Patent Application
20070168040
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”).
Surgeons currently desire an instrument that will accurately and consistently seat a motion disc within a disc space. There are several qualities to a properly seated disc. When the teeth on the outer surfaces of the inserted disc are fully engaged, there is a significantly reduced risk that the motion device will shift after surgery, which could result in expulsion of the prosthesis.
The current state of the art in motion discs typically involves the use of a spreader device that is inserted between and pressed against the opposing prosthetic disc endplates. Upon mechanical actuation, the spreader device opens and the prosthetic endplates are spread apart. One problem with these spreader devices is that they are often very cumbersome. The spreader devices also provide the surgeon with little tactile feel, which assists the surgeon in determining whether the device has been properly seated. Lastly, there is limited space for fitting a spreading mechanism, especially, in the cervical spine.
In some instances, surgeons apply a perpendicular force to the prosthetic vertebral endplates by use of distraction pins.
US Published Patent Application No. 2004/0167537 (“Errico”) discloses an instrument called a leveler 600 that has a tuning fork shape and is adapted to be inserted between the endplates of an articulating intervertebral motion disc. According to Errico, this leveler functions as a wedge to force the endplates apart and secure purchase of the stabilizing spikes. However, the use of a wedge between the endplates is problematic in that it typically requires high impaction forces in order to properly locate itself deep within the disc space. These high impaction force may undesirably jostle the motion disc, and may also cause undesirable posterior movement of the endplate (and core, if present) components.
Therefore, current seating techniques can not provide both tactile feedback and visual confirmation, and require additional fluoroscopic imaging to confirm the appropriateness of the seating.
It is an object of the present invention to ensure that the teeth on the outer surface of the prosthetic endplates are fully engaged with the bony vertebral endplates without having high impaction forces.
The invention comprises a tuning fork-like seating device having a proximal shaft, an intermediate portion, and distal tynes extending from the intermediate portion. The seating device has a head portion that is relatively thin in relation to the distance between the endplates, so that when it is inserted between the prosthetic endplates that are at least partially engaging their respective bony endplates, only one of the upper and lower surfaces of the tynes contacts an inner surface of the prosthetic endplates. By moving the proximal shaft either superiorly or inferiorly, the device will pivot about its intermediate portion upon a proximal portion of a first endplate, and the distal tynes will bear against the distal inner surface of the second prosthetic endplate, thereby causing the prosthetic endplates to separate from each other and pushing the exterior teeth into the bony vertebral endplates. This process can then be repeated by moving the proximal portion of the device in the opposite direction, so that the device will pivot about its intermediate portion upon a proximal portion of the second endplate, and the distal tynes will bear against the distal inner surface of the first prosthetic endplate,
The slim nature of the design of the present invention not only greatly improves the instrument's tactile feel and enables visual confirmation of the proper placement of the prosthetic components, it also does so with requiring high impaction forces.
Therefore, in accordance with the present invention, there is provided an assembly for seating prosthetic endplates of an intervertebral disc between upper and lower vertebral endplates, comprising:
a and 3b disclose perspective and side views of a second embodiment of the seating device of the present invention, wherein the upper and lower surfaces of the tynes are concave.
In some embodiments, the invention includes a proximal shaft and distally extending tynes. In some embodiments, there is provided an intermediate section that extends transverse to the proximal shaft, and from which the distal tynes extend distally. In this manner, the intermediate and tynes portions comprise a head portion, and the device is shaped substantially similar to a tuning fork. The head is inserted between the prosthetic endplates, with one tyne being inserted on either side of the device's bearing surfaces.
Now referring to
In some preferred embodiments, there is provided a method for seating endplates of an intervertebral disc between upper and lower vertebral endplates, comprising the steps of:
The resultant assembly that results from the above method is shown in
Upon superior or inferior movement of the proximal shaft, a lever is created by which the dovetail becomes a fulcrum and the distal end of the seating device applies a force opposite the movement of the handle. Repeated back and forth motion of the handle applies this levered force to the prosthetic endplates, which results in a seating of the teeth.
The seating device of the present invention enables the surgeon to insert a slim instrument into the disc space and apply a precision force perpendicular to the teeth that will assist in properly seating the prosthetic endplates. The seating device of the present invention does not require an actuation mechanism to apply the seating force and instead uses the mechanical advantage provided by a simple lever.
The seating device of the present invention is designed such that it provides both tactile feedback as well as visual confirmation of accurate placement. Both of these beneficial qualities could greatly reduce the need for additional fluoroscopic imaging that is currently required to confirm seating.
In some embodiments, the intermediate section of the seating device extends transverse to the proximal shaft, and the distal tynes extend from the ends of the transverse intermediate section. The U-shaped head formed by this arrangement allows the seating device to be inserted into the disc space and avoid contact with a core component that has been placed between the prosthetic endplates.
Now referring to
The instrument disclosed herein may be suitably manufactured from any suitable biomaterial, including metals such as titanium alloys, chromium-cobalt alloys and stainless steel), ceramics (such as alumina and zirconia, and mixtures thereof) and polymers (such as PEEK, carbon fiber-polymer composites and UHMWPE).
In some embodiments, at least the upper and lower surfaces of the tynes are coated with a polymer. The polymer coating protects the peripheral rims of the prosthetic endplates from any unwanted abrasion that could occur during the spreading of the endplates by the tynes. In some embodiments, the transverse intermediate section is also coated with the polymer. In some embodiments, the proximal shaft is also coated with the polymer.
In some embodiments, the tynes are contoured with a protrusion to provide point contact with the inner surface of the respective endplate. Preferably, the contour is provided as a concave or convex upper and/or lower surface. Therefore, and now referring to
In some embodiments, torsional movement of the proximal portion of the device is used to seat the prosthetic endplates. By moving the proximal shaft radial in a first direction, the device will pivot about a first tyne upon a first endplate, and the second tyne will bear against the second prosthetic endplate, thereby causing the prosthetic endplates to separate from each other and pushing the exterior teeth into the bony vertebral endplates. This process can then be repeated by moving the proximal portion of the device in the opposite radial direction, so that the device will pivot about its second tyne upon the second endplate, and the first tyne will bear against the first prosthetic endplate.
In some embodiments, the device of the present invention is intended to be used in conjunction with a distractor that has been seated with caspar pins. However, the presence of the caspar pins (or the distractor tubes that overlie the pins) may interfere with the ability of the device of the present invention to fully pivot. Therefore, in some embodiments of the present invention, a portion of the shaft of the device is offset in order to avoid the caspar pins and/or distractor tubes during operation.
In particular, and now referring to
In some embodiments, the proximal shaft of the present invention can be modified to include a docking arm. This docking arm can dock to a nearby structure (such as the above mentioned distractor arm) and provide a fulcrum upon which the device of the present invention can pivot. By using the docking arm, the fulcrum is moved more proximal to the surgeon (i.e., from the intermediate portion of the device to the proximal shaft), and so the is advantageous because additional leverage is provided, the clinician needs to produce less of an angle in order to achieve the same bias, and the docking is now being achieved off of a more stable surface.
In particular, and now referring to
In some docking arm embodiments, the device of the present invention has a scissors configuration, wherein the docking arm and head portion are each coupled to pivotally connected shafts.
Now referring to
a) first 603 and second 605 handles defining a first longitudinal axis;
b) first 607 and second 609 shafts respectively pivotally connected with the first and second handles, each shaft having a distal end 611;
c) a head portion 613 for seating prosthetic endplates connected to the distal end of the first shaft, the head portion comprising:
In some embodiments, the tynes are curved to form arcs, and one tyne is shorter than the other tyne. In particular, and now referring to
Therefore, in accordance with the present invention, there is provided a seating device for seating endplates of an intervertebral disc between upper and lower vertebral endplates, comprising:
wherein the end 811 of the second tyne forms an angle β with respect to the distal end of the shaft and the midpoint, wherein the angle β is less than 90 degrees.
Preferably, the first tyne forms an arc describing an angle α of greater than 135 degrees, while the second tyne forms an arc describing an angle β of less than 45 degrees.
Preferably, angle α and angle β total less than 180 degrees, in this condition, the device may be inserted substantially laterally from the side of the endplate.
Preferred articulating motion devices for use with the present invention are disclosed in U.S. Pat. Nos. 5,556,431 and 5,674,296, the specifications of which are incorporated by reference.
In some embodiments, the general structure of the three piece articulating motion disc comprises:
a) a first prosthetic vertebral endplate comprising:
b) a second prosthetic vertebral endplate comprising:
c) a core member 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.
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.
