WO2009073655A1

WO2009073655A1 - Spinal fixation assembly

Info

Publication number: WO2009073655A1
Application number: PCT/US2008/085251
Authority: WO
Inventors: David A. Walsh; Leon W. Bester
Original assignee: Cormed Nv/Sa
Priority date: 2007-12-04
Filing date: 2008-12-02
Publication date: 2009-06-11
Also published as: WO2009073655A9

Abstract

A looking mechanism (100) and method of fixation, such as the fixation of a fixation device (104) like a bone screw and of a rod (106) to the spine. The locking mechanism (100) includes a body (102), a washer (110) and a set screw (112). The washere (110) has at least two internal steps (128a, 128b) that engage the head (140) of a fixation device (104), such as a screw with a spherical head (140).

Description

TITLE OF THE INVENTION SPINAL FIXATION ASSEMBLY

FIELD OF THE INVENTION

[0001] The present invention relates generally to prostheses for treating spinal pathologies, and more specifically to spinal fixation assemblies including an anchor for holding a fixation device and a stabilization rod.

BACKGROUND OF THE INVENTION

[0002] Various methods of spinal immobilization have been used in the treatment of spinal instability and displacement. The most common treatment for spinal stabilization is immobilization of the joint by surgical fusion, or arthrodesis. This has been known for almost a century. In many cases, however, pseudoarthrosis occurs, particularly in cases involving fusion across the lumbosacral articulation and when more than two vertebrae are fused together. Early in the century, post operative external immobilization, such as through the use of splints and casts, was the favored method of spinal fixation. As surgical techniques became more sophisticated, various new methods of internal and external fixation were developed.

[0003] Internal fixation refers to therapeutic methods of stabilization that are wholly internal to the patient and include commonly known devices such as bone plates, screws, rods and pins. External fixation, in contrast, involves at least some portion of the stabilization device being located external to the patients' body. As surgical technologies and procedures became more advanced and the likelihood of infection decreased, internal fixation eventually became the favored method of immobilization since it is less restrictive on the patient.

[0004] Internal fixation of the spine may be used to treat a variety of disorders including kyphosis, spondylolisthesis and rotation, segmental instability, such as disc degeneration and/or fracture caused by disease, trauma, congenital defects and tumor diseases. One of the main challenges associated with internal spinal fixation is securing the fixation device to the spine without damaging the spinal cord. The pedicles of a vertebra are commonly used for fixation as they generally offer an area that is strong enough to hold the fixation device in place even when the patient suffers from degenerative instability such as osteoporosis.

[0005] Current fixation devices and hardware systems used internally for spinal fixation in modern surgical procedures are generally designed to meet one or more criteria, such as: providing rigidity as is indicated, generally along the long axis of the patient's spine; accommodating a broad variation in the size and shape of the spinal member with which it is used; having the capability of handling the stresses and strains to which the devices will be subjected resulting from movement of the spine; and providing easy surgical access during both implantation and removal of the implant.

[0006] The present invention includes a novel fixation device.

BRIEF SUMMARY OF THE INVENTION

[0007] Disclosed is a locking mechanism comprising: a body having a bottom portion and a side portion, the side portion being configured to receive a rod; a fixation device extending at least partially through a hole in the bottom portion of the body, the fixation device comprising an at least partially spherical head; and a washer. The washer includes an opening for receiving a top portion of the head at least two internal steps, each having an edge configured to engage the top portion of the head.

[0008] The edge of one of the internal steps may define the opening of the washer and the cross sections of the washer may be generally circular. In addition, the edges of the internal steps may define generally circular openings. [0009] The body may also have a bottom portion that has at least one lip configured to engage a bottom portion of the head of the fixation device. In addition, each of the at least one lips may define a distinct edge, which may be a right angle. The lips may also define generally circular openings. [0010] Also disclosed is a method for locking the relative positions of a fixation device and a rod comprising. The method comprises: placing a fixation device having a generally spherical head through a hole in the top portion of a body of the locking mechanism; placing a washer having opening and at least two internal steps through the hole in the top portion of a body of a locking mechanism; placing a rod in a side portion of the body such that the rod and head are on opposite sides of the washer; and urging the rod toward the washer such that the at least two internal steps of the washer engage a top portion of the head.

[0011] The method may further comprise causing the hole in the top portion of the body to expand prior to placing the washer through the hole.

[0012] In addition, the step of urging the rod may further comprise causing an edge of each of the internal steps of the washer to engage the top portion of the head.

[0013] The method may further comprise urging the washer and head toward the bottom portion of the body and causing a bottom portion of the head to engage at least one lip in the bottom portion of the body.

[0014] The features of the present invention will be apparent with reference to the following description and attached drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the ways in which the principles of the invention may be employed, but it is understood that the invention is not limited correspondingly in scope. Rather, the invention includes all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto.

[0015] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0016] Figure 1 is a cross-sectional view of a locking mechanism of the present invention with a fixation device and a rod in a locked position; and [0017] Figures 2A-B are full and cross-sectional perspective views of an embodiment of the novel washer of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The invention relates to a novel locking mechanism and method for locking the relative positions of a rod and a fixation device. The locking mechanism provides an improved lock between a rod and the head of a fixation device, such as a screw. The apparatus includes a body and a washer that partially surrounds the head of the fixation device. The washer has multiple steps, each preferably providing a contact surface with the head of the fixation device. [0019] Turning initially to Figure 1 , illustrated is a cross-sectional view of a locking mechanism of the present invention in a locked position. The locking mechanism 100 is configured to engage and lock the position of a fixation device 104 with respect to the position of a rod 106. The locking mechanism 100 includes a body 102, a washer 1 10 and a locking element 1 12. [0020] When the locking mechanism 100 is used for spinal fixation, "above" or "top" means posterior with respect to the patient and "below" or "bottom" means anterior with respect to the patient. Thus, the bottom portion 1 14 of the body 102 is anterior with respect to the patient and the rod 106 is received by the body 102 as the rod 106 is moved in a posterior to anterior direction. [0021] The body 102 includes a bottom portion 1 14 that includes a hole 1 18. The fixation device 104 passes partially through the hole 118. Preferably, the hole 1 18 is large enough to allow the shaft 142 of the fixation device 104 to pass through but not large enough to allow the bottom portion 148 of the head 140 of the fixation device 104 to pass through. Thus, the hole 1 18 is preferably dimensioned to prevent the fixation device 104 from passing entirely there through and exiting the body 102.

[0022] The fixation device 104 is preferably inserted through the top of the body 102 prior to insertion of the washer 1 10 and rod 106. The washer is then preferably inserted through the top of the 102 so that the bottom portion of the washer 1 10 is positioned for interaction with the top portion 146 of the head 140 of the fixation device. As will be understood by those skilled in the art, the washer 1 10 may be wider than the opening in the top of the body 102. Thus, to insert the washer 1 10, a tool may be used to increase the size of the opening in the top of the body 102.

[0023] The body 102 also includes a side portion 120 that is configured to receive the rod 106, such as by way of a channel 124 that enables placement of the rod 106 by either sliding the rod 106 through the side portion 120 of the body or by inserting the rod 106 into the channel 124 through the top portion of the body 102. The washer 1 10 is preferably inserted into the body 102 prior to insertion of the rod 106 such that the washer 1 10 is eventually positioned between the rod 106 and the head 140 of the fixation device 104.

[0024] The locking mechanism 100 may also include a locking element 1 12 that is configured to engage the body 102 and the rod 106 so as to force the rod 106 toward the fixation device 104. The locking element 1 12 and body 102 may be, for example, slidably engageable, rotatably engageable and/or snapably engageable. Accordingly, the body 102 may include threads 122 for engaging the locking element 1 12. In addition, while Figure 1 shows internal threads, it will be understood by those of ordinary skill in the art that the threads may also be external threads and the locking element 1 12 may surround the body 102 during engagement. Preferably, the locking element 1 12 is a set screw, which may be either internally or externally threaded to engage either an externally or internally threaded body 102.

[0025] In use the locking mechanism 100 includes a body 102, a washer 1 10 and a locking element 1 12 for engaging a fixation device 104 and a rod 106. Each of the body 102, the washer 1 10, the locking element 1 12, the fixation device 104 and the rod 106 may be made from a variety of materials known in the art and preferably is made from a biocompatible material when the locking mechanism 100 is used for bone fixation. Such materials include, but are not limited to, titanium, titanium alloys (e.g. titanium/aluminum/vanadium (Ti/AI/V) alloys), cobalt-chromium alloys, stainless steel, ceramics (alumina ceramic, zirconia ceramic, yttria zirconia ceramic, etc.), high strength polymers (e.g. PEEK, PEKK, etc.), pyrolytic carbon, tantalum, carbon composite materials and combinations thereof, which may include mechanically compatible mixtures of the above materials. Such materials are commonly used in bone fixation and the like. Preferably, the materials are rigid and in one embodiment, the body 102, fixation device 104, rod 106, washer 1 10 and locking element 1 12 are all made from Ti/AI/V alloys, such as Ti/6AI/4V ELI.

[0026] While one of skill in the art will recognize that fixation devices 104 other than a screw can be used without departing from the scope of the present invention, a screw is shown and described herein to illustrate the engagement of the fixation device 104 and the body 102, as well as the method for locking the relative positions of a fixation device 104 and a rod 106. Furthermore, various types of screws may be used. Preferably, however, the fixation device 104 has an at least partially spherical head 140.

[0027] The size of the body 102 may be similar to that of known devices. For example, the height of body 102 may range from about 0.4 inch to about 1 inch. Also, the width of body 102 may range from about 0.25 inch to about 1 inch. [0028] The body 102 has a side portion 120 and a bottom portion 1 14. The bottom portion 1 14 may be tapered and may have a socket 1 16 and a hole 1 18. Because the general shape of the type of body 102 illustrated in Figures 1 , 2A-B and 4A-B somewhat resembles a tulip flower, the type of body 102 is often referred to as a "tulip" by those skilled in the art. The socket 1 16 is preferably sized to accept the head 140 of the fixation device 104, such as a screw. The hole 1 18 is preferably located at the bottom of the body 102. [0029] Preferably, the washer 1 10 is configured to at least partially surround the head 140 of the fixation device 104. The diameter of the head 140 is preferably larger than the hole 1 18 so that the head 140 cannot be removed through the hole 1 18 in the bottom 1 14 of the body 102. The washer 1 10 also preferably includes a top hole 132 and a bottom hole 126 to provide access to the head 140 of the fixation device 104 from the top of the body 102. Thus, a driver or similar device may be used to engage the head 140 of the fixation device 104 via the washer 1 10. In this manner, the fixation device 104 can be tightened using a driver or the like without permanently fixing the position of the fixation device 104 with respect to the body 102 and rod 106.

[0030] Turning next to Figures 2A-B, full and cross-sectional perspective views of an embodiment of the washer of the present invention are illustrated. The washer 1 10 includes a bottom hole 126 that is sized to accept part of the top portion 146 of the head 140 of the fixation device 104. The washer 1 10 may be generally circular disc shaped such that cross sections of the washer 1 10 are generally circular.

[0031] The washer 1 10 also preferably includes at least two internal steps 128a and 128b. The internal steps 128a and 128b each have an edge 130a and 130b, respectively for contacting the surface of the top portion 146 of the head 140 of the fixation mechanism 104 during engagement. In addition, the edge 130a may define the opening 126 of the washer 1 10 and both edge 130a and edge 130b may define circular openings.

[0032] Referring again to Figure 1 , the body 102 also includes a channel 124 in the side portion 120 for receiving the rod 106 or other stabilization element, such as a dynamic stabilization element. While a channel 124 is preferred for receiving the rod 106, it will be understood by those skilled in the art that an aperture in the side portion 120 could also receive the rod 106, though a body 102 with an aperture may be more cumbersome to deploy during surgery as a surgeon would have to place the rod 106 through the aperture instead of placing the rod 106 in the channel 124. Using a channel 124 to receive the rod 106 provides greater flexibility for a surgeon.

[0033] After placement of the rod 106 within the channel 124, it is desirable to retain the rod 106 within the channel 124. Accordingly, the side portion 120 of the body 102 also includes threads 122 configured to engage locking element 1 12, which is preferably a set screw. Although internal threads 122 are illustrated in Figure 1 , the threads 122 may be either internal or external to the body 102 depending on the configuration of the body 102 and the locking element 1 12. [0034] The locking element 1 12 is thus engaged with the threads 122 of the side portion 120 of the body 102 to keep the rod 106 within the channel 124. It should be understood, however, that the locking element 1 12 need not engage the body 102 via threaded engagement. The locking element 1 12 and the body 102 may be slidably engageable, rotatably engageable, and/or snapably engageable. In the embodiment disclosed in Figure 1 , the locking element 1 12 and the body 102 are rotatably engageable. To fix the rod 106 with respect to the fixation device 104, the locking element 1 12 preferably is tightened down to apply increasing force to the rod 106 in order to engage and lock the rod 106 and fixation device 104. More specifically, the tightening of the locking element 1 12 causes linear compression of the rod 106 onto the washer 1 10, which in turn forces the fixation device 104 toward the bottom portion 1 14 of the body 102. [0035] The socket 1 16 is configured for locking engagement of the fixation device 104. In order to facilitate locking engagement, the surface of the socket 1 16 may include a rough or knurled surface and/or a surface fixation mechanism, such as ridges, grooves, bumps, pips, or the like to increase the coefficient of friction of the surface. In addition, the head 140 may have rough or knurled surfaces and/or surface fixation mechanisms, such as ridges, grooves, bumps, pips, or the like to increase the coefficient of friction of the surfaces. For example, the surfaces may roughened by blasting, for example, with titanium oxide, glass beads or other suitable blasting material. One of skill in the art will understand that other surface treatments may also be used on the surfaces of the socket 1 16 and the head 140.

[0036] Thus, as the rod 106 is forced downward, such as by tightening of the locking element 1 12, the washer 1 10 and head 140 combination is forced downward into the socket 1 16, which preferably includes a lip 1 17. As shown, the lip 1 17 is tapered and preferably has an edge. Accordingly, the lower portion 148 of the head 140 is caused to contact the lip 1 17, and preferably, the edge of the lip, thereby preventing the head 140 of the fixation device 104 from moving further through the hole 1 18. As the locking element 1 12 is further tightened, the rod 106 is forced more tightly against the top of the washer 1 10 and the edges 130a and 130b are brought into tighter contact with the top portion 146 of the head 140 of the fixation device while the lip 1 17 is brought into tighter contact with the bottom portion 148 of the head 140 of the fixation device 104. Thus, the position of the rod 106 is fixed with respect to the position of the fixation device 104. [0037] While the present invention has been described in association with exemplary embodiments, the described embodiments are to be considered in all respects as illustrative and not restrictive. Such other features, aspects, variations, modifications, and substitution of equivalents may be made without departing from the spirit and scope of this invention which is intended to be limited only by the scope of the following claims. Also, it will be appreciated that features and parts illustrated in one embodiment may be used, or may be applicable, in the same or in a similar way in other embodiments.

[0038] Although the invention has been shown and described with respect to certain embodiments, it is obvious that certain equivalents and modifications may be apparent to those skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the following claims.

Claims

CLAIMS What is claimed is:

1. A locking mechanism (100) comprising: a body (102) having a bottom portion (1 14) and a side portion (120), the side portion (120) being configured to receive a rod (106); a fixation device (104) extending at least partially through a hole (1 18) in the bottom portion (1 14) of the body (102), the fixation device (104) comprising an at least partially spherical head (140); and a washer (1 10) comprising: an opening (126) for receiving a top portion (146) of the head

(140), at least two internal steps (128a, 128b), each having an edge

(130a, 130b) configured to engage the top portion (146) of the head

(140).

2. The locking mechanism (100) of claim 1 wherein the edge of one of the internal steps (128a, 128b) defines the opening (126) of the washer (1 10).

3. The locking mechanism (100) of any one of the previous claims wherein cross sections of the washer (1 10) are generally circular.

4. The locking mechanism (100) of claim 3 wherein the edges (130a, 130b) of the internal steps (128a, 128b) define generally circular openings.

5. The locking mechanism (100) of any one of the previous claims wherein the bottom portion (1 14) of the body (102) comprises at least one lip (1 17) configured to engage a bottom portion (1 14) of the head (140).

6. The locking mechanism (100) of claim 5 wherein each of the at least one lips (1 17) defines a distinct edge.

7. The locking mechanism (100) of claim 6 wherein the edge is a right angle.

8. The locking mechanism (100) of any one of the claims 5-7 wherein each of the at least one lips (107) defines a generally circular opening.

9. A method for locking the relative positions of a fixation device and a rod comprising: placing a fixation device having a generally spherical head through a hole in the top portion of a body of the locking mechanism; placing a washer having opening and at least two internal steps through the hole in the top portion of a body of a locking mechanism; placing a rod in a side portion of the body such that the rod and head are on opposite sides of the washer; and urging the rod toward the washer such that the at least two internal steps of the washer engage a top portion of the head.

10. The method of claim 9 further comprising causing the hole in the top portion of the body to expand prior to placing the washer through the hole.

1 1. The method of any one of claims 9-10 wherein the step of urging the rod further comprises causing an edge of each of the internal steps of the washer to engage the top portion of the head.

12. The method of any one of claims 9-1 1 further comprising urging the washer and head toward the bottom portion of the body and causing a bottom portion of the head to engage at least one lip in the bottom portion of the body.