Patent Application
20080167686
This disclosure is generally directed to prostheses and methods of implanting the prostheses, and more particularly, to intervertebral spacers and methods of implanting the intervertebral spacers in intervertebral spaces.
Spinal discs between the endplates of adjacent vertebrae in a spinal column of the human body provide critical support. However, due to injury, degradation, disease or the like, these discs can rupture, degenerate and/or protrude to such a degree that the intervertebral space between adjacent vertebrae collapses as the disc loses at least a part of its support function. This can cause impingement of the nerve roots and severe pain. In some cases, surgical correction may be required.
Some surgical corrections include the removal of the natural spinal disc from between the adjacent vertebrae. In order to preserve the intervertebral disc space for proper spinal-column function, a rigid spacer can be inserted between the adjacent vertebrae.
Typically, conventional spinal spacers are implanted anteriorly between the adjacent vertebrae. Because anterior procedures often require displacement of organs, such as the aorta and vena cava, they must be performed with great care. Further, because scar tissue may grow about the surgical site, any required second treatment can be more difficult, and may introduce additional distress to the patient.
What is needed is an intervertebral spacer that is simple and allows posterior implantation. The intervertebral spacers disclosed herein address one or more deficiencies in the art.
In one exemplary aspect, this disclosure is directed to an intervertebral spacer including a non-rigid body having an upper beam member and a lower beam member. The upper beam member may include a lower inner surface and may include an upper outer surface configured to interface with a vertebral plate of an upper vertebra. The lower beam member may include an upper inner surface and may include a lower outer surface configured to interface with a vertebral plate of a lower vertebra. The upper inner surface of the lower beam member and the lower inner surface of the upper beam member may define an oval-shaped hollow portion.
In another exemplary aspect, this disclosure is directed to an intervertebral spacer including a non-rigid body having an upper beam member and a lower beam member. The upper beam member may include an arcing upper outer surface configured to interface with a vertebral plate of an upper vertebra. The lower beam member may include an arcing lower outer surface configured to interface with a vertebral plate of a lower vertebra. The body also may include a hollow portion between the upper and lower outer surfaces. The upper and lower beam members may connect in a manner such that the body can be compressed from a first height to a second smaller height.
In another exemplary aspect, this disclosure is directed to a method of surgically implanting an intervertebral spacer. The method may include accessing an intervertebral space defined by an upper vertebra and a lower vertebra. A non-rigid intervertebral spacer having a body with an upper beam member and a lower beam member may be introduced into the intervertebral space so that an arcing upper outer surface of the upper beam member interfaces with a vertebral plate of the upper vertebra, and so that an arcing lower outer surface of the lower beam member interfaces with a vertebral plate of the lower vertebra. The body may be compressed from a first height to a second smaller height.
This disclosure relates generally to an implantable non-rigid intervertebral spacer. For the purposes of promoting an understanding of the principles of the intervertebral spacer, reference will now be made to embodiments or examples illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the described embodiments and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which this disclosure relates.
The non-rigid intervertebral spacers disclosed herein may be implanted to maintain a height of a vertebral space and support adjacent vertebral bodies while allowing spinal motion. Compressing or flexing the spacers from a greater height to a lower height during implantation may minimize the required size of the surgical access site. Once implanted, the spacer height may elastically or mechanically increase to maintain the vertebral space and support the vertebrae. In the vertebral space, the spacer may provide, in some embodiments, axial compression and shock absorption via deformation under load. Its shape may allow spinal flexion motion and extension motion through rocking motion, while also allowing some lateral bending motion by compressing the spacer on a bending side. Its shape also may match the concave curvature of the adjacent vertebral plates and in some embodiments, the vertebral plates slide and rock over the spacer.
A joint comprises two adjacent vertebrae separated by an intervertebral disc.
The spacer 100 is illustrated in greater detail in
In
The spacer 100 may be formed of any suitable biocompatible material, including, for example, metals such as cobalt-chromium alloys, titanium alloys, nickel titanium alloys, and/or stainless steel alloys. Some embodiments of the spacer 100 are formed of any member of the polyaryletherketone (PAEK) family such as polyetheretherketone (PEEK), carbon-reinforced PEEK, or polyetherketoneketone (PEKK); polysulfone; polyetherimide; polyimide; ultra-high molecular weight polyethylene (UHMWPE); and/or cross-linked UHMWPE, among others. In the embodiment shown, the spacer 100 is integrally formed of a single material. Yet in other embodiments, multiple materials may be used. For example, the upper beam member 108 may be formed of a first material and the lower beam member 110 may be formed of a second different material. In such embodiments, some elements of the spacer 100 may be formed of a non-rigid material while other elements of the spacer 100 are formed of a rigid material, such as a rigid metal.
The outer surfaces 112, 114 may include features or coatings which enhance the fixation of the spacer 100 to the vertebral endplates of the vertebrae 14, 16. For example, the surfaces 112, 114 may be roughened such as by chemical etching, bead-blasting, sanding, grinding, serrating, and/or diamond-cutting. All or a portion of the outer surfaces 112, 114 may also be coated with a biocompatible and osteoconductive material such as hydroxyapatite (HA), tricalcium phosphate (TCP), and/or calcium carbonate to promote bone in growth and fixation. Alternatively, osteoinductive coatings, such as proteins from transforming growth factor (TGF) beta superfamily, or bone-morphogenic proteins, such as BMP2 or BMP7, may be used. Other suitable features may include spikes, ridges, and/or other surface textures and features.
Under normal spinal loads applied at the upper and lower outer surfaces 112, 114, the body 102 may appear as shown in
In addition, the flexibility of the spacer 100 may provide support during spinal flexion and extension, where the direction of applied loads may further depart from straight axial loads. This flexibility may allow the spinal flexion and extension motion. Also, the flexibility of the spacer 100 may allow less invasive implantation techniques to be used. For example, the spacer 100 may be introduced posteriorally or laterally in the lower second height H2, and then once in the vertebral space, expanded or released to elastically or mechanically return to its greater first height H1.
The spacer 100 also includes a width W1 (shown in
The support members 144, 174 affect the flexibility and compressive properties of the respective spacers 130, 160. Their shape may provide symmetric or non-symmetric compressive characteristics. These compressive characteristics may at least partially determine how the spacers respond under load, in flexion and extension, and in lateral bending. It should be noted that although the support member 144 is a wavy or sinusoidal shape and the support member 174 is an X-shape, support members may be in any shape that provides support to the spacer under load and affects its compressive characteristics. For example, other support members may be shaped in a straight line, as a Y-shape, or other shape. In some embodiments, the spacers include more than one support member within the hollow portions, independent from each other. For example, the spacers may include two support members that form a V-shape or that don't contact to each other at all. Other shapes also are contemplated.
In some embodiments, the cutout 234 is symmetrically centered about the longitudinal centerline 236, while in others it is offset toward one side of the centerline 236. In these embodiments, the rigidity or flexibility of the spacer is offset, providing more support along one side of the spacer than the other. Additional embodiments include a first cut-out, such as at one end, sized differently than a second cut-out, such as at the other end or alternatively, a cutout at one end without a cutout at the other end. Other embodiments include multiple cutouts located at the ends or in some alternative embodiments, along the beam members. In yet other embodiments, the cutouts are formed not at the ends 230, but are formed elsewhere in the beam members 226, 228. Other variations also are contemplated.
It should be noted that the spacer's flexibility and rigidity also may be controlled using the structure of the body. For example, some regions of the body, such as the ends, may be formed to have a cross-sectional thickness different than at other regions, such as the central areas of the beam members. Other embodiments have a greater cross-sectional thickness at the beam members than at the ends. Still other arrangements are contemplated. The varying thickness can be used to provide desired rigidity characteristics, such as flexibility and spring rate.
In this embodiment, the flat interfacing surface 258 includes bone engaging features 264 formed thereon. Here the bone engaging features 264 include a knurled surface formed of multiple protuberances. In other embodiments, spikes, protrusions, angled ridges, or other surface features make up the bone engaging features.
In some embodiments, the support member 326 may be as described above, while in other embodiments the support member 326 is an extending and retracting actuator that operates to change the length and/or height of the intervertebral spacer 310. For example, one embodiment of the support member 326 is an actuatable displacement element, as described in co-pending U.S. patent application Ser. No. ______, titled Active Vertebral Prosthetic Device, having the same filing date as the present application, and listing at least one common inventor (Attorney Docket No. P26217/31132.587), incorporated herein in its entirety by reference. Accordingly, the support member in some embodiments may be a piezoelectric actuator or an artificial muscle comprised of electroactive polymers (EAP) that actuates in response to electrical current. In other embodiments, the support member may be formed of ionic polymer-metal composites (IPMC) that actuate by voltage switching. In yet other embodiments, the support member is formed of a traveling wave actuator. In yet other embodiments, the support member may be hydraulically or pneumatically actuated. Still other embodiments include screws, ratchet means or other mechanical for changing the length and/or height. Electrical, thermal, and chemical actuators that change the length and/or height of the spacer 310 also are contemplated.
Actuation of the support member 326 causes deformation of the upper and lower beam members 318, 320, which affects rigidity and flexibility of the body 314. Accordingly, by actuating the support member 326, the properties of the non-rigid spacer 310 may be changed. For example, actuating the support member 326 increases or decreases the length of the body 314. If the body length decreases, the height increases. Likewise, if the body length increases, the height decreases.
The connecting element 316 extends between and connects the bodies 312, 314. Thus, the spacer 310 may provide relatively stable support to the adjacent vertebral bodies by connecting the bodies 312, 314 and increasing the size of the spacer footprint. The connecting element 316 may be formed of any material, either rigid or non-rigid, and in the embodiments shown, extends from the support members of each body 312, 314. In other embodiments, the connecting element 316 may extend from the beam members of one body to the beam members of the other body.
Although described with two bodies and one connecting element, the spacers may include additional bodies and connecting elements. For example, in some embodiments, the spacer includes three bodies placed so that their respective longitudinal axes form a rectangular shape. These bodies may or may not be attached to each other by connecting elements. In one exemplary embodiment, each of the three bodies is connected by connecting elements at ends to form the triangular shape. Other arrangements are contemplated.
The spacers may be implanted between the vertebrae 14, 16 using any common approach, including an anterior approach, a posterior approach, a posterior transforaminal approach, a far lateral approach, a direct lateral approach, among others. According to at least one of these approaches, an incision may be made in the patient to access the vertebrae and some or all of the affected disc and surrounding tissue may be removed. The superior endplate surface of the vertebra 14 may be milled, rasped, or otherwise resected to match the profile of the spacer to normalize stress distributions on the superior endplate surface of the vertebra 14 and/or to provide initial fixation prior to bone ingrowth. The preparation of the endplate of vertebra 14 may result in a flattened surface or in surface contours such as pockets, grooves, or other contours that may match corresponding features on the spacers. The inferior endplate of the vertebra 16 may be similarly prepared.
The spacer may then be introduced into the disc space. In some embodiments, the spacer is introduced through a cannula in a compressed condition, thereby minimizing the height of the spacer during insertion through the incision and during introduction to the disc space. Once in place, the spacer may be allowed or actuated to return to its uncompressed condition having a greater height, as limited by the adjacent bone structure. It should be noted that one or more spacers can be placed within the disc space. For example, some procedures may call for implanting a single spacer when using a lateral approach and two spacers when using a bilateral posterior approach. In any implantation, the spacers or their bodies may or may not be connected.
In some embodiments, having more than one body, such as in the embodiments disclosed in
When implanting spacers having an actuatable support member, the rigidity of the spacer may be controlled by actuating the support before or after implantation into the disc space. In some embodiments, the actuation may occur post-operatively while in other embodiments, the actuation occurs as a part of the surgical procedure. The actuation may be accomplished percutanteously using non-invasive procedures, such as RF wireless remote control systems. Alternatively, the actuation may be accomplished using wired remote control or alternatively, direct access during the surgical procedure, such as when hydraulically actuating with a syringe.
In some procedures, an operating physician may desire to fuse the spacer in place. In such circumstances, the physician may pack the spacer with bone growth promoting substances. For example, during the surgery, the hollow portion of a spacer body may be packed with bone graft material, tissue, or other osteogenic materials that promote bone growth. In other examples, the area between connectors of a connecting element, such as the connecting element 346 in
Any of the features described with respect to one spacer embodiment may be used with any of the other spacer embodiments. For example and without limitation, the connecting member may be used with any of the spacer embodiments. In addition, although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. Accordingly, all such modifications and alternative are intended to be included within the scope of the invention as defined in the following claims. Those skilled in the art should also realize that such modifications and equivalent constructions or methods do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. It is understood that all spatial references, such as “horizontal,” “vertical,” “top,” “upper,” “lower,” “bottom,” “left,” “right,” “cephalad,” “caudal,” “upper,” and “lower,” are for illustrative purposes only and can be varied within the scope of the disclosure. In the claims, means-plus-function clauses are intended to cover the elements described herein as performing the recited function and not only structural equivalents, but also equivalent elements.
