US 20070073406 A1
An artificial functional spinal unit is provided comprising, generally, an expandable artificial intervertebral implant that can be placed via a posterior surgical approach and used in conjunction with one or more artificial facet joints to provide an anatomically correct range of motion. Expandable artificial intervertebral implants in both lordotic and non-lordotic designs are disclosed, as well as lordotic and non-lordotic expandable cages for both PLIF (posterior lumber interbody fusion) and TLIF (transforaminal lumbar interbody fusion) procedures. The expandable implants may have various shapes, such as round, square, rectangular, banana-shaped, kidney-shaped, or other similar shapes. By virtue of their posteriorly implanted approach, the disclosed artificial FSU's allow for posterior decompression of the neural elements, reconstruction of all or part of the natural functional spinal unit, restoration and maintenance of lordosis, maintenance of motion, and restoration and maintenance of disc space height.
107. A spinal implant assembly comprising:
at least one intervertebral implant comprising:
a lower body having an inferior surface and a superior surface, the superior surface having an upwardly projecting wall forming a channel thereupon, the wall having an opening defined therethrough;
an upper body located above the lower body, the upper body having a superior surface and a substantially concave inferior surface;
a joint insert having an inferior surface and a substantially convex superior surface, the joint insert residing within the channel on the lower body; and
an expansion device capable of being inserted through the opening in the wall on the lower body such that, upon insertion of the expansion device, the joint insert is lifted above the channel causing the insert to articulate with the substantially concave inferior surface of the upper body; and
at least one artificial facet joint.
108. The spinal implant assembly of
an upper multi-axial pedicle screw having a non-locking head with a hole defined therethrough;
a lower multi-axial pedicle screw having a non-locking head with a hole defined therethrough; and
a rod having a central rod portion and two washer-type heads on each end of the central rod portion, the central rod portion slidingly positioned through the hole in the non-locking head of the upper multi-axial pedicle screw and the lower multi-axial pedicle screw such that the heads of the upper and lower multi-axial pedicle screws slide freely along the central rod portion.
109. The spinal implant assembly of
an upper pedicle screw having a lockable head with a hole defined therethrough;
a lower multi-axial pedicle screw having a non-locking head with a hole defined therethrough; and
a rod having a central rod portion, an upper end and a lower end, the lower end having a washer-type head, the central rod portion slidingly positioned through the hole in the non-locking head of the lower multi-axial pedicle screw such that the washer-type lower head prohibits dislocation of the lower multi-axial pedicle screw from the central rod portion, and the upper end of the rod slidingly positioned through the hole in the lockable head of the upper pedicle screw such that, upon locking of the lockable head, rotational and translational motion of the upper end of the rod is prohibited.
110. The spinal implant assembly of
an upper pedicle screw having a lockable head with a hole defined therethrough;
a lower pedicle screw having a lockable head with a hole defined therethrough; and
a rod having an upper end, a lower end and a central ball joint connecting the upper and lower end that permits the rod to bend, the upper end of the rod slidingly positioned within the hole of the head of the upper pedicle screw, the lower end of the rod slidingly positioned within the hole of the lower pedicle screw, the lockable heads of the upper and lower pedicle screw being locked such that rotational and translational motion of the rod is prohibited.
111. The spinal implant assembly of
112. The spinal implant assembly of
113. The spinal implant assembly of
114. The spinal implant assembly of
115. The spinal implant assembly of
116. An artificial functional spinal unit, comprising:
at least one intervertebral implant, wherein at least one intervertebral implant comprises a lower body configured to couple to a first human vertebra and an upper body configured to couple to a second human vertebra, and wherein the upper body is moveable relative to the lower body to accommodate at least flexion of the first human vertebra relative to the second human vertebra; and
at least one artificial facet joint configured to couple to the first human vertebra and the second human vertebra.
117. The artificial functional spinal unit of
a first pedicle screw;
a second pedicle screw; and
a rod configured to couple to the first pedicle screw and the second pedicle screw such that a head of the first pedicle screw and a head of the second screw are able to slide relative to the rod after installation of the artificial facet joint.
118. The artificial functional spinal unit of
a first pedicle screw;
a second pedicle screw; and
a rod configured to couple to the first pedicle screw and the second pedicle screw such that the rod is secured to a head of the first pedicle screw, and the rod is able to slide relative to a head of the second pedicle screw after installation of the artificial facet joint.
119. The artificial functional spinal unit of
a first pedicle screw;
a second pedicle screw;
a rod configured to couple to the first pedicle screw and the second pedicle screw,
wherein the rod includes a ball joint that allows the rod to bend, and wherein the rod is secured to a head of the first pedicle screw and to a head of the second pedicle screw during installation of the artificial facet joint.
120. The artificial functional spinal unit of
121. The artificial functional spinal unit of
122. The artificial functional spinal unit of
123. A method of forming an artificial functional spinal unit, comprising:
placing one or more intervertebral implants between a first human vertebra and a second human vertebra, wherein at least one intervertebral implant is configured to accommodate flexion of the first human vertebra relative to the second human vertebra; and
securing at least one artificial facet joint to the first human vertebra and the second human vertebra.
124. The method of
125. The method of
126. The method of
This application is a continuation of U.S. patent application Ser. No. 10/634,950 entitled “ARTIFICIAL FUNCTIONAL SPINAL UNIT ASSEMBLIES” filed on Aug. 5, 2003, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to functional spinal implant assemblies for insertion into the intervertebral space between adjacent vertebral bones and reconstruction of the posterior elements to provide stability, flexibility and proper biomechanical motion. More specifically, the present invention relates to artificial functional spinal units comprising an expandable artificial intervertebral implant that can be inserted via a posterior surgical approach and used in conjunction with one or more artificial facet joints to provide a more anatomically correct range of motion.
2. Description of Related Art
The human spine is a complex mechanical structure composed of alternating bony vertebrae and fibrocartilaginous discs that are connected by strong ligaments and supported by musculature that extends from the skull to the pelvis and provides axial support to the body. The intervertebral discs primarily serve as a mechanical cushion between adjacent vertebral segments of the spinal column and generally comprise three basic components: the nucleus pulposus, the anulus fibrosis, and two vertebral end plates. The end plates are made of thin cartilage overlying a thin layer of hard cortical bone that attaches to the spongy, cancellous bone of the vertebral body. The anulus fibrosis forms the disc's perimeter and is a tough outer ring that binds adjacent vertebrae together. The vertebrae generally comprise a vertebral foramen bounded by the anterior vertebral body and the neural arch, which consists of two pedicles and two larninae that are united posteriorly. The spinous and transverse processes protrude from the neural arch. The superior and inferior articular facets lie at the root of the transverse process. The term “functional spinal unit” (“FSU”) refers to the entire motion segment: the anterior disc and the posterior facet joints, along with the supporting ligaments and connective tissues.
The spine as a whole is a highly flexible structure capable of a high degree of curvature and twist in nearly every direction. However, genetic or developmental irregularities, trauma, chronic stress, and degenerative wear can result in spinal pathologies for which surgical intervention may be necessary.
It is common practice to remove a spinal disc in cases of spinal disc deterioration, disease or spinal injury. The discs sometimes become diseased or damaged such that the intervertebral separation is reduced. Such events cause the height of the disc nucleus to decrease, which in turn causes the anulus to buckle in areas where the laminated plies are loosely bonded. As the overlapping laminated plies of the anulus begin to buckle and separate, either circumferential or radial anular tears may occur. Such disruption to the natural intervertebral separation produces pain, which can be alleviated by removal of the disc and maintenance of the natural separation distance. In cases of chronic back pain resulting from a degenerated or herniated disc, removal of the disc becomes medically necessary.
In some cases, the damaged disc may be replaced with a disc prosthesis intended to duplicate the function of the natural spinal disc. U.S. Pat. No. 4,863,477 discloses a resilient spinal disc prosthesis intended to replace the resiliency of a natural human spinal disc. U.S. Pat. No. 5,192,326 teaches a prosthetic nucleus for replacing just the nucleus portion of a human spinal disc.
In other cases it is desired to fuse the adjacent vertebrae together after removal of the disc, sometimes referred to as “intervertebral fusion” or “interbody fusion.”
Many techniques and instruments have been devised to perform intervertebral fusion. There is common agreement that the strongest intervertebral fusion is the interbody (between the lumbar bodies) fusion, which may be augmented by a posterior or facet fusion. In cases of intervertebral fusion, either structural bone or an interbody fusion cage filled with morselized bone is placed centrally within the space where the spinal disc once resided. Multiple cages or bony grafts may be used within that space.
Such practices are characterized by certain disadvantages, most important of which is the actual morbidity of the procedure itself. Placement of rigid cages or structural grafts in the interbody space either requires an anterior surgical approach, which carries certain unavoidable risks to the viscous structures overlying the spine (intestines, major blood vessels, and the ureter), or they may be accomplished from a posterior surgical approach, thereby requiring significant traction on the overlying nerve roots. The interval between the exiting and traversing nerve roots is limited to a few millimeters and does not allow for safe passage of large intervertebral devices, as may be accomplished from the anterior approach. Alternatively, the anterior approach does not allow for inspection of the nerve roots, is not suitable alone for cases in which the posterior elements are not competent, and most importantly, the anterior approach is associated with very high morbidity and risk where there has been previous anterior surgery.
Another significant drawback to fusion surgery in general is that adjacent vertebral segments show accelerated deterioration after a successful fusion has been performed at any level. The spine is by definition stiffer after the fusion procedure, and the natural body mechanics place increased stress on levels proximal to the fused segment. Other drawbacks include the possibility of “flat back syndrome” in which there is a disruption in the natural curvature of the spine. The vertebrae in the lower lumbar region of the spine reside in an arch referred as having a sagittal alignment. The sagittal alignment is compromised when adjacent vertebral bodies that were once angled toward each other on their posterior side become fused in a different, less angled orientation relative to one another. Finally, there is always the risk that the fusion attempt may fail, leading to pseudoarthrosis, an often painful condition that may lead to device failure and further surgery.
Conventional interbody fusion cages generally comprise a tubular metal body having an external surface threading. They are inserted transverse to the axis of the spine, into preformed cylindrical holes at the junction of adjacent vertebral bodies. Two cages are generally inserted side by side with the external threading tapping into the lower surface of the vertebral bone above, and the upper surface of the vertebral bone below. The cages include holes through which the adjacent bones are to grow. Additional materials, for example autogenous bone graft materials, may be inserted into the hollow interior of the cage to incite or accelerate the growth of the bone into the cage. End caps are often utilized to hold the bone graft material within the cage.
These cages of the prior art have enjoyed medical success in promoting fusion and grossly approximating proper disc height. As previously discussed, however, cages that would be placed from the safer posterior route would be limited in size by the interval between the nerve roots. It would therefore, be a considerable advance in the art to provide a fusion implant assembly which could be expanded from within the intervertebral space, thereby minimizing potential trauma to the nerve roots and yet still providing the ability to restore disc space height.
Ultimately though, it is important to note that the fusion of the adjacent bones is an incomplete solution to the underlying pathology as it does not cure the ailment, but rather simply masks the pathology under a stabilizing bridge of bone. This bone fusion limits the overall flexibility of the spinal column and artificially constrains the normal motion of the patient. This constraint can cause collateral injury to the patient's spine as additional stresses of motion, normally bone by the now-fused joint, are transferred onto the nearby facet joints and intervertebral discs. Thus, it would be an even greater advance in the art to provide an implant assembly that does not promote fusion, but instead closely mimics the biomechanical action of the natural disc cartilage, thereby permitting continued normal motion and stress distribution.
Accordingly, an artificial functional spinal unit (FSU) is provided comprising, generally, an expandable artificial intervertebral implant that can be placed via a posterior surgical approach and used in conjunction with one or more artificial facet joints to provide an anatomically correct range of motion. Expandable artificial intervertebral implants in both lordotic and non-lordotic designs are disclosed, as well as lordotic and non-lordotic expandable cages for both PLIF (posterior lumber interbody fusion) and TLIF (transforaminal lumbar interbody fusion) procedures. The expandable implants may have various shapes, such as round, square, rectangular, banana-shaped, kidney-shaped, or other similar shapes. By virtue of their posteriorly implanted approach, the disclosed artificial FSU's allow for posterior decompression of the neural elements, reconstruction of all or part of the natural functional spinal unit, restoration and maintenance of lordosis, maintenance of motion, and restoration and maintenance of disc space height.
The posterior implantation of an interbody device provides critical benefits over other anterior implanted devices. Placement of posterior devices that maintain mobility in the spine have been limited due to the relatively small opening that can be afforded posteriorly between the exiting and transversing nerve roots. Additionally, placement of posterior interbody devices requires the removal of one or both facet joints, further destabilizing the spine. Thus conventional posteriorly placed interbody devices have been generally limited to interbody fusion devices.
Since a properly functioning natural FSU relies on intact posterior elements (facet joints) and since it is necessary to remove these elements to place a posterior interbody device, a two-step procedure is disclosed that allows for placement of an expandable intervertebral implant and replacement of one or both facets that are necessarily removed during the surgical procedure. The expansile nature of the disclosed devices allow for restoration of disc height once inside the vertebral interspace. The expandable devices are collapsed prior to placement and then expanded once properly inserted in the intervertebral space. During the process of expansion, the endplates of the natural intervertebral disc, which essentially remain intact after removal or partial removal of the remaining natural disc elements, are compressed against the device, which thereby facilitates bony end growth onto the surface of the artificial implant. Once the interbody device is in place and expanded, the posterior element is reconstructed with the disclosed pedicle screw and rod system, which can also be used to distract the disk space while inserting the artificial implant. Once the interbody device is in place and expanded, the posterior element is further compressed, again promoting bony end growth into the artificial implant. This posterior compression allows for anterior flexion but replaces the limiting element of the facet and interspinous ligament and thereby limits flexion to some degree, and in doing so maintains stability for the anteriorly located interbody device.
The posterior approach avoids the potential risks and morbidity of the anterior approach, which requires mobilization of the vascular structures, the ureter, and exposes the bowels to risk. Also, the anterior approach does not offer the surgeon an opportunity to view the posterior neural elements and thereby does not afford an opportunity for decompression of those elements. Once an anterior exposure had been utilized a revision procedure is quite risky and carries significant morbidity.
The artificial FSU generally comprises an expandable intervertebral implant and one or more artificial facet joints. The expandable intervertebral implant generally comprises a pair of spaced apart plate members, each with a vertebral body contact surface. The general shape of the plate members may be round, square, rectangular, banana shaped, kidney shaped, or some other similar shape, depending on the desired vertebral implantation site. Because the artificial intervertebral implant is to be positioned between the facing surfaces of adjacent vertebral bodies, the plate members are arranged in a substantially parallel planar alignment (or slightly offset relative to one another in accordance with proper lordotic angulation) with the vertebral body contact surfaces facing away from one another. The plate members are to mate with the vertebral bodies so as to not rotate relative thereto, but rather to permit the spinal segments to axially compress and bend relative to one another in manners that mimic the natural motion of the spinal segment. This natural motion is permitted by the performance of an expandable joint insert, which is disposed between the plate members. The securing of the plate members to the vertebral bone is achieved through the use of a osteoconductive scaffolding machined into the exterior surface of each plate member. Alternatively, a mesh of osteoconductive surface may be secured to the exterior surface of the plate members by methods known in the art. The osteoconductive scaffolding provides a surface through which bone may ultimately grow. If an osteoconductive mesh is employed, it may be constructed of any biocompatible material, both metal and non-metal. Each plate member may also comprise a porous coating (which may be a sprayed deposition layer, or an adhesive applied beaded metal layer, or other suitable porous coatings known in the art, i.e. hydroxy appetite). The porous coating permits the long-term ingrowth of vertebral bone into the plate member, thus permanently securing the prosthesis within the intervertebral space.
In more detail, the expandable artificial implant of the present invention comprises four parts: an upper body, a lower body, an expandable joint insert that fits into the lower body, and an expansion device, which may be an expansion plate, screw, or other similar device. The upper body generally comprises a substantially concave inferior surface and a substantially planar superior surface. The substantially planar superior surface of the upper body may have some degree of convexity to promote the joining of the upper body to the intact endplates of the natural intervertebral disc upon compression. The lower body generally comprises a recessed channel, having a rectangular cross section, which extends along the superior surface of the lower body in the medial-lateral direction and substantially conforms to the shape of the upper and lower bodies. The lower body further comprises a substantially planar inferior surface that may have some degree of convexity to promote the joining of the lower body to the intact endplates of the natural intervertebral disc upon compression. The expandable joint insert resides within the channel on the superior surface of the lower body. The expandable joint insert has a generally flat inferior surface and a substantially convex superior surface that articulates with the substantially concave inferior surface of the upper body. Prior to expansion of the artificial implant, the generally flat inferior surface of the expandable joint insert rests on the bottom surface of the channel. The expandable joint insert is raised above the bottom of the channel by means of an expansion screw, an expansion plate, or other similar device, that is inserted through an expansion hole or slot. The expansion hole or slot is disposed through the wall of the lower body formed by the channel. The expansion hole or slot gives access to the lower surface of the channel and is positioned such that the expansion device can be inserted into the expansion hole or slot via a posterior surgical approach. As the expansion device is inserted through the expansion slot, into the channel, and under the expandable joint insert, the expandable joint insert is raised above the floor of the channel and lifts the upper body above the lower body to the desired disc height. The distance from the inferior surface of the lower body and the superior surface of the upper body should be equal to the ideal distraction height of the disk space. As the artificial implant is flexed and extended, the convex superior surface of the expandable joint insert articulates with the concave inferior surface of the upper body.
After the insertion and expansion of the expandable intervertebral implant, the posterior facet joints may be reconstructed by employing the disclosed artificial facet joints. One embodiment of the artificial facet joint generally comprises a lower and upper multi-axial pedicle screw joined by a rod bridging the vertebral bodies above and below the artificial implant. The rod comprises a washer-type head at its lower (caudad) end. The rod fits into the heads of the pedicle screws and a top loaded set screw is placed in the pedicle screw heads. The disclosed pedicle screw system may employ different types of pedicle screws so that the top loaded set screw may or may not lock down on the rod depending on surgeon preference. If a non-locking pedicle screw is used the caudad end remains fully multi-axial. The upper (cephalad) end of the rod is held within the head of the upper pedicle screw with a set screw which locks down on the rod and eliminates any rod movement at the cephalad end, which by nature has limited multi-axial function. In an alternative embodiment of an artificial facet joint, the rod may comprise washer-type heads on both ends (caudad and cephalad) so that both pedicle screws can be of the non-locking variety. In the event of a two level surgical procedure, three pedicle screws would be employed with a single rod, which would have washer-type heads at both ends. The middle pedicle screw would be a locking-type and the upper most and lower most pedicle screws would be of the non-locking variety.
In addition, another embodiment of the artificial facet joint is disclosed that generally comprises two locked pedicle screws joined by a rod having a ball and socket joint centrally located on the rod between the two pedicle screws. The locking of the pedicle screws prevents the screw head from swiveling, but allows rotation and translation of the rod.
In instances where a fusion procedure is unavoidable, a PLIF and TLIF cage are disclosed that utilize the expansion principal of the functional artificial intervertebral implant. The cage generally comprises three parts: An external body, an internal body, and an expansion device. The external and internal bodies will have substantially the same shape and will be shaped accordingly to the procedures for which they will be used, more specifically, a rectangular cage is employed for a PLIF procedure and round or banana shaped cage is employed for the TLIF procedure. Both the external and internal bodies comprise a mesh structure in which an osteoconductive substance can be placed (i.e., morsilized autograph or an osteobiologic substitute). The external body of the cage contains an internal void space that houses the internal body. The external body further comprises an expansion window on its superior surface through which the internal body is raised upon expansion of the cage. The internal body comprises a planar plate member that is slightly larger than the expansion window in the superior surface of the external body such that when the cage is expanded the planar plate member secures itself against the interior side of the expansion window, thereby interlocking the external and internal bodies and eliminating mobility between the two bodies. Similar to the functional expandable implant, an expansion device is placed through an expansion slot. The expansion device lifts the internal body relative to the external body, interlocking the planar plate member of the internal body against the interior of the expansion window, and pushing the mesh structure of the internal body through the expansion window and above the superior surface of the external body. Varying the height of the expansion device and the dimensions of the external and internal bodies allows for various distraction heights to regain disc space. As with the functional intervertebral implant, the PLIF and TLIF cages may take the form of either an expandable lordotic cage or a non-lordotic cage.
Advantages of the present invention will become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings in which:
While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
The expandable artificial intervertebral implant 10 generally comprises an upper body 12 and a lower body 14 in a substantially parallel planar configuration. The superior surface 2 of the upper body 12 and the inferior surface 4 of the lower body 14 comprise a machined osteoconductive scaffolding 13 through which the bone may ultimately grow. Osteoconductive scaffolding 13 may also include spines or barbs that project into and secure against the bony endplates of the adjacent bony vertebral bodies upon expansion of the joint and minimize the possibility of sublaxation and/or dislocation. The upper body 12 has a substantially concave inferior surface 16. The lower body 14 has a channel 15 in superior surface 17. Channel 15 has a rectangular cross-section that extends along the lower body 14 in the medial-lateral direction and substantially conforms to the shape of the upper 12 and lower 14 bodies. An expandable joint insert 19 resides within the channel 15 on the lower body. The expandable joint insert 19 has a generally flat inferior surface 20 and a substantially convex superior surface 21 that articulates with the substantially concave inferior surface 16 of the upper body 12. The expandable joint insert 19 is lifted from the bottom of channel 15 by means of an expansion screw 21, or other device, that is inserted between the generally flat inferior surface 20 of the expandable joint insert 19 and the bottom of the channel 15 extending along the lower body 14 through an expansion slot 18. A void space is created between the expandable joint insert 19 and the floor of the channel 15 in cross sections not including the expansion device. A securing means, such as the cables 25, may be employed to ensure the upper body 12 and the lower body 14 remain intact during flexion and extension of the FSU. Alternative means for securing the upper body 12 and lower body 14 may also be employed, such as retaining pegs, torsion springs, or similar devices.
The disclosed techniques of expanding an artificial implant by inserting an expansion plate or similar device may also be employed to expand a PLIF or TLIF cage. As shown in
One embodiment of an artificial facet joint 100 is shown in
Another embodiment of an artificial facet joint 110 is shown in
Another embodiment of an artificial facet joint 200 is shown in
The lower hinged body 414 comprises a lower portion 420 and an upper portion 430. Lower portion 420 and upper portion 430 are posteriorly hinged via hinge 440. Hinge 440 effectively fixes the posterior disk height 460 (shown in
Upper body 412 has a substantially concave inferior surface 416 that articulates with the substantially convex superior surface 432 of upper portion 430 of lower hinged body 414. When viewed in the medial or lateral direction, as shown in
The rotational lifting mechanism described above may also be employed to achieve proper lordosis with an expandable PLIF and TLIF cage, as shown in
Another embodiment of an expandable lordotic artificial intervertebral implant is illustrated in
Although the present invention has been described in terms of specific embodiments, it is anticipated that alterations and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all alterations and modifications that fall within the true spirit and scope of the invention.