Vertebral fusion device and method

A device for facilitating bone fusion of two vertebrae. The device is sized and shaped to at least extend between the two vertebrae to be fused, and includes an outer wall member disposed about an inner portion. A space between the outer wall member and the inner compartment is adapted to contain an osteogenic bone fusion material. The inner portion includes a compartment adapted to contain an inner fill material, such as a bone cement or an in situ curable polymer. The inner portion may operate as a structural member to maintain a desired amount of spacing between the vertebrae to be fused, and to support the spinal column prior to formation of the fused bone joint. The device is also configured to locate the osteogenic material away from the centers of the vertebrae to be fused, providing a fused joint with high bending and torsional rigidity.

TECHNICAL FIELD

The present invention is related to spinal stabilization devices. More particularly, this invention relates to a device for facilitating the bony fusion of two vertebrae.

BACKGROUND

The spinal column is a highly complex system of bones and connective tissues that provides support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one on top of the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Between each vertebral body is an intervertebral disc that cushions and dampens forces experienced by the spinal column. A vertebral canal containing the spinal cord and nerves is located behind the vertebral bodies.

There are many types of spinal column disorders including scoliosis (abnormal lateral curvature of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnormal backward curvature of the spine, usually in the lumbar spine), spondylolisthesis (forward displacement of one vertebra over another, usually in a lumbar or cervical spine) and other disorders caused by abnormalities, disease, or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like. Patients suffering from such conditions usually experience extreme and debilitating pain, as well as diminished nerve function. Such disorders can also limit range of movement and threaten the critical elements of the nervous system housed within the spinal column.

One well known method of treating certain spinal disorders via surgical intervention is to immobilize regions of the spine, usually by fusing or joining adjacent vertebrae to one another. A variety of techniques have been disclosed in the art for achieving this immobilization. One such fusion technique involves removal of all or part of the intervertebral disc between two vertebrae, and implanting a bone fusion mass or bone graft in the resulting space and in contact with the vertebral end plates. As a result, natural bone growth fuses the two vertebrae together. In a similar procedure, known as a corpectomy procedure, one or more vertebral bodies and adjacent intervertebral discs are removed and a bone graft is then implanted into the space between the vertebrae to be fused. Corpectomy is commonly utilized to treat spinal disorders in the cervical (i.e., neck) region, although it can also be effectively used in the middle and lower spinal regions.

The above-mentioned fusion techniques may require the implantation of one or more devices to facilitate implantation of the bone graft and to stabilize the patient's spinal column until the target vertebrae have been fused by natural bone growth.

Accordingly, there is a need in the art for a device to facilitate the formation of a strong bone fusion joint between adjacent vertebrae. Additionally, there is a need for such a device to facilitate the distraction of the vertebrae to be fused and to provide structural stability to the joint prior to formation of the fused bone joint.

SUMMARY

The present invention, in one embodiment, is an implantable orthopedic device for implantation between opposed vertebral end plates of a pair of vertebrae. The device includes an inner portion that has a pair of spaced-apart end caps and an inner wall member between the end caps, and an outer wall member disposed about and coupled to the inner portion. There is a separation between the outer wall member and the inner portion that defines an outer space. The device has a size and shape such that it can extend at least between the opposed vertebral end plates, such that at least the end caps can be in contact with the vertebral end plates and the outer space can be in communication with the vertebral end plates.

The present invention, in another embodiment, is a method of fusing a pair of vertebrae in a spine, including identifying a pair of vertebrae to be fused and removing a substantial portion of a disc between opposed vertebral end plates of the pair of vertebrae to be fused. A spacing between the pair of vertebrae to be fused is then created, and an implantable orthopedic device is inserted between the end plates. The device may include a compartment having first and second end caps, and a wall member wall member disposed about the compartment. There is a separation between the wall member and the compartment which defines an outer space. Next, a fill material is introduced into the compartment to longitudinally expand the compartment such that the end caps are in contact with the vertebral end plates. Then, an osteogenic material is introduced into the outer space such that the osteogenic material is in contact with the vertebral end plates.

DETAILED DESCRIPTION

FIG. 1illustrates a human spinal column2including vertebrae5belonging to one of a cervical region a, a thoracic region b, a lumbar region c and a sacral region d of the spinal column2. Each vertebra5includes a superior end plate6and an inferior end plate7. Intervertebral discs8are positioned in intervertebral spaces9between adjacent vertebrae5.

FIG. 2illustrates a human spinal column2in which one of the discs8has been removed and replaced with an implantable orthopedic device10according to one embodiment of the present invention. As shown inFIG. 2, the device10generally occupies the same space as a natural disc8between the adjacent vertebrae5aand5b.

FIG. 3illustrates a human spinal column in which one of the vertebra5and the adjacent discs8have been removed and replaced with an implantable orthopedic device10, as in a corpectomy procedure. As shown inFIG. 3, the device10generally occupies the same space as a natural vertebra/disc combination between the vertebrae5aand5b. Although inFIGS. 2 and 3the device10is shown implanted into the lumbar region c, the device10is readily adapted in size and shape for implantation into the cervical region a and thoracic region b.

As discussed and shown in detail below, the device10is configured to contain an osteogenic bone graft or bone fusion material for effectively fusing the vertebrae5aand5btogether. Additionally, as further described and shown below, the device10of the present invention includes a central structural support to maintain a desired amount of separation between and/or to provide a desired amount of distraction of the vertebrae5aand5band to support the patient's spinal column until the bone fusion joint forms.

FIG. 4is a perspective view of an implantable orthopedic device10according to one embodiment of the present invention. As shown inFIG. 4, the device10has a superior region12and an inferior region14, and includes an outer wall member15and an inner portion20. The outer wall member15and inner portion20are connected, in one embodiment, by at least one connecting member26. Between the outer wall member15and the inner portion20is an outer space30which is open (i.e., not enclosed) in both the superior region12and the inferior region14such that, as shown and discussed in detail below, the outer space30is exposed to and in communication with the vertebral end plates6,7(seeFIGS. 2,3) when the device10is placed between the vertebrae5aand5bas in a fusion or corpectomy procedure.

In the illustrated embodiment, the device10also includes an inner portal34extending from the inner portion20and including an inner portal lumen38, and an outer portal42extending from the outer wall member15and having an outer portal lumen46. As illustrated inFIG. 4, the inner portal34may be disposed within the outer portal lumen46.

As shown and discussed in detail below, the outer space30is adapted to contain an osteogenic bone fusion material, such as, for example, morselized bone, which promotes and facilitates bone growth and formation of a natural rigid bone mass fusing the vertebrae5aand5b(seeFIGS. 2-3). Additionally, as further illustrated and discussed below, the inner portion20operates to maintain a desired amount of separation between the vertebrae5aand5bto be fused, and also to structurally support and stabilize the patient's spinal column until natural bone growth fuses the vertebrae5aand5b.

FIG. 5is a cross-sectional elevation view of the device10taken along the line Y-Y inFIG. 4. As shown inFIG. 5, the inner portion20includes, in one embodiment, an inner wall member58, a superior end cap60and an inferior end cap70. The inner wall member58is attached to the superior and inferior end caps60,70to define an inner compartment76. In another embodiment, the inner portion20may include top and bottom members (not shown) which, along with the inner wall member58, define the inner compartment76(i.e., the inner wall member58is not attached directly to the superior and inferior end caps60,70). In the embodiment illustrated inFIG. 5, the inner portal lumen38extends to and fluidly communicates with the inner compartment76, and the outer portal lumen46extends to and fluidly communicates with the outer space30. As further shown, the end caps60and70may include one or more projections78, which when present may operate to engage the vertebral end plates7and6, respectively, during implantation of the device10, and/or to promote bone ingrowth and long-term positive attachment of the end caps60,70to the vertebral end plates7,6. In the illustrated embodiment, the projections78are shown as generally rounded in shape, although in other embodiments, the projections78may have other shapes (e.g., sharp or pointed) to promote positive engagement with the vertebral end plates6,7.

FIG. 6is a partial cross-sectional elevation view of the device10in use in a vertebral fusion or corpectomy procedure, in which the device10is inserted between two vertebrae5aand5bto be fused (seeFIGS. 2 and 3). For illustration purposes, inFIG. 6, two of the connecting members26have been partially omitted. As illustrated inFIG. 6, in use, the inner compartment76contains an inner fill material80, and the outer space30contains an outer fill material82.

In one embodiment, the inner fill material80may include an injectable, in situ curable polymer or a bone cement such as polymethylmethacrylate (PMMA). In another embodiment, the inner fill material80may include other biocompatible materials such as, for example, injectable dental cements. Additional materials suitable for use as the inner fill material80will be apparent to those skilled in the art based on the foregoing. Such exemplary materials may be introduced into the inner compartment76in a liquid state, and subsequently cure and harden within the inner compartment76such that the inner portion20forms a substantially rigid structure.

In one embodiment, the outer fill material82may include an osteogenic material (i.e., a material that promotes or permits bone growth). Such osteogenic materials may include, for example, morselized bone or some other bone fusion material. In use, the outer fill material82may be tightly packed into and substantially completely fill the outer space30and, accordingly, may contact the vertebral end plates6and7.

In the illustrated embodiment, the inner portal34and the outer portal42provide means for introducing the fill materials80and82into the inner compartment76and the outer space30, respectively. Accordingly, in this embodiment, the inner fill material80is introduced into the inner compartment76through the inner portal lumen38, and the outer fill material82is introduced into the outer space30via the outer portal lumen46.

The inner portal34and/or the outer portal42may each further include means (not shown) to facilitate closure and sealing of the inner portal lumen38and/or the outer portal lumen46in order to retain the inner and outer fill materials80and82within the inner compartment76and the outer space30, respectively. Such means may be integrated into the inner and outer portals portal34and38, or may be integrally formed as part of the inner and outer wall members wall member58and15. An exemplary closure means may be a ligature arrangement consisting of ties or draw strings, which may be tied together, drawn closed, or pulled tight like a purse string to close and seal the inner and/or outer portal lumens34,46. Alternatively, or additionally, the closure means may include interlocking latches, adhesives, or other fibers that can be tied and which are integrated into the inner and outer portals34,42, and/or the inner and outer wall members wall member58,15. Closure ties such as draw strings may be made of Dacron™ or suitable material. In still further embodiments, the device10may include a mechanical closure integrated into the inner portal34, the outer portal42, the inner wall member58, and/or the outer wall member15. Such closures may include valves (e.g., check valves, duckbill valves, flapper valves) plugs, screw caps, etc., which may be incorporated into the inner device10by any methods known in the art including, for example, sonic welding, sewing, or stitching.

As shown inFIG. 6, the device10has a size and shape suitable to at least extend between the target vertebrae5aand5bto be fused, with at least the end caps60and70contacting and bearing upon the end plates7and6, respectively. When so positioned, because the outer space30is open in both the superior region12and the inferior region14of the device10(seeFIG. 4), the outer fill material82can contact the vertebral end plates6and7when the device10is inserted between the vertebrae5aand5b(seeFIGS. 2 and 3). When the outer fill material82includes an osteogenic bone fusion material such as morselized bone, the illustrated structure provides a substantially continuous bone pathway between the two vertebrae5aand5b, which promotes rapid bone growth therebetween and a strong fusion joint.

Additionally, location of the fused bone mass near the perimeter of the device10provides a fused bone joint with relatively large bending and rotational moments of inertia and, consequently, high bending and torsional rigidity. The inner portion20, including the inner compartment76containing the cured inner fill material80such as PMMA, can maintain a desired spacing between the vertebrae5aand5bas determined by the physician, and operates to support the vertebrae and the spinal column prior to formation of the fused bone joint. Additionally, the device10can be sized such that the inner portion20can distract the vertebrae5aand5bby a desired amount.

The device10is generally sized and shaped to provide a maximum amount of contact area between the outer fill material82and the vertebral end plates6and7. AlthoughFIGS. 2 and 3depict a device10utilized in the lumbar area of the spine, it should be noted that the size and shape of the device10may vary depending on the area of treatment and the particular vertebrae to be fused. For example, the size and shape of the device10for use in a cervical corpectomy procedure is generally different than the size and shape of a device10for use in a fusion procedure in the lumbar spine area.

FIG. 7is a plan view of the device10according to one embodiment of the present invention. In the illustrated embodiment, from a plan view perspective, the outer wall member15is in the shape of a generally elliptical annular ring having a major diameter D1and a minor diameter D2. In such an embodiment, the outer wall member15may have an eccentricity ratio (i.e., a ratio of the major diameter D1to the minor diameter D2) ranging from just over 1.0 to about 3.0. In one embodiment, the eccentricity ratio of the outer wall member15is about 1.8. In other embodiments, the outer wall member15may be substantially circular—that is, having an eccentricity ratio of about 1.0. In yet other embodiments, the outer wall member15may have other shapes, such as, for example, substantially rectangular or irregular.

Additionally, in one embodiment, as illustrated inFIG. 7, the outer wall member15and inner portion20are sized and shaped relative to each other such that the outer space30is generally annular with a capacity to contain enough outer fill material82to provide a structurally sound bone fusion joint. In the embodiment illustrated inFIG. 7, from a plan view perspective, the inner portion20has substantially the same general shape (i.e., elliptical) as the outer wall member15. In other embodiments, the inner portion20and the outer wall member15may have different shapes. For example, in one embodiment, the outer wall member15may have a generally elliptical shape, and the inner portion20may be substantially circular, and vice-versa. As an additional example, the outer wall member15and inner portion20may both be generally elliptical with different eccentricity ratios.

In one embodiment, the device10is expandable from a first, collapsed state to a second, expanded state by filling the inner compartment76with the inner fill material80via the inner portal lumen38.FIGS. 4 and 5depict the device10in the expanded state. In the collapsed state, the inner portion and outer wall member15are generally flaccid, and the device10has a reduced profile. As a result, in the collapsed state, the end caps60and70have a reduced separation there between to facilitate insertion between adjacent vertebrae. This also allows for a less invasive surgical insertion.

As the inner compartment is subsequently filled with the inner fill material80the inner compartment76, and consequently, the inner portion20, expand longitudinally until the expanded state is attained. If an inner fill material80such as those described above (e.g., PMMA) is introduced into the inner compartment76in a liquid state, the inner portion20will beneficially tend to conform to the intervertebral space in which the device10is implanted. Additionally, because the outer wall member15is attached to the inner portion20(as by, for example, the connecting members26), the outer wall member15expands substantially concurrently with the inner portion20. In one embodiment, one or both of the outer wall member15and inner wall member58may be configured to have a bellows construction (not shown) to facilitate expansion from the collapsed state to the expanded state.

The outer wall member15may be configured to be substantially taut when the device10is in the second or expanded state. Thus, when the device10is in the expanded state, and after the outer fill material82is packed into the outer space30, the outer wall member15resists radial expansion which, in turn, creates a compressive load on the inner portion20. This compressive load stabilizes the inner portion20and in turn, the patient's spinal column, until the bone fusion is complete.

In one embodiment, the outer wall member15and/or the inner wall member58may be made from a textile material. Fabrication processes for the textile material making up the outer wall member15and/or the inner wall member58may include variations and combinations of braiding, knitting and weaving. In one embodiment, one or both of the outer wall member15and the inner wall member58are made from a braided, woven, or knitted textile that has been manufactured in such a manner so as to permit longitudinal expansion when the inner fill material80is introduced into the inner compartment76, but resist radial expansion and torquing. Such a textile may be made using any method known in the art to produce a textile which permits longitudinal expansion and resists radial expansion.

In another embodiment, one or both of the wall members15,58may be constructed of a fiber-reinforced elastomeric composite material. In one such embodiment, the wall members15and/or58may be formed from an elastomeric polymer in which a textile material is partially or fully embedded. Any biocompatible elastomeric polymer, such as, for example, polyurethane or silicone, may be used.

In one embodiment, at least the inner wall member58may be made substantially non-porous to prevent leakage and loss of the inner fill material80, particularly where the inner fill material80is PMMA or other comparable material introduced into the inner compartment76in a liquid state. Additionally, the inner wall member58may optionally include a flexible, non-porous internal liner (not shown) to retain the uncured, liquid inner fill material80within the inner compartment76.

In one embodiment, the end caps60and70may be formed of any of several types of materials that are biocompatible or bio-inert and have good strength and rigidity/flexibility characteristics. In one embodiment, the end caps60and70are generally more rigid than the inner wall member58because the end caps60and70are configured to contact and apply a force to the vertebrae to be fused. One suitable type of material is a biocompatible engineering polymer, such as polyetheretherketone (PEEK™), polyaryletherketone, polyimide, polysulfone, fiber forms of polyethelene therephthalate (PET) (also known as Dacron®), solid forms of PET, polyetherimides and liquid crystalline polymers. Another such type of material is thermoplastic engineering elastomer, such as polyurethane or any other engineering elastomer having suitable stiffness. Yet another such type of material is a biocompatible metal, such as titanium or stainless steel.

In one embodiment, the end caps60and70may be semi-porous such that a controlled amount of the inner fill material80may pass through them to form an adhesive or mechanical connection between the end caps60and70and the vertebral end plates7and6, respectively. In another embodiment, at least an outer surface of the end caps60and70may be formed of, or coated with, a porous material chosen to permit or promote bone and/or tissue ingrowth. An exemplary porous material is described in U.S. Pat. No. 5,282,861 to Kaplan, which is hereby incorporated by reference in its entirety for all that it teaches and discloses. Such materials may include porous metals, for example, open cell tantalums such as Trabecular™ Metal, and Fiber Metal (both available from Zimmer, Inc. at www.zimmer.com).

In yet another embodiment, the end caps60and70may be made from a textile material. In such embodiments, the textile material forming the end caps60and70may be the same as the textile used to form the inner wall member58. Alternatively, the textile used to make the inner wall member58may be different than that used for the end caps60and70. In other variations of this embodiment, different combinations of textile materials and fiber-reinforced elastomeric composite materials may be used for the inner wall member58and the end caps60,70. In still other embodiments, the end caps60,70may be made from a textile material substantially impregnated with a substantially rigid engineering polymer such as, without limitation, PET and/or polyetheretherketone.

The projections78, if present, may be made from any material that is sufficiently rigid and strong such that the projections78, when properly shaped, can positively grip the vertebral end plate6,7during implantation of the device10. In one embodiment, the projections78may be made from a biocompatible engineering polymer, such as polyetheretherketone, polyaryletherketone, polyimide, polysulfone, polyethelene therephthalate, polyetherimides and liquid crystalline polymers. The projections78may also be made of a thermoplastic engineering elastomer, such as polyurethane or any other engineering elastomer having suitable rigidity. Still alternatively, the projections78may be made from a biocompatible metal, such as titanium or stainless steel. Additionally, the projections78may include a coating to promote bone ingrowth. One exemplary coating material hydroxyapatite, which may promote bone ingrowth and long term positive attachment to the vertebral end plates6,7. Alternatively, the projections78may be made of a porous bone ingrowth material, such as Trabecular™ Metal and Fiber Metal as described above. When made from such materials, the projections78advantageously provide both initial attachment to the vertebral end plates6,7and also long term positive attachment of the end caps60,70to the vertebral end plates7and6, respectively, through bone ingrowth.

The connecting members26may be made from the same or similar materials as the end caps60,70. Alternatively, the connecting members26may be made from a textile material such as those used for the outer and inner wall members15and58. A biocompatible elastomeric material, either fiber-reinforced or non-reinforced, may also be used for the connecting members26. Any method of attachment known in the art (e.g., stitching, adhesives, etc.) may be used to attach the connecting members26to the outer wall member15and the end caps60and70(or other region of the inner portion20).

FIG. 8Ais a perspective view of an alternative embodiment of the device10, in which the connecting members26in the superior region12are replaced by a connecting ring90. As illustrated, the connecting ring90is attached to the outer wall member15around substantially the entire circumference of the outer wall member15. Similarly, the connecting ring90is also attached to substantially the entire periphery of the superior end cap60.

In such embodiments, the connecting ring90is adapted to substantially retain the outer fill material82, such as morselized bone or other osteogenic material, but not significantly interfere with bone fusion between the vertebrae5aand5b. In one embodiment, the connecting ring90may be constructed of a textile material configured to facilitate bone fusion there through. In another embodiment, the connecting ring90may be made from a porous bone ingrowth materials such as Trabecular™ Metal and Fiber Metal (available from Zimmer, Inc. at www.zimmer.com) described above. In yet another embodiment, the connecting ring90may be made from a biocompatible elastomeric material, which may or may not be fiber-reinforced. In any of the foregoing embodiments, the connecting ring90may include perforations or openings (not shown) to permit direct communication and contact between the outer fill material82and the vertebral end plate7when used in a fusion procedure. As will be appreciated by those of ordinary skill in the art, although not shown inFIG. 8A, the connecting members26in the inferior region14may also be replaced by another connecting ring90which may also be connected to the outer wall member15and the inner portion20in the same manner as described above with respect to the superior region12.

FIG. 8Bis a perspective view of yet another embodiment of the device10including flaps94extending from the outer wall member15in both the superior and inferior regions12and14The flaps94may be folded or extended upward (in the superior region12) and downward (in the inferior region14) such that when the device10is positioned between the vertebrae5aand5b, the flaps94are adjacent to and can be tacked to the vertebrae5a,5b. The flaps94thus operate to hold the device10in a desired position during the implantation process, and also to assist in retaining the outer fill material82inside the outer space15until bone fusion occurs. The flaps94may be made from the same material as the outer wall member15, but this is not a requirement. To the contrary, any biocompatible, flexible material may be used for the flaps94, which may be attached to the outer wall member15using any methods known in the art (e.g., stitching, adhesives, bone screws, bone anchors).

FIG. 9depicts a perspective view of an implantable orthopedic device150according to another embodiment of the present invention. The device150may advantageously be used to facilitate fusion of vertebrae5aand5bthat are adjacent one another (seeFIG. 2). In such a procedure, only the nucleus of the intervertebral disc8is substantially or completely removed, and the outer portion or annulus of the disc8is left substantially intact. As shown inFIG. 9, the device150is shaped like a tubular sleeve and includes a side wall156, a pair of end caps160and166, and a portal170having a lumen176therethrough. The side wall156and the end caps160and170define a compartment (not shown) for containing a fill material such as PMMA. The lumen176communicates with and facilitates the introduction of the fill material into the compartment.

In general, the device150is constructed and configured to operate in a manner substantially similar to the inner portion20of the device10described in detail above. For example, the side wall156may be constructed of textile materials similar to those used for the inner wall member58of the device10. Similarly, the end caps160and166may be constructed of materials similar to those used for the end caps60and70of the device10. As shown, at least one of the end caps160and166may include one or more projections180which are substantially similar in both construction and operation as the projections78discussed above.

In operation, when filled with an appropriate fill material, the device150is adapted to maintain a desired amount of spacing between and/or provide a desired amount of distraction of the adjacent vertebrae to be fused, similar to the operation of the inner portion20containing the cured inner fill material80of the device10described above. A bone graft or bone fusion material may then be packed around the outside of the device. Additionally, in one embodiment, as discussed in more detail below, the outer portion, or annulus, of the intervertebral disc8is left intact and operates to contain the bone fusion material in much the same way as the outer wall member15of the device10described above.

FIG. 10illustrates a method of performing a vertebral fusion procedure utilizing the device10(FIG. 2) according to one embodiment of the present invention. As shown inFIG. 10, the two vertebrae5aand5bto be fused are identified by a physician, and this, in turn defines the intervertebral space into which the device10is to be inserted (200). In one embodiment, the vertebrae5a,5bto be fused may be adjacent one another (seeFIG. 2). Alternatively, as in a corpectomy procedure (seeFIG. 3), the vertebrae5a,5bto be fused may naturally be separated by one or more intervening vertebra and adjacent intervertebral discs8which must be removed by the surgeon. Based on the specific vertebrae5aand5bto be fused and the resulting intervertebral spacing, an appropriately sized and shaped device10is selected and provided (210). The area of treatment is then accessed using techniques and instruments known in the art, and, depending on the vertebrae chosen for fusion, the intervertebral disc8or one or more vertebra5and adjacent intervertebral discs8are removed (220). The vertebra5a,5bto be fused are then prepared for implantation of the device10and subsequent bone fusion, according to standard procedures known to those in the art (230).

In one embodiment, the physician positions the patient and creates a desired spacing between the vertebrae5aand5bto be fused before inserting the device10into the intervertebral space. The device10, in the collapsed state, may then be positioned in the space between the vertebra5a,5bto be fused, such that when the device10is in the expanded state, the end caps60,70will contact the vertebral end plates7,6, respectively, and the outer space30will communicate with the end plates6,7(240). The inner fill material80, such as PMMA, may then be introduced into the inner compartment76via the inner portal lumen38, causing the inner portion20and the device10in general to attain its expanded state, such that the end caps60,70are in contact with the vertebral end plates7,6, respectively. In one embodiment, the physician may use the appropriately sized device10, and in particular, the inner portion20, to distract the vertebrae5a,5bby a desired amount by filling the inner compartment76with the inner fill material80(250).

In one embodiment, liquid PMMA or other comparable inner fill material80may be introduced into the inner compartment76via a pump (not shown) coupled to the inner portal34. A syringe or other manual device may also be used to inject the inner compartment76with the inner fill material80. Pressure within the inner compartment76is maintained until the inner fill material80cures and hardens to create a support capable of maintaining the desired amount of spacing between the vertebrae5aand5b, and also of supporting the patient's spinal column until the natural bone fuses. For example, where the inner fill material80is pumped into the inner compartment76, the pump may remain coupled to the inner portal lumen38and configured to maintain a desired internal pressure in the inner compartment76. Alternatively, or additionally, the inner portal lumen38may be sealed using any of the closure means described above, if present.

After the inner fill material80, such as PMMA, is cured and hardened, and the inner portion20is capable of supporting the patient's spinal column and/or maintaining the desired amount of separation between the vertebrae5a,5b, the inner portal34may optionally be totally or partially removed (260) by any means known in the art (e.g., scissors, scalpel). Removal of the inner portal34may facilitate introduction of the outer fill material82into the outer space30, particularly where the inner portal34is disposed within the outer portal lumen46.

If present, the flaps94may be extended and tacked to the vertebrae5aand5bprior to introducing the outer fill material82into the outer space30. In such embodiments, the flaps94operate to inhibit migration of the outer fill material82from the outer space30at the interface between the outer wall member15and the vertebral end plates6and7. The outer fill material82, such as morselized bone or other osteogenic bone fusion material, is then introduced and packed into the outer space30via the outer portal lumen46(270). The outer fill material56may be introduced into the outer space30using any method known in the art (e.g., large bore syringe, spatula, tamp and cannula). The outer portal lumen46may then be closed and sealed using any of the closure means described above, thereby retaining the outer fill material56in the outer space30.

In another embodiment of a method utilizing the devices10or150of the present invention, only a desired amount of the central portion or nucleus of the intervertebral disc8is removed, using known techniques and surgical instruments. In some embodiments, only a portion of the disc nucleus may be removed. In other embodiments, the entire nucleus may be removed as dictated by the physician based on the needs of the patient. The outer portion or annulus of the disc8may be left substantially intact, thus forming a cavity between the vertebrae5a,5bsubstantially enclosed by the remaining disc annulus. When left intact, the disc annulus may beneficially operate to support the device10or150, and accordingly, the bone fusion joint, prior to fusion. Additionally, when using the device150to facilitate vertebral fusion, the substantially intact disc annulus operates to retain the bone fusion material until fusion is complete.

The device10or150may then be positioned in the cavity between the vertebrae5a,5b. Where the device10is used, the implantation and fusion procedure may proceed as described above. Where the device150is used in this embodiment, a fill material (e.g., PMMA) is then injected into the device150in the same manner as that described above with respect to filling the inner compartment76of the device10. An osteogenic material (e.g., morselized bone) is then packed into the cavity between the vertebrae5aand5band around the device150, and is substantially retained therein by the remaining disc annulus material.

Various modifications and additions may be made to the exemplary structures and steps discussed without departing from the scope of the present invention. Various combinations, permutations, and rearrangements of those structures and steps may similarly be made without departing from the scope of the present invention. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, permutations and variations as fall within the scope of the claims, together with all equivalents thereof.