CN100577123C - Intervertebral disc implant - Google Patents

Abstract

The invention relates to an artificial intervertebral disc for placement between adjacent vertebrae. The artificial intervertebral disc is preferably designed to restore disc height and lordosis, allow for a natural range of motion, absorb shock and provide resistance to motion and axial compression. Furthermore, the intervertebral disc (10) may be used in the cervical, the thoracic, or the lumbar regions of the spine. The artificial intervertebral disc may include either singularly or in combination: an interior (19) at least partially filled with a fluid (22); a valve (20) for injecting fluid into the interior of the disk; a central region having a stiffness that is preferably greater than the stiffness of the cuter regions thus enabling the disc to pivot about the central region. The central pivot may be formed by a center opening (108), a central chamber (162), an inner core or a central cable (258).

Description

Intervertebral disc implant

field of invention

The present invention relates to devices and methods for treating trauma and disease of the spine. More specifically, the present invention relates to intervertebral disc substitutes.

Background of the invention

A variety of conditions such as spondylolisthesis, herniated discs, spinal nerve root compression, degenerative disc disease, and trauma are known to cause severe discomfort and require medical attention. One of the current therapies used to alleviate these conditions is spinal fusion, such as intervertebral and posterolateral fusion or arthrodesis. In these treatments, two adjacent vertebrae are fused together. The infected disc is removed first, and then an implant is inserted that accommodates the bone growth between the two vertebral bodies to effectively bridge the gap left by the removed disc. A number of different implant materials and implant designs have been employed for fusion with varying degrees of success. Although intervertebral and posterolateral fusion techniques are widely used, disadvantages of their use include reduced physiological range of motion and other complications associated with fusion, such as degeneration of adjacent intervertebral discs and instability of functional spinal units. As a result, there is a need for alternative treatments with fewer complications and similar efficacy to fusion. One such alternative to spinal fusion is arthroplasty and the use of prosthetic or artificial discs.

Typically, arthroplasty is used in the replacement of diseased joints. Arthroplasty includes a group of therapies used to preserve the joint's motion, thereby preserving its integrity and keeping adjacent moving parts from deterioration, which tends to follow fusion. Depending on the location and condition of the affected joint, specific arthroplasty treatments may be employed. For example, insertive reconstructive surgery, which reshapes the joint and inserts a prosthetic disc between the two bones that form the joint, is commonly used on the elbow, shoulder, ankle, and knuckles. Total joint replacement, or total arthroplasty, replaces the entire diseased joint with an artificial prosthesis and has become the surgical option for most knee and hip problems in recent years.

Hip and knee replacements in particular are widely used, with nearly 300,000 hip replacements and about as many knee replacements performed in the United States in 2001. For knee and hip replacement surgery, several implants or prostheses are available. For a hip prosthesis, in one exemplary design there are two parts, a metal ball attached to a metal stem that fits into the femur, and a matching plastic implant implanted in the pelvis ball socket. Metal parts are typically formed from stainless steel, cobalt and chromium alloys, titanium and titanium alloys; plastic parts are typically formed from high density polyethylene. For knee prostheses, in one exemplary embodiment, metal and plastic components may also be used to replace damaged bone ends and cartilage. Metal parts are typically formed from stainless steel, cobalt and chromium alloys, titanium and titanium alloys; plastic parts are typically formed from high density polyethylene.

Although the progression of spondyloarthroplasty and the use of prostheses in the spine is similar to other joints in the body, however, the progression from fused joints to replacement of functional joints, the advent of spondyloarthroplasty has been more advanced than arthroplasty of other major joints in the body The technique is slower. Some possible reasons why spondyloarthroplasty has been delayed are spinal problems associated with disc degeneration are difficult to diagnose, spinal treatment is often driven by critical illness such that conservative options such as fusion are acceptable, and spinal anatomy quite complicated.

Spondyloarthroplasty has been in development for the past 40 years and in the past 10 years spondyloarthroplasty has captured the attention of leading surgeons and implant manufacturers. The development of spondyloarthroplasty began roughly in the 1950s, and one of the emerging concepts was the spherical concept of intervertebral disc prostheses. The spherical concept is to simply place a roughly round ball into the nucleus pulposus cavity after the discectomy procedure has been performed. The annulus is held in place and the ball is used as a replacement for the nucleus. Various materials have been tested for this spherical concept. For example, implants using silicone ball bearings were implanted in patients' necks in the early 1960's with inconclusive results. Stainless steel (ball bearing) prostheses were implanted in patients in the mid 1960's. The results of this therapy are initially promising, but over time the disc space loses height as the steel ball sinks into the vertebral body. The spherical prosthesis concept continues to be investigated using different materials, the latest being modified carbon fibers.

Another concept that emerged was mechanical concept design. The mechanical concept design is basically an outgrowth of total intervertebral disc replacement, which aims to restore the range of motion of the spinal motion segment unit. These devices typically consist of metal endplates secured to adjacent vertebral bodies by a stabilizing mechanism, and a core formed of polyethylene or other polymeric material. Alternatively, instead of the core, a support surface may be used, the material of which may be ceramic-ceramic, metal-metal or metal-polyethylene. Mechanistically Designed Concepts Based on the same principles as joint reconstruction products such as knee and hip replacements, a variety of mechanistically designed prosthetic concepts have been and will continue to be proposed.

Another concept is a physiological concept. Physiological concepts employ hydrogel, elastomer, or polyurethane-based cores that aim to restore disc function by absorbing and releasing fluid between the patient's spinal endplates while maintaining the disc's natural shock-absorbing or cushioning properties. Physiologically concepted devices are often only considered partial solutions because they are designed to replace only the nucleus or part of the disc.

All methods of disc replacement aim to achieve some or all of the following: relief of disc pain, restoration of range of motion, preservation of the disc's natural shock-absorbing function, restoration of natural shape or disc height, and restoration of physiologic motor function. In general, four exemplary types of artificial discs have been developed to replace part or all of a resected disc: elastomeric/fluid-filled discs, ball and socket discs, mechanical spring discs, and hybrid discs.

Elastomeric/fluid-filled discs typically include an elastomeric spacer or fluid-filled chamber disposed between inferior and superior rigid endplates. The spacers and chambers of these implants may function mechanically similar to the removed disc tissue.

Ball and socket discs typically include two plates with an inner ball and socket portion that fit together to allow articulation of the plates during spinal motion.

Mechanical spring discs typically include one or more coil springs disposed between metal endplates. The coil springs define a cumulative spring constant that is designed to be sufficient to maintain the gap setting between adjacent vertebrae while allowing normal motion of the vertebrae during flexion and extension of the spine in any direction.

A fourth type of artificial disc, the hybrid disc, involves two or more of the above design principles. For example, one known hybrid disc arrangement includes a ball and ball joint surrounded by an elastomeric ring.

While each of the prostheses described above can address some of the problems associated with disc replacement, each implant has significant disadvantages. Therefore, there is a need for an intervertebral implant that can accommodate the anatomy and geometry of the intervertebral space to be filled, as well as the anatomy and geometry of the adjacent vertebral body ends, while providing reliability and simplicity in design sex. More specifically, there is a need for an implant for an intervertebral disc that provides stability for supporting the high loads placed on the vertebrae, allows sufficient flexibility to allow the patient a substantially normal range of motion, and provides Between the axial compression, and has shock-absorbing properties.

Contents of the invention

The present invention relates to an intervertebral disc that is preferably designed to restore disc height and lordosis, allow a natural range of motion, absorb shock, and provide resistance to motion and axial compression. Additionally, intervertebral discs may be used in the cervical, thoracic, or lumbar regions of the spine.

The intervertebral disc includes a body having a footprint that preferably conforms in size and shape to at least a portion of the distal end of an adjacent vertebra. The shape of the intervertebral disc includes, but is not limited to, round, oval, ellipsoid, bean-shaped, circular, C-shaped, D-shaped, and the like.

In one embodiment, the body of the intervertebral disc includes an upper endplate, a lower endplate, and an elastic membrane disposed between the upper and lower endplates. Alternatively, an elastic membrane can surround and seal the endplates. The elastic membrane defines an interior at least partially filled with fluid. The fluid is preferably selected from gas, liquid, gel or any combination thereof. Additionally, the fluid is compressible and may be selected eg from gases, liquids or hydrogels, or incompressible and may be selected eg from saline.

The disc also preferably includes a valve for allowing fluid to enter the interior of the disc. The valve may be located on the elastic membrane, however alternatively the valve may be located in the upper and lower endplates of the intervertebral disc.

The superior and inferior endplates are preferably formed from metals such as titanium, stainless steel, titanium alloys, cobalt-chromium alloys or amorphous alloys. Alternatively, however, the superior and inferior endplates may be made of ceramics, composites, polymers such as polyetheretherketone (ie, PEEK) or ultrahigh molecular weight polyethylene (ie, UHMWPE), including solid bone, cancellous bone, allografts bone, autograft bone, xenograft bone, demineralized or partially demineralized bone, or any other material that can be used as a load-bearing support. The materials used for the endplates, along with the required fluids, are preferably selected to reduce the amount of wear and thus increase the longevity of the joint.

The outer surfaces of the upper and lower endplates can be generally planar, wedge-shaped, etc. The outer surfaces of the superior and inferior endplates may also be dome-shaped with radii defined in the sagittal and coronal planes to generally match those of the adjacent vertebral ends. The vaulted shape allows the superior and inferior endplates to better conform to the ends of adjacent vertebrae to provide better in situ fit.

The intervertebral disc also preferably includes a movement-resistant structure disposed on the outer surface of at least one or both of the endplates to prevent movement, displacement or dislodgement of the endplates from or into adjacent vertebral ends. Structures that can resist movement include, but are not limited to, fins, spikes, teeth, fins, deployable spikes, deployable teeth, flexible spikes, flexible teeth, profiled teeth, insertable or expandable Fins, screws, hooks, sawtooth structures, ribs and textured surfaces.

In addition, the superior and inferior endplates are also preferably coated with a bony growth inducing or guiding substance to promote bony ingrowth to permanently secure the disc to the adjacent vertebrae. Alternatively, the upper and lower endplates may have rough surfaces; porous surfaces; laser-treated endplate layers; incorporate osteoconductive/osteoinductive scaffolds; or may be provided with or made of osteoconductive and/or osteoinductive materials to Promotes bone ingrowth. The endplates may also include membranes and/or barriers to limit the amount and/or depth of bony ingrowth.

The upper and lower endplates can also have implanted instrument connection, guide and fixation structures. For example, endplates may have holes, slots, threads, or dovetail joints for implantation of the implant and/or distraction of adjacent vertebrae. For example, the intervertebral disc may include slots formed in the upper and/or lower endplates configured to receive an insertion device, a distraction device, or both of the implant.

The superior and inferior endplates may also preferably include articulating surfaces, thereby providing greater flexibility to the intervertebral disc. The articulating surface preferably includes a polished or similar wear-reducing finish such as diamond, titanium-nickel finish, etc., to reduce wear, reduce particle generation, and improve disc longevity.

In some embodiments, additional structure may be included in addition to or instead of the fluid to provide additional stiffness. Such structures include, but are not limited to, springs, elastomers, bellows, balloons, closed containers, hollow bodies, biocompatible fibers, and cables.

In some embodiments, the intervertebral disc also preferably has an articulation mechanism to allow the endplates to pivot relative to each other so that related parts of the endplates can be brought closer together under compression, while different related parts of the endplates can separate under tension. The articulation mechanism may be in the form of a central pivot axis or fulcrum. The disc preferably also allows and provides a mechanism, or is configured to allow the position of the pivot axis within the disc to be varied in response to loading conditions, thereby providing a movable momentary axis of rotation. The intervertebral disc also preferably includes a mechanism, such as providing fluids, elastomers, springs, cables, etc., to absorb axial pressure and provide shock absorption.

In some embodiments, the disc includes an upper end, a lower end, and a lateral wall disposed therebetween. The intervertebral disc may have an interior volume formed between the upper and lower ends and the outer sidewall, the interior volume preferably including a central pivot and at least one cavity peripheral to and surrounding the central pivot. The central pivot preferably includes a central wall defining a central chamber, the at least one peripheral chamber being disposed between the outer side wall and the central wall. A first fluid may be disposed in the at least one peripheral chamber. A second fluid may be disposed in the central chamber. The first and second fluids may be the same or different. The disc may include additional peripheral chambers that may or may not be in fluid communication with the central chamber and with each other. Additionally, the side walls may be formed from a first material and the center wall may be formed from a second material, wherein the first material has a different stiffness than the second material. Preferably, the central pivot and/or the central chamber may allow the upper and lower ends to pivot relative to each other and may include resilient members such as springs.

In another embodiment, an intervertebral disc includes a body having an upper surface spaced from an opposing lower surface. The spacing between the upper surface and the lower surface is optional. The body also includes an outer sidewall forming an outer wall and a throughbore defining an inner wall, wherein the inner wall defines an opening. Additionally, the body may be generally C-shaped. A chamber may also be provided within the body. Additionally, at least one portion extending from the body for contacting a vertebra defines an aperture for receiving the anchor.

The intervertebral disc can be implanted in modular form or, if possible, it can also be implanted pre-assembled. The disc can be implanted using an anterior, anterior lateral, or lateral surgical approach. Additionally, depending on the disc to be implanted, a minimally invasive surgical approach or a simultaneous distraction and implantation approach may be employed. Also, depending on the disc to be implanted, the anterior longitudinal ligament can attach directly to the disc or to the adjacent vertebral body. The anterior longitudinal ligament can be formed from partially demineralized or demineralized autografts, allografts or xenografts. Alternatively, the anterior longitudinal ligament may be formed from biocompatible materials such as elastomers or braided polymers. To aid in implantation of the disc, the disc may include alignment marks.

Brief introduction to the drawings

To facilitate the understanding and for the purpose of explaining the invention, exemplary and preferred features and embodiments are disclosed in the drawings, it being understood, however, that the invention is not limited to the precise arrangements and instruments shown, wherein Like numerals denote like parts throughout the several views, in the drawings:

1 is a perspective view of a first embodiment of an artificial intervertebral disc according to the present invention;

Figure 2 is a cross-sectional view of the artificial intervertebral disc shown in Figure 1 along line A-A;

Figure 2a is another cross-sectional view of the artificial intervertebral disc shown in Figure 1 along line A-A;

Figure 3a is a side view of a retractable spike according to the present invention;

Figure 3b is a side view of another retractable spike according to the present invention;

Figure 3c is a side view of a flexible spike according to the present invention;

Figure 3d is a side view of a profiled tooth according to the present invention;

Figure 3e is a side view of an anchor according to the present invention;

Figure 4 is a perspective view of a second embodiment of an intervertebral disc according to the present invention;

Figure 5 is a cross-sectional view of the intervertebral disc shown in Figure 4 along line B-B;

Figure 6 is a perspective view of another embodiment of the intervertebral disc shown in Figure 4;

Figure 7 is a perspective view of a third embodiment of an intervertebral disc according to the present invention;

Figure 8 is a cross-sectional view of the intervertebral disc shown in Figure 7 along line C-C;

Figure 9 is a cross-sectional view of another embodiment of the intervertebral disc shown in Figure 7 along line D-D;

10 is a perspective view of a fourth embodiment of an intervertebral disc according to the present invention;

Figure 11 is a side view of the fourth embodiment of the intervertebral disc shown in Figure 12;

Fig. 12 is a schematic diagram of a fifth embodiment of an intervertebral disc according to the present invention.

Detailed introduction of the preferred embodiment

Any of a variety of different implant configurations can be prepared as shown in the illustrative examples of intervertebral discs disclosed herein. The discs of the present invention are preferably designed to restore lordosis, disc height, to allow natural range of motion, absorb shock and provide resistance to motion and axial compression.

The discs are preferably sized and adapted for use in the cervical, thoracic or lumbar regions of the spine. In addition, the disc can be customized for each patient to allow for the disc characteristics to be tailored to each patient. For example, the core of an intervertebral disc may include different components, different components, and/or various types of materials in order to create desired properties for each patient.

In addition, the intervertebral disc allows for flexion, extension, lateral bending, rotation, and translation. Flexion is the movement of a joint or two parts of the body into a bent position; in the spine, flexion is the movement of the spine that begins straight and then moves into a forward bend. Elongation is the movement that pulls two parts apart from each other; in the spine, elongation is the movement that causes the spine to start straight and then move to a backward bend. Lateral flexion is a bending motion toward the side; in the spine, this motion generally consists of bending (sideways) and combined rotation. Rotation is movement that causes a portion of the spine to twist, rotate, or turn relative to the spinal axis. Translation is limited motion generally transverse to the axis of the spine.

In addition, the artificial disc preferably allows a momentary rotational axis of motion similar to the natural disc. For each instant of the body in planar motion, there exists in the body a straight line which does not move or an imaginary extension of this line. The instantaneous axis of rotation is the straight line. Movable momentary axis of rotation refers to the ability of the momentary axis of rotation to be able to move (ie translate) under different loading conditions; in other words, the position of the momentary axis of rotation is moving relative to the intervertebral disc. The preferred mean position of the movable instantaneous rotational axis of the lumbar region of the spine is preferably in the posterior half of the intervertebral disc space, or close to the adjacent (superior or inferior) endplate, and preferably close to the inferior/caudal endplate, spine thoracic The preferred mean position of the movable instantaneous rotational axis of the region is preferably in the lower part of the intervertebral disc space and close to the caudal vertebral body extending posteriorly into the spinal canal, while the preferred mean position of the movable instantaneous rotational axis of the cervical region of the spine Preferably in the posterior half of the caudal vertebral body.

Also, similar to natural discs, the response characteristics of artificial discs are preferably non-linear. For example, in response to successive axial compressions, the artificial intervertebral disc preferably undergoes an initial large amount of compression followed by a non-linear decrease in the amount of compression.

Referring to the drawings, preferred embodiments and features of the artificial intervertebral disc will now be described in detail. It should be noted, however, that these descriptions of specific embodiments and features are merely exemplary. It is contemplated that one or more features of different embodiments can be combined or used independently, that modifications to the various embodiments and other embodiments will be conceived and will be apparent to those skilled in the art.

Referring first to Figures 1 and 2, a perspective view of an exemplary first embodiment of an artificial intervertebral disc 10 is shown. As shown, the intervertebral disc 10 has a generally bean-shaped profile including a front face 11 , a back face 13 , and first and second sides 15 , 17 . The front face 11 and the sides 15, 17 are generally convex in shape, while the rear face 13 is generally concave in shape. However, the intervertebral disc 10 may take other shapes that preferably conform geometrically and anatomically to adjacent vertebral bodies, including but not limited to circular, elliptical, ellipsoidal, circular, D-shaped, C-shaped, and the like.

As shown, the intervertebral disc 10 includes an upper endplate 12 , a lower endplate 14 , and an elastic membrane 16 extending generally from the upper endplate 12 to the lower endplate 14 and preferably disposed near the periphery of the intervertebral disc 10 . Alternatively, the elastic membrane 16 may surround and/or enclose the superior endplate 12 and the inferior endplate 14 . The elastic membrane 16 together with the upper endplate 12 and the lower endplate 14 define an interior volume which can be at least partially filled with a fluid 22 . The elastic membrane 16 is preferably formed from an elastomer such as polyurethane, silicone, woven polymer, or any other suitable elastic material known in the art. The elastic membrane may be impermeable. Alternatively, elastic membrane 16 may be permeable or semi-permeable to allow fluid flow into and out of the interior of the disc (as described in more detail below). The elastic membrane 16 preferably resists translational movement between the upper and lower endplates 12, 14, also prevents soft tissue ingrowth between the endplates 12, 14, and contains any wear particles that develop within the interior volume. The elastic membrane 16 may be attached to the superior and inferior endplates 12, 14 by any fixation method known in the art, including but not limited to adhesives, ultrasonic welding, screws, nails, mechanical wedging, and pins .

Alternatively, the elastic membrane 16 may be in the form of a bellows which is "foldable" in shape so that it can expand and contract under different loading conditions. The bellows may be rigidly attached to the upper and lower endplates 12, 14 by any means known in the art, including, but not limited to, circular grooves formed in each endplate 12, 14, adhesive compound, ultrasonic welding, screws, nails, mechanical wedges and pins. The bellows are preferably made of metal, however other materials such as elastomers or polymers can also be used.

The disc 10 may also include a valve 20 that provides access to the interior 19 of the disc 10 so that fluid may be injected into or out of the interior 19 of the disc 10 . The valve 20 is preferably a one-way valve known to those skilled in the art, so that fluid once injected cannot escape from the interior 19 of the intervertebral disc 10 . As shown in Figures 1 and 2, the valve 20 is preferably disposed in the elastic membrane 16, but the valve 20 may also be disposed in the upper endplate 12 and/or the lower endplate 14, as shown in Figure 2a. When the valve is disposed in the superior endplate 12 and/or the inferior endplate 14, preferably a channel 30 is included in the endplate to interconnect the valve 20 with the interior 19 of the disc 10.

The fluid 22 disposed in the interior volume may be a gas, liquid, gel, or any combination thereof. Where gas is provided as the filling medium for the inner volume or a combination of gas and liquid is provided, the final gas pressure in the inner volume should be chosen to provide adequate shock absorption during axial compression of the disc 10 . The fluid may also allow limited articulation or movement of upper endplate 12 and upper endplate 14 relative to each other. The fluid is preferably an incompressible liquid, such as a saline solution. In use, fluid 22 may be injected into the interior 19 of the disc 10 prior to insertion of the disc 10 between adjacent vertebrae. Alternatively, fluid 22 may be injected in situ to facilitate insertion of intervertebral disc 10 and subsequent distraction between adjacent vertebrae. The stiffness and distraction ability of the disc 10 may be a function of the amount of fluid 22 injected into the interior 19 of the disc 10 and/or the elastic properties of the membrane 16 . In general, the more fluid 22 provided into the interior 19 of the disc 10, the more rigid the disc 10 will be, and the greater the distraction capacity. Additionally, flexibility and enhanced articulation can be achieved by filling only a portion of the internal volume 19 of the intervertebral disc 10 . Finally, variably filling the interior 19 of the intervertebral disc 10 with fluid 22 allows the overall height H of the intervertebral disc 10 to be varied as necessary according to the needs of the individual patient.

As shown in Figure 2a, the upper endplate 12 may have an inner surface with a curved ball socket 32, while the lower endplate 14 may have an inner surface with a curved protrusion 34, or vice versa. The socket 32 and protrusion 34 are configured and sized to generally match or coincide with each other. The type and amount of articulation required may dictate the curvature of the socket 32 and protrusion 34 provided. For example, if the protrusion 34 has the same radius as the ball socket 32, the disc 10 may provide greater support but more constrained movement. Alternatively, if the ball socket 32 has a larger radius than the protrusion 34, the disc will provide enhanced articulation. Additionally, protrusion 34 and/or socket 32 may also include flattened portions that allow translational movement of upper endplate 12 relative to lower endplate 14 . By allowing translational motion, the intervertebral disc 10 provides a movable momentary axis of rotation as described above.

The ball socket 32 and protrusion 34 may also take on different profiles than those described above in order to achieve the desired articulation. Additionally, while the socket 32 and protrusion 34 are shown with profiles that generally allow their surfaces to mate, the socket 32 and protrusion 34 may be provided with non-matching profiles in order to achieve the desired articulation.

The use of the fluid-filled interior volume 19 in conjunction with the articulating surfaces may allow the ball socket 32 and protrusion 34 to more easily translate relative to each other by reducing friction between the sliding surfaces.

Alternatively, where the fluid is a compressed gas, the articulating surfaces may not necessarily be in constant engagement, but may only come into engagement when sufficient pressure is exerted on the disc by adjacent vertebrae. Thus, the disc of this embodiment would have dual capabilities, performing a function similar to a fluid-filled disc in one load-bearing scenario and a mechanical protrusion/ball-and-socket jointed disc in a second scenario.

Depending on where the disc 10 is implanted in the spinal column, the disc 10 preferably recovers a height in the range of from about 4 millimeters (mm) to about 26 mm. Additionally, disc 10 preferably restores lordosis in the range of from about 0° to about 20°. The intervertebral disc preferably also recovers stiffness in the range of from about 1 Newton meter per degree (Nm/deg) to about 11 Nm/deg in axial rotation, and in the range of about 0 Nm/deg to about 7 Nm/deg in flexion/extension and a stiffness in the range of about 0 Nm/deg to about 5 Nm/deg in lateral bending. Additionally, the intervertebral disc 10 preferably provides a compressive stiffness of from about 100 N/mm to about 5000 N/mm, and a tensile stiffness of from about 50 N/mm to about 1000 N/mm. Additionally, depending on where the disc 10 is implanted in the spine, the disc 10 preferably allows a range of motion of from about 5° to about 45° in flexion/extension and from about 3° to about 33° in lateral flexion range, from about 1° to about 60° of motion in axial rotation. The intervertebral disc 10 preferably also allows axial compression in the range of about 0.2 millimeters to about 2 millimeters.

The superior and inferior endplates 12, 14 are preferably formed from a metal such as titanium, stainless steel, titanium alloys, cobalt-chromium alloys, or amorphous alloys. Alternatively, however, the upper endplate 12 and the lower endplate 14 may be made of ceramics, composite materials, polymers such as PEEK or UHMWPE, including solid bone, cancellous bone, allograft bone, autograft bone, xenograft bone, desquamated bone, etc. Bone, including mineral or partially demineralized bone, or any other suitable material that can serve as a load-bearing support. More preferably, the material selected for the endplates along with the fluid is selected to reduce wear.

In addition, any articulating surfaces in the discs of the present invention include surfaces that are polished or similar wear-reducing finishes, such as diamond-finished, titanium-nickel-finished, etc., to reduce wear, reduce particle generation, and increase disc longevity.

The outer surfaces of the upper and lower endplates can be generally planar, wedge-shaped, etc. The outer surfaces of the upper endplate 12 and the lower endplate 14 may also be dome-shaped with radii defined in the sagittal and coronal planes to generally match the shape of the adjacent vertebral ends, thereby providing a better In-situ assembly.

In addition, as shown in FIGS. 1-2 a , the intervertebral disc 10 also includes features that can resist movement, such as spike-like structures 18 disposed on the outer surfaces of the upper endplate 12 and the lower endplate 14 . The anti-movement feature facilitates the engagement of the intervertebral disc 10 with the ends of adjacent vertebrae by providing a mechanical interlock resulting from penetration and/or deformation of the ends of the adjacent vertebrae. The initial mechanical stability provided by the spikes 18 reduces the risk of post-operative instability, movement, displacement or detachment of the intervertebral disc 10, for example. Other features that may resist movement may include, but are not limited to, fins, teeth, retractable teeth, retractable spikes, flexible spikes, flexible teeth, flexible Inserted or expandable fins, anchors, screws, ridges, serrations, or other similar embellishments. As shown in FIG. 3a, a retractable spike 21 may be provided, and a cam mechanism 23 is used to extend and retract the spike 21 . Alternatively, as shown in Fig. 3b, a tool may be used to retract and retract the spike 21. Examples of flexible spikes 24, shaped teeth 25 and anchors 26 are shown in Figures 3c to 3e, respectively. Alternatively or additionally, an adhesive such as a calcium phosphate adhesive or the like may be used to secure the intervertebral disc 10 to adjacent vertebrae.

In addition, the upper endplate 12 and the lower endplate 14 may also be coated with a bone growth inducing substance such as hydroxyapatite to promote bony ingrowth to permanently fix the intervertebral disc 10 to the adjacent vertebrae. Alternatively, the upper and lower endplates 12, 14 may have roughened or porous surfaces in order to promote bony ingrowth. Alternatively, the upper and lower endplates 12, 14 may have laser-treated endplate layers to form a porous structure, or may incorporate an osteoconductive and/or osteoinductive scaffold. The endplates 12, 14 may also be made of osteoconductive and/or osteoinductive materials in order to promote bony ingrowth. The endplates 12, 14 may also include membranes and/or barriers to limit the depth of bony ingrowth allowed.

The upper endplate 12 and the lower endplate 14 may also have implant instrument connection, guidance and fixation structures. For example, the endplates 12, 14 may have holes, slots, threads, or dovetail joints to accept tools for implanting the disc 10 and/or distracting adjacent vertebrae. For example, the intervertebral disc may include a groove formed in the superior endplate 12 and/or the inferior endplate 14 configured to receive an insertion device, a distraction device, or both of the implant.

As a result of the materials and structural members used, the intervertebral disc 10 can allow flexion/elongation, lateral bending, axial rotation, and translation depending on the loads placed on the intervertebral disc. Additionally, under varying spinal loading conditions due to spinal motion, the fluid 22 can move within the interior volume, compress (in the case of gas) or move radially outward when the elastic membrane expands, allowing the endplates to interact with each other. sports. This variable movement or displacement of fluid 22 provides a movable momentary axis of rotation.

As shown in Figures 4 and 5, a second exemplary embodiment of an artificial intervertebral disc is provided. Intervertebral disc 100 has a generally annular shape and includes an upper surface 102, a lower surface 104, an outer side wall 106 forming an outer wall, and an inner side wall 107 defining an opening 108 (ie, through hole). However, the intervertebral disc 100 may take other shapes that preferably conform geometrically and anatomically to adjacent vertebral bodies, including but not limited to kidney bean, round, oval, ellipsoid, C-shaped, D-shaped, and the like. The intervertebral disc 100 is preferably made of an elastomeric material, which forms a closed container with an inner volume 103 . The disc 100 may also include a valve 118 for introducing or draining fluid 120 into the interior volume 103 of the disc 100, as described above. Valve 118 preferably comprises a one-way valve and is disposed on outer side wall 106 as shown in FIG. 5 , however, valve 118 may also be disposed on upper surface 102 , lower surface 104 or inner side wall 107 .

As best shown in FIG. 5 , disc 10 may also include a metal mesh 105 molded or otherwise secured to upper surface 102 and/or lower surface 104 . Metal mesh 105 may provide additional strength and stiffness to intervertebral disc 100 . The metal mesh 105 may also be flexible so as to conform to the concavity of the distal end of the adjacent vertebral body, thereby facilitating a higher degree of surface contact with the intervertebral disc. The metal mesh 105 may also be textured, its surface may be porous, and it may be used in conjunction with bone growth inducing or guiding substances to further enhance engagement and fusion with adjacent vertebral portions.

Through hole 108 is preferably filled with an elastomeric material (not shown). The elastomeric material may have a different stiffness than the disc 100 . The elastomeric material preferably has a higher stiffness than that of the intervertebral disc 100, allowing the through hole 108 to be stiffer and thus serve as a central pivot or central post about which the upper and lower surfaces 102, 104 articulate. The central pivot may allow one portion or one side of the disc 100 to compress while allowing another portion of the disc 100 to expand. In an alternative embodiment, the elastomeric material may have a stiffness lower than that of the disc 100 . Alternatively, the vias 108 may be filled with hydrogel.

In addition, the upper surface 102 and the lower surface 104 of the intervertebral disc 100 may include the anti-movement features, permanent fixation devices and/or implant instrumentation connections, guidance and fixation described above for the intervertebral disc 10 in FIGS. 1-3 structure. The intervertebral disc 100 preferably can be provided with at least one fixation feature (ie, tab) 110 to facilitate engagement of the intervertebral disc 100 with the vertebral body of an adjacent vertebra. As shown in FIG. 4 , two tabs 110 are preferably provided, one tab 110 for the upper surface 102 and the other tab 110 for the lower surface 104 . The tab 110 may be provided as a single piece that extends beyond the upper surface 102 and the lower surface 104, or the tab 110 may be provided as two or more pieces. Tabs 110 preferably extend from side 106 above and below surfaces 102, 104, respectively, and are sized to interface with a portion of the outer surface of the vertebral body of an adjacent vertebra. Tabs 110 may include through holes 114 for receiving anchors such as set screws (not shown). Fixation screws may be used to secure the intervertebral disc 100 to the vertebral bodies of adjacent vertebrae.

Alternatively, as shown in FIG. 6 , the disc 100 may also include an indentation 126 on its perimeter that creates opposing end faces 122 , 124 that give the disc 100 a generally C-shaped appearance. The end faces 122, 124 are preferably configured to be resiliently biased apart, however, the end faces 122, 124 may naturally be arranged to be spaced apart from each other without the need for a resilient bias. The gap 126 formed between the end surfaces 122, 124 provides increased flexibility to the disc 100 to facilitate insertion and placement of the disc 100 between the vertebrae. The notch 126 allows the diameter of the intervertebral disc 100 to be reduced by pressing the end faces 122, 124 together. The notch 126 may also allow the disc to expand by pulling the end faces 122, 124 apart. Thus, gap 126 allows intervertebral disc 100 to be configured to have at least one smaller outer dimension compared to its resting state, which in turn allows intervertebral disc 100 to pass through a cavity or other opening that is smaller than the uncompressed (i.e., resting) dimension of intervertebral disc 100. Instead, it is inserted into the anatomical region, allowing posterior insertion.

Depending on where the disc 100 is implanted in the spine, the disc 100 preferably restores height, lordosis, stiffness, provides compressive stiffness, and allows a range of motion similar to that described in the previous embodiments.

As a result of the materials, geometry, and components used, the intervertebral disc 100 can allow flexion/extension, lateral bending, axial rotation, and translation depending on the loads placed on the intervertebral disc. Similar to the embodiment shown in Figures 1 to 2a, under different spinal loading conditions due to spinal motion, fluid 22 can move within the internal volume, compressing (in the case of gas) or radially as the elastic membrane expands. Move outward, allowing the endplates to move relative to each other. This variable movement or displacement of fluid 22 provides a movable momentary axis of rotation.

A third exemplary embodiment of an artificial intervertebral disc will now be described with reference to FIGS. 7 to 9 . The intervertebral disc 150 preferably has a generally cylindrical shape with a circular outline, having an upper end 152, a lower end 154, and an outer side wall 156 disposed therebetween. The disc also includes an interior volume defined between upper end 152 , lower end 154 , and lateral wall 156 . Although shown as cylindrical, the intervertebral disc 150 may take any other shape that preferably conforms geometrically and anatomically to the adjacent vertebral body, including but not limited to kidney bean, circular, elliptical, ellipsoidal, D-shaped, C-shaped etc.

The intervertebral disc 150 may be made of any material known in the art to function as a load bearing support, including but not limited to elastomers, polymers, ceramics, composites, and the like. Disc 150 may also include a valve (not shown) for introducing fluid 158 into the interior of the disc, as described in other embodiments described above.

The intervertebral disc 150 may also include upper and lower endplates (not shown) as described in other embodiments above. Alternatively, disc 150 may comprise a metal mesh molded or otherwise secured to upper surface 152 and/or lower surface 154 as described in other embodiments above. In addition, the intervertebral disc 150 may also include anti-movement features, permanent fixation devices, and/or implant instrumentation connection, guidance, and fixation structures as described in other embodiments above.

Depending on where the disc 150 is implanted in the spine, the disc 150 preferably restores height, lordosis, stiffness, provides compressive stiffness, and allows a range of motion similar to that described in the previous embodiments.

Referring to Fig. 8, the interior of the intervertebral disc 150 is shown. The interior of the disc 150 preferably includes a plurality of interconnected peripheral chambers 160 and a single central chamber 162 . The multi-chambered interior of the disc 150 allows controlled flow of fluid within the disc 150, allowing controlled articulation or movement under load-bearing conditions. Peripheral chamber 160 may be in fluid communication with central chamber 162 through an open channel, porous central wall 165, permeable membrane, and the like. However, the peripheral chamber 160 is preferably in fluid communication with the central chamber 162 through baffles and/or valves. More preferably, the baffles and/or valves are configured to provide selective fluid exchange such that fluid 158 from peripheral chamber 160 can flow into In the central chamber 162. Alternatively, central chamber 162 may be sealed relative to peripheral chamber 160 . In this case, peripheral chamber 160 and central chamber 162 may be filled with the same or different fluids.

The peripheral chamber 160 is defined by a wall 163 , while the central chamber 162 is separated from the peripheral chamber 160 by a central wall 164 . In addition to defining the geometry of the chambers 160, 162, the walls 163, 165 also serve as support between the surfaces 152, 154 by resisting loads acting on the disc 150 in use.

Central chamber 162 and peripheral chamber 160 are preferably arranged such that central chamber 162 is stiffer than peripheral chamber 160 (for example by being completely filled with an incompressible fluid), thereby allowing central chamber 162 to act as an upper surface 152 and lower surface 154 are articulateable central pivots or posts about which they are articulated. The central pivot allows one portion or one side of the disc 150 to be compressed while allowing another portion of the disc 150 to expand. The walls 163 of the peripheral chamber 160 may be made of a less rigid material than the material used to make the central wall 165, allowing the central chamber 162 to be stiffer and act as a central pivot. Alternatively, the wall 163 of the peripheral chamber 160 may be formed from the same material as the central wall 165, but whose geometry provides a lower stiffness than the geometry of the central wall 165 of the central chamber 162, thereby allowing the central chamber 162 Serves as a central pivot for the intervertebral disc 150 . In addition, the combination of material and geometric properties of the chamber walls 163, 165 can be selected such that the central chamber 162 is stiffer than the peripheral chamber 160 so that the central chamber 162 can serve as a center about which the disc 150 can pivot. pivot.

The geometry of the chambers 160, 162, the geometry and material of the walls 163, 165, together with the fluid disposed therein, should be selected to obtain the desired properties of the intervertebral disc, including the desired stiffness, height, flexibility, and preferably the center. The relative stiffness of chamber 162 relative to peripheral chamber 162 is such that the desired articulation between upper end 152 and lower end 154 is provided. Accordingly, the intervertebral disc 150 can move, deform or extend in flexion/extension, lateral bending, axial rotation, and translation according to the loads placed on the disc because fluid can flow in the periphery under various spinal loading conditions. chamber 160 and/or central chamber 162 . This movement of the chambers relative to each other and the movement of fluid within and between the chambers allows the disc 50 to have a movable momentary axis of rotation. It should be noted that the central chamber 162 need not be located in the center of the disc, but may be located in any other location in the disc that is suitable for the desired movement of the endplates relative to each other.

Alternatively, as shown in FIG. 9 , the central chamber 162 may house a spring 167 . Spring 167 serves as additional support for intervertebral disc 150 to further allow central chamber 162 to act as a central pivot and/or strut. When the spring 167 is located in the central chamber 162, fluid may or may not be provided. Spring 167 may be formed from any material known in the art, such as cobalt-chromium alloys, titanium alloys, stainless steel, amorphous alloys, polymers, or composite materials.

Alternatively, the central chamber 162 may contain a bladder. The balloon may be integrally formed with or attached to the ends 152, 154. Alternatively, the bladders may be separate from the ends 152,154. The balloon can articulate, compress and/or translate within the central chamber 162, providing the disc with a movable momentary axis of rotation that allows for a greater degree of articulation or movement of the disc 150 under various loading conditions. Activity. Additionally, the central balloon can serve as additional support for the disc 150 such that the central chamber 162 can act as a central pivot and also allow for desired motion.

Referring to Figures 10 and 11, a fourth embodiment of the artificial intervertebral disc will be described below. The intervertebral disc 250 has a generally bean-shaped profile with an upper endplate 252 , a lower endplate 254 and at least one cable member 256 , 258 . Although the intervertebral disc 250 is shown as having a bean-shaped outline, the intervertebral disc 250 may take any other shape that generally conforms geometrically and anatomically to the adjacent vertebral body, including but not limited to circular, circular, elliptical, ellipsoidal , D shape, C shape, etc. In addition, the endplates 252, 254 preferably include movement-resistant features, permanent fixation devices, and/or implant instrument connection, guidance, and fixation structures as described with respect to the above-described embodiments.

Upper endplate 252 and lower endplate 254 are preferably formed from a metal such as titanium, stainless steel, titanium alloys, cobalt-chromium alloys, or amorphous alloys. Alternatively, the upper endplate 252 and the lower endplate 254 can be made of ceramics, composite materials, polymers such as PEEK or UHMWPE, including solid bone, cancellous bone, allograft bone, autograft bone, xenograft bone, demineralized bone or partially demineralized bone, or any other suitable material suitable for use as a load-bearing support.

The outer surfaces of the upper and lower endplates can be generally planar, wedge-shaped, etc. Alternatively, the outer surfaces of the upper and lower endplates 252, 254 may be dome-shaped with radii defined in the sagittal and coronal planes to generally match the shape of the ends of adjacent vertebrae, thereby providing better In-situ assembly.

The intervertebral disc 250 may also include an elastic membrane extending generally from the upper endplate 252 to the lower endplate 254, as described in the above embodiments. The disc 250 may also include a valve that provides access to the interior of the disc 250 so that fluid may be at least partially injected into the interior of the disc, as described in the above embodiments.

Depending on where the disc 250 is implanted in the spine, the disc 250 preferably restores height, lordosis, stiffness, provides compressive stiffness, and allows a range of motion similar to that described in the previous embodiments.

As shown, the intervertebral disc 250 includes a plurality of peripheral cable members 256 and a central cable member 258 . Peripheral cable members 256 may be positioned near the periphery of disc 250, while central cable members 258 are preferably positioned near the center of the disc. Peripheral cable member 256 and central cable member 258 are attached to superior endplate 252 and inferior endplate 254 by any fixation means known in the art, including but not limited to adhesives, ultrasonic welding, screws, nails, mechanical Wedges and dowels. However, cable members 256 , 258 preferably engage upper and lower endplates 252 , 254 through bores 260 formed therein. The ends of the cable members 256 , 258 are crimped where they penetrate the outer surfaces of the upper and lower endplates 252 , 254 . This allows the surgeon to properly size the disc 250 by crimping/attaching the appropriately sized cables to the endplates just prior to implantation. Peripheral cable 256 and central cable 258 may be made of metal, polymer, composite material, or any other suitable material known in the art.

In one embodiment, the central cable 258 is shorter than the peripheral cable 256 . This allows the peripheral cable member 256 to assume a curved or bowed shape between the endplates 252,254. As a result, the length of central cable member 258 determines the maximum distance between upper endplate 252 and lower endplate 254 under tension. Additionally, since the peripheral cable 256 is longer than the central cable 258, the shorter central cable 258 keeps the peripheral cable 256 under compression. The elasticity of the bowed peripheral cable 256 provides the disc 250 with shock absorption, axial compression and articulation properties.

As a result of the materials, geometry, and components used, the intervertebral disc 250 can allow flexion/extension, lateral bending, axial rotation, and translation depending on load-bearing conditions. Additionally, the peripheral cable members 256 may bend or compress different amounts under different spinal loading conditions due to spinal motion. This variable bending/compression provides the desired movable momentary axis of rotation.

Referring to Figure 12, an exemplary installation procedure will now be described. In general, the intervertebral disc 300 includes an upper endplate 302, a lower endplate 304, and a core structure 306, which may be any of the aforementioned cable, elastomer, fiber, or fluid filled discs. The intervertebral disc 300 may be implanted in modular form, eg, the endplates 302, 304 of the intervertebral disc 300 may be inserted into the intervertebral cavity using instruments such as distractors and/or fixation instruments. The intervertebral disc space can be distracted using standard spinal distractors that engage the endplates 302,304. A trial spacer is then preferably used to determine the proper size of the core mechanism 306 to be inserted into the final intervertebral disc space. In an exemplary embodiment, the core mechanism 306 is inserted and connected to the endplates 302, 304 using dovetail joints, slots, or similar connections. This modular insertion technique avoids overstretching of the intervertebral disc space, which can damage surrounding tissue and/or blood vessels.

Alternatively, the intervertebral disc 300 may be inserted pre-assembled using a specific insertion tool. For example, endplate fixation clips may be used, which may allow the endplates 302, 304 to be held and locked in a parallel and spaced relationship when inserted into the intervertebral disc space. Once implanted, the clips can be released and removed from the endplates 302,304. The clip can then be removed from the disc space. Additionally, disc 300 may be implanted under compression to prevent over-distraction. Introduction of the intervertebral disc 300 in a compressed state may be achieved by surgically inserted instruments or by internal mechanisms provided in the intervertebral disc 300 .

The intervertebral disc 300 may be approached using an anterior, lateral or anterior lateral approach. Additionally, depending on the intervertebral disc 300 to be implanted, a minimally invasive surgical approach or a simultaneous distraction and implantation surgical approach may be employed. For example, a simultaneous distraction and implantation procedure may be achieved during implantation by using grooves formed on the outer surfaces of the endplates 302, 304 to guide the implant down toward the distractor. Also, depending on the intervertebral disc to be implanted, either the artificial ALL or the natural ALL can be attached directly to the disc or to the adjacent vertebral body. The attachment of the anterior longitudinal ligament helps prevent movement, displacement, or detachment of the implant. To aid in implantation of the disc, the disc may include alignment marks.

Although various descriptions of the invention have been presented above, it should be understood that various features can be used alone or in combination. Accordingly, the invention is not limited to the particular preferred embodiments described herein.

In addition, it should be understood that those skilled in the art to which the present invention pertains may conceive changes and modifications that fall within the spirit and scope of the present invention. For example, certain portions of the implants disclosed herein may be formed from bone, such as allograft bone, autograft bone, and xenograft bone, which may be partially or fully demineralized. In addition, some implants may include bone material or other bone growth inducing material within them or on/in their endplates. These internal substances may be allowed to interact with surrounding tissue, for example via channels or other pores formed in the implant wall. Additionally, intra-operative or post-operative alignment marks may be used to aid in implanting the disc. In addition, the disc can be made relatively rigid where fusion must occur. For example, a disc can be made relatively rigid by allowing fusion between the endplates, inserting a spacer between the endplates, or by injecting a curing fluid between the endplates. Accordingly, all advantageous modifications which fall within the spirit and scope of the invention and which can be readily effected by a person skilled in the art from the foregoing description herein are to be considered as alternative embodiments of the invention. Accordingly, the scope of the invention is defined by the appended claims.

Claims (10)

1. An intervertebral disc for placement between first and second vertebrae, the intervertebral disc comprising: a superior endplate having a first inner surface and a first outer surface, the first outer surface being in contact with the first vertebra; a lower endplate having a second inner surface and a second outer surface, the second outer surface being in contact with a second vertebra; a lateral wall disposed between the superior and inferior endplates; an interior volume defined between the first interior surface of the superior endplate and the second interior surface of the inferior endplate and the interior surface of the lateral wall, the interior volume comprising a plurality of interconnected peripheral chambers a surrounding central chamber from which the plurality of interconnected peripheral chambers are sealed; and a valve in communication with the plurality of interconnected peripheral chambers for at least partially filling the plurality of interconnected peripheral chambers with a first fluid; Wherein, the central chamber has rigidity, and the rigidity of the plurality of peripheral chambers is less than the rigidity of the central chamber. 2. The intervertebral disc of claim 1, wherein at least a portion of the valve is disposed in the lateral wall. 3. The intervertebral disc of claim 1, wherein the intervertebral disc is formed of an elastomeric material. 4. The intervertebral disc of claim 1, wherein the fluid is incompressible. 5. The intervertebral disc of claim 1, wherein a second fluid is disposed within the central chamber. 6. The intervertebral disc of claim 1, wherein the central chamber is defined by a first wall, and the plurality of peripheral chambers are disposed between the outer side wall and the first wall . 7. The intervertebral disc of claim 6, wherein the first wall is formed from a first material having a first stiffness and the outer side wall is formed from a second material having a second stiffness. 8. The intervertebral disc of claim 6, wherein the first wall has a first configuration of a first stiffness and the outer side wall has a second configuration of a second stiffness. 9. The intervertebral disc of claim 1, wherein a spring is disposed in the central chamber. 10. The intervertebral disc of claim 1, wherein a balloon is disposed in the central chamber.

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