Patent Application
20160095637
The present disclosure relates to orthopaedic fixation systems, and in particular to cervical fixation systems in which bone screws extend through openings in a plate configured to span two or more cervical vertebrae.
Fixation plates are often used to help stabilize the cervical spine, such as to assist an interbody implant(s) in the fusion of two or more adjacent cervical vertebrae. In the typical fixation procedure, the curved bottom surface of the cervical plate is placed on the anterior faces of the vertebral bodies and screws are driven through openings in the plate into the underlying bone.
One problem of cervical fixation systems is maintaining screw fixation in the bone, or more specifically preventing one or more bone screws from backing out of the vertebral body. Prior devices address this problem with complicated locking mechanisms or locking tools that can affect the cost, complexity, prominence and reliability of the fixation system. One further problem with prior locking mechanisms is that a special instrument is required to actuate the mechanism once the bone screw is seated within the plate and bone.
A cervical fixation plate comprises a body defining one or more bone screw openings sized and configured to receive the shank of a bone screw therethrough with the head of the bone screw seated within the opening. A locking post extends from the body adjacent one or more of the bone screw openings with a locking element rotatably mounted thereon. The locking element includes a wing corresponding to each of the bone screw openings, with each wing sized to overlap a portion of the bone screw opening when the locking element is in a locking orientation and the head of a bone screw is seated within the bone screw opening. A swaged interface between the locking post and the locking element retain the locking element on the body while permitting the locking element to be rotated from a locking orientation to an orientation in which the bone screw openings are unimpeded to permit introduction of a bone screw.
In another aspect, a tool is provided for rotating the locking element when the fixation plate is in situ. The tool includes a guide post that is received within a bore defined in the locking post to facilitate placement of the tool. The tool further includes an engagement body at the end of a tool shaft that is configured to engage the locking element. The engagement body defines opposite notches that can receive a corresponding wing of the locking element to permit rotation of the locking element by rotation of the tool.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains.
A cervical fixation plate 10 is provided with a locking mechanism 20, as depicted in
In one aspect of the present disclosure, the plate is provided with a locking post 26 disposed between pairs of bone screw openings 12. In the illustrated embodiment, a locking post is disposed between all of the bone screw openings 12. However, it is contemplated that a locking post and associated locking mechanism 20 may be provided for a single bone screw opening or for less than all of the openings on a given fixation plate.
The locking post defines a bore 26a and a conical surface 26b. For manufacturing simplicity, the bore 26a can extend through the thickness of the body 11 of the plate 10, although it is understood that the bore 26a can be configured as a blind bore. A locking element 22 of the locking mechanism 20 includes a central opening 24 that includes a conical portion 24a and a cylindrical portion 24b that is sized for a close fit over the locking post 26, as shown in
The locking element 22 includes opposite wings 28 that are arranged to overlap a portion of the bone screw openings 12 when screw heads are present within the openings. The wings 28 includes relief surfaces 29 that coincide with the outer circumference of the screw openings 12 when the locking element 22 is in a first orientation in which the wings extend across the width of the plate 10 with the relief surfaces 29 immediately adjacent a corresponding bone screw opening. In this orientation, the locking element does not encroach into the openings. The locking element can thus be rotated to the first orientation in which the wings 28 do not impede placement of a bone screw into each of the openings 12 (180° opposite to the orientation shown in
The locking element 22 can be formed of a biocompatible material with sufficient rigidity to avoid bending under force from the bone screw should it attempt to back out of the vertebral bone. The locking element may be a metal, and particularly the same metal used to form the fixation plate to avoid any galvanic reaction between dissimilar metals. In one example, the locking element and plate can be formed of titanium or a medical grade stainless steel. Alternatively, the locking element may be formed of a biocompatible plastic or resin material that resists degrading over time.
The cervical plate 10 may be provided to the surgeon with the locking elements fastened to the plate—i.e., with the post 26 swaged onto the locking element 22. Preferably, the plate is provided with the locking elements in the first orientation described above in which the relief surfaces 29 are aligned with the bone screw openings 12. The surgeon can position the plate 10 on the vertebral body and introduce all of the bone screws through the openings 12 to engage the plate to the vertebral body. Once a pair of bone screws are disposed in an adjacent pair of openings, the associated locking element 22 may be rotated by a tool 30, as illustrated in
In the illustrated embodiment, the wings 28 are arranged 180° opposite each other to overlap bone screw openings that are themselves on directly opposite sides of the fixation plate 10. It can be appreciated that some fixation plates may include bone screw openings that are offset along the length of the fixation plate. In this instance, the wings 28 of the locking element 22 may be correspondingly offset from the 180° opposite position. It can be further appreciated that the locking element may be provided with three wings arranged at 120° intervals to overlap three similarly arranged bone screw openings.
In the illustrated embodiment, the locking post 26 projects from the surface of the fixation plate 10. Alternatively, the locking post may be situated within a recess with the locking element 26 seated within the recess. This configuration reduces the profile of the locking mechanism; however, the recessed locking mechanism will also reduce the height of the bone screw head that can be accepted within the bone screw opening of the plate.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.
This application is a utility filing from and claims priority to U.S. Provisional Application No. 62/059,953, filed on Oct. 5, 2014, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62059953 | Oct 2014 | US |
