Patent Application
20120232597
Vertebral fixation (a.k.a. spinal fixation) is a neurosurgical procedure in which two or more vertebrae are anchored to each other through a synthetic vertebral fixation device. The purpose of the vertebral fixation device is to reduce vertebral mobility in order to mitigate the risk of damage to the spinal cord or spinal nerve roots. A vertebral fixation procedure may be necessary to address instances of vertebral deformity, degenerative vertebral disorders (such as spondylolisthesis), or vertebral fractures.
Today spinal pathologies are being treated more and more often using minimally invasive posterior transpedicular or extrapedicular approaches to emplace spinal implant devices. The devices used to achieve vertebral fixation are often some type of permanent rigid or semi-rigid device made of titanium, titanium alloys, polyetheretherketone or carbon fiber amongst others and may comprise rods, plates, spacers, and various combinations thereof. In order to maintain a spinal implant in place, some form of fixation to bone can be used. In other cases, a vertebral fixation device may be used without the use of supplemental fixation (posterior/plate fixation) in which case, fixation is performed through the vertebral fixation device itself.
The most common means for fixing a device to the bone is to use some form of screw (a.k.a. threaded shaft). Common types of screws used in medical procedures include pedicle screws, facet screws, and plate screws. Stable device fixation can also be achieved using blades, nails, hooks, and other such means, but few (if any) of these approaches can provide the same degree of purchase achievable using a screw-type fixation device.
One of the main drawbacks of screws, however, is that they are rigid and inflexible. Consequently, when a screw (or multiple screws) must be emplaced into a fixed body at an awkward angle with respect to the surgical opening necessary for implanting the spacer or other spinal device, a larger or more extensive opening is necessary to properly engage the screws. Unfortunately, the use of a larger or extended opening may not be consistent with the performance of a “minimally invasive” procedure.
Disclosed herein are embodiments of a flexible fixation apparatus (and methods of using same) wherein the flexible fixation apparatus substantially comprises a flexible fixation device comprising a threaded head coupled to a bendable helical structure, and a guide device comprising a threaded fitting corresponding to the threaded head and a helical grooved channel corresponding to the helical structure.
Further disclosed herein embodiments of a flexible fixation device comprising a threaded head and a helical structure couple to the threaded head, wherein the helical structure is bendable upon the application of force.
Further disclosed herein are embodiments of a guide device for a flexible fixation device wherein the guide device comprises an encasement manufactured from a material of greater rigidity than the flexible fixation device, and a shaped channel comprising an ingress and an egress for the flexible fixation device, said channel further comprising a bending feature for bending the flexible fixation device.
To facilitate an understanding of and for the purpose of illustrating the present disclosure, exemplary features and implementations are disclosed in the accompanying drawings, it being understood, however, that the present disclosure is not limited to the precise arrangements and instrumentalities shown, and wherein similar reference characters denote similar elements throughout the several views, and wherein:
In order to allow for minimally invasive insertion of both a spinal device and the fixation device(s) necessary to hold the spinal device in place and/or to provide adequate stability to eliminate the need for supplemental fixation, several embodiments disclosed herein are directed to a flexible fixation device and method that can provide adequate purchase into bone at angles that are awkward for properly engaging inflexible and rigid screws. For certain embodiments, the fixation device is comprised of a head to effect engagement of the device and to acts as an insertion-stop for the device, as well as a helical portion of a suitable cross-sectional geometry to allow for adequate purchase into bone. In such embodiments, the helical portion provides fixation as the helical form engages the bone over a relatively large surface area relative to the size of the entry point. In some embodiments, the helical portion may be configured to resemble a cork screw while in other embodiments the helical portion may be configured to resemble a coiled spring. Regardless of configuration, several embodiments offer both flexibility (to make angled insertion achievable) while retaining enough helical-directional rigidity to achieve the desired implantation and fixation.
In
The helical structure 120 achieves fixation as its coils gain adequate purchase into the bone over a large area compared to the size of the entry point. In certain embodiments, the helical structure may resemble the screw-portion found on a corkscrew but having enough flexibility to be directionally redirectable (from a first or initial direction to a second or subsequent direction) during insertion (e.g., by a guide device having a stiffer composition) and yet is itself stiffer than the bone it is engaging in order to retain its coiled structure and provide the desired fixation. In some embodiments, the helical structure may be formed such that subsequent helical coils are spaced further apart than the cross-sectional diameter of the coils, while other embodiments may be formed such that the subsequent helical coils are spaced a distance equal to the cross-sectional diameter of the coils. In
To effect the desired change in angle of the flexible fixation device 100, a guide device may be used.
The helical-grooved channel 324 further comprises a bending feature 326 that guides the coils of the helical structure 120 into a new direction corresponding to a desired resultant angle different from the direction of travel at the ingress 320a. The bending feature 326 initially distorts the spacing between the coils of the helical structure 120 to make the bend and change the direction of travel, and then the bending feature 326 returns the coils to of the helical structure 120 to roughly their original spacing between the coils before such coils exit the encasement 310 at the egress 320b.
For certain embodiments, more than one flexible fixation devices 100 may be used to secure a particular guide device 300 in place. Yet other embodiments may utilize a guide wire through the central channel of the guide device 300 (between the ingress 320a and the egress 320b). Yet other embodiments are directed to the utilization of a flexible fixation device in a fixation target other than bone such as, for example, wood, plaster, rock, or any other solid materials. Yet other embodiments are directed to the use of a guide device that is not inserted but operates external to the fixation target.
The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.
