Bellows-like expandable interbody fusion cage

Abstract

An interbody fusion device having an accordion-like structure, wherein the device in inserted into the disc space in its collapsed configuration and then expanded into its expanded configuration by compressing the accordion-like portion of the device. In some embodiments, a pre-formed tube with an accordion-like structure over a portion of its length is inserted in a relaxed (collapsed) configuration, giving the tube a minimum possible diameter. This tube has a cable running through it that is fixed to a distal end portion of the tube and extends past the proximal end portion of the tube to the outside of the patient. Once the tube is positioned on the rim of the endplate, the proximal end of the cable is pulled, thereby tensioning the cable and causing the accordion portion of the tube to become shorter in length but larger in diameter.

Claims

1. A method of implanting an intervertebral fusion device into an intervertebral disc space between an upper vertebral endplate and a lower vertebral endplate, the device including: a) an upper wall configured to engage an upper vertebral endplate; b) a lower wall configured to engage a lower vertebral endplate, wherein the device defines an internal space that is both disposed between and aligned with the upper wall and the lower wall; and c) an elongate element disposed in the internal space, the method comprising the steps of: a) inserting the device into the disc space in a collapsed condition having a collapsed height from the upper wall to the lower wall, b) applying a localized force entirely outside the internal space to an end of the device that causes the end of the device to change its orientation; and c) expanding the inserted device from the collapsed condition to an expanded condition having an expanded height from upper teeth defined on the upper wall to lower teeth defined on the lower wall by moving the elongate element, wherein the expanded height is greater than the collapsed height.

2. The method of claim 1, wherein the expanding step comprises moving the elongate element in the internal space.

3. The method of claim 1, further comprising the step of maintaining the upper wall oriented substantially parallel to the lower wall in both the collapsed condition and the expanded condition.

4. The method of claim 1, wherein in the expanded condition, an intermediate portion of the upper wall of the fusion device is spaced further from a central axis of the device compared to opposed longitudinally outer portions of the upper wall that are disposed on opposite sides of the intermediate portion of the upper wall.

5. The method of claim 4, wherein in the expanded position, an intermediate portion of the lower wall is spaced further from the central axis compared to opposed longitudinally outer portions of the lower wall that are disposed on opposite sides of the intermediate portion of the lower wall.

6. The method of claim 1, wherein the applying step comprises coupling a member to the end of the device, and applying a force to the member so as to apply the localized force to the end of the device.

7. The method of claim 6, wherein the force applied to the member comprises a tensile force.

8. The method of claim 1, wherein the device has a side disposed between the upper wall and the lower wall, wherein the side defines a convex outer profile.

9. The method of claim 1, wherein the applying step is performed separate from the expanding step.

10. The method of claim 1, wherein the expanding step further comprises the step of applying an expansion force to the elongate element so as to cause the elongate element to move relative to the upper and lower walls.

11. The method of claim 10, wherein the step of applying the expansion force causes the elongate element to move relative to the upper and lower walls along the axis.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 discloses an intervertebral fusion device of the present invention in its collapsed state.

(2) FIG. 2 discloses an intervertebral fusion device of the present invention in its expanded state.

(3) FIG. 3 discloses an intervertebral fusion device of the present invention wherein the first plurality of pleats associated with the convex outer curve are spaced more widely and are greater in number than the second plurality of pleats associated with the concave inner curve.

DETAILED DESCRIPTION OF THE INVENTION

(4) Now referring to FIGS. 1 and 2, there is provided an intervertebral fusion device for fusing an intervertebral disc space, comprising: a) a tube 1 having a distal end portion 3, an intermediate portion 5, a proximal end portion 7, a longitudinal axis LA, and comprising a plurality of pleats 9 arranged substantially perpendicular to the longitudinal axis, and b) a first cable 11 disposed within the tube, wherein the cable is fixed to the distal end portion of the tube, wherein the tube has a radially collapsed configuration (FIG. 1) when the first cable is relaxed and a radially expanded configuration (FIG. 2) when the first cable is tensioned.

(5) In some embodiments, the intermediate portion of the tube bulges when in its expanded configuration. In some embodiments thereof, the pleats are spaced relatively close in the distal and proximal end portions of the tube in its collapsed configuration, and relatively distant in the intermediate portion of the tube in its collapsed configuration, so that, in its expanded configuration, the tube forms large diameter rings in the intermediate portion and small diameter rings in the proximal and distal end portions. This bulging tube is thought to advantageously conform to the contour of the concave surfaces of the opposing endplates that define a disc space. Thus, the folds in this section are designed in such a way that the expanded tube convexly curves to conform to the concave contour of the endplate.

(6) In some embodiments, the inserted tube is caused to curve along its length into a banana shape so that a single device can fully support a disc space. Thus, the banana shape has a concave inner surface and a corresponding convex outer surface.

(7) In some embodiments thereof, and now referring to FIG. 1, the device of the present invention further comprises a second cable 51 disposed outside the tube and fixed to the distal end portion of the tube. Tensioning of this second cable causes the tube to curve.

(8) Now referring to FIG. 3, in some embodiments in which the device has a concave inner curve and a corresponding convex outer curve (such as a banana shape), there is provided a first set of pleats 21 associated with the convex outer curve 23 and a second set of pleats 25 associated with the concave inner curve 27. In this condition, the first set of pleats associated with the convex outer curve are spaced more widely and are greater in number than the second set of pleats associated with the concave inner curve. In such a condition, the bellows is pleated in such a fashion that when it expands the outer curve of the bellows has a larger radius than the inner curve. This may allow the implant to conform to the geometry and curvature of the vertebral endplate.

(9) Therefore, in accordance with the present invention, there is provided an intervertebral fusion device for fusing an intervertebral disc space, comprising:

(10) a banana-shaped tube having a concave inner curve, a corresponding convex outer curve, a distal end portion, an intermediate portion, a proximal end portion, and a longitudinal axis, the intermediate portion comprising a first plurality of pleats 21 associated with the convex outer curve 23 and a second plurality of pleats 25 associated with the concave inner curve 27, wherein the first plurality of pleats associated with the convex outer curve are spaced more widely and are greater in number than the second plurality of pleats associated with the concave inner curve.

(11) In some embodiments, the tube is pleated in such a fashion that, in its expanded configuration, the distal end portion of the tube has a distal radius and the proximal end portion of the tube has a proximal radius, and the distal radius is larger than the proximal radius. This may allow the implant to conform to the geometry and curvature of the vertebral endplate.

(12) In some preferred embodiments, the ridges created on the tube could also be used as a rasp to roughen the endplate.

(13) In some embodiments, and now referring to FIG. 1, the tube forms a plurality of rings 52 in its expanded configuration, wherein each ring comprises a plurality of teeth 53.

(14) The device may be made of materials typically selected for use in surgical instruments and implants. Preferably, the entire device is sterile.

(15) In some embodiments, the device of the present invention is intended to be permanent. In these cases, the material of construction of pleated tube is a nonresorbable material. In some embodiments thereof, the tube is made from a biocompatible metal (such as a titanium alloy, chrome-cobalt or stainless steel). In others, it is a nonresorbable polymer.

(16) The tube could be filled with hardenable filler, if desired, for additional support. When the tube is made from a nonresorbable material, the filler material is preferably non-resorbable as well.

(17) In some embodiments, the material construction of the tube is a resorbable material. In these embodiments, preferred resorbable materials are PLLA, PGA, and PLGA. When the tube is resorbable, it is desirable for the filler to comprise a bone-forming agent, preferably selected from the group consisting of a porous scaffold, an osteoinductive agent and viable cells.

(18) In other embodiments, the tube may also be filled in accordance with the methods and hardenable materials recited in US Published Patent Application 2004/0230309, filed Feb. 13, 2004 entitled “In-situ formed intervertebral fusion device and method”, the specification of which is incorporated by reference in its entirety.

(19) Hardenable, resorbable compositions include setting ceramics, polymerizable monomers and polymers, polymers flowable at temperatures above body temperature, and polymers solubilized in a biocompatible solvent. Examples of resorbable setting ceramics include calcium phosphates, hydroxyapatites and calcium sulfates. Examples of polymerizable resorbable monomers and polymers include polypropylene fumarate), polyoxaesters, polyurethanes and polyanhydrides. In one preferred embodiment, the hardenable composition is a photopolymerized polyanhydride. In this embodiment, irradiation can be used to control the polymerization process, therefore, a partially polymerized putty can be made, then hardened by continuing the polymerization with irradiation after the composition has been placed. Examples of resorbable polymers flowable at temperatures above body temperature include polymers and copolymers of lactic acid, glycolic acid, carbonate, dioxanone, and trimethylene carbonate. An example of a biocompatible solvent that can be used to solubilize the aforementioned polymers include dimethyl sulfoxide.

(20) In order to improve the osteoconductivity of the aforementioned hardenable, resorbable compositions, they may be delivered to the site as an in-situ formed porous scaffold. Techniques of in situ forming porous scaffolds are known in the art and include porogen leaching and foaming with gas-producing elements.

(21) In preferred embodiments of this invention, the hardenable, resorbable compositions incorporate an osteoinductive component. Osteoinductive components include growth factors such as bone morphogenetic proteins that can be grafted onto or mixed into the hardenable compositions. The term “growth factors” encompasses any cellular product that modulates the growth or differentiation of other cells, particularly connective tissue progenitor cells. The growth factors that may be used in accordance with the present invention include, but are not limited to, members of the fibroblast growth factor family, including acidic and basic fibroblast growth factor (FGF-1 and FGF-2) and FGF-4; members of the platelet-derived growth factor (PDGF) family, including PDGF-AB, PDGF-BB and PDGF-AA; EGFs; members of the insulin-like growth factor (IGF) family, including IGF-I and -II; the TGF-.beta. superfamily, including TGF-.beta.1, 2 and 3 (including MP-52); osteoid-inducing factor (OIF), angiogenin(s); endothelins; hepatocyte growth factor and keratinocyte growth factor; members of the bone morphogenetic proteins (BMP's) BMP-1, BMP-3; BMP-2; OP-1; BMP-2A, BMP-2B, and BMP-7, BMP-14; HBGF-1 and HBGF-2; growth differentiation factors (GDF's), members of the hedgehog family of proteins, including indian, sonic and desert hedgehog; ADMP-1; members of the interleukin (IL) family, including IL-1 thru IL-6; GDF-5 and members of the colony-stimulating factor (CSF) family, including CSF-1, G-CSF, and GM-CSF; and isoforms thereof.

(22) In addition, bone-producing cells, such as mesenchymal stem cells (MSCs), can be delivered with the hardenable compositions by first encapsulating the cells in hydrogel spheres then mixing them in. MSCs provide a special advantage because it is believed that they can more readily survive relatively harsh environments; that they have a desirable level of plasticity; and that they have the ability to proliferate and differentiate into the desired cells.

(23) In some embodiments, the mesenchymal stem cells are obtained from bone marrow, preferably autologous bone marrow. In others, the mesenchymal stem cells are obtained from adipose tissue, preferably autologous adipose tissue.

(24) In some embodiments, the mesenchymal stem cells are used in an unconcentrated form. In others, they are provided in a concentrated form. When provided in concentrated form, they can be uncultured. Uncultured, concentrated MSCs can be readily obtained by centrifugation, filtration, or immuno-absorption. When filtration is selected, the methods disclosed in U.S. Pat. No. 6,049,026 (“Muschler”), the specification of which is incorporated by reference in its entirety, are preferably used. In some embodiments, the matrix used to filter and concentrate the MSCs is also administered into the container.