer covering is fixed to it, with the polymer closing all of the frame's openings and its open ends so that a chamber is formed within the frame and covering. The stent is adapted to be expanded uniformly radially from a first insertion diameter to a second supporting diameter following insertion into an orthopedic support location. In the second diameter the chamber within the frame and covering is sealed from the outside by the covering. A filler material may be within the chamber when the stent has the second diameter, so that the filler material is prevented from leaving the chamber by the covering when said stent is in the support location.

In particular embodiments, the material of the covering is a self-sealing elastomeric polymer. The frame may be fixed or engaged to an exterior surface of the covering so that the covering is between the chamber and the frame, e.g. the stent has a radially innermost extent defined by the radially innermost portions of its struts, and the covering contacts the frame at least at a number of those radially innermost portions of the struts. Alternatively, the frame may be fixed to an interior surface of the covering so that at least part of the frame faces the chamber, e.g. the stent has a radially outermost extent defined by the radially outermost portions of its struts, and the covering contacts the frame at least at a number of those radially outermost portions of the struts. The covering can extend over the open ends of the frame beyond the extent of the frame in a substantially hemispheric configuration. In that configuration, the hemispheric portions of the covering may have a burst strength sufficient to prevent bursting during compression by normal orthopedic compression loads. Filler materials may be or include one or more hydrogel components, such as a hyaluronic acid gel, and they may approximate the biomechanical properties of cartilage and/or intervertebral disk material with the stent. Some embodiments of the stent are self-expandable, and/or the covering is adapted to have the filler material injected through it into the chamber following the stent's self-expansion. In other embodiments, where the stent is not self- expandable, the stent may further include at least one port through the covering adapted to permit access to the chamber for inserting the filler material into the chamber and maintaining the chamber sealed following insertion of the filler material. The stent's second or expanded diameter is at least slightly larger than a normal width of an intervertebral disk space and/or corresponds to a width of a wedge osteotomy in a long bone, in certain embodiments. The frame may be adapted to withstand natural compression forces at the desired orthopedic location without complete collapse when the frame has its second diameter, i.e., the frame by itself could withstand natural compression without collapsing completely.

Methods are also disclosed, and may include inserting a stent into a patient to a location in need of orthopedic correction, where the stent has a frame being substantially cylindrical and having first and second open ends and a passage between the ends, and a polymeric covering engaged to the frame to define a sealed chamber within the stent. The stent is expanded radially uniformly within that correction location from a first diameter to a second diameter, thus also expanding the chamber. A filler is delivered into the chamber so that the chamber is filled to a predetermined degree. In certain embodiments, the delivering and expanding are performed in the same action, so that delivering a filler operates to expand the stent from the first diameter. The predetermined degree of filling may correspond to expanding the stent all the way to the second diameter, or may correspond to delivering a predetermined volume of filler material. In other embodiments, the delivering of filler occurs after the expanding is complete. The delivering can include inserting a needle through a portion of the covering and into the chamber, and injecting the filler through the needle into the chamber. At a desired point, such as when such filling is finished, the needle is removed from the chamber and the covering is allowed to reseal.

An orthopedic implant as disclosed herein may include a stent having a cylindrical shape and defining a passage from a first open end to a second open end, and having a first collapsed at least part circular diameter and a second expanded at least part circular diameter and being expandable from the first diameter to the second diameter. A polymer covering engaged to the stent and covering its open ends forms a sealed chamber at least partially within the passage. The covering is expandable with the stent so that the chamber remains sealed during expansion from the first diameter to the second diameter. A hydrogel filler material is placed within the chamber, e.g. after expansion of the stent or as a way of expanding the stent.

These embodiments and others provide an orthopedic device for

intervertebral disk repair, for filling osteotomy (such as a wedge osteotomy used in correction of knock-knees), or for placement in other areas for orthopedic support. The device is easy to place over a guidewire or through an access sheath, particularly along the same percutaneous track used to remove malformed or damaged tissue (e.g. disk material or bone tissue). The stent resolves issues of migration or dislocation from orthopedic implant locations and approximation of natural movement at the location, and provides variable expandability,

biomechanical similarity to natural tissue, and implantation-friendly cylindrical shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, part cutaway view of an embodiment of a stent for orthopedic use.

FIG. 2 is a side, part cutaway view of an embodiment of a stent for orthopedic use.

FIG. 3 is a lateral view in partial cross-section of the embodiment of FIG. 1 in an embodiment of implantation in an intervertebral disk space.

FIG. 4 is a side view in partial cross-section of an embodiment of a procedure and structure used with the embodiment of FIG. 1.

FIG. 5 is a posterior view of two devices according to FIG. 1 implanted in an intervertebral disk space.

FIG. 6 is a posterior view of one device according to FIG. 1 implanted in an intervertebral disk space.

FIG. 7 is a lateral view of the embodiment of FIG. 2 in an embodiment of implantation in an intervertebral disk space.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made to certain embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure and the claims is thereby intended, such alterations, further modifications and further applications of the principles described herein being contemplated as would normally occur to one skilled in the art to which this disclosure relates.

Referring now generally to the Figures, there is shown an embodiment of a stent 20 for orthopedic augmentation or repair of bodily tissues, for example intervertebral disk tissue, knee joint tissues or related long bones, and the like.

Device 20 includes a structure or frame 22 adapted for introduction into a human or veterinary patient. "Adapted" means that the structure 22 is shaped and sized for such introduction. Frame 22 is formed of a series of struts in a repetitive pattern, and for clarity, only a portion of the structure 22 is shown in FIG. 1.

By way of example, structure or frame 22 of stent 20 is particularly adapted for insertion into or between supportive bodily tissues or structures of a patient, for orthopedic support, correction or therapy at a given site. Indeed, frame 22 can have any of a variety of stent configurations. Moreover, because the problems addressed by the present disclosure arise with respect to those portions of the device actually positioned within the patient, frame 22 or its part inserted into or between tissues need not be an entire device, but can merely be that portion of an orthopedic or other device which is intended to be introduced into the patient or into a particular location in the patient. Accordingly, stent 20 can be configured as at least one of, or any portion of, a variety of orthopedic devices, appliances, implants, or

replacements. Stent 20 can also be configured as a combination of portions of any of these.

In particular embodiments, frame 22 has a configuration identical or similar to those commercially available as the FORMULA® or ZILVER® stent from Cook Incorporated (Bloomington, Ind.). Other types of stent configurations could also be used for structure 22, such as the Gianturco-Roubin FLEX-STENT® or GR II ® products also available from Cook Incorporated. While the configuration, including the arrangements and connections among struts (e.g. wires or filaments) and/or other physical structures, of these types of stents can be used for frame 22, the size (e.g. the dimensions of the physical structures as well as overall length and diameter pre- and post-expansion) of frame 22 will be determined by the dimensions, location, biomechanical forces, orthopedic needs, or other physical characteristics of the part of the body into which stent 20 is to be implanted.

Frame 22 is composed of a material suitable for the intended use of frame 22. The material is preferably biocompatible, although cytotoxic or other poisonous materials could be employed if they are adequately isolated from the patient. Such incompatible materials may be useful in, for example, radiation treatments in which a radioactive material is positioned by in or close to specific tissues to be treated. Under most circumstances, however, the material of frame 22 should be

biocompatible. The material may be either elastic or inelastic, as further discussed below. In the present embodiment, the material of frame 22 is non-biodegradable so as to provide lasting support, but it will be understood that a variety of

biodegradable substances (e.g. sturdy polymers) could be used.

Accordingly, the frame material can include at least one of stainless steel, tantalum, titanium, nitinol, gold, platinum, inconel, iridium, silver, tungsten, or another biocompatible metal, or alloys of any of these; carbon or carbon fiber;

cellulose acetate, cellulose nitrate, silicone, polyethylene teraphthalate,

polyurethane, polyamide, polyester, polyorthoester, polyanhydride, polyether sulfone, polycarbonate, polypropylene, high molecular weight polyethylene, polytetrafluoroethylene, or another biocompatible polymeric material, or mixtures or copolymers of these; polylactic acid, polyglycolic acid or copolymers thereof, a polyanhydride, polycaprolactone, polyhydroxybutyrate valerate or another biodegradable polymer, or mixtures or copolymers of these; a protein, an

extracellular matrix component, collagen, fibrin or another biologic agent; or a suitable mixture of any of these. Stainless steel and nitinol are particularly useful as the material for frame 22 when stent 20 is configured for intervertebral or similar orthopedic use.

Stent 20 may be expandable through application of radial or other force on the inside of frame 22 (termed "balloon-expandable") in some embodiments, for example in the configuration and material of the FORMULA® vascular stent noted above. In other embodiments, stent 20 is self-expandable, for example in the configuration and material of the ZILVER® vascular stent noted above. In either of these particular embodiments, and in other embodiments, stent 20 is expandable as will be discussed further below, and include openings between individual struts or structural members to permit expansion. In particular embodiments the expansion is substantially uniform throughout the length of frame 22 of stent 20, from end 24 to end 26. An internal passage, space or lumen 28 is within frame 22.

Frame 22 is engaged to a layer or covering 30 that contacts the struts of frame 22. In the illustrated embodiment, covering 30 is a polymer draped or applied to the struts of stent 22 in a thin membrane or film so as to seal or close all of the openings between respective struts. Covering 30 is of a material that is substantially nonporous, hydrophobic and/or impervious to liquid entrance or exit, in the illustrated embodiments, and is flexible and/or elastic as well. In particular embodiments, the polymer forming covering 30 is a polyurethane elastomer of a thickness in one example of about 50 microns, and in other examples may be more than 50 microns, such as between about 100 and 300 microns. Covering 30 is of approximately a uniform thickness in the illustrated embodiments. Exemplary elastomers for covering 30 include polyurethane urea (e.g. THORALON®, available from Thoratec Corporation, Pleasanton, California), which provides the advantage of self-healing or resealing following small punctures, particularly when containing or holding viscous fluids. The term "covering" as used above is to be distinguished from the term "coating." "Coating" refers in the stent-related arts to the addition of a drug or similar biologically- affective compound to the struts of a stent but not blocking the openings between the struts, so that the drug can affect a blood vessel against which the stent is applied while the vessel tissue is pressed into the openings between the struts. A "covering," as indicated above, is a drape, blanket or sealing layer that closes the openings in frame 22.

In the illustrated embodiments, covering 30 is a layer on the exterior of the struts of frame 22. In particular embodiments, individual struts or other portions of frame 22 form visible ridges in covering 30, and the portion of covering 30 between those portions form small hollows at least slightly below the outermost level of those portions. Frame 22 is thus essentially between passage 28 and covering 30, and passage 28 extends to or contacts the struts of frame 22 as well as covering 30 in the spaces between them. In other embodiments, covering 30 may be applied to the interior of frame 22, i.e. between the struts and passage 28, with the individual struts or other portions of frame 22 (and the voids between them) outside covering 30. In such embodiments, the struts of frame 22 are open to the orthopedic environment on implantation, and only covering 30 faces passage 28.

Covering 30 not only covers the spaces between the struts of stent 22, but also forms end portions or caps 32, 34 that enclose ends 24, 26 of frame 22 in the illustrated embodiments. In the non-expanded state, caps 32, 34 may be rounded (e.g. FIG. 1), extended from or inserted into their respective ends 24, 26, or with an appropriate material for covering 30 that will withstand such stretching without breaking, caps 32, 34 may be substantially planar in the non-expanded state.

Similarly, the expanded state of stent 20 may have caps 32, 34 in a rounded state, particularly extended from ends 24, 26 and in a substantially hemispherical or part- spherical shape, or in other embodiments caps 32, 34 may be substantially planar in the expanded condition of stent 22. It will be understood that in other embodiments caps 32 and/or 34 may be initially separate from covering 30 contacting frame 22, of the same or different materials, and joined to covering 30 and/or frame 22 to form a sealed interior 28. The illustrated embodiments show caps 32, 34 as a monolithic portion of covering 30 (e.g. made of the same material in essentially the same process as the rest of covering 30).

Accordingly, the illustrated embodiment of stent 20 has a frame 22 of an expandable mesh or group of interlinked struts (e.g. wires or filaments) that are adapted to be flexible both when stent 20 is in a collapsed state and when it is in an expanded state, with a covering 30 to form a sealed passage or chamber 28. In particular embodiments, stent 20 is encapsulated by a polyurethane elastomer covering 30, that includes the end portions 32, 34 as a monolithic whole. In the case of a balloon-expandable stent 20, for example, covering 30 can be laid over the stent after attachment to a balloon. There are a number of possible configurations for a mesh or interlinked struts in frame 22, but those identified above are believed to have particular application in orthopedic procedures. End caps 32, 34 enclose ends 24, 26 of frame 22. In the embodiment shown in FIG. 1, cap 32 forms a first or right end of stent 20, while cap 34 is on a second or left end of stent 20. As will be discussed further below, on insertion into the body, stent 20 may be inserted so that end caps 24 and 26 are generally anterior and posterior, or in other relative positions or locations rather than on the left and right. End caps 32, 34 along with the rest of covering 30 delimit internal pocket or chamber 28 that is at least partially within central portion 22 and coating 32, and may be in part within end caps 24 and/or 26.

The illustrated embodiment also shows a pair of radiopaque markers 36, 38, which are bands in that embodiment, and may be dots or other forms or shapes of markers in other embodiments. Markers 36, 38 are located at or just beyond ends 24, 26 of frame 22, as illustrated, with end caps 32, 34 of covering 30 beneath or around them. Markers 36, 38 are provided to indicate the positioning of frame 22, e.g. the relative position of ends 24, 26 and caps 32, 34 with respect to each other and/or to surrounding tissue. It will be understood that only one marker (e.g. 36) at one end of frame 22, or one or more markers at other positions with respect to frame 22, end caps 32, 34, or covering 30, may be provided in other embodiments.

Stent 20 is designed to have injected within its internal space or chamber 28 a material for support and for providing desirable biomechanical properties, such as properties approximating those of disk tissue, cartilage or other bone-related tissue. Accordingly, a filler material 42 is provided within chamber 28. In certain embodiments, filler 42 is a polymer such as a hydrogel or similar material. For example, a cross-linkable hyaluronic acid gel can be used that has an initial low viscosity for ease of loading and delivery (e.g. through a syringe and catheter). That or a similar low viscosity is maintained in such embodiments during delivery to fill stent 20, as further discussed below. Such a polymer filler cures within stent 20 through one or more of temperature elevation (e.g. an increase from room

temperature or about 18° C to body temperature or about 38° C), a change in pH (e.g. through presence of bodily fluids), an exposure to a cross-linking agent (e.g. an agent within or painted on the inside of the chamber 28 in which filler 42 is inserted). These and perhaps other techniques change the properties of filler 42 from an injectable, fluid-like viscosity to one that is cured sufficiently to withstand full weight bearing by the patient. Fillers like cross-linkable hyaluronic acid gels provide flexibility with support, allowing some stress on adjacent tissue, which in the case of bone tissue results in better, stronger bone tissue. Such gels in particular embodiments can provide a compressive stiffness in the range of 500 N/mm

(newtons per millimeter) to 5000 N/mm, which is believed to be suitable for the final cured filler in either a balloon-expandable or self-expandable stent 20 as similar or corresponding to stiffnesses of human cervical, thoracic and lumbar disk material. Such gels can also provide a compressive strength in the range of 5000 to 8000 N.

Other embodiments of filler 42 can include at least a portion of a hyaluronic acid gel, or can be or include other types of cross-linkable viscous hydrogels, or polyvinyl alcohols, polyethylene glycol, polyvinyl pyrrolidine, and blends of one or more of them. The gel is injected into chamber 28, e.g. through one or both end caps 32, 34, to substantially fill chamber 28. Stent 20 with filler 42 provides not only the orthopedic support of frame 22 (e.g. to an intervertebral disk space or knee joint), but also is resilient and compressible as will be discussed below to establish a normal or approximately normal range of motion for associated bone, connective and related tissues relatively quickly following the procedure to implant stent 20. Such a result is generally not possible with common orthopedic procedures such as vertebral fusion or correction of valgus knee malalignment.

As noted above, stent 20 is self-expanding in some embodiments, or expandable with internally- applied radial force in other embodiments. For convenience, further discussion below is primarily of the embodiment of stent 20 as self-expanding (e.g. nitinol in a superelastic state). It will be understood that aspects of this embodiment are applicable to other embodiments, and vice versa. As seen in FIG. 3, stent 20 has a first relatively collapsed diameter (indicated by portion A in FIG. 3) for insertion into an intervertebral disk space. For a self-expanding stent 20, the first or relatively collapsed diameter is dependent on a sleeve or sheath (e.g. 62 in FIG. 3) in which stent 20 is made or placed. Expanding stent 20, e.g. by moving it out of a sheath, causes stent 20 to assume a second expanded diameter (indicated by portion B in FIG. 3). In this embodiment, such a second expanded diameter is the expansion limit of self-expanding stent 20, which is either the largest diameter stent 20 can expand to, or the width of the orthopedic space into which stent 20 is inserted (e.g. an intervertebral disk space).

A description of using an embodiment of stent 20 that is self-expandable in the context of intervertebral implantation for replacement or augmentation of intervertebral disk tissue follows. It will be understood that stent 20 may be used in a variety of orthopedic contexts.

Once the surgeon has determined that at least a portion of an intervertebral disk must be excised, an opening is made in the patient to access the disk space. Stent 20 is particularly useful in percutaneous or otherwise-minimally-invasive procedures, although it can also be used in open procedures. While the following discussion is in the context of a percutaneous procedure, it will be understood that identical or similar steps can be performed in the context of other types of surgical procedures.

The surgeon creates a percutaneous opening through dermal and subdermal tissues to the spinal column, and specifically to one or more vertebral segments. A tube or sheath 50 is inserted through the opening to maintain the opening and to provide a passageway through which to pass instruments with little risk of damaging tissue. Cutting and retrieval or suction tools are passed through sheath 50

(simultaneously or serially) to a portion of the intervertebral disk, and the disk or at least a portion of it is excised. FIG. 3 indicates an intervertebral disk space S between vertebrae VI and V2 from which a portion or all of the disk has been removed. It will be understood that enough disk material could be removed for one or more stents 20, while leaving a portion of natural disk material D between the vertebrae (e.g. FIG. 6), or substantially all of the disk material can be removed (e.g. FIG. 5). Stent 20 can be used following a variety of excisions in the disk, from substantial entire removal, to removal of a portion, to removal of a minimal portion, e.g. drilling a hole in the disk material.

The surgeon may also roughen, abrade or otherwise prepare the endplates of the vertebrae VI and/or V2 or remaining disk tissue, if desired. For example, where the disk material has been removed up to one or both vertebral endplates, the endplates may be abraded down to bleeding bone so as to increase tissue growth at the site, or may be roughened to help secure stent 20 when implanted. As another example, a drill, trocar or other tool (not shown) to smooth the opening in the disk tissue or to give it a substantially cylindrical shape could be used.

With the disk space prepared, stent 20 can be inserted into the disk space. In the illustrated embodiment, self-expanding stent 20 may be loaded into (or prepared or manufactured within) the distal end of a delivery tube 62, with a pusher or blocker 64 proximal of stent 20 in tube 62. Delivery tube 62 is moved through sheath 50 to disk space S. When delivery tube 62 is positioned within the disk space S so that its distal end is at approximately the position desired for a distal end of stent 20, the operator withdraws tube 62 while pusher 64 is held in position, blocking any rearward movement of stent 20. In other embodiments, pusher 64 could be moved within tube 62 to eject stent 20 from the distal end of tube 62. As stent 20 moves out of tube 62, it expands radially all around its circumference within disk space S, until it contacts opposing tissue parts, e.g. the endplates of vertebrae VI and V2 or remaining disk tissue. Vertebrae VI and V2 and/or tissue between them may be distracted slightly from a normal distance between them in order to allow stent 20 to expand a distance slightly larger than that normal distance.

With stent 20 in an expanded condition against the tissue, with an expanded diameter defined by the space within the tissue, filler material 42 is injected into chamber 28, e.g. through proximal end cap 34 (e.g. FIG 4). In one embodiment, a needle 76 connected to a syringe (not shown) or other source of filler material 42 is inserted through sheath 50 and through end cap 34. If one or more markers 36 and/or 38 are provided on stent 20, needle 76 can be visualized fluoroscopically to a position with respect to such marker(s), e.g. beyond a marker at or adjacent to end cap 34. When needle 76 is in a satisfactory position within chamber 28, filler material 42 is injected through needle 76 and into chamber 28. The surgeon or other professional can inject a predetermined volume of filler material, or can inject until resistance to further injection or further extension of stent 20 and/or distraction of the vertebrae is observed. Filler material 42 is contained by covering 30, and end caps 32, 34 may assume a rounded, hemispherical or other bulge outside the length of frame 22 of stent 20, if expandable to that shape and not already so shaped. With chamber 28 filled with filler material 42 as desired, needle 76 is withdrawn, and the injection hole through end cap 26 reduces or reseals to hold filler material 42 within stent 20.

Once stent 20 is filled with filler material 42, any distraction that remains between vertebrae VI and V2 may be relieved, allowing vertebrae VI and V2 to move toward each other and against stent 20, with stent 20 counteracting their compression (pushing back against the vertebrae) to maintain the desired normal distance between the vertebrae. In that case, stent 20 assumes a more flattened and/or irregular configuration at the locations of contact between stent 20 and vertebrae VI and V2 or adjacent tissue. Such tissue (e.g. abraded endplate tissue and/or remaining disk tissue) is pressed against the exterior of stent 20, and into the hollows between the struts of frame 22. Whether covering 30 is outside or inside of frame 22, the tissue can press on and at least slightly between the struts of frame 22 to provide not only mechanical engagement (as the struts tend to dig into the tissue) but also provide a texture encouraging tissue ongrowth or close apposition to stent 20. In addition to or instead of the textures noted above, covering 30 may be roughened or textured to provide such connection advantages, and the material for covering 30 may be selected to allow proximate tissue growth and anchorage. With stent 20 implanted, the surgeon can take other surgical steps with respect to the intervertebral disk space, vertebrae VI and/or V2, and/or other tissues in order to assist in healing. When the surgeon has completed all tasks at the vertebral site, the sheath and other equipment for inserting stent 20 can be removed from the patient and the minimally-invasive or other surgical opening can be closed.

Stent 20, with filler material 42 contained by covering 30 and end caps 32, 34, permits compression between vertebrae VI and V2, with such compression generating push-back by the flexible frame 22 and filler material 42. Separation between vertebrae VI and V2 is maintained while allowing some or all of the natural range of compression, shear and/or rotational motion between them.

Distraction forces on the vertebrae draw upper and lower surfaces of stent 20 away from each other, generating stresses on filler material 42 and frame 22 that counteract such distraction. Twisting or rotational motion between vertebrae VI and V2 are possible because of the ability of parts of stent 20 and filler material 42 to flex from side to side and shift with respect to tissues. The struts of frame 22, along with the flexibility of covering 30 and the ability to handle strain of a gel or similar filler material 42 allow the top part of stent 20 to move relative to the bottom part. Similarly, shifting motion between vertebrae VI and V2 can be accommodated by some rolling motion of stent 20 and/or by shifting of a top part with respect to a bottom part. While frame 22 holds most of the load of the tissues into or next to which it is implanted, filler 42 provides some load-bearing capacity and support as well as flexibility, cushion and malleability to the overall stent 20. Stent 20 accomplishes the goal of supporting tissues in an orthopedic context while allowing those tissue freedom in all of their general types of motion, which supports having rigid solid parts restrict or prohibit.

The above discussion regarding implantation of stent 20 should not be considered to be limited to implantation of a single stent 20. As indicated in FIG. 6, a single stent 20 can be implanted as noted above. In cases in which much or all of an intervertebral disk must be or is desired to be excised, multiple stents 20 may be inserted, e.g. two stents 20, one on either side of a centerline of the vertebral column (e.g. FIG. 5). It will be understood that depending on the size of stents 20 and the amount of disk matter removed, more than two stents 20 could be placed. However, it is understood that a stent' s expanded diameter that is approximately the normal distance between two vertebrae will frequently be large enough to permit only two stents 20 to be implanted in a single disk space. Multiple stents 20 may be indicated in other orthopedic cases, such as wedge osteotomy cases, where a first stent expanded to a smaller diameter can be placed in the narrow end of the wedge, and one or more stents expanded to larger diameter(s) can be placed in wider portions of the wedge.

In another embodiment stent 120 is a stent with an original collapsed state and size, and is expandable by application of internal pressure. In the context of this disclosure, the term "balloon-expandable" does not necessarily mean that a balloon is used to expand the stent, but that the stent does not expand on its own, and requires internal pressure to expand. Stent 120 includes frame 122 with covering 130 (similar or identical to covering 30). In a particular embodiment, frame 122 is similar or identical to frame 22, except not of superelastic material, or may be of the same configuration as the FORMULA® vascular stent noted previously. One or both end caps 132, 134 in this embodiment have a cannula or port 123 providing a sealable passage through to chamber 128. Cannula(s) 123 may include a fitting 125 to accommodate an injector of filler 42 into covered frame 122. Fitting(s) 125, if present, may be luer-lock fittings, threaded fittings or other stable connections in certain embodiments. Fitting(s) 125 or cannula(s) 123 may have an internal seal, and/or be sealed internally or externally by a portion of covering 30.

Stent 120 is used much as self-expanding stent 20, described above. With a minimally-invasive or other approach made and the surgical site prepared (e.g. FIG. 7), a catheter 131 (or other guide and/or insertion device(s)) is connected to cannula 123 so that stent 120 (in a first collapsed diameter) is at the end of catheter 131. Catheter 131 with stent 120 is inserted and maneuvered so that stent 120 is within the intervertebral disk space. If necessary, a sheath or outer conduit (not shown) may be placed along a path to the insertion location, to facilitate passage of stent 120. With stent 120 in the desired location, it is then inelastically expanded to a second diameter of a desired extent, e.g. to a natural or distracted width of an intervertebral space. In some embodiments, expansion is accomplished by passing sufficient filler material from a syringe or other injection device (not shown) via catheter 131 and cannula 123 into chamber 128, so that the filler material presses against covering 130 and/or frame 122 to force stent 120 to expand. Covering 130 acts in many respects like an inflation balloon, without having to move a balloon into the stent and risk damage, unwanted movement, or other difficulties with stent 120. When chamber 128 is filled sufficiently so that stent 120 engages tissue (e.g. vertebrae VI and V2, which may be previously distracted or pressed by stent 120) or is otherwise expanded as the surgeon desires, catheter 131 is disconnected from cannula 123 and/or fitting 125. In this embodiment, filler material is prevented from escaping via cannula 123 and fitting 125 (if present) by sealing action of covering 130, and/or by capping (e.g. connecting a cap (not shown) to fitting 125), by crimping cannula 123, or by other physical or mechanical methods.

In other examples, an expansion medium or fluid (e.g. air or saline) could be used for initial inelastic expansion of stent 120, then after withdrawal of such fluid a filler material can be introduced. When stent 120 is expanded as desired, the inflation medium can be withdrawn (with venting if needed), and filler material can be injected into chamber 128 via catheter 131 and cannula 123, as discussed above. Alternatively, a needle (not shown) can be inserted through a portion of covering 130 along frame 122 or through an end cap 132, 134 so that filler material can be injected through the needle into chamber 128. With stent 120 in its expanded state and filler material within it, any distraction remaining on vertebrae VI and V2 may be released and the surgery ended, as discussed above.

It will be understood that stents 20, 120 may be placed percutaneously over a guidewire, as a part of or in place of insertion through a percutaneous sheath. If a guidewire is used, stents 20, 120 may be placed over it by running the guidewire through end caps 32, 34 or a respective port or cannula 123 in one or both end caps 132, 134. The resealing quality of some embodiments of covering 30 maintains the integrity of covering 30 if a guidewire is passed through it. After placement of stents 20, 120 a needle can be placed over the guidewire to inject filler into stent 20, 120, or the guidewire can be removed and the needle can be inserted into stent 20, 120.

The embodiments noted above provide self-expandable and balloon- expandable stents that supply orthopedic support and maintenance of mobility of tissues in which or adjacent to which they are implanted. For example, one or more such stents may be placed in vertebral segments, as repair or replacement for all or part of an injured, herniated, diseased or otherwise damaged or ineffective intervertebral disk. As another example, one or more such stents may be placed in knee tissue as an alternative to use of a wedge osteotomy in correcting knee malalignment. Rather than cut a wedge of bone from the tibia and externally fixating the leg bones, one or more stents 20, 120 can be placed in or between bones to realign and support them. Use of stents 20, 120 avoids the pain and immobility of external fixation, as well as attendant infection hazards. The stents are easily delivered percutaneously via a sheath or other access, and/or over a guidewire inserted to the intervertebral disk space. The sheath, guidewire or track for placement of the stent(s) can be the same as that used to remove disk material, or to move or insert equipment for removing disk material.

Stents 20, 120 have been described as having a sealed internal chamber 28, 128. It is to be understood that various embodiments could include multiple internal chambers 28, 128, which may be filled or inflated to the same degree or to different degrees. For example, in cases where a stent 20, 120 is to be placed in an angled or uneven space (e.g. a wedge osteotomy in a long bone), a stent 20, 120 having two or more chambers 28, 128 may be used. A chamber 28, 128 in the narrow portion of the space may be expanded and filled to a degree sufficient for that narrow portion, while a second (or additional) chamber 28, 128 may be expanded and filled to a greater degree sufficient for a wider portion of the space.

Filler material 42 has been primarily discussed in terms of a polymer (e.g. hydrogel) that is easily flowable for delivery and cures to a flexible state that provides sufficient support for the weight of the patient with movability of a joint. Such motion-capability assist in both therapies that seek continued motion of the joint as well as those that seek fusion of the joint in either short or long-term. In fusion cases, initial movability of the joint provides stress on the adjacent bones, and such stresses tend to cause the bone to make stronger bone tissue for healing, replacement and/or fusion. However, it is to be understood that other types of filler may be used with or instead of such hydrogel materials. Cement materials are used in a number of orthopedic procedures, with polymethylmethacrylate (PMMA) commonly used for its ease of use and hardening properties, particularly where fusion in the short term is desired. Calcium-based cements, however, are generally thought of negatively with respect to certain orthopedic procedures because they do not share such hardening properties. Calcium-based cements can be used with stents 20, 120, so that their initial malleable physical properties within the supportive stent can allow the patient to be up and move around, and the cement will provide for long-term fixation as it hardens in vivo. Orthopedic implants that have open areas for placement of treatment material use bone chips, graft or thick, quick-hardening cements as such treatment materials, because other materials will leak or migrate away. Stents 20, 120 eliminate or reduce the need for bone graft, and can use materials that are slower-hardening or do not harden.

Covering 30, 130 and/or frame 22, 122 can also include growth factors (e.g. TGF-β, or bone morphogenetic proteins like BMP-2), tissue-regenerative materials such as a particulate form of extracellular matrix material (e.g. small intestine submucosa (SIS)), or other chondroinductive, angiogenic or osteoinductive agents. Such materials, either within covering 30, 130 and/or frame 22, 122 or applied over one or both of them, can promote bone or other tissue formation in or around stent 20, 120 once implanted. Such tissue ongrowth or extension provides additional securing for stent 20, 120 as well as an enhanced environment for healing.

Vertebroplasty and kyphoplasty procedures for treatment of damaged vertebrae have been developed as alternatives to attachments of implants for vertebral fusion and other procedures. In kyphoplasty, bone cement is injected into a balloon-created void in a damaged vertebra so as to attempt to restore height or angle of the vertebra, while vertebroplasty injects the cement into the vertebra without creating or augmenting a space. In both cases, there is the risks of overfilling the vertebra with cement, resulting in excess cement around the vertebra or a change in the size of the vertebra or orientation of its surfaces. There is also the risk of the cement affecting the kinematics of a vertebral joint or segment. It has been estimated that 88% of vertebroplasty cases result in a new fracture in the treated bone or adjacent bones. Treatment of bones or vertebral segments using stent 20, 120 reduces or eliminates the risks of overfilling, and use of a filler material that helps maintain the biomechanics of the bones or joints is expected to minimize new injuries or damage.

The embodiments of the stents noted above are "covered" stents, that is, they have a layer of polymer that expands with the wires or struts of the stent frame and maintains a filler material within the stent. The layer forms end seals or caps, which may be hemispherical or part-spherical in shape and may include a cannula or port for expanding the stent and for containing and holding the filler material. The filler material may be a hydrogel or other polymer material so as to provide compression, stress, strain and force transmission characteristics similar to that of natural disk material. The physical design of the stent, i.e. its wires or struts, provides for load- bearing with good purchase with flat vertebral endplates as well as rough or irregular tissue surfaces, which can be a problem if disk material is not or cannot be adequately removed. The cylindrical shape of the stent, along with the

characteristics of its wires or mesh and the flexible filler, provide accommodation and damping reaction to compression, shear and rotational loading forces. Further, the mesh or wires in the stent provide narrow surfaces that can dig into end plates or other tissue to provide security as well as the above-noted loading characteristics.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain specific

embodiments have been shown and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. It will be understood that features shown and described in the context of one or embodiments may be used with or incorporated in the context(s) of other embodiment(s).

Claims

What is claimed is:

1. A stent for use in orthopedic applications, comprising:

a frame formed of a set of struts having openings between them, said frame having a generally cylindrical shape with first and second open ends,

a polymer covering engaged to said frame, said polymer closing all of said openings and said first and second open ends so that a chamber is formed within said frame and said covering,

wherein said stent is adapted to be expanded uniformly radially from a first insertion diameter to a second supporting diameter following insertion of said stent into an orthopedic support location, and in said second diameter said chamber within said frame and said covering is sealed from the outside by said covering,

and further comprising a filler material within said chamber when said stent has said second diameter, wherein said filler material is prevented from leaving said chamber by said covering when said stent is in the orthopedic support location.

2. The stent of claim 1, wherein said frame is fixed to an exterior surface of said covering so that said covering is between said chamber and said frame.

3. The stent of claim 1, wherein said frame is fixed to an interior surface of said covering so that at least part of said frame faces said chamber.

4. The stent of claim 1, wherein said covering extends over said open ends of said frame beyond the extent of said frame in a substantially hemispheric configuration.

5. The stent of claim 4, wherein said hemispheric portions of said covering have a burst strength sufficient to prevent bursting during compression by normal orthopedic compression loads.

6. The stent of claim 1, wherein said filler material is a hydrogel.

7. The stent of claim 6, wherein said filler material is a hyaluronic acid gel.

8. The stent of claim 1, wherein said stent is self-expandable, and said covering is adapted to have said filler material injected therethrough into said chamber following self-expansion of said stent.

9. The stent of claim 1, wherein said stent is not self-expandable, and wherein said stent further includes at least one port through said covering adapted to permit access to said chamber for inserting said filler material into said chamber and maintaining said chamber sealed following insertion of said filler material.

10. The stent of claim 1, wherein said second diameter is at least slightly larger than a normal width of an intervertebral disk space.

11. The stent of claim 1, wherein said second diameter corresponds to a width of a wedge osteotomy in a long bone.

12. A method, comprising:

inserting a stent into a patient to a location in need of orthopedic correction, said stent having a frame being substantially cylindrical and having first and second open ends and a passage between said ends, said stent further having a polymeric covering fixed to said frame to define a sealed chamber within said stent;

expanding said stent radially uniformly within said location from a first diameter to a second diameter, thereby expanding said chamber;

delivering a filler to said chamber so that said chamber is filled to a predetermined degree.

13. The method of claim 12, wherein said delivering and said expanding are performed in the same action, so that said delivering a filler operates to expand said stent from said first diameter.

14. The method of claim 13, wherein said predetermined degree corresponds to expanding said stent all the way to said second diameter.

15. The method of claim 12, wherein said delivering occurs after said expanding is complete.

16. The method of claim 15, wherein said delivering includes inserting a needle through a portion of said covering and into said chamber, and injecting said filler through said needle into said chamber.

17. The method of claim 16, further comprising removing said needle from said chamber and allowing said covering to reseal.

18. The method of claim 12, wherein said predetermined degree corresponds to delivering a predetermined volume of filler material.

19. An orthopedic implant, comprising:

a stent having a cylindrical shape and defining a passage from a first open end to a second open end, said stent being adapted to be expandable having a first collapsed at least part circular diameter and a second expanded at least part circular diameter, said stent being expandable from said first diameter to said second diameter;

a polymer covering fixed to said stent and covering said open ends to form a sealed chamber at least partially within said passage, said covering being expandable with said stent so that said chamber remains sealed during expansion from said first diameter to said second diameter; and

a hydrogel filler material within said chamber.