WO2008112607A2

WO2008112607A2 - Spinal implant

Info

Publication number: WO2008112607A2
Application number: PCT/US2008/056359
Authority: WO
Inventors: Andrew F. Cannestra
Original assignee: Blue Fury Consulting, Llc
Priority date: 2007-03-09
Filing date: 2008-03-10
Publication date: 2008-09-18
Also published as: WO2008112607A3

Abstract

A spinal implant that includes a body and extendable teeth within the body is provided. The teeth within the body are extended after positioning of the implant so that the teeth engage the vertebrae/bone and maintain the cage in position. The installed cage provides structural support for the joint. The cage also provides a lattice that facilitates fusion.

Description

SPINAL IMPLANT

BACKGROUND OF THE INVENTION

The present invention relates to interbody implants and more particularly to fusion cages.

Spinal fusion surgery has become a common procedure for the treatment of degenerative disease of the spine. In such surgery, spinal hardware is installed to stabilize the movement across the affected joint, thereby facilitating fusion between the vertebrae. Historically, spinal hardware includes plates, screws, and rods. A number of years ago it was discovered that fusion rates can be dramatically increased if the affected disc is removed entirely and a spacer inserted into the disc space. Spinal hardware called "spinal implants" or "fusion cages" was designed to be inserted into the disc space. These implants were created in a variety of designs and configurations.

Presently used fusion cages are either cylindrical or rectangular devices having an external threaded or toothed portion for engaging the vertebral end plates in order to prevent the cage from slipping. Such cages are generally hollow. They can be filled with graft in order to induce fusion of the two vertebrae together. Such devices provide great potential for eliminating the large incisions required for posterior instrumentation and open a door for minimally invasive surgery. The cages are typically classified by the insertion technique (e.g. anterior, posterior, lateral, or posterior lateral) or by a characteristic of the cage (e.g. threaded, expandable, or stackable). Threaded cages must be rotated or turned into position. Expandable cages include a body that changes height as part of the implantation procedure. Stackable cages must be assembled in situ in a procedure similar to building with Lego^® building blocks. All of these cages are undesirably complicated structurally and/or undesirably difficult to install.

Additionally, most fusion devices presently in use are large and bulky. Size is an extremely important factor in minimally invasive surgery wherein the device is placed inside the body using a cannula to minimize the incision size and therefore hospital recovery time. In this process, it is desirable to use as small of an incision as possible. The surgeon implants the cage or cages into the disc by use of a cannula. This allows for small skin incision to minimize soft tissue trauma and reduce recovery time and hospital stay. To properly relieve the pressure on the nerves and spinal cord, the collapsed disc space should be open to as close as possible to its precollapsed stage. With the present cage designs, the cage is designed to open the disc space to 16 mm, such cage requiring a cannula of 18 to 20 mm. Such a cannula requires a large incision.

The cages or implants must also be inserted in such a way and using sufficient hardware so as to ensure that the implant will not unintentionally move after implantation. This is a difficult task, because the implants must be able to provide some flex to ensure that patient movement is not unduly restricted, while not slipping out of position and causing further damage. The prior art implants have typically utilized a variety of bone screws to accomplish this task. However, failure of such a bone screw can cause additional damage and in an effort to limit the size of the implant usually few screws are used to hold the implant in place. Therefore, failure of a screw can impact the effectiveness/stability of the entire implant.

Another problem with presently used implant cages is an incomplete consideration of load sharing, Wolfs law and fusion quality. The prior art provides a fixed device which is inserted between the vertebral end plates and filled with graft. It has been previously assumed that if the graft is placed properly, fusion will occur. However, bone quality is related to stress. Wolfs law states that bone grows along lines of stress. The prior art cages hold the vertebral bodies apart and act merely as solid spacers. Therefore, the graft material inside the cage resorbs and is never stressed. Without stress, the graft material inside the cage does not effectively provide fusion quality. If a fusion takes place, which is difficult to determine at best in metal cages using X-rays or most other diagnostic techniques, the quality of fusion can be poor at best.

SUMMARY OF THE INVENTION

The present invention provides a spinal implant includes a body and extendable teeth within the body. The teeth are extended after positioning so that the teeth engage the vertebrae/bone and maintain the cage in position. The installed cage provides structural support for the joint. The cage also provides a lattice that facilitates fusion.

The present invention has distinct advantages over prior art implants. First, it can be inserted smoothly and easily during an atraumatic procedure. Second, the extendable teeth enable the cage to be secured or anchored in position effectively and easily.

These and other objects, advantages, and features of the invention will be more fully understood and appreciated by reference to the detailed description of the current embodiment and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side elevational view of the spinal cage of the present invention (the opposite side view being the mirror image thereof);

Fig. 2 is a top plan view of the spinal cage (the bottom plan view being the mirror image thereof); Fig. 3 is a sectional view taken along Line HI-III in Fig. 2 and showing the teeth retracted;

Fig. 4 is a sectional view taken along Line IV-IV in Fig. 3;

Fig. 5 is an elevalional view of one pair of retracted teeth; Fig. 6 is a sectional view similar to Fig. 3 but showing the teeth extended;

Fig. 7 is a sectional view similar to Fig. 4 but showing the teeth extended;

Fig. 8 is an elevational view similar to Fig. 5 but showing the teeth extended;

Fig. 9 is an end view of the cage;

Fig. 10 is a sectional view of the inserter; Fig. 11 is a sectional view of the cage positioned within the inserter positioned in a disc space;

Fig. 12 is a sectional view taken along Line XII-XII in Fig. 11 ;

Fig. 13 is a sectional view showing the cage inserted into its final position within the disc space; Fig. 14 is a sectional view showing the cage remaining in position in the disc space while the inserter is partially withdrawn; and

Fig. 15 is a sectional view showing the cage in position in the disc space with the inserter fully withdrawn.

DESCRIPTION OF THE CURRENT EMBODIMENT

A spinal implant or fusion cage in accordance with a current embodiment of the present invention is illustrated in the drawings and generally designated 10. The illustrated implant is an example, and alternative implants can be used. The implant includes an implant body 12 and an extendable tooth assembly 14. The tooth assembly is retracted (Figs. 3-5) during insertion of the implant between vertebrae. The tooth assembly is extended (Figs. 6-8) after the implant is in position within the disc space to anchor the cage to the adjacent vertebrae.

Generally, the implant 10 includes a body portion generally indicated at 12. The body portion 12 can be manufactured from various materials, such as composite materials of one or more metals, plastics, hydroxyapatite, resorbable material, polymer, and ceramic, and may additionally incorporate bone chips, bone particulate, bone fibers, bone growth materials, bone cement, or other materials well known in the art. Such devices can be either machined or molded, depending upon the material from which the implant 10 is made. The implant 10 can be made from a material having spring like qualities. Alternatively, the body 12 can be made from a plastic material or composite which can be molded into the desired shape.

The present invention can be made from a shape memory polymer or alloy such as Nitinol. Such materials can be bent to a desired shape, such as bending the body 12 into contracted shape and maintaining the contracted shape. Once implanted, an instrument can be used to cause an electric current, heat or cold to be applied to the body thereby inducing the memory metal to return to its original expanded shape. Thusly, the implant can be inserted into a collapsed or substantially collapsed disc space between two vertebrae. The stimulus, such as heat, electric current, or cold can be applied to the implant whereby the implant will then return to its expanded shape thereby expanding the disc space to effectuate relief of the pinched nerves or the like. The implant will then maintain the spacing thereby effectuating relief to the patient.

Also, while solid-walled structures are described herein, the structures optionally may include perforations extending from outer to inner surfaces, or recesses formed in outer surfaces that do not extend through inner surfaces. Geometries such as circular depressions, dimples formed from a spherical geometry, diamond shapes, or rectangular shapes may be used to promote bone fusion.

In the current embodiment, the body 12 defines a single horizontal slot 16 and a pair of vertical slots 18. The slots reduce the mass of the implant body 12 and provide a lattice to facilitate fusion. The body 12 also defines a plurality of vertical holes 20 and a pair of horizontal holes 22 for purposes to be described.

The implant body 12 includes a rounded anterior or insertion end 13 and a blunt posterior end 15. Optionally, the implant body 12 can be shaped differently for example to reduce or eliminate sharp or cornered edges. The horizontal holes 22 open through the posterior end as illustrated in Fig. 9. Additionally, the posterior end 15 defines a hole 17 for receiving a press 50 (to be described).

The body 12 includes an outer surface 19 and an inner surface (not visible).

The inner surface defines a hollow inner chamber (not visible) for containing a graft material

(not visible) therein. Such general shapes of cages are well known in the art. The outer surface 19 can include a porous coating, as is known in the art, for allowing bone growth. The outer surface 19 can also be otherwise textured to enhance bone fixation.

The tooth assembly 14 is illustrated in Figs. 5 and 8. The tooth assembly 14 includes a plurality of upper teeth 30, a plurality of lower teeth 32, a cam actuator 34 or other engagement device therebetween. The teeth 30 and 32 are each installed within one of the vertical holes 20 and are capable of traveling within the holes. The cam actuator 34 is accessible through the horizontal holes 22.

The "teeth" are defined herein as spikes or other similarly shaped protrusions that can extend out from the implant body or any other shape suitable for accomplishing the function disclosed herein. The teeth can have a smooth exterior surface or can have a jagged exterior surface. The smooth surface enables the implant to be removed more easily as the teeth are easily removed from bone tissue. The jagged or otherwise modified exterior surface creates a more firm connection between the implant and the bone, because the jagged surface creates more surface area contact between the teeth and the bone. The teeth can also include a coating on the exterior surface that promotes bone growth. Alternatively, the teeth can be hollow and can include a lattice or otherwise porous surface that enables the interior to be filled with graft material that can diffuse through the tooth into the bone enabling stronger fusion.

In the current embodiment, the teeth are present on at least one exterior surface of the implant. The teeth can be present at each end of the surface and can also be present in the middle or the surface, thereby ensuring that even if one tooth fails, the implant will remain in place. In order to accomplish this, the teeth can be in at least two conditions: a disengaged/retracted condition in which the teeth are generally retracted within or drawn into the body of the spinal implant; and an engaged/extended condition in which the teeth extend from the body to engage the bony surface onto which the spinal implant is placed. Additionally, the extended condition can include a partially extended configuration and a fully extended configuration. This enables greater control with regard to the extent that the teeth are extended into the bone. In other words, the extent to which the teeth are inserted into the bone can be adjusted.

The "engagement device" can be any device that is capable to moving the teeth from a retracted to an extended condition. In the current form, the engagement device is a cam actuated rod, which, when turned, forces the teeth into engagement with the bone. Multiple rods can also be used, wherein each rod controls the action of one or more teeth. Alternatively, a variety of other devices and combinations of devices can also be used. For example, a plunger can be used that forces the teeth into engagement or a hydraulic system can be used. An expandable solution/fluid that can provide sufficient strength to force the teeth into engagement without having negative side effects can also be used. Examples of such fluids include sol gels and other similar substances. Alternatively, the teeth can be "spring-loaded" within the implant body such that prior to insertion, the teeth are held in a retracted position before positioning, and once the implant is positioned, all of the teeth are allowed to extend. Also, a tapered screw can be used that drives the teeth out of the cage as the tapered screw is engaged within the cage.

The actuator device used to manipulate the engagement device changes based upon the chosen engagement device. For example, when using a cam, a wrench or other similar device can be used to twist or turn the cam into the desired position. Other actuator devices can include an Allen wrench, a plunger or any other device capable of manipulating the engagement device, and preferably is able to function within the small confines of the body and through the incision. In the case of a spring-loaded engagement device, it is possible that no actuator device would be required or that only a release device would be required. In the current embodiment, the cam actuators 34 on each side of the implant

10 are interconnected by a rod (not visible). Consequently, all of the cam actuators 34 on either side of the implant 10 can be operated using the single rod. The cam actuators 34 may be rotated between a retracted position and an extended position. The retracted position is illustrated in Fig. 5, and the extended position is illustrated in Fig. 8. The implant can be any spinal implant. Examples include, but are not limited to, fusion cage, spinal plate, artificial disc, transverse connector and spinal fixation assemblies.

In order to maximize chances for fusion to occur, various materials have been used to fill the insides of cages. Each material is chosen based on availability and to provide the best chance of good fusion. These include autograft (material taken from the patient during the surgery), allograft (bone removed from another patient) and/or processed allograft, which may be in small pieces and treated in a variety of ways. With the desire to decrease fusion time, biologically active materials may be used. These include bone treated with morphogenic proteins, calcium sulfate, and other artificial bone substitutes. Installation/Use

Hardware and the procedure for inserting the implant 10 within a disc space are illustrated in Figs. 10-15.The implant is inserted into the spine of a patient and can be used to promote bone fusion while maintaining the stability of the spine. The teeth enable the implant to be rigidly affixed to the bone of the spine and to prevent slippage of the implant. The implant 10 is inserted using an insertional device or inserter 40 (Fig. 10). The inserter includes an upper sled 42 and a lower sled 44 which are spaced from one another a distance to closely receive the implant 10. One or more slops 46 are provided on the exterior of the upper and lower sleds 42 and 44 to limit the travel of the inserter into a disc space. The inserter 40 can provide retraction of the thecal sac by using a silastic collar around the upper and lower sleds (allowing medial and lateral retraction).

After the deteriorated disc has been removed, the inserter 40 is inserted into the disc space between the two adjacent vertebrae. As the sleds are inserted between the adjacent vertebrae, the sleds expand the disc space providing adequate room in which to insert the implant 10. Fig. 11 illustrates the implant 10 within the inserter 40 after the inserter has been positioned within the disc space with the stops 46 essentially adjacent the vertebrae. The sleds 42 and 44 are positioned between the vertebrae with the implant 10 not yet pushed forward between the vertebrae.

A press 50 is that inserted into the hole 17 within the implant 10 so that the implant can be pushed forward through the inserter 40. See Figs. 11-12. The implant 10 is then pushed forward until the implant is positioned between the sleds 42 and 44 and therefore within the disc space. See Fig. 13. When fully inserted, the posterior end 15 of the implant 10 is generally aligned with the posterior edge of the adjacent vertebrae.

As the next step, the inserter 40 is withdrawn while the press 50 is used to retain the implant in position within the disc space. The inserter 40 is shown partially withdrawn in Fig. 14 and fully withdrawn in Fig. 15. After the inserter has been full withdrawn, the implant 10 remains in position within the disc space with its posterior end 15 generally aligned with the posterior edge of the vertebrae.

An actuator device (not shown) then is inserted into each of the holes 22 to rotate or to actuate the cam mechanisms 34. As each cam mechanism 34 is rotated, the teeth 30 and 32 are extended from the implant body 12 to engage and become anchored within the adjacent vertebrae. At this point, the implant 10 has been fully placed and anchored in position.

The present invention provides a spinal implant that can be readily and securely installed within a disc space to enhance fusion. The device creates a minimum of trauma and produces excellent fusion results.

The above description is that of a current embodiment of the invention.

Various changes and alterations can be made without departing from the spirit and broader aspects of the invention. Any reference to a claim element in the singular, for example, using the articles '"a," "an," "the" or "said," is not to be construed as limiting the element to the singular.

Claims

CLAIMSThe embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A fusion implant comprising; a spinal implant body; and extendable teeth on at least one exterior surface of said spinal implant body for extending into a bony surface within a patient.

2. The spinal implant according to claim 1, wherein said teeth are extendable between at least a retracted condition and an engaged condition.

3. The spinal implant according to claim 2, wherein said extended condition of said teeth is defined as extending said teeth past said exterior surface of said spinal implant into the bony surface within the patient.

4. The spinal implant according to claim 2, wherein said extended condition includes a partially extended and a fully extended condition.

5. The spinal implant according to claim 1, wherein said extendable teeth comprise engagement means for engaging and moving said extendable teeth.

6. The spinal implant according to claim 5, wherein said engagement means comprises: moving means for actuating said teeth; and actuating means for actuating said teeth.

7. The spinal implant according to claim 6, wherein said moving means is selected from the group consisting of a cam actuator, a balloon expansion kit, hydraulics, and at least one rod, interconnected to said teeth, whereby movement of said moving means causes movement of said teeth between said retracted condition and said extended condition.

8. The spinal implant according to claim 7, wherein said rod includes at least two separate actuated rods.

9. The spinal implant according to claim 7, wherein said actuating means is a cam actuator.

10. The spinal implant according to claim 1, wherein said spinal implant is selected from the group consisting of a fusion cage, spinal plate, artificial disc, transverse connector and spinal fixation assemblies.

1 1. A spinal fusion cage comprising: a body; and teeth carried by said body and movable between a retracted position in which said teeth are retracted with respect to said body and an extended position in which said teeth are extended with respect to said body.

12. The spinal implant according to claim 11, wherein said extended condition of said teeth is defined as extending said teeth out from said body into a bony surface within a patient.

13. The spinal implant according to claim 11, wherein said extended condition includes a partially extended and a fully extended condition.

14. The spinal implant according to claim 11, wherein said extendable teeth comprise engagement means for engaging and moving said extendable teeth.

15. The spinal implant according to claim 14, wherein said engagement means comprises: moving means for actuating said teeth; and actuating means for actuating said teeth.

16. The spinal implant according to claim 15, wherein said moving means is selected from the group consisting of a cam actuator, a balloon expansion kit, hydraulics, and at least one rod. interconnected to said teeth, whereby movement of said moving means causes movement of said teeth between said retracted condition and said extended condition.

17. A method of inserting a spinal implant into a patient by: preparing a space for a spinal implant; placing a spinal implant having extendable teeth into the prepared space; and extending the teeth into bone, thereby maintaining the spinal implant in place.

18. The method according to claim 17, further including retracting the teeth for removal of the implant.

19. The method according to claim 17, wherein: the teeth are spring-loaded; and said extending step includes allowing the spring-loaded teeth to move.