The leading cause of lower back pain arises from rupture or degeneration of lumbar intervertebral discs. Pain in the lower extremities is caused by the compression of spinal nerve roots by a bulging disc, while lower back pain is caused by collapse of the disc and by the adverse effects of articulation weight through a damaged, unstable vertebral joint. One proposed method of managing these problems is to remove the problematic disc and replace it with a prosthetic disc that allows for the natural motion between the adjacent vertebrae (“a motion disc”).
U.S. Pat. No. 4,759,766 (“Buttner-Janz”) discloses one such motion device comprising three components: an inferior endplate, a superior endplate, and a core having two articulation interfaces. Both the inferior and superior endplates have raised bosses with concave spherical articulation surfaces in the center. The core has convex surfaces on both the top and bottom that are surrounded by raised rims. The articulation surfaces of the core are designed to articulate with the articulation surfaces of the endplates.
Because articulating motion discs such as those described in Buttner-Janz seek to mimic the natural motion of the natural disc, it is desirable to place the disc at the precise location whereby the disc will have a center of rotation precisely equal to that of the natural disc. Accordingly, the device must be precisely placed at a predetermined spot during implantation in order mimic the natural center of rotation. However, it has been found that this is difficult to do in practice due to the fact that the prosthetic components are available only in discrete sizes varying by as much as one mm.
Although the surgeon can select a revision surgery to re-position the motion disc, such a surgery is costly and typically painful to the patient, and may include a risk of morbidity.
The present inventors have noted that there may be a need to correct the height or angulation of a motion disc after the motion disc has been implanted. For example, because of the implantation is an inexact procedure, there may be times when the implanted disc is to tall or too short, or there is improper angulation. Accordingly, there may be a need to post-operatively correct the height or angle of the implant in order to adjust the height or angle to the new needs of the patient.
The present inventors have developed an intervertebral implant having an adjustable height and angle.
The implant of the present invention is advantageous because it can be inserted into the spine at a first height, and then adjusted to a second height to meet the needs of a particular patient.
In a first preferred embodiment, the height or angle of the implant is adjusted intra-operatively in order to fine tune the implant to the surgical needs of the patient. For example, such adjustment may allow precise tensioning of the annulus fibrosus, thereby preventing stenosis or ankylosis. In some embodiments, when the angle is adjusted, it is adjusted in either the coronal or saggital plane.
In a second preferred embodiment, the height of the implant is adjusted intra-operatively in order to fine tune the implant to the post-operative needs of the patient. This may occur if, for example, the prosthetic endplate sinks into the bony endplate.
Therefore, in accordance with the present invention, there is provided a prosthetic endplate in an intervertebral motion disc, the endplate comprising:
i) an outer plate comprising
ii) an inner plate comprising:
a is a cross-section of a motion disc having a worm and pinion gear.
b is a top view of the worm and pinion gear of
a is a cross-section of a motion disc having a wedge for angle adjustment.
b is a top view of the lower plate of a motion disc having a wedge for angle adjustment.
a is a cross-section of a motion disc having a wedge for angle adjustment.
b is a top view of the lower plate of a motion disc having a wedge for angle adjustment.
a-c show the insertion of motion discs for scoliosis correction.
a-c show the insertion and tethering of motion discs for scoliosis correction.
a-c show the insertion and tethering of motion discs for scoliosis correction.
a-d show the insertion of cushion-type motion discs for scoliosis correction.
Now referring to
a) a first prosthetic vertebral endplate component 11 comprising:
Because the lower endplate 31 comprises a pair of threadably mated plates, and the outer plate thereof is anchored to the adjacent bone, it is apparent that inner plate can be rotated by a sufficiently strong applied force. Accordingly, when height adjustment is desired, an external magnetic force may be applied to the magnetic inner component of the lower endplate in a manner sufficient to cause rotation of the inner component. This rotation of the inner plate upon the threadform causes a change in height of the overall disc.
In this particular embodiment, the lower endplate comprises an inner plate having magnetic north N and south S poles. In use, a powerful external magnet (not shown) is placed near or on the patient's skin in the vicinity of the prosthetic endplate and rotated a predetermined amount in an orientation predetermined to causes rotation of the magnetic plate. The attractive-repulsive force produced between the external magnet and the magnetic nut is sufficient to effect rotation of the magnetic inner plate in a predetermined amount. As above, rotation of the magnetic inner plate causes relative movement of the inner plate in relation to the fixed outer plate, thereby adjusting the height of the motion disc.
These adjustments can be made based upon post-operative imaging results, as well as sensor-based determinations of distance or load indicating device mal-placement or movement and patient feedback.
The use of magnets to drive the height adjustment of implants is well known in the art. See, for example, U.S. Pat. No. 6,336,929 (“Justin”), the specification of which is hereby incorporated by reference in its entirety.
In some embodiments, the selected magnet comprises a rare earth metal. In other embodiments, the selected magnet is an electromagnet.
In the event that the actual surgery results in an acceptable positioning of the device, but a post-surgical shift occurs (for example, by adjacent level disc disease, trauma, injury or insufficient securement to the vertebral body) and produces a misalignment, the present invention can also be used to post-operatively adjust the height of the device.
The present invention may also allow the surgeon to adjust the relative positions of the components in order to optimize these relative positions based upon outcomes research that may appear in the literature after the disc has been implanted.
In some embodiments, the present invention further includes an implanted controller and an implanted sensor. These features may be easily adapted to provide automatic or closed loop adjustment of the center of rotation of the device without the need for physician or surgical intervention.
In some embodiments, sensor technology may be used to record the height of the disc as well as changes in height. For example, in some embodiments, the magnetic field created by the plate-based magnet of
In one aspect of the invention using Hall Effect sensors, there is provided in the endplate-endplate combination comprising at least one magnet in one of the endplates (the magnetic component), and at least one Hall Effect sensor in the other endplate (the sensor component). Preferably, the sensor component does not have any magnets thereon.
In some embodiments, height determination may be provided by the inclusion of radioopaque markers within two of the components within the disc.
In preferred embodiments, the prosthetic endplate (as opposed to a core component) is selected as the sensor component. This accommodates the need for robust circuitry needed to actuate the sensor and allows for thin film manufacturing techniques.
The motion disc component of the present invention can be, any prosthetic capable of restoring the natural motions of the intervertebral disc. In preferred embodiments, the motion disc is selected from the group consisting of an articulating disc, a cushion disc and a spring-based disc.
In some embodiments, the general structure of the articulating motion disc comprises:
a) a first prosthetic vertebral endplate comprising:
In some embodiments, the general structure of the articulating motion disc is a two piece design and comprises:
a) a first prosthetic vertebral endplate comprising:
b) a second prosthetic vertebral endplate comprising:
Preferably, the articulation interfaces form partial spheres.
In some two piece designs, the second prosthetic endplate can comprise a metal component comprising the outer surface adapted to mate with a second vertebral body, and a polyethylene component comprising the inner surface comprising a second articulation surface. In some embodiments thereof, the polyethylene component could be part of the adjustable component.
In some embodiments, the motion disc does not have an articulating interface. In some embodiments thereof, the motion disc is a cushion-type design having a pair of rigid endplates and a flexible center portion attached thereto. One of the endplates of this embodiment can be provided with a wedge or cam to help adjust the angle or height of the disc. In other embodiments lacking an articulating interface, the motion disc has upper and lower surfaces that articulate with the opposing natural endplates (such as a football-type design). A wedge or cam can be interpositioned between upper and lower pieces of the football-type disc to help adjust the angle or height of the disc.
In still other embodiments, and now referring to
The motion discs of the present invention can be adapted for use any of the lumbar, thoracic or cervical spine regions. In some embodiments wherein the motion disc is adapted for use in the lumbar region, the three-piece design having a core is selected. In some embodiments wherein the motion disc is adapted for use in the cervical region, the two-piece design is selected.
Preferred articulating motion devices are disclosed in U.S. Pat. Nos. 5,556,431 and 5,674,296, the specifications of which are incorporated by reference. In preferred embodiments thereof, the articulation surface is made of a material selected from the group consisting of a metallic material (such as a titanium alloy, cobalt chromium and stainless steel), and a ceramic material (such as alumina, zirconia and mixtures thereof). Preferably, the core component is adapted for articulation (and so preferably has a surface roughness Ra of no more than 50 um) and more preferably is made of polyethylene, more preferably high molecular weight polyethylene.
Now referring to
In some embodiments, manual means are employed to drive the adjustment means. This manual means may be carried out by minimally invasive or percutaneous procedures. In some embodiments thereof, the inner plate is associated with a worm and pinion gear adapted to rotate the inner plate upon actuation, thereby providing anti-backlash capabilities.
Now referring to
Now referring to
i) an outer plate 51 comprising
ii) an inner plate 61 comprising:
iii) a pinion gear 71 having:
iv) a worm gear 81 having:
In some embodiments, the angle of the articulation interface (vis-a-vis the natural endplates) may be adjusted. This may be conveniently performed by adding wedge-type components to the adjustment means.
Therefore, in some embodiments, there is provided a prosthetic endplate in an intervertebral motion disc, the endplate comprising:
i) an outer plate comprising
ii) an inner plate comprising:
In some embodiments, the wedge is oriented to point towards the center of the device, so that moving the wedge towards the center of the device results in increasing the angle of the articulation surface vis-a-vis the natural endplate, while moving the wedge away from the center of the device results in decreasing the angle of the articulation surface vis-a-vis the natural endplate.
For example, and now referring to
In use, the rotation of the captive screw causes the wedge to move either towards or away from the center of the device, thereby altering the angle of the articulation surface vis-a-vis the natural endplate.
Wedge designs such as that shown in
In other embodiments, angle adjustment is effect by translation. Now referring to
As shown in
Therefore, in some embodiments, there is provided a device similar to that of
As shown in
Therefore, in some embodiments, the screw lengths are reduced so they they do not traverse the center of the device. Such as design is shown in
In other embodiments, the wedges of the angle adjustment means are replaced with pneumatic or hydraulic devices. When these expandable devices are filled with fluid and expand, the angle of the device vis-a vis the endplates is increased. When these expandable devices deflate, the angle of the device vis-a vis the endplates is decreased. In some embodiments, the expandable device may be expanded by simply injecting a fluid such as saline or air into the expandable device. In some embodiments, the expandable device may be filled with hygroscopic material that collects water, and thereby expands. In some embodiments, the expandable device may be filled with a chemical fluid that expands in response to an environmental stimulus such as pH.
As shown in
In preferred embodiments, the screws are captured so that they are contained within the outer plate and are limited to rotational movement only.
In the particular embodiment of
In this embodiment, capture of the screw is achieved by providing anterior and posterior shoulder on the mating plate. Anterior movement of the screw will cause annular clip to contact the anterior shoulder (thereby preventing movement in the anterior direction). Posterior movement of the screw will cause the posterior circumferential projection to contact the posterior shoulder (thereby preventing movement in the posterior direction). In some embodiments, a circle clip replaces the snap ring.
In some embodiments, the captured screw comprises a head selected from the group consisting of a slotted head, an Allen head, a Torx® head, a Phillips head, and a Robertson® head.
Although the above devices are suitably used for treatment of degenerative disc disease, in some embodiments, the wedged discs may also be advantageously used to treat spinal deformity. Surgical correction of spinal deformity typically requires fusion of the operated motion segments, severely reducing the flexibility of the spine. Although conventional artificial disc implants are designed to maintain the motion of the spine, they do not conventionally facilitate correction of a deformed spine. Conventional vertebral body tethering can preserve spinal motion, but requires high forces to achieve intraoperative correction.
In some embodiments, the wedged devices of the present invention may be used to correct spinal deformity.
In some embodiments of the present invention, there is provided a a method and device for correcting spinal deformity comprising removing a portion or all of one more intervertebral discs of a deformed spine, then inserting a wedged prosthetic disc designed to correct the spinal deformity while maintaining a majority of the normal spinal range of motion. In another embodiment, the wedged prosthetic disc is designed to act in concert with a vertebral body tether to correct the spinal deformity. The tethers (rods) could also have adjustable height (length).
The method of this invention provides for correction of spinal deformity using an appropriately designed wedged intervertebral disc prosthesis optionally in concert with a vertebral body tether. The wedged prosthetic disc is designed to maintain surgical correction of the deformity while maintaining most of the normal range of motion of the motion segment.
In one embodiment of this invention, a prosthetic disc alone is used to correct the deformed spinal segment(s) as shown in
In another embodiment of the method of this invention, the prosthetic disc is used in concert with a vertebral body tether to correct the spinal deformity (
The aforementioned illustrations describe correcting spinal segments in which the intervertebral disc is the primary cause for the deformity. However, in some cases the vertebral bodies are the primary cause for the deformity, exhibiting a wedged appearance. In such a case, the prosthetic disc is preferably configured to accommodate a wedged configuration upon correction of the spinal segment, as illustrated in
Now referring to
Now referring to