Apparatus for anterior intervertebral spinal fixation and fusion

[0001] This invention relates to a spinal fusion device. More specifically, the present invention relates to an implant and fixation device used to reconstruct a spinal disk space and facilitate fusion across the spinal disk space.

[0002] 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 weigh-bearing fibrous structure with a non-compressible viscous center. The spinal disk articulates with a bony vertebra above and below through a large surface area circular interface known as an endplate (FIG. 1). The endplate is a thin (1-3 mm) approximately round 2-4 cm in diameter plate of dense bone and cartilage accounting for majority of the vertebral weight-bearing capacity (FIG. 2).

[0003] 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 allow for growth of 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] A device utilized in reconstruction and fusion of a human spine providing direct rigid fixation of an anterior spinal column in flexion, extension and rotation. The device includes a housing with a leading deep surface conforming to a posterior aspect of an intervertebral disk and a trailing outer surface conforming to an anterior surface of the intervertebral disk, weight bearing sides and top and bottom surfaces with a plurality of openings enabling ingrowths of bone. The device further includes 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, the shaft being affixed at least to the leading deep surface of the housing. The device also includes at least one flat metal member threaded onto the shaft with a sharp leading edge which upon clockwise or counterclockwise rotation about the axis of the shaft will break an endplate, hook into a vertebra and rigidly secure the vertebra to the entire device preventing separation of the vertebra from the device during spinal motion.

[0028] 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.

[0029] 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, which runs through its central axis from the back to the front and is fixed to the shell at its back (FIG. 7).

[0030] In the preferred embodiment the shell is impacted into the disk space (FIG. 14) using the shell introducer (FIG. 13). The shell introducer fits tightly to the sides of the shell but is open in the center to allow for blades (FIG. 12).

[0031] Once the shell is placed in a correct position, individual blades (FIG. 11) are selected, mounted onto the introducer (FIG. 15) and threaded onto the shaft 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 (FIG. 17). The blades alternate between clockwise and counterclockwise orientation. Variable size blades can be selected to better approximate the configuration of the disk space.

[0032] Once all the blades are engaged, a tightening nut is threaded onto the end of the shaft of FIG. 7.

[0033] In an alternative embodiment alternating clockwise and counterclockwise blades (FIG. 18) are pre-loaded onto the shaft and inside the housing (FIG. 19). With the help of an introducer (FIG. 20) the blades are rotated sequentially going from the superficial to the deep.

[0034] 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, pre-loaded clockwise and counterclockwise blades threaded on different shafts imbricate between each other. After the cage is expanded, blades are pulled apart.

[0035] In another embodiment body of the blade is configured as an oval (FIGS. 8, 9, 11, 17) so that the disk space is expanded as a blade is rotated FIG. 17.