Patent Application
20080234680
Various types of implantable devices are useful in fixing bones in the body. The structure of the device is typically dependent on the bone or bone sections being fused. One type of fixation device is a cervical plate, which are implanted to increase neck stability and to promote fusion of adjacent vertebrae following surgery to remove a diseased or damaged disc in the spine. The cervical plates are available as either static or dynamic structures.
A typical static cervical plate is a single metal piece that uses screws to attach the plate to two (or more) adjacent vertebrae. Because these plates are one piece of metal, they are relatively rigid, allowing little of no movement between the connected vertebrae.
More recently, a “dynamic” plate technology has been developed, whereby two or more individual plate sections or pieces are joined together to form the implanted cervical plate. The union between the sections allows for some movement between the individual pieces, while still providing stability and promoting bone fusion. Therefore, when it is installed, the vertebrae will have a small level of movement. Typically, dynamic plate sections are mated together using a male/female dovetail design, but other mating designs are possible.
In both cases, the cervical plate is typically made from a rigid biocompatible material, such as Titanium or stainless steel.
One challenge to constructing dynamic fixation plates is in connecting the individual parts in a manner that allows movement of the plates, but does not allow the plates to become unintentionally disassembled. In accordance with particular embodiments of the invention, individual plate sections can be internally interlocked to maintain the assembled plate and to limit relative motion between the sections.
In accordance with a particular embodiment of the invention, a dynamic bone fixation plate can include a first plate section, a second plate section, and a compressible interlock member. The first plate section includes a first joint structure and the second plate section includes a second joint structure, where the second joint structure can be dynamically mated with the first joint structure. The compressible interlock member can be disposed within the first joint structure and the second joint structure to limit relative motion of the first joint structure and the second joint structure.
More particularly, the first joint structure and the second joint structure can mate as a dovetail joint. When joined, the first and second plate sections can form a dynamic cervical plate.
The first joint structure can include a slot and the second joint structure can include a channel, the slot and channel being aligned. Furthermore, the interlock member can be disposed within the slot and channel. The first plate section can be moveable relative to the second plate section by a distance based on the dimensions of the channel. In addition, an access port can extend from the channel to the outside of the second joint structure.
The interlock member can comprise a superelastic material, which can be machined. More particularly, the material can be a Nickle-Titanium alloy, such as Nitinol materials.
In accordance with another particular embodiment, a dynamic cervical plate can comprise a first plate section, a second plate section, and a compressible interlock member. The first plate section can include a male dovetail structure and the second plate section can include a female dovetail cavity, where the male dovetail structure is slidably mated with the female dovetail cavity. The compressible interlock member is disposed within the male dovetail structure and the female dovetail cavity to limit relative motion of the male dovetail structure within the female dovetail cavity.
In accordance with another particular embodiment, a dynamic cervical plate can comprise a first plate section, a second plate section, and a superelastic interlock member. The first plate section can include a male dovetail structure and the second plate section can include a female dovetail cavity, where the male dovetail structure is slidably matable with the female dovetail cavity. The superelastic interlock member can be disposed within the male dovetail structure and the female dovetail cavity to limit relative motion of the male dovetail structure within the female dovetail cavity.
Embodiments of the invention can also include methods of manufacturing and using the described plates.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Multi-section dynamic bone fixation devices are known in the art and are commercially available from various manufacturers. In general, each manufacturer incorporates its own specific solution for mating the sections. For cervical plates, dovetail mating is typical. For illustration purposes, the concepts of the invention are described with reference to a specific dynamic cervical plate. The invention, however, is not limited to the described cervical plate its specific mating solution.
As shown, the first section 100 includes a first main body 110 and the second section includes a second main body 210. Mounting holes 115a, 115b, 215a, 215b extend through the main body 110, 210 for receiving screws that mount the assembled plate 10 to the desired vertebrae. Also shown are interior contours 112, 212 and exterior contours 114, 214.
The plate sections 100, 200 mate using a male/female dovetail interconnect. Each section 100, 200 is generally U-shaped having leg structures 120 and 220, respectively. The leg structures 120, 220 slidably mate to provide dynamization when attached to the bone. The first section 100 includes legs 120a, 120b that are fabricated as male dovetails. The second section 200 includes legs 218a, 218b that have respective female cavities 220a, 220b dimensioned to receive the male legs 120a, 120b.
Once assembled, the plate sections 100, 200 are secured to the bone, but the plate sections 100, 200 are free to move relative to each other because the leg structures 120, 218 can slide relative to each other. The sections 100, 200 can slide apart, especially during surgery. One challenge to constructing dynamic fixation plates is in connecting the individual parts in a manner that allows movement of the plates, but does not allow the plates to become unintentionally disassembled.
During assembly, a compressible interlock member 300 is seated in the interlock slots 125. The interlock member 300 is then compressed into the slot 125 and the male dovetail leg 120 is slid into the female dovetail cavity 220. As shown, the interlock member 300 is an arch shaped member resembling a miniature leaf spring.
Returning to
Also shown is an access port 230, which extends from the female dovetail cavity 225 to the exterior of the female leg 218. To remove the male dovetail leg 125 from the female dovetail cavity 220, the interlock member 300 must be compressed into the interconnect slot 125 or channel 225. To that end, a tool such as pin or needle can then be inserted into the access port 230 to engage and compress the interlock member 300. In the particular embodiment of
As shown in
In a particular embodiment, the compressible interlock member 300 is fabricated from a malleable biocompatible material. In a particular embodiment, the malleable material is a Nickle-Titanium alloy, such as Nitinol, which has shape memory and superelastic properties at body temperatures. In use, the Nitinol interlock member 300 deforms under compression, but because of the superelastic effect, the spring will return to its original shape.
More particularly, the interlock member 300 can be machined from a Nitinol bar, which can provide improved performance over similarly shaped springs that are stamped from Nitinol sheet material. In a specific embodiment, the interlock member 300 is machined from a 0.250 inch (nominal) diameter bar of SE-510 Nitinol, commercially available from Nitinol Devices and Components, Inc. of Fremont, Calif. A particular alloy bar is superelastic straight, centerless ground, with an Aƒ at about 10° C. Any Nitinol alloy having an Aƒ at between about 10° C. and 25° C. would be acceptable, with 18° C. being a target temperature. Depending on the design specifics, other Nitinol alloys, or other superelastic materials, with varying characteristics can also be used for the interlock member 300. Because the interlock member 300 can be machined, its shape is not constrained by limitations inherent in wire or sheet materials.
As shown, the interlock member 300 is an arch-shaped member similar to a miniature leaf spring. The dimensional constraints on the interlock member 300 are that it should fit within the interconnect slot 125 when compressed (such as being flattened) and that its expanded free height should be higher than the interconnect slot 125. In a particular embodiment, the expanded free height of the interlock member is at least as high as the combined heights of the interconnect slot 125 and the interconnect channel 225. Consequently, the dimensions of the interlock member 300, the interconnect slot 125 and the interconnect channel 225 are interrelated.
It should be understood that other interlock members forms can be employed with corresponding modifications to the interconnect slots and interconnect channels. While not limiting, examples of such other forms are disclosed in the incorporated provision application. The concepts of the invention are not limited to the disclosed forms, as one of ordinary skill in the art can readily appreciate other useable forms. In addition, the concepts of the invention are not limited to cervical plates and can be applied to other dynamic plate systems beyond that shown in
While this invention has been particularly shown and described with references to particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the embodiments without departing from the scope of the invention encompassed by the appended claims. For example, various features of the embodiments described and shown can be omitted or combined with each other.
This application claims the benefit of U.S. Provisional Application No. 60/886,916 entitled “Dynamic Cervical Plate”, filed on Jan. 26, 2007, the entire teachings of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60886916 | Jan 2007 | US |
