Spinal fixation locking mechanism

The present invention relates to a locking mechanism and method of fixation, such as the fixation of a fixation device like a bone screw and of a stabilization device like a rod to the spine. The locking mechanism includes a seat and a locking element. The seat includes a bottom portion configured to receive the fixation device such that a socket of the bottom portion engages part of the fixation device and prevents the fixation device from passing entirely therethrough. The seat further includes a side portion configured to receive the stabilization device and a locking element. The locking element, when fully engaged with the side portion of the seat, causes locking of the relative positions of the fixation device and the stabilization device.

FIELD OF THE INVENTION

The present invention relates generally to prostheses for treating spinal pathologies, and more specifically to a bone interface anchor for holding a stabilization rod.

BACKGROUND OF THE INVENTION

Various methods of spinal immobilization have been used during this century 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 is a problem, 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 the use of splints and casts was the favored method of spinal fixation. As surgical techniques became more sophisticated, various methods of internal and external fixation were developed.

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 patient's body. As surgical technologies and procedures became more advanced and the likelihood of infection decreased, internal fixation became the favored method of immobilization since it is less restrictive on the patient.

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 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 to fix the treatment area even when the patient suffers from degenerative instability such as osteoporosis. Early fixation devices involved the use of screws extending through the facets and into the pedicles.

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.

Of these factors, the most difficult to achieve may very well be providing easy surgical access when the implant is being deployed and/or removed by surgeon. In particular, surgeons often wish to fit, test, adjust and refit fixation devices numerous times during a procedure in order to ensure that the device is optimally positioned. This is particularly important when dealing with the spinal column due to the risk of paralysis.

One example of a device designed as an attempt to meet the above-described criteria is disclosed in U.S. Pat. No. 5,466,237. The fixation device disclosed includes what is described as a variable position locking anchor having a bone screw and a seat.

The disclosed device uses a nut as a locking mechanism. As disclosed, the nut is tightened to the seat to compress an attached rod along a longitudinal axis of the screw, causing the screw to engage in mating contact with the seat and thereby locking the screw in place. In use, it is difficult to maintain proper positioning of the fixation device while tightening a nut or other such locking mechanism. Moreover, many existing fixation devices suffer from splaying apart of the sides of the seat of the fixation device when compressive force is used to locking a rod in position with a screw. The sides of the seat can splay apart and creates gaps in the fixation device and decreases its effectiveness. It would preferable if the fixation device was resistant to splaying.

It would be preferable if the screw could be locked without having to generate the necessary compressive force by tightening the nut or other such locking mechanism. It would also be preferable if the locking mechanism included a partial or preliminary lock for assisting the surgeon in fitting the implant prior to finally locking the implant in place. It would further be preferable if the locking mechanism was designed to prevent, or at the very least, minimize splaying of the various parts of the locking mechanism.

The present invention includes a novel fixation device that overcomes the disadvantages of the prior art.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a locking mechanism configured to engage and lock a relative position of a bone fixation device and a relative position of a stabilization device. The locking mechanism comprises a seat having a bottom portion configured to receive the fixation device and prevent the fixation device from passing entirely therethrough, as well as a side portion configured to receive the stabilization device and a locking element between the fixation device and the stabilization device. The side portion of the seat is configured to receive the locking element such that receipt of the locking element causes locking of the relative positions of the fixation device and the stabilization device.

According to another aspect of the present invention, there is provided a locking mechanism configured to engage and lock a relative position of a bone fixation screw and a relative position of a rod. The locking mechanism comprises a tulip shape seat having a bottom portion configured to receive a fixation screw having a head and a shaft where the head is wider than the shaft. The bottom portion has a hole larger than the shaft and smaller than the head such that when a fixation screw is passed through the hole, the bottom portion engages the head. The tulip shape seat also has a side portion configured to receive the rod and a wedge between the rod and the fixation screw. The side portion of the tulip shape seat is configured to receive the wedge such that receipt of the wedge by the side portion of the tulip shape seat forces the fixation screw and the rod apart and causes locking of the relative positions of the fixation screw and the rod.

According to another aspect of the present invention, there is provided a method for locking the relative positions of a fixation device and a stabilization device comprising: fixing to bone a fixation device extending through a bottom portion of a seat; placing a stabilization device through a side portion of the seat; and slidingly engaging a locking element with the side portion of the seat between the stabilization device and the fixation device to cause locking of the relative positions of the fixation device and the stabilization device.

DETAILED DESCRIPTION OF THE INVENTION

Turning initially to FIGS.1and2A-D,FIG. 1shows an exploded perspective view of the locking mechanism of the present invention, andFIGS. 2A-Bshow cross sectional views of the locking mechanism of the present invention. The locking mechanism100is configured to engage and lock the relative position of a fixation device104with respect to the relative position of a stabilization device106. The locking mechanism100includes a seat102and a locking element108. The seat102includes a bottom portion114that is configured to receive the fixation device104such that the socket116of the bottom portion114engages part of the fixation device104and prevents the fixation device104from passing entirely therethrough.

The fixation device104may be, for example, a screw having a head140and shaft142with threads144. Examples of fixation devices104are shown inFIGS. 5A and 5B. In order to prevent the fixation device104from passing entirely through the seat102, the seat102preferably includes a hole118that is larger than the shaft142and smaller than the head140. When the fixation device104is forced toward the bottom portion114of the seat102, the socket116of the bottom portion114of the seat102engages the head140of the fixation device104. In addition, the socket116of the bottom portion114may be tapered to receive and engage the fixation device104.

The seat102also includes a side portion112that is configured to receive the stabilization device106and a locking element108. The stabilization device106may be, for example, a rod, and the side portion112of the seat102may include a channel124for receiving the stabilization device106.

The locking mechanism100may also include a retaining element110that is configured to engage the seat102and the stabilization device106such that the retaining element110acts to limit movement of the stabilization device106away from the fixation device104. The retaining element110and seat102may be, for example, slidably engageable, rotatably engageable and/or snapably engageable. Accordingly, the seat102may include a retaining groove122for receiving the retaining element110. In addition, the seat102may also include a lip to reduce splaying of the sides of the seat102.FIGS. 2C-Dshow different types of configurations of retaining grooves122and retaining elements110that can be used to help prevent splaying of the sides112of the seat102.

The locking element108is configured for engagement with the side portion112of the seat102to cause locking of the relative positions of the fixation device104and the stabilization device106. The locking element108is preferably engageable with the side portion112of the seat102between the fixation device104and the stabilization device106such that the locking element108causes the fixation device104and the stabilization device106to be forced apart.

To facilitate engagement with the locking element108, the side portion112of the seat102may include at least one locking groove120configured to accept a slidably engageable locking element108. The locking groove120may be positioned in the side portion112of the seat102such that the locking element108is generally parallel to a longitudinal axis of the stabilization device106when engaged with the seat102. The locking element108may be partially engageable with the seat102such that the fixation device104and the stabilization device106are caused to become partially locked so as to facilitate placement and alignment of the fixation device104and the stabilization device106. Once the locking element108is fully engaged, repositioning may be more difficult.

The locking element108is preferably disengageable from the seat102once partially engaged with the seat102so as to facilitate a change in placement or alignment of the fixation device104and/or the stabilization device106. In order to make the locking element108more readily disengageable from the seat102, the locking element108may be longer than the width of the seat102so that when the locking element108and seat102are fully engaged, the locking element108protrudes from the side portion112of the seat102. The locking element108may also be configured such that the locking element108permits access to the fixation device104when the locking element108is partially engaged with the seat102.

The locking element108may include, for example, a wedge, a normally open biased structure or an inflatable structure. Preferably, the locking element108has a fixation device side132and stabilization device side130wherein the surface of at least one of the fixation device side132or stabilization device side130is a ramped surface. It will also be understood that the present invention may utilize a locking element108that is not ramped at all. In addition, the stabilization device side130may be contoured to interact with the contour of the stabilization device106and the fixation device side132may be contoured to interact with the contour of the fixation device108.

Turning now toFIGS. 2A and 2B, the locking mechanism100of the present invention is illustrated in greater detail.FIG. 2Ais a cross-sectional side view of the locking mechanism100of the present invention with a fixation device104and a stabilization device106.FIG. 2Bis a cross-sectional front view of the locking mechanism100of the present invention with a fixation device104and a stabilization device106.

The locking mechanism100includes a seat102and a locking element108for engaging a fixation device104and a stabilization device106. The locking mechanism100may also include a retaining element110to assist in engagement. Each of the seat102, fixation device104, stabilization device106, locking element108and retaining element110may be made from a variety of materials known in the art and preferably are made from biocompatible materials when the locking mechanism100is used for bone fixation. Such materials include, but are not limited to, titanium, titanium alloys (e.g. titanium/aluminum/vanadium (Ti/Al/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. Some materials are more appropriate for fixation surfaces, such as cobalt-chromium alloys, titanium, and (Ti/Al/V) alloys, but any material known in the art for use with fixation surfaces can be used in the present invention. Such materials are commonly used in bone fixation and the like. Preferably, the materials are rigid and in one embodiment, the seat102, fixation device104, stabilization device106, locking element108and retaining element110are all made from Ti/Al/V alloys, such as Ti/6Al/4V ELI.

While one of skill in the art will recognize that fixation devices104other 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 device104and the seat102, as well as the method for locking the relative positions of a fixation device104and a stabilization device106. Furthermore, various types of screws may be used. Two exemplary types of screws are illustrated inFIGS. 5A and 5B.

The size of the seat102may be similar to that of prior art devices. For example, the height of seat102may range from about 0.4 inch to about 1 inch. In one embodiment, the height of the seat102ranges from about 0.588 inch to about 0.598 inch. Also, the width of seat102may range from about 0.25 inch to about 1 inch. In one embodiment, the width of the seat102ranges from about 0.405 inch to about 0.415 inch.

The seat102has a side portion112and a bottom portion114. The bottom portion114may be tapered as shown inFIG. 2Band includes a socket116and a hole118. Because the general shape of the type of seat102illustrated in FIGS.1and2A-B somewhat resembles a tulip flower, this type of seat102is often referred to as a “tulip” by those skilled in the art. The socket116is preferably sized to accept a fixation device104, such as a screw, and the hole118is preferably sized to prevent the fixation device104from passing entirely therethrough. The hole118is preferably located at the bottom of the seat102.

The socket116is configured for locking engagement of the fixation device104, or more specifically, the engagement surface146of the head140of the fixation device104. In order to facilitate locking engagement, the surface of the socket116may include a rough or knurled surface and/or a surface fixation mechanism, such as ridges, grooves, bumps, pips, or the like. In addition, an engagement surface146of the fixation device104may have a similar surface.

The seat102also includes a channel124in the side portion112for receiving the stabilization device106, such as a rod or a dynamic stabilization element. While a channel124is preferred for receiving the stabilization device106, it will be understood by those skilled in the art that an aperture in the side portion112could also receive the stabilization device, though a seat102with an aperture may be more cumbersome to deploy during surgery as a surgeon would have to place the stabilization device106through the aperture instead of placing the stabilization device in the channel124. Using a channel124to receive the stabilization device106provides greater flexibility for a surgeon.

After placement of the stabilization device106within the channel124, it is desirable to retain the stabilization device106within the channel124so that a locking element, such as locking element108, can fix the position of the stabilization device106. Accordingly, the side portion112of the seat102also includes retaining grooves122aand122bconfigured to receive a retaining element110. The retaining grooves122aand122bare located at least above the centerline of the stabilization element106in the channel124and may be located above the top of the stabilization element106in the channel124. When the locking mechanism100is used for spinal fixation, “above” means posterior with respect to the patient and “below” means anterior with respect to the patient. Thus, the bottom portion114of the seat102is anterior with respect to the patient and the fixation device104and stabilization device106are received by the seat102as the fixation device104and stabilization device106are moved in a posterior to anterior direction.

The retaining element110is thus engaged with the retaining grooves122aand122bof the side portion1124of the seat102to keep the stabilization device106within the channel124. The retaining element110and the seat102may be slidably engageable, rotatably engageable, and/or snapably engageable. In the embodiment disclosed in FIGS.1,2A-B and3A-D, the retaining element110and the seat102are rotatably engageable. It will be understood by those of skill in the art that the primary purpose of the retaining element110is not to force the stabilization device106into engagement with the fixation device104. Rather, the primary purpose of the retaining element110is to prevent the stabilization device106from being forced out of the channel124by the locking element108. In other words, the retaining element110is not screwed down to apply increasing force to the stabilization device106in order to engage and lock the stabilization device106and fixation device104. Without the locking element108, the retaining element110by itself is not designed to lock the fixation device104and engagement device106.

The side portion112of the seat102is also configured to receive a locking element108that is configured to engage the side portion112of the seat102. In the exemplary embodiment ofFIGS. 1,2A-B and3A-D, the locking element is slidably engageable with locking grooves120aand120bof the side portion112of the seat102. In this embodiment, the locking grooves120aand120bare below the centerline of the stabilization element106and above the centerline of the head140of the fixation element104.

It will be understood by one of skill in the art that whileFIGS. 2A and 2Billustrate a seat102configured to receive a locking element108having a linear axis generally parallel to the linear axis of the stabilization device106, the seat102may also be configured to receive a locking element108that has a linear axis that is generally not parallel to the linear axis of the stabilization device106. For example, the linear axis of the locking element108may have an axis that is generally orthogonal, generally parallel, or anywhere in between, with respect to the axis of the stabilization device106. In other words, the locking element108may be received by the seat102at any location around the seat102.

When the locking element108engages the locking grooves120aand120b, the locking element108forces the fixation device104and the stabilization device106apart and causes the locking of the relative positions of the fixation device104and stabilization device106. In addition, the locking element108may be longer than the width of the seat102so that once fully engaged with the locking grooves120aand120b, the locking element108protrudes from the side portion112of the seat102. This may be advantageous for certain uses of the locking mechanism100of the present invention, such as to enable a surgeon to more easily engage and disengage the locking element108, either partially or fully. In addition, the size of the portion of the locking element108that protrudes may be visible to a surgeon and act as a visible indicator of the level of engagement.

As shown inFIGS. 4A-D, the locking element108is configured for placement between a fixation device104and a stabilization device106and may be in the form of a wedge having a front side126and a back side128. The locking element108also includes a fixation device side132and a stabilization device side130. The surface of the fixation device side132may be ramped from the front side126to the back side128. The surface of the stabilization device side130may also be ramped from the front side126to the back side128. In other words, either one or both of the surfaces of the fixation device side132and stabilization device side130may be ramped. In addition, both of the surfaces of the fixation device side132and stabilization device side130may not be ramped at all.

The degree of incline of the ramp may vary, but generally ranges from about 0.5 to about 6 degrees. In one embodiment, the degree of include ranges from about 1.5 to about 4 degrees.

In addition, the surface of the fixation device side132and/or the stabilization device side130may be relatively smooth, as opposed to other engagement surfaces of the locking mechanism100. In addition, the locking element108may be made from a titanium alloy and the surfaces of the fixation device side132and/or stabilization device side130may have a rough or knurled surface and/or a surface fixation mechanism, such as ridges, grooves, bumps, pips, or the like to increase the surface coefficient of friction. For example, the stabilization device side130or fixation device side132may be roughened by aluminum oxide blasting.

One of skill in the art will understand that other surface treatments may also be used on the surfaces of the fixation device side132and stabilization device side130. One of skill in the art will also understand that any of the surfaces of the locking mechanism100, and/or any of the surfaces of the fixation device104, and/or any of the surfaces of the stabilization device106may also be surface treated.

The fixation device side132may be contoured to improve engagement with the fixation device104. The contour may increase the area over which the locking element108and fixation device104are engaged. For example, if the locking mechanism100is being used to engage a fixation device104with a generally spherical head140, the fixation device side132may be contoured such that it includes a channel with a curvature that approximates the curvature of the head140. Similarly, the stabilization device side130may be contoured to increase the area over which the locking element108and stabilization device106are engaged. Where the stabilization device106is a rod, the stabilization device side130may be contoured such that it includes a channel with a curvature that approximates the curvature of the outer surface of the rod. It will understood by those in the art that the contour may alternatively decrease in the area over which the locking element108and fixation device104are engaged.

Also, the fixation device side132may be designed so that it enhances the fixation of the fixation device to a target. For example, the fixation device side132may include interdigitating fingers201, shown inFIG. 6A, ridges or other mechanism for increasing the interaction between the fixation device side132and the fixation device104, such as a screw.

In the exemplary embodiment ofFIGS. 1,2A-B and4A-D, the locking element108is slidably engageable with locking grooves120aand120bof the side portion112of the seat102. Accordingly, the locking element108also includes edges138aand138bconfigured for sliding engagement with the locking grooves120aand120b. The edges138aand138bmay each include a nose lead-in156aand156bto facilitate the initial placement of the edges138aand138bin the locking grooves120aand120b, respectively.

In addition, the locking element108may include an access hole134for providing access to the fixation device104after the locking element108is partially engaged with the side portion112of the seat102. The access hole134may also provide access for adjusting or placing a fixation device104where a locking element108is placed prior to placement or adjustment of the fixation device104. The access hole134is preferably offset toward the front side126of the locking element108. Thus, when the locking element108is only partially engaged, the access hole134is more directly located above the fixation device104than it would otherwise be if the access hole134were located in the center of the locking element108. Thus, when the locking element108is partially engaged with the side portion112, a drive mechanism can pass through the access hole134to exert drive force on the fixation device104.

Also, the locking element108may have a self-retaining mechanism, such as a ridge, on the fixation device side132to act as a self-retaining mechanism. The ridge162may also be on the stabilization device side130. Preferably, the ridge is located toward the front side126of the locking element108so that when the locking element108is engaged with seat, the ridge helps prevent the locking element108from withdrawing.

Further, the locking element108may be narrower in width at the access hole134so that a lesser engagement of the locking element108and the fixation device104exists when the access hole134is located above the fixation device104. Further, the locking element108may have a taper158on the fixation device side132, the stabilization device side130, or both. Preferably, the locking element108has a taper158on the fixation device side132to assist the locking element108with engagement of the fixation device104.

The locking element108may also be configured so that locking element108is locked when fully engaged with the side portion112. To facilitate locking, the locking element108may include a latch, catch, tooth or the like to act as an anchor preventing the locking mechanism100from being retracted once the locking mechanism108has been fully engaged.

In addition, the locking element108and seat102may include a feedback mechanism to indicate the engagement of the locking element108and seat102. For example, the locking element108may be color coded or have ridges or bumps designed to mate with ridges or bumps on the seat102so that, for example, a surgeon could feel the interaction of the mating ridges or bumps in order to determine the level of engagement of the locking element108with the seat102.

In order for a locking element108that is placed between the fixation device104and stabilization device106to lock the relative positions of the fixation device104and stabilization device106, the locking mechanism100preferably also includes a retaining element110that limits upward movement of the stabilization device106caused by force exerted on it by the locking element108. It will be understood by one of skill in the art that other types of retaining elements110may be used. For example, the side portion112of the seat102could act as a retaining element110where the stabilization device106is inserted into the seat102through a hole in the side portion112of the seat102. Any other type of retaining element110may also be used.

It will also be understood by those skilled in the art that an intermediate element may be used between the locking element108and either or both the fixation device104and stabilization device106may departing from the scope of the present invention. For example, the intermediate element may be a spacer108a, shown inFIG. 6B, between the locking element108and the fixation device104. The spacer may thus be configured to have contoured surface, and/or interdigitating fingers, like those described with reference to the fixation device surface132of the locking element108. Similarly, in intermediate element between the locking element108and stabilization device106may have a surface similar to the stabilization device surface130.

FIGS. 1,2A-B and3A-D illustrate perspective, top plan and side plan views of an exemplary retaining element110according to the present invention. As described above, the retaining element110keeps the stabilization device106in the channel124and prevents the stabilization device106from moving away from the locking element108when the locking element108is engaged the side portion112of the seat102to force the stabilization device106and fixation device104apart. Also as described above, the retaining element110may be a cap like that illustrated inFIGS. 3A-D. In addition, the retaining element110may be, for example, hingedly connected to the seat102, either vertically or horizontally. Also, the retaining element110could, for example, be incorporated into the side portion112of the seat102, such as where the stabilization device106is prevented from moving away from the fixation device104by the upper edge of a hole in the side portion112through which the stabilization element106runs.

In the specific embodiment ofFIGS. 1,2A-B and3A-D, the retaining element110is in the form of a cap. The retaining element110is preferably longer in one direction than in the other such that when the retaining element110is rotated 90 degrees, it engages the retaining grooves122aand122bof the side portion112of the seat102. As shown, the retaining element110includes a turning element148that is configured to receive a tool that facilitates rotating the retaining element110into engagement with the retaining grooves122aand122b. Specifically, the retaining element110includes wings150aand150bconfigured to engage the retaining grooves122aand122b. The wings150aand150beach include a nose160aand160b, respectively, on the edge of the wings150aand150bto facilitate engagement with the retaining grooves122aand122b. The retaining element110is preferably engageable with the retaining grooves122aand122bby placing the retaining element110adjacent to the retaining grooves122aand122band then rotating the retaining element 90 degrees clockwise so that the noses160aand160bengage the retaining grooves122aand122b, thereby facilitating the engagement of the wings150aand150bwith the retaining grooves122aand122b.

The retaining element110also includes a stabilization device surface152that prevents the stabilization device106from moving up the channel124when the wings150aand150bare engaged with the retaining grooves122aand122b. The stabilization device surface152may also include a contour154that approximates the outer surface of the stabilization device106. The contour154may include, for example, at least one channel running across the stabilization device side1524of the retaining element110.

In addition, the retaining element110and seat102may include a feedback mechanism to indicate the engagement of the retaining element110and seat102. For example, the retaining element110may have ridges or bumps designed to mate with ridges or bumps on the seat102so that, for example, a surgeon could feel the interaction of the mating ridges or bumps in order to determine the level of engagement of the retaining element110with the seat102.

It will be understood by those skilled in the art that the specific embodiment of the retaining element illustrated in the accompanying figures is only one of a variety of types of retaining elements that could be used without departing from the scope of the present invention. For example, the retaining element110could be slidingly engageable with the retaining grooves122aand122bin a linear manner. Those skilled in the art will understand that the specific shapes and types of the grooves120a,120b,122aand122bmay vary substantially. For example, the retaining groove122amay include miniature slots within the retaining groove122ato interact with small bumps on the wing150aso that it is apparent when the wing150aand retaining groove122aare properly engaged. Similarly, the wings150aand150bmay have a surface with small ridges to create increased friction between the wings150aand150band the retaining grooves122aand122bto help prevent the retaining element110from disengaging.

Such surfaces may be rough or knurled and/or include at least one surface fixation mechanism, such as ridges, grooves, bumps, pips, or the like to increase the surface coefficient of friction. For example, the surfaces may be roughened by aluminum oxide blasting. One of skill in the art will understand that other surface treatments may also be used.

In addition as shown inFIGS. 2C-D, the retaining grooves122aand122band the wings150aand150bmay be configured to prevent the splaying apart of the sides112of the seat102. Many configurations may be apparent to one of skill in the art. For example, the wings150aand150band retaining grooves122aand122bmay be configured such that the retaining grooves122aand122bhave top surfaces that form acute angles with the side surfaces of the retaining grooves122aand122b. In addition, the wings150aand150band retaining grooves122aand122bmay have locking lips, as shown inFIG. 2D.

In use, the fixation mechanism100of the present invention provides a convenient method for engaging and locking a relative position of a fixation device104and a stabilization device106. According to one aspect of the present invention, the fixation device104is passed through the bottom portion114of the seat102and then fixed to a target, such as a spinal vertebra or other bone. A stabilization device106is then placed through a side portion112of the seat102. In a specific embodiment, the stabilization device is placed in a channel124. Following placement of the stabilization device106, a locking element108is slidably engaged with the side portion112of the seat102between the fixation device104and the stabilization device106to cause locking of the relative positions of the fixation device104and the stabilization device106. In addition, the retaining element110may be engaged with the seat following the placement of the stabilization device106and before fully engaging the locking element108.

In addition, the fixation mechanism100may permit partial locking of the fixation device104prior to placing the stabilization device106. For example, a locking element108can be partially engaged with the fixation device104either before or after placing the stabilization element106. In addition, the locking element108may include a hole that permits access to the fixation device104by a drive mechanism to fix the fixation device104to a target, such as a vertebra or bone. In this instance, the locking element108may be partially engaged before fixing the fixation device104to a target.

The locking mechanism100also permits readjustment of the stabilization device106prior to full engagement of the locking element108. Accordingly, the locking element108can be partially engaged, then the fixation device104can be fixed to a target, then the stabilization device106can be positioned and readjusted as necessary before fully engaging the locking element108to fix the relative positions of the fixation device104and the stabilization device106. Also, the locking element108may be partially engaged following fixation of the fixation device104to a target. In addition, the locking element108may not be partially engaged at all, but simply fully engaged once the fixation device104and stabilization device106are appropriately placed.

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.