Apparatus and method for anterior intervertebral spinal fixation and fusion

[0001] The present application is a divisional of Ser. No. 11/321,936 U.S. Pat. No. 7,594,932 to Aferzon et al., filed Dec. 29, 2005, and entitled “APPARATUS FOR ANTERIOR INTERVERTEBRAL SPINAL FIXATION AND FUSION”, the contents of which is incorporated herein by reference in its entirety.

[0002] This invention relates to a spinal fusion device. More specifically, the present invention relates to an implant and fixation device used to reconstruct spinal disk space and facilitate fusion across the spinal disk space.

[0003] Articulations between bony vertebras of a human spine frequently deteriorate with age or trauma and become a source of pain. A spinal disk is one of these articulations and with the aging process it loses its normal consistency and volume and collapses allowing for abnormally painful motion within the anterior spinal column. The spinal disk is a complex cylindrical weight-bearing fibrous structure with a non-compressible viscous center. The spinal disk articulates with bony vertebra above and below through a large surface area circular interface known as an endplate. The endplate is a thin (1-3 mm) approximately round 2-4 cm in diameter plate of dense bone and cartilage accounting for a majority of the vertebral weight-bearing capacity.

[0004] Surgical treatment of disk disorders frequently requires elimination of movement across an abnormal spinal disk. This is accomplished by allowing bone to grow between adjacent vertebra and through a disk space of the abnormal spinal disk. It is desirable to reconstruct the disk space to its prior normal height by opening the space previously occupied by the removed spinal disk while retaining normal curvature of the spine determined by the differential height between the front and the back of the spinal disk (FIG. 3). This is commonly achieved by using inserts or implants which open the disk space and which allows for growth of the bridging bone. The ultimate effectiveness of an implant is based on the following factors: (i) ability to reconstruct and maintain a normal configuration of a vertebral column; (ii) ease of insertion; (iii) facilitation of bony fusion and; (iv) restriction of movement across the disk space.

[0005] Implants utilized in fusion of a human spine and delivered in a straight trajectory through the front of the spine and into the disk space are well known to those skilled in the art. They vary in shape but possess similar characteristics with upper and lower surfaces conforming to a shape of vertebral endplates and a vertical design aiming to open or reconstruct the collapsed disk space. These implants are sufficiently porous or hollow to allow bone to grow through the implants and bridge two vertebras referred to as bone fusion. These implants perform well with vertical loading of the spine or in flexion. However, these implants are not able to restrict the movement between two vertebras when vertebras are pulled apart or are in extension and lateral bending. Further, these implants provide negligible restriction during sliding motion (translation) and rotation.

[0006] Devices that cut into or have protrusions directed into or through the endplate, are also known in the related art. These protrusions penetrate the endplate and potentially create channels for a bone growth, yet the protrusions do not alter structural properties of the endplate. The protrusions also reduce the risk of extrusion of the implant out of the disk space. These protrusions negligibly restrict translation or sliding motion but they do not restrict extension and lateral bending. This necessitates additional fixation (immobilization) usually consisting of posterior pedicle screws.

[0007] There would be a substantial benefit in an anterior fixation device which would on its own rigidly fixate the spine in all direction of motion.

[0008] A device for reconstruction, fixation and bone fusion through anterior approach to the human spine. This device enables rigid fixation in all planes of motion including extension of the spine, it possesses structural characteristics necessary to reconstruct and maintain disk height, it provides space for bone grafting material and produces a plurality of perforations through endplates above and below to enhance bony fusion.

[0009] In a first aspect, embodiments of the present invention provide a fixation device, the device includes a housing with a leading deep surface, a trailing outer surface, weight bearing sides, and top and bottom surfaces, a shaft running from the leading deep surface to the trailing outer surface of the housing, and a plurality of blades preloaded onto the shaft in the housing, at least one first blade having at least one cutting extension in a first orientation about the axis of the shaft and at least one second blade having at least one cutting extension in a second orientation about the axis of the shaft that is opposite to the first orientation, each cutting extension having a sharp leading edge, wherein upon clockwise or counterclockwise rotation of each blade of the plurality of blades about the axis of the shaft in a direction in which the at least one cutting extension of each blade is oriented, the at least one cutting extension of each blade will break an endplate of a vertebra, hook into the vertebra and rigidly secure the vertebra to the device to prevent separation of the vertebra from the device during spinal motion.

[0010] In many embodiments, the housing is configured in a shape of a box, a cylinder or other geometric shape including configurations with a height of the leading deep surface smaller than a height of the trailing outer surface, the shape conforming to a shape of a spinal disk space.

[0011] In many embodiments, the housing is expandable at least in part in vertical and horizontal directions.

[0012] In many embodiments, the housing comprises at least one material of metal, plastic, ceramic, graphite, coral or human bone products.

[0013] In many embodiments, the housing is absorbable.

[0014] In many embodiments, the housing is formed at least in part of a porous material.

[0015] In many embodiments, the shaft comprises a plurality of shafts that serve as axis of rotation to the plurality of blades, the at least one first blade and the at least second blade are preloaded on different shafts.

[0016] In many embodiments, each blade of the plurality of blades includes two opposing cutting extensions with sharp leading edges which hook into adjacent vertebrae to rigidly secure the adjacent vertebrae in relation to each other and to the device to prevent separation of the vertebrae from the device during spinal motion.

[0017] In many embodiments, the blades vary in size to accommodate the configuration of the housing.

[0018] In many embodiments, the blades alternate between the first orientation and the second orientation.

[0019] In many embodiments, the device further includes means for rotating each of the plurality of blades from a horizontal into a vertical orientation.

[0020] In many embodiments, the blades are rotated individually or as a group from within the housing while inside the disk space.

[0021] In many embodiments, the device further includes means for locking the plurality of blades in a final engaged position preventing dislodging from the vertebra

[0022] In many embodiments, the at least one blade of the plurality of blades includes a body having a shape configured to provide weight bearing support to the secured vertebra through at least one opening of the top and bottom surfaces.

[0023] In many embodiments, the shape of the body is an oval so that the disk space is expanded as the blade is rotated.

[0024] In many embodiments, the leading deep surface conforms to a posterior aspect of an intervertebral disk and the trailing outer surface conforms to an anterior surface of the intervertebral disk.

[0025] In many embodiments, the housing includes a plurality of openings enabling ingrowths of bone.

[0026] In many embodiments, the shaft runs perpendicular to the leading deep surface of the housing.

[0027] In many embodiments, the shaft runs from a center of the leading deep surface to a center of the trailing outer surface.

[0028] In another aspect, embodiments of the present invention provide a method of using a fixation device between two adjacent vertebrae, the method including providing a fixation device, the fixation device having a housing with a leading deep surface conforming to a posterior aspect of an intervertebral disk and trailing outer surface conforming to an anterior surface of the intervertebral disk, a shaft running from a center of the leading deep surface and perpendicular to the leading deep surface of the housing to the center of the trailing outer surface of the housing, and a plurality of blades preloaded onto the shaft in the housing, at least one first blade having at least one cutting extension in a first orientation about the axis of the shaft and at least one second blade having at least one cutting extension in a second orientation about the axis of the shaft that is opposite to the first orientation. The method further including inserting the fixation device between the adjacent vertebrae, rotating each blade of the plurality of blades about the axis of the shaft in a direction in which the at least one cutting extension of each blade is oriented, and breaking an endplate of each vertebra with the at least one cutting extension of each blade, hooking into the vertebra and rigidly securing the vertebra to the device to prevent separation of the vertebra from the device during spinal motion.

[0049] An implant device for reconstruction, fixation and bone fusion of bone vertebras through an anterior approach to the human spine. This implant device enables rigid fixation in all planes of motion including extension of the spine, it possesses structural characteristics necessary to reconstruct and maintain disk height, it provides space for bone grafting material and produces a plurality of perforations through endplates above and below to enhance bony fusion.

[0050] The implant device consists of the outer structure or shell which is designed to conform to the disk space, provide openings for bony ingrowths and maintain the disk height by providing adequate structural strength and sufficient weight bearing surface. The shell or housing contains a shaft (10) which runs through its central axis from the back (9) to the front (8) and is fixed to the shell (FIG. 7).

[0051] In the preferred embodiment the shell is impacted into the disk space (FIG. 14) using the shell introducer (FIG. 13). The shell introducer includes prongs (15) that fit inside the sides (5) of the shell but is open (16) in the center to allow for blades (FIG. 12).

[0052] Once the shell is placed in a correct position between vertebras (1), individual blades (FIG. 11) are selected, mounted onto the introducer (FIG. 15) and threaded onto the shaft (10) in horizontal orientation (FIG. 16). The blade is placed as deep as it can go and then rotated into vertical orientation breaking the endplate and hooking into the vertebra (1) (FIG. 17). Blades alternate between clockwise and counterclockwise orientation. Variable size blades can be selected to better approximate configuration of the disk space.

[0053] Once all the blades are engaged, a tightening nut is threaded onto the end (21) of the shaft (10) of FIG. 7.

[0054] In an alternative embodiment, alternating clockwise and counterclockwise blades (FIG. 18) are pre-loaded onto the shaft (10) and inside the housing (FIG. 19). The blades include a central opening (12) and control openings (19) on opposing sides of the central opening (12) to rotate the blade about the shaft (10). With the help of a blade rotating tool with prongs (20) engaging the control openings (19) (FIG. 20), the blades are rotated sequentially going from superficial to deep.

[0055] In another embodiment the housing expands horizontally and contains two shafts, which separate from each other upon expansion of the housing. In the initial collapsed configuration, preloaded clockwise and counterclockwise blades threaded on different shafts imbricate between each other. After the cage is expanded, blades are pulled apart.

[0056] In another embodiment, a body (14) of a blade is configured as an oval so that the disk space is expanded as a blade is rotated.