Retention structure for in situ formation of an intervertebral prosthesis

An assembly for the in situ formation of a prosthesis in an intervertebral disc space between adjacent vertebrae of a patient. At least one retention structure is located in the intervertebral disc space. A distal end of at least one lumen is located proximate the at least one retention structure. One or more in situ curable biomaterials are delivered to the intervertebral disc space through the first lumen and into engagement with the retention structure. The retention structure serves to retain at least a portion of the biomaterial in the intervertebral disc space by surface tension, adhesion, mechanical capture, friction, viscosity, and/or a variety of other mechanisms. The at least partially cured biomaterial and the at least one retention structure cooperate to comprise the prosthesis.

FIELD OF THE INVENTION

The present invention relates to various retention structures for forming an intervertebral prosthesis in situ, and in particular to a retention structure for an intervertebral disc space adapted to engage with an in situ curable biomaterial and a method of delivering the curable biomaterial.

BACKGROUND OF THE INVENTION

The intervertebral discs, which are located between adjacent vertebrae in the spine, provide structural support for the spine as well as the distribution of forces exerted on the spinal column. An intervertebral disc consists of three major components: cartilage endplates, nucleus pulposus, and annulus fibrosus.

In a healthy disc, the central portion, the nucleus pulposus or nucleus, is relatively soft and gelatinous; being composed of about 70% to about 90% water. The nucleus pulposus has high proteoglycan content and contains a significant amount of Type II collagen and chondrocytes. Surrounding the nucleus is the annulus fibrosus, which has a more rigid consistency and contains an organized fibrous network of about 40% Type I collagen, about 60% Type II collagen, and fibroblasts. The annular portion serves to provide peripheral mechanical support to the disc, afford torsional resistance, and contain the softer nucleus while resisting its hydrostatic pressure.

Intervertebral discs, however, are susceptible to disease, injury, and deterioration during the aging process. Disc herniation occurs when the nucleus begins to extrude through an opening in the annulus, often to the extent that the herniated material impinges on nerve roots in the spine or spinal cord. The posterior and posterolateral portions of the annulus are most susceptible to attenuation or herniation, and therefore, are more vulnerable to hydrostatic pressures exerted by vertical compressive forces on the intervertebral disc. Various injuries and deterioration of the intervertebral disc and annulus fibrosus are discussed by Osti et al., Annular Tears and Disc Degeneration in the Lumbar Spine,J. Bone and Joint Surgery,74-B(5), (1982) pp. 678-682; Osti et al., Annulus Tears and Intervertebral Disc Degeneration,Spine,15(8) (1990) pp. 762-767; Kamblin et al., Development of Degenerative Spondylosis of the Lumbar Spine after Partial Discectomy,Spine,20(5) (1995) pp. 599-607.

Many treatments for intervertebral disc injury have involved the use of nuclear prostheses or disc spacers. A variety of prosthetic nuclear implants are known in the art. For example, U.S. Pat. No. 5,047,055 (Bao et al.) teaches a swellable hydrogel prosthetic nucleus. Other devices known in the art, such as intervertebral spacers, use wedges between vertebrae to reduce the pressure exerted on the disc by the spine. Intervertebral disc implants for spinal fusion are known in the art as well, such as disclosed in U.S. Pat. No. 5,425,772 (Brantigan) and U.S. Pat. No. 4,834,757 (Brantigan).

Further approaches are directed toward fusion of the adjacent vertebrate, e.g., using a cage in the manner provided by Sulzer. Sulzer's BAK® Interbody Fusion System involves the use of hollow, threaded cylinders that are implanted between two or more vertebrae. The implants are packed with bone graft to facilitate the growth of vertebral bone. Fusion is achieved when adjoining vertebrae grow together through and around the implants, resulting in stabilization.

Apparatuses and/or methods intended for use in disc repair have also been described for instance in French Patent Appl. No. FR 2 639 823 (Garcia) and U.S. Pat. No. 6,187,048 (Milner et al.). Both references differ in several significant respects from each other and from the apparatus and method described below.

Prosthetic implants formed of biomaterials that can be delivered and cured in situ, using minimally invasive techniques to form a prosthetic nucleus within an intervertebral disc have been described in U.S. Pat. No. 5,556,429 (Felt) and U.S. Pat. No. 5,888,220 (Felt et al.), and U.S. Patent Publication No. US 2003/0195628 (Felt et al.), the disclosures of which are incorporated herein by reference. The disclosed method includes, for instance, the steps of inserting a collapsed mold apparatus (which in a preferred embodiment is described as a “mold”) through an opening within the annulus, and filling the mold to the point that the mold material expands with a flowable biomaterial that is adapted to cure in situ and provide a permanent disc replacement. Related methods are disclosed in U.S. Pat. No. 6,224,630 (Bao et al.), entitled “Implantable Tissue Repair Device” and U.S. Pat. No. 6,079,868 (Rydell), entitled “Static Mixer”, the disclosures of which are incorporated herein by reference.

FIG. 1illustrates an exemplary prior art catheter11with mold or balloon13located on the distal end. In the illustrated embodiment, biomaterial23is delivered to the mold13through the catheter11. Secondary tube11′ evacuates air from the mold13before, during and/or after the biomaterial23is delivered. The secondary tube11′ can either be inside or outside the catheter11.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to an intervertebral prosthesis and method for forming an intervertebral prosthesis located in an intervertebral disc space. A retention structure and an in situ curable biomaterial combine in situ to form the intervertebral prosthesis. The present method and prosthesis can be used, for example, to implant a prosthetic disc nucleus using minimally invasive techniques that leave the surrounding disc tissue substantially intact or to implant a prosthetic total disc. The phrase intervertebral disc prosthesis is used generically to refer to both of these variations.

One embodiment is directed to an assembly for the in situ formation of a prosthesis in an intervertebral disc space between adjacent vertebrae of a patient. At least one retention structure is located in the intervertebral disc space. A distal end of at least a first lumen is located proximate the at least one retention structure. One or more in situ curable biomaterials are delivered to the intervertebral disc space through the first lumen and into engagement with the retention structure. The curable biomaterial preferably adheres to and is at least partially captured by the retention structure. Consequently, the retention structure serves to retain at least a portion of the biomaterial in the intervertebral disc space. The at least partially cured biomaterial and the at least one retention structure cooperate to comprise the prosthesis.

In one embodiment, the retention structure includes a band with openings opposite end plates of the adjacent vertebrae. The band is preferably oriented perpendicular relative to an axis of the spine to restrain the biomaterial from creating excessive pressure on the annular walls.

In another embodiment, the retention structure includes one or more collapsed retention structures adapted to expand when located in the intervertebral disc space. In another embodiment, the retention structure expands during delivery of the curable biomaterial.

The retention structure can be a discrete member or a plurality of retention structures adapted to be delivered sequentially through a lumen into the intervertebral disc space. The retention structure can be expandable and/or reorientable.

In another embodiment, the retention structure is adapted to be assembled within the intervertebral disc space. For example, the retention structure optionally includes a plurality of interlocking members that are assembled in situ. In one embodiment, the retention structure comprises a plurality of magnetic members that are assembled in situ.

The retention structure can be one or more inflatable members, woven or non-woven mesh, or coiled or kinked members. The retention structure preferably includes a plurality of tension and compression members. The retention structure may include one or more of individual strands, coils, woven or non-woven webs, open cell foams, closed cell foams, combination of open and closed cell foams, scaffolds, cotton-ball fiber matrix, or a generally honeycomb retention structure.

In another embodiment, the retention structure includes a plurality of interconnected cavities. Fluid flow devices interposed between at least some of the interconnected cavities selectively control the flow of biomaterial into at least some of the cavities. The retention structure includes a plurality of discrete cavities at least a portion of which are at least partially filled with biomaterial.

The at least partially cured biomaterial preferably substantially encapsulates the retention structure. The retention structure when in the intervertebral disc space preferably comprises at least one cross-sectional area greater than a diameter of an opening in the lumen.

The distal end of the lumen is optionally coupled to at least one retention structure. The lumen is optionally releasably attached to the retention structure. In one embodiment, at least one valve is provided to retain the biomaterial in the cavity after the lumen is removed.

One or more of the retention structure or the biomaterial optionally include a bioactive agent. In one embodiment, at least a portion of an anatomical annulus contains the retention structure and the curable biomaterial. In one embodiment, a mold optionally contains the retention structure and the curable biomaterial. The mold can be a balloon or a porous envelope.

The present invention is also directed to a method for the in situ formation of a prosthesis in an intervertebral disc space between adjacent vertebrae of a patient. The method includes locating at least one retention structure in the intervertebral disc space. A distal end of at least a first lumen is located proximate at least one retention structure. One or more flowable, curable biomaterials is delivered into the intervertebral disc space through the first lumen. The flowable biomaterial engages with the retention structure located in the intervertebral disc space so that the retention structure retains at least a portion of the biomaterial in the intervertebral disc space. The at least partially cured biomaterial and the retention structures cooperating to comprise the prosthesis.

Minimally invasive refers to a surgical mechanism, such as microsurgical, percutaneous, or endoscopic or arthroscopic surgical mechanism. In one embodiment, the entire procedure is minimally invasive, for instance, through minimal incisions in the epidermis (e.g., incisions of less than about 6 centimeters, and more preferably less than 4 centimeters, and preferably less than about 2 centimeters). In another embodiment, the procedure is minimally invasive only with respect to the annular wall and/or pertinent musculature, or bony structure. Such surgical mechanism are typically accomplished by the use of visualization such as fiber optic or microscopic visualization, and provide a post-operative recovery time that is substantially less than the recovery time that accompanies the corresponding open surgical approach. Background on minimally invasive surgery can be found in German and Foley,Minimal Access Surgical Techniques in the Management of the Painful Lumbar Motion Segment,30 SPINE 16S, n. S52-S59 (2005).

Retention structure generally refers to the portion or portions of the present invention used to receive, constrain, shape and/or retain a flowable biomaterial in the intervertebral disc space during curing the biomaterial in situ. A retention structure may include or rely upon natural tissues (such as the annular shell of an intervertebral disc or the end plates of the adjacent vertebrae) for at least a portion of its conformation or function. For example, the retention structure may form a fully enclosed cavity or chamber or may rely on natural tissue for a portion thereof. The retention structure, in turn, is responsible, at least in part, for determining the position and final dimensions of the cured prosthetic implant. As such, its dimensions and other physical characteristics can be predetermined to provide an optimal combination of such properties as the ability to be delivered to a site using minimally invasive means, filled with biomaterial, control moisture contact, and optionally, then remain in place as or at the interface between cured biomaterial and natural tissue. In a particularly preferred embodiment the retention structure can itself become integral to the body of the cured biomaterial.

In some embodiments, the retention structure may be used in combination with a mold. Mold generally refers to a flexible member including at least one cavity for the receipt of biomaterial and at least one lumen to that cavity. Multiple molds, either discrete or connected, may be used in some embodiments. Some or all of the material used to form the mold will generally be retained in situ, in combination with the cured biomaterial, while some or the entire lumen will generally be removed upon completion of the procedure. The mold and/or lumens can be biodegradable or bioresorbable. Examples of biodegradable materials can be found in U.S. Publication Nos. 2005-0197422; 2005-0238683; and 2006-0051394, the disclosures of which are hereby incorporated by reference. The mold can be an impermeable, semi-permeable, or permeable membrane. In one embodiment, the mold is a highly permeable membrane, such as for example a woven or non-woven mesh or other durable, loosely woven fabrics. The mold and/or biomaterial can include or be infused with drugs, pH regulating agents, pain inhibitors, and/or growth stimulants.

Biomaterial generally refers to a material that is capable of being introduced to the site of a joint and cured to provide desired physical-chemical properties in vivo. In a preferred embodiment the term will refer to a material that is capable of being introduced to a site within the body using minimally invasive means, and cured or otherwise modified in order to cause it to be retained in a desired position and configuration. Generally such biomaterials are flowable in their uncured form, meaning they are of sufficient viscosity to allow their delivery through a lumen of on the order of about 1 mm to about 10 mm inner diameter, and preferably of about 2 mm to about 6 mm inner diameter. Such biomaterials are also curable, meaning that they can be cured or otherwise modified, in situ, at the tissue site, in order to undergo a phase or chemical change sufficient to retain a desired position and configuration.

The method and apparatus of the present invention uses one or more discrete access points or annulotomies into the intervertebral disc space, and/or through the adjacent vertebrae. The annulotomies facilitate performance of the nuclectomy, imaging or visualization of the procedure, delivery of the retention structure and biomaterial through one or more lumens, drawing a vacuum on a mold before, during and/or after delivery of the biomaterial, and securing the prosthesis in the intervertebral disc space during and after delivery of the biomaterial.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2is a cross-sectional view of a human body20showing various access paths22through38to the intervertebral disc40for performing the method of the present invention. The posterior paths22,24extend either between superior and inferior transverse processes42, or between the laminae (interlaminar path) on either side of the spinal cord44. The posterolateral paths26,28are also on opposite sides of the spinal cord44but at an angle of about 35-45 degrees relative to horizontal relative to the posterior paths22,24. The lateral paths30,32extend through the side of the body. The anterior path38and anterolateral path34extend past the aorta iliac artery46, while the anterolateral path36is offset from the inferior vena cava, iliac veins48.

Depending on the disc level being operated on, and the patient anatomy. Generally, the aorta and vena cava split at the L4 vertebral body. At L5 SI the approach is typically a midline anterior approach. At L4/5 the approach may be either midline anterior or anterolateral, depending on the patient anatomy and how easy it is to retract the vessels. In some usages, the anterior approach is deemed a midline approach and the anterolateral approach is deemed an angled approach offset from the midline anterior approach.

The present method and apparatus use one or more of the access paths22through38. While certain of the access paths22through38may be preferred depending on a number of factors, such as the nature of the procedure, any of the access paths can be used with the present invention.

In one embodiment, delivery catheter instruments are positioned along two or more of the access paths22through38to facilitate preparation of the intervertebral disc40. Preparation includes, for example, formation of two or more annulotomies through the annular wall, removal of some or all of the nucleus pulposus to form a nuclear cavity, imaging of the annulus and/or the nuclear cavity, and positioning of the present multi-lumen mold in the nuclear cavity. In another embodiment, the present multi-lumen mold is positioned in the intervertebral disc40without use of delivery catheters.

FIG. 3Aillustrates one embodiment of a mold assembly50in accordance with the present invention. The mold assembly50includes lumen52fluidly coupled to mold54. In the illustrated embodiment, valve56is provided at the interface between the lumen52and the mold54. In one embodiment, valve58is optionally located at a separate location on the mold54.

The method of using the present mold assembly50involves forming an annulotomy60at a location in the annulus62. The nucleus pulposus64located in the disc space66is preferably substantially removed to create a nuclear cavity68. As illustrated inFIG. 3A, some portion of the nucleus pulposus64may remain in the nuclear cavity68after the nuclectomy. The mold assembly50is then inserted through the annulotomy60so that the mold54is positioned in the nuclear cavity68.

As illustrated inFIG. 3B, biomaterial70is delivered through the lumen52into the mold54. As the biomaterial70progresses through the mold54, at least a portion of the air located in the mold54is preferably pushed out through the valve58. In the illustrated embodiment, the valves56and58are preferably check valves that are forced into the closed position by the pressure of the biomaterial70. Once delivery of the biomaterial70is substantially completed, the lumen52is detached from the mold54removed from the annulotomy60. In the illustrated embodiment, the valve56permits the lumen52to be separated and removed before the biomaterial70has cured.

In one embodiment, one or more of the mold54, the valves56,58, and/or the lumens52have radiopaque properties that facilitate imaging of the prosthesis72being formed. In another embodiment, the lumen52is releasably attached to the valve56to facilitate removal.

In one embodiment, the lumen52is threaded to the valve56. In another embodiment, a quick release interface is used to attach the lumen52to the valve56.

FIGS. 3C and 3Dare assembly views of a mold assembly500with a connection assembly502recessed in the mold504in accordance with the present invention. Open end506of the mold504is inserted into sleeve508. The connector assembly502is then coupled to the sleeve508. The open end506is secured between the sleeve508and connector assembly502. In the illustrated embodiment, distal end of the connector assembly502includes a mechanical interface510that mechanically couples with the sleeve508. The connector assembly502can be coupled to the open end506of the mold504and the sleeve508using a variety of techniques, such as adhesives, mechanical interlocks, fasteners, and the like.

The exposed end512of the connector assembly502preferably includes a mechanical interlock514, such as for example internal threads, that couple with a corresponding interlock516, such as external threads, on the lumen518. As best illustrated inFIG. 3E, the biomaterial70is retained in the mold by valve520preferably located in the connector assembly502. In the illustrated embodiment, the connector assembly502and/or the valve520are substantially flush with the outer surface of the mold504. In another embodiment, the connector assembly502may protrude above the outer surface of the mold504. The lumen518is preferably removed from the mold assembly500before the biomaterial70is cured. The exposed mechanical interlock514on the connector assembly502can optionally be used to attach a securing device522to the prosthesis524.

FIG. 4Aillustrates an alternate mold assembly80in accordance with the present invention. Mold82includes a plurality of openings84. The openings84can be any shape and a variety of sizes. Internal flaps86are located over the openings84. As best illustrated inFIG. 4B, biomaterial70is delivered through lumen88to the mold82. Pressure from the biomaterial70presses the flaps86against the openings84, substantially sealing the biomaterial70within the mold82.

In one embodiment, the flaps86permit any air or biomaterial in the mold82to be pushed out through the openings84during delivery of the biomaterial70. In another embodiment, the flaps86to not completely seal the openings84until the mold82is substantially inflated and pressing against inner surface92of the annulus62.

The flaps86can be constructed from the same or different material than the mold82. In one embodiment, the flaps86are constructed from a radiopaque material that is easily visible using various imaging technologies. Prior to the delivery of the biomaterial70, such as illustrated inFIG. 4A, the spacing between the flaps86indicates that the mold82is not inflated. After delivery of the biomaterial70, such as illustrated inFIG. 4B, the spacing between the flaps86provides an indication of the shape and position of the intervertebral prosthesis90relative to the annulus62. By strategically locating the openings84and flaps86around the outer surface of the mold82, a series of images can be taken during delivery of the biomaterial70which will illustrate the prosthesis90during formation and provide reference points for evaluating whether the prosthesis90is properly positioned and fully inflated within the annulus62.

FIG. 5Aillustrates an alternate mold assembly100in accordance with the present invention. Mold102includes a plurality of openings104with corresponding external flaps or valves106. As best illustrated inFIG. 5B, delivery of the biomaterial70causes the mold102to inflate. When the mold102is substantially inflated, the flaps106are pressed against the openings104by interior surface108of the nuclear cavity68.

In the illustrated embodiment, portion110of the biomaterial70forms a raised structure112over some or all of the openings104. These raised structures serve to anchor the resulting prosthesis114in the nuclear cavity68. Other examples of raised structures include barbs, spikes, hooks, and/or a high friction surface that can facilitate attachment to soft tissue and/or bone. Also illustrated inFIG. 5B, portion116of the biomaterial70optionally escapes from the mold102prior to the flaps106being pressed against the openings104. The portion116of the biomaterial70serves to adhere the prosthesis114to the inner surface108of the annulus62. Again, one or more of the mold102, the flaps106may include radiopaque properties.

FIGS. 6A and 6Billustrate a prosthesis136including one or more retention structures124,126. In the illustrated embodiment, retention structure124is positioned horizontally between adjacent vertebrae128,130. Retention structure126is oriented perpendicular to the retention structure. Lumen120is preferably engaged with one or both of the retention structures124,126.

The retention structure preferably limits the amount of pressure the resulting prosthesis136places on the annular walls62. A compressive force placed on the prosthesis136by the end plates132,134is directed back towards the end plates, rather than horizontally into the annular wall62. The retention structure preferably limits inflation of the mold122in the vertical direction. The retention structure can optionally be used to set a maximum disc height or separation between the adjacent vertebrae128,130when the mold122is fully inflated.

In the illustrated embodiment, the retention structure124,126are preferably radiopaque. As with the flaps86,106ofFIGS. 4 and 5, the retention structure124,126provide an indication of the shape and position of the prosthesis136in the intervertebral disc space138. As the biomaterial is delivered, the retention structures124,126are deployed and positioned in accordance with the requirements of the prosthesis136. A series of images can be taken of the intervertebral disc space138to map the progress of the prosthesis formation. Because the size and width of the retention structure124,126are known prior to the procedure, the resulting images provide an accurate picture of the position of the prosthesis136relative to the vertebrae128,130.

In one embodiment, the retention structures124,126are used in combination with mold122. In an alternate embodiment, one or both of the retention structures124,126can be located at the interior of the mold122. The retention structures124,126can optionally be attached to the mold122.

FIGS. 6C and 6Dillustrate a retention structure142in accordance with the present invention. The retention structure142is preferably positioned horizontally between adjacent vertebrae128,130. In the illustrated embodiment, the retention structure142also serves as a mold for retaining at least a portion of the biomaterial70. The annulus wall62may also act to retain the biomaterial70in the intervertebral disc space.

In one embodiment, the retention structure142preferably extends to the endplates132,134so that the biomaterial70is substantially retained in center region144formed by the retention structure142. In the embodiment ofFIG. 6C, the biomaterial70extends above and below the retention structure142to engage with the endplates132,134. As best illustrated inFIG. 6D, the retention structure142is open at the top and bottom. In some embodiments, the biomaterial70may flow around the outside perimeter of the retention structure142.

FIGS. 7A and 7Billustrate an alternate prosthesis158in accordance with the present invention. Retention structure154configured in a compressed state is delivered into the nuclear cavity68of the annulus62through delivery lumen156.

As best illustrated inFIG. 7B, once the retention structure154is released from the delivery lumen156, it assumes its original expanded shape within the nuclear cavity68. The biomaterial70is delivered to the nuclear cavity68, where it flows into and around the retention structure154. The retention structure154serves to retain at least a portion of the biomaterial in the nuclear cavity68by surface tension, adhesion, mechanical capture, friction, viscosity, and a variety of other mechanisms. In an alternate embodiment, the retention structure154is deployed by the pressure of the biomaterial70being delivered into the nuclear cavity68.

In the illustrated embodiment, the retention structure154is a mesh woven to form a generally tubular structure. The mesh154can be constructed from a variety of metal, polymeric, biologic, and composite materials suitable for implantation in the human body. In one embodiment, the mesh operates primarily as a tension member within the prosthesis158. Alternatively, the retention structure154is configured to act as both a tension and compression member within the prosthesis158.

In another embodiment, the retention structure154, or portions thereof, are constructed from a radiopaque material. In the expanded configuration illustrated inFIG. 7B, the radiopaque elements of the retention structure154provide a grid or measuring device that is readily visible using conventional imaging techniques. The retention structure154thus provides a way to determine the shape, volume, dimensions, and position of the prosthesis158in the annular cavity68.

FIG. 8illustrates an alternate prosthesis160with an internal retention structure162having a shape generally corresponding to the nuclear cavity68. As illustrated inFIG. 7, the retention structure162is compressed within the delivery lumen156(seeFIG. 7A) and delivered into mold164located in the nuclear cavity68. Once in the expanded configuration illustrated inFIG. 8, the retention structure162can operate as a tension and/or compression member within the prosthesis160.

FIG. 9illustrates an alternate prosthesis170in accordance with the present invention. Retention structure172is again positioned in the nuclear cavity68in a compressed configuration through a delivery lumen156(seeFIG. 7A). The retention structure172is preferably constructed of a shape memory alloy (SMA), such as the nickel-titanium alloy Nitinol or of an elastic memory polymer that assumes a predetermined shape once released from the delivery lumen156or once a certain temperature is reached, such as for example the heat of the body. In the preferred embodiment, the retention structure172has radiopaque properties which can be used to facilitate imaging of the prosthesis170.

In another embodiment, the retention structure172is a mold configured with a coil shape. When inflated with biomaterial70, the mold forms a coil-shaped retention structure. Additional biomaterial70is preferably delivered around the coil structure172.

FIGS. 10A and 10Billustrate an alternate prosthesis188in accordance with the present invention. A plurality of discrete helical retaining structures182are delivered through a delivery lumen184into the annular cavity68. As best illustrated inFIG. 10B, the helical retaining structures182intertwine and become entangled within the annular cavity68. In one embodiment, the helical retaining structures182are rotated during insertion to facilitate engagement with the retaining structures182already in the annular cavity68.

Alternatively, these retaining structures182can be kinked strands, which when compressed have a generally longitudinal orientation to provide easy delivery through the lumen184. Once inside the annular cavity68, the retaining structures182are permitted to expand or reorient. The cross-sectional area of the retaining structures182in the expanded or reoriented state is preferably greater than the diameter of the lumen184, so as to prevent ejection during delivery of the biomaterial70.

The plurality of retaining structures182are preferably discrete structures that act randomly and can be positioned independently. The discrete retaining structures182of the present invention can be delivered sequentially and interlocked or interengaged in situ. Alternatively, groups of the retaining structures182can be delivered together.

Once the biomaterial70is delivered and at least partially cured, the relative position of the retaining structures182is set. The retaining structures182can act as spring members to provide additional resistance to compression and as tension members within the prosthesis188. Some or all of the helical retaining structures182preferably have radiopaque properties to facilitate imaging of the prosthesis188.

FIGS. 11A and 11Billustrate an alternate prosthesis200in accordance with the present invention. A plurality of retaining structures204are delivered into the nuclear cavity68. Biomaterial70is then delivered to the nuclear cavity68. The retention structures204assist in holding the biomaterial70in place. The retention structures204typically arrange themselves randomly within the intervertebral disc space202.

In the illustrated embodiment, the retention structures204are a plurality of spherical members206. The spherical members206flow and shift relative to each other within the intervertebral disc space202. In one embodiment, the spherical members206are constructed from metal, ceramic, and/or polymeric materials. The spherical members206can also be a multi-layered structure, such as for example, a metal core with a polymeric outer layer.

In another embodiment, the spherical members206are hollow shells with openings into which the biomaterial70can flow. In this embodiment, the biomaterial70fills the hollow interior of the spherical members206and bonds adjacent spherical members206to each other.

In one embodiment, the spherical members206have magnetic properties so they clump together within the intervertebral disc space202before the biomaterial70is delivered. Some or all of the spherical members206optionally have radiopaque properties.

FIG. 12is a side sectional view of an intervertebral disc space138containing prosthesis210in accordance with the present invention. A plurality of polyhedron retention structures212are delivered into the intervertebral disc space138through lumen216. For example, the retention structure can be pyramidal, tetrahedrons, and the like. In one embodiment, the pyramidal retention structures212have magnetic properties causing them to bind to each other within the intervertebral disc space138. In another embodiment, the pyramidal retention structures212include a plurality of holes or cavities into which the biomaterial70flows, securing the retention structures212relative to each other and relative to the prosthesis210.

FIG. 13is a side sectional view of an intervertebral disc space138with prosthesis224having coiled or loop shaped retention structures220in accordance with the present invention. The retention structures220can be compressed for delivery through the lumen222, and allowed to expand once inside the nuclear cavity68. Biomaterial70is then injected to secure the relative position of the retention structures220within the prosthesis224.

The retention structures220are preferably constructed from a spring metal that helps maintain the separation between the adjacent vertebrae128,130. In one embodiment, the retention structures220are resilient and flex when loaded. In an alternate embodiment, the retention structures220are substantially rigid in at least one direction, while being compliant in another direction to permit insertion through the lumen222. The retention structures220optionally define a minimum separation between the adjacent vertebrae128,130. The retention structures220can operate as tension and/or compression members.

FIG. 14is a side sectional view of an alternate prosthesis258in accordance with the present invention. A plurality of reinforcing fibers252are delivered into the intervertebral disc space254through lumen256. The biomaterial70is then delivered and secures the relative position of the reinforcing fibers252within the intervertebral disc space138. The reinforcing fibers252can be in the form of individual strands, coils, woven or non-woven webs, open cell foams, closed cell foams, combination of open and closed cell foams, scaffolds, cotton-ball fiber matrix, or a variety of other structures. The reinforcing fibers252can be constructed from metal, ceramic, polymeric materials, or composites thereof. The reinforcing fibers252can operate as tension and/or compression members within prosthesis258.

FIG. 15Ais a side sectional view of an alternate prosthesis278in accordance with the present invention. A three-dimensional honeycomb structure272is compressed and delivered into the intervertebral disc space274through the lumen276. Once in the expanded configuration, illustrated inFIG. 15A, the biomaterial70is delivered, fixing the honeycomb structure272in the illustrated configuration. In another embodiment, the delivery of the biomaterial expands or inflates the honeycomb structure272.

The biomaterial70flows around and into the honeycomb structure272providing a highly resilient prosthesis278. In one embodiment, the honeycomb structure272still retains its capacity to flex along with the biomaterial70when compressed by the adjacent vertebrae128,130. The honeycomb structure272can be constructed from a plurality of interconnected tension and/or compression members. In yet another embodiment, the honeycomb structure is an open cell foam.

In one embodiment, the honeycomb structure272has fluid flow devices, such as for example pores, holes of varying diameter or valves, interposed between at least some of the interconnected cavities280. The fluid flow devices selectively controlling the flow of biomaterial70into at least some of the cavities280or filling the cavities280differentially, thus combining the different mechanical properties of the honeycomb structure272with the biomaterial70in an adaptable manner. The generally honeycomb structure272can optionally be combined with open or closed cell foam.

FIGS. 15B and 15Care side and top sectional views of a prosthesis282with a plurality of three-dimensional honeycomb structures284A,284B (referred to collectively as “284”) in accordance with the present invention. The honeycomb structures284are constructed so that the inflow of biomaterial70can be selectively directed to certain cavities286. In alternate embodiments, more than two honeycomb structures284A,284B can optionally be used.

In one embodiment, holes interconnecting adjacent cavities286can be selectively opened or closed before the honeycomb structures284are inserted into the patient. In another embodiment, a plurality of lumens288A,288B,288C, . . . (referred to collectively as “288”) are provided that are each connected to a different cavity286. One or more of the lumens288can also be used to evacuate the annular cavity68.

Selective delivery of the biomaterial70into the honeycomb structures284can be used to create a variety of predetermined internal shapes. Using a plurality of lumens288permits different biomaterials70A,70B,70C, . . . to be delivered to different cavities286within the honeycomb structure284. The biomaterials70A,70B,70C, . . . can be selected based on a variety of properties, such as mechanical or biological properties, biodegradability, bioabsorbability, ability to delivery bioactive agents. As used herein, “bioactive agent” refers to cytokines and preparations with cytokines, microorganisms, plasmids, cultures of microorganisms, DNA-sequences, clone vectors, monoclonal and polyclonal antibodies, drugs, pH regulators, cells, enzymes, purified recombinant and natural proteins, growth factors, and the like.

FIG. 16illustrates an alternate mold assembly300in accordance with the present invention. In the illustrated embodiment, two annulotomies60A,60B are formed in the annulus62. The mold assembly300is threaded through one of the annulotomies so that the lumens302,304each protrude from annulotomies60A,60B, respectively. Lumen302is fluidly coupled to mold306while lumen304is fluidly coupled with mold308. Retention structure310is attached to molds306,308at the locations312,314, respectively.

FIG. 17Ais a side sectional view of the mold assembly300ofFIG. 16implanted between adjacent vertebrae128,130. Biomaterial70is delivered to the molds306,308, which applies opposing compressive forces316on the retention structure310. In the illustrated embodiment, the retention structure310is a coil, loop, or bend (arc) of resilient material, such as a memory metal, spring metal, and the like. The resulting prosthesis312includes a pair of molds306,308containing a cured biomaterial70holding the retention structure310against adjacent end plates132,136of the vertebrae128,130respectively. The retention structure can serve to resist compression of the prosthesis312or to establish a minimum separation between the adjacent end plates132,134.

FIG. 17Bis an alternate embodiment of the mold assembly300ofFIG. 16. In the illustrated embodiment, retention structure310includes a series of fold lines or hinges318. Expansion of the molds306,308with biomaterial70generates forces316that converts the generally flat retention structure310(seeFIG. 16) into the shaped retention structure322illustrated inFIG. 17B. Alternatively, the hinge318could be facing the molds306,308rather than the endplates. In the embodiments ofFIGS. 17A and 17B, delivery of the biomaterial70deploys the retention structure310to an expanded configuration.

FIGS. 18A and 18Billustrate an alternate mold assembly350in accordance with the present invention. Lumens352,354extend into the annulus62through different annulotomies60A,60B. Lumen352is fluidly coupled with mold356and lumen354is fluidly coupled with mold358. Reinforcing mesh structure364is connected to the molds356,358at locations360,362, respectively. As illustrated inFIG. 18B, biomaterial70is delivered to the molds356,358causing the retention structure364to be compressed and/or stretched within the nuclear cavity68.

In one embodiment, additional biomaterial70can optionally be delivered into the nuclear cavity68proximate the retention structure364. In the illustrated embodiment, the same or a different biomaterial70A flows around and into the retention structure364. The biomaterial70A bonds the retention structure364to the annulus62. The resulting prosthesis366has three distinct regions of resiliency. The areas of varying resiliency can be tailored for implants that would be implanted via different surgical approaches, as well as various disease states. The retention structure364optionally includes radiopaque properties. A series of images taken during delivery of the biomaterial70illustrates the expansion and position of the prosthesis366in the nuclear cavity68.

FIG. 18Cis an alternate configuration of the mold assembly350for use with mono-portal applications in accordance with the present invention. Lumens352,354extend into the annulus62through a single annulotomy60. Lumen352is fluidly coupled with mold356and lumen354is fluidly coupled with mold358. Reinforcing mesh structure364is connected to the molds356,358at locations360,362, respectively. As illustrated inFIG. 18B, delivery of the biomaterial70causing the retention structure364to be compressed and/or stretched within the nuclear cavity68. Additional biomaterial70A can optionally be delivered into the nuclear cavity68proximate the retention structure364.

FIGS. 19A and 19Bare side sectional views of mold assembly400in accordance with the present invention. The mold402includes a plurality of radiopaque markers404. In the illustrated embodiment, the radiopaque markers404are arranged in a predetermined pattern around the perimeter of the mold402. As best illustrated inFIG. 19B, once the mold402is inflated with the biomaterial, the spacing406between the adjacent radiopaque markers404increases. By imaging the intervertebral disc space138before, during and after delivery of the biomaterial70, a series of images can be generated showing the change in the spacing between the radiopaque markers404. Because the spacing between the radiopaque markers404is known prior to delivery of the biomaterial, it is possible to calculate the shape and position of the prosthesis408illustrated inFIG. 19Busing conventional imaging procedures.

FIGS. 20A and 20Billustrate an alternate mold assembly420in accordance with the present invention. Mold422includes a plurality of radiopaque strips424located strategically around its perimeter. When the mold422is inflated with biomaterial, the spacing426between the radiopaque strips424changes, providing an easily imagable indication of the shape and position of the prosthesis428in the intervertebral disc space138.

FIG. 21illustrates an alternate mold assembly450in accordance with the present invention. Inner mold452is fluidly coupled to lumen454. Outer mold456is fluidly coupled to lumen458. Biomaterial is delivered through the lumen454into the inner mold452. A radiopaque fluid is preferably delivered to the space460between the inner mold452and the outer mold456.

In one embodiment, as the biomaterial70is delivered to the inner mold452, the radiopaque material462located in the space460is expelled from the nuclear cavity68through the lumen458. A series of images of the annulus62will show the progress of the biomaterial70expanding the inner mold452within the nuclear cavity68and the flow of the radiopaque fluid462out of the space460through the lumen458.

In another embodiment, once the delivery of the biomaterial70is substantially completed and the radiopaque material462is expelled from the space460, a biological material or bioactive agent is injected into the space460through the delivery lumen458. In one embodiment, the outer mold456is sufficiently porous to permit the bioactive agent to be expelled into the annular cavity68, preferably over a period of time. One of the molds452,456optionally includes radiopaque properties. The mold456is preferably biodegradable or bioresorbable with a half life greater than the time required to expel the bioactive agents.

In another embodiment, one or more retention structures464, such as disclosed herein, is located in the space460between the inner and outer molds452,456. For example, the retention structure464may be a woven or non-woven mesh impregnated with the bioactive agent. In another embodiment, the retention structure464and the outer mold456are a single structure, such as a reinforcing mesh impregnated with the bioactive agent. In yet another embodiment, the outer mold456may be a stent-like structure, preferably coated with one or more bioactive agents.

FIGS. 22 and 23illustrate use of a mold assembly550to maintain the separation between spinous process552and/or transverse processes554on adjacent vertebrae556,558in according with the present method and apparatus. The mold assembly550may be used alone or in combination with an intervertebral mold assembly, such as discussed herein. The mold assembly550can also be used to separate the superior articulating process and inferior articulating process, more commonly referred to as the facet joint, on adjacent vertebrae.

In the illustrated embodiment, the mold560preferable includes extension562,564that couple or engage with the spinous process or transverse processes552,554. Center portion566acts as a spacer to maintain the desired separation. In one embodiment, the mold assembly has an H-shaped or figure-8 shaped cross section to facilitate coupling with the various facets on the adjacent vertebral bodies. Attachment of the molds550or560to the spinous or transverse processes may be further facilitated using sutures, cables, ties, rivets, screws, clamps, sleeves, collars, adhesives, or the like. Any of the mold assemblies and retention structures disclosed herein can be used with the mold assembly550.

Any of the features disclosed herein can be combined with each other and/or with features disclosed in commonly assigned U.S. patent application Ser. No. 11/268,786, entitled Multi-Lumen Mold for Intervertebral Prosthesis and Method of Using Same, filed Nov. 8, 2005, which is hereby incorporated by reference. Any of the molds and/or lumens disclosed herein can optionally be constructed from biodegradable or bioresorbable materials. The lumens disclosed herein can be constructed from a rigid, semi-rigid, or pliable high tensile strength material. The various components of the mold assemblies disclosed herein may be attached using a variety of techniques, such as adhesives, solvent bonding, mechanical deformation, mechanical interlock, or a variety of other techniques.

The mold assembly of the present invention is preferably inserted into the nuclear cavity68through a catheter, such as illustrated in commonly assigned U.S. patent application Ser. No. 11/268,876 entitled Catheter Holder for Spinal Implants, filed Nov. 8, 2005, which is hereby incorporated by reference.

Various methods of performing the nuclectomy are disclosed in commonly assigned U.S. patent Ser. No. 11/304,053 entitled Total Nucleus Replacement Method, filed on Dec. 15, 2005, which is incorporated by reference. Disclosure related to evaluating the nuclectomy or the annulus and delivering the biomaterial70are found in commonly assigned U.S. patent application Ser. No. 10/984,493, entitled Multi-Stage Biomaterial Injection System for Spinal Implants, filed Nov. 9, 2004, which is incorporated by reference. Various implant procedures and biomaterials related to intervertebral disc replacement suitable for use with the present multi-lumen mold are disclosed in U.S. Pat. No. 5,556,429 (Felt); U.S. Pat. No. 6,306,177 (Felt, et al.); U.S. Pat. No. 6,248,131 (Felt, et al.); U.S. Pat. No. 5,795,353 (Felt); U.S. Pat. No. 6,079,868 (Rydell); U.S. Pat. No. 6,443,988 (Felt, et al.); U.S. Pat. No. 6,140,452 (Felt, et al.); U.S. Pat. No. 5,888,220 (Felt, et al.); U.S. Pat. No. 6,224,630 (Bao, et al.), and U.S. patent application Ser. Nos. 10/365,868 and 10/365,842, all of which are hereby incorporated by reference. The present mold assemblies can also be used with the method of implanting a prosthetic nucleus disclosed in a commonly assigned U.S. patent application Ser. No. 11/268,856, entitled Lordosis Creating Nucleus Replacement Method and Apparatus, filed on Nov. 8, 2005, which are incorporated herein by reference.

The mold assemblies and methods of the present invention can also be used to repair other joints within the spine such as the facet joints, as well as other joints of the body, including diarthroidal and amphiarthroidal joints. Examples of suitable diarthroidal joints include the ginglymus (a hinge joint, as in the interphalangeal joints and the joint between the humerus and the ulna); throchoides (a pivot joint, as in superior radio-ulnar articulation and atlanto-axial joint); condyloid (ovoid head with elliptical cavity, as in the wrist joint); reciprocal reception (saddle joint formed of convex and concave surfaces, as in the carpo-metacarpal joint of the thumb); enarthrosis (ball and socket joint, as in the hip and shoulder joints) and arthrodia (gliding joint, as in the carpal and tarsal articulations).

The present mold apparatus can also be used for a variety of other procedures, including those listed above. The present mold assembly can also be used to modify the interspinous or transverse process space. The mold can operate as a spacer/distractor between the inferior and superior spinous processes, thus creating a local distraction and kyphosis of wanted. The theory behind these implants is that they expand the intervertebral foramen and thereby relieve pressure on the nerve root and spinal cord. The present injectable prosthesis is adapted to the individual anatomy and clinical situation of the patient, without the need for multiple implant sizes.

Patents and patent applications disclosed herein, including those cited in the Background of the Invention, are hereby incorporated by reference. Other embodiments of the invention are possible. Many of the features of the various embodiments can be combined with features from other embodiments. For example, any of the securing mechanisms disclosed herein can be combined with any of the multi-lumen molds. It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.