Multi-axial bone screw assembly

ES 2 250 201 T3

DESCRIPTION

Multiaxial bone screw assembly.

Field of the invention

The present invention relates to devices and implants used in osteosynthesis and other orthopedic surgical procedures. In particular, the current invention contemplates a lower loaded bone anchor assembly capable of achieving multiple angular orientations relative to an elongated member extending through bone tissue.

Background of the invention

Various techniques and systems have been developed to correct and stabilize damage or malformation of the bones, especially the long bones and the spine. In one type of system, an elongated member such as a collapsible bar is placed longitudinally all the way through the bone. In spinal applications, the bar is preferably bent to accommodate the normal curvature of the spine in the region being instrumented. For example, the bar can be bent to form a kyphotic curve for the thoracic region of the spine or a lordotic curve for the lumbar region. According to such a system, the bar is hooked to various vertebrae along a certain length of the spinal column by means of a series of fixation elements. Various fixation elements can be provided configured to engage specific parts of the vertebrae and other bones. For example, such a fixation element is a hook configured to hook the lamellae of the vertebrae. Another very common fixation element is a screw that can be screwed into various parts of the vertebrae or other bones.

In a commonly used spinal procedure using a folding bar, the bar is placed on both opposite sides of the spine or in the spinous processes. Various types of bone screws thread into one part of various vertebral bodies, often at the pedicles of these vertebrae. The rods are attached to this wide variety of bone screws to apply corrective and stabilizing forces to the spine.

An example of a bar-type spinal fixation system is the TSRH® Spinal System, sold by Medtronic Sofamor Danek, Inc. The TSRH® System includes elongated bars and various hooks, screws, and pins, all configured to create a construction by segments through the entire spine. In one aspect of the TSRH system^®, the spinal rod is connected to the various spinal fixation elements by a ring screw. In this configuration, the fasteners engage the spinal bar laterally adjacent to the bar. In another aspect of the TSRH system^®, a variable angle screw is attached to the spinal rod by a ring screw. The Variable Angle Screw allows the bone screw to be rotated in a single plane, parallel to the plane of the spinal rod. Detailed information about the variable angle screw can be found in US Patent No. 5,261,909 to Sutterin et al., Owned by the assignee of the present invention. A successful goal of the TSRH® system is that the surgeon can apply vertebral fixation elements, such as a spinal hook or bone screw, to the spine in the appropriate anatomical positions. The TSRH system^® it also allows the surgeon to easily hook a bent spinal rod to each of the fixation elements for final adjustment.

Another bar-type fixation system is the Cotrel-Dubosset / CD® spinal system sold by Medtronic Sofamor Danek, Inc. As is the TSRH system^®, the CD system^® provides a variety of fixation elements for engaging an elongated rod and the spine. In one aspect of the CD system^®, the fixation elements themselves include a body that defines a slot into which the spinal rod is inserted. The slot includes a threaded bore into which a threaded plug engages to hold the rod within the body of the fastener. The CD system^® includes bone hooks and screws with this “back open” configuration. Detailed information on this technology can be found in US Patent No. 5,005,562 to Cotrel. One of the advantages of this feature of the CD system^® is that the fastener is placed directly under the elongated bar. This helps to reduce the bulk of the implant structure and reduces trauma to the surrounding tissues.

On the other hand, these fixing elements of the CD system^® they can only rotate around the spinal bar to achieve varying angle positions relative to the bar. Although this limited range of relative angular placement is acceptable for many conditions of the spine, many other cases require a more creative orientation of a bone screw, such as related to a spinal rod. Some aspects of this problem are addressed by the variable angle screw of the TSRH® system, as outlined in the '909 patent. However, there is a need for a bone screw capable of angular orientation in numerous planes relative to the spinal rod. Preferably, the bone screw is capable of various three-dimensional orientations relative to the spinal rod. Screws of this type are called polyaxial or multiaxial bone screws.

Others have approached the solution to this problem with various designs of polyaxial screws. For example, US Patent No. 5,466,237 to Byrd et al. Describes a screw that includes a spherical projection at the top of the bone screw. An externally threaded receiver element supports the bone screw and a spinal rod at the top of the spherical projection. An external nut is fitted on the receiving element to press the spinal rod against the spherical projection and to accommodate various angular orientations of the bone screw relative to the rod. Although this particular approach uses a minimum of components, the security of fixation of the bone screw to the bar is poor. In other words, the fit or fixation between the small spherical projection of the bone screw and the spinal rod easily deteriorates when the instrumentation is subjected to the high loads borne by the spine, especially in the lumbar region.

In another approach shown by US Patent No. 4,964,458 to Harms et al., A ball head bone screw is supported between two halves of a receiver element. The bottom of the two mi2

ES 2 250 201 T3 tades is held by a retaining ring. The top of the receiving halves are compressed around the bone screw by threaded nuts on a threaded spinal rod. In another approach taken by Harms et al., In US Patent No. 5,207,678 a receptor element is flexibly connected around the partially spherical head of a bone screw. Conical nuts on opposite sides of the receiver element are threaded onto a threaded rod that passes through the receiver. As the conical nuts are screwed against each other, the receiver element flexibly compresses around the head of the bone screw to hold the bone screw in its variable angular position. A drawback of the systems reported in the two Harms et al. is that the spinal rod must be screwed in to allow it to accept the compression nuts. It is known that threaded rods tend to weaken the rods due to heavy loads on the spinal column. In addition, the design of the patents 458 and 678 bone screws requires many components and it is very difficult to achieve complete bone screw fixation.

Another approach illustrated in U.S. Patent 5,797,911 to Sherman et al., Owned by the licensee of the present invention, is to provide a U-shaped bracket through which a finished bone bolt is loaded into a Crown. The bracket houses a bar in a channel above the crown member and a compression member above the bar. The compression member presses on the bar and the crown member to lock the bolt against the bracket at a series of three-dimensional angles to the bar. This approach has proven to be quite effective in solving the previously identified problems. However, it does not allow the bolt to be loaded from the bottom. In addition, the support is quite bulky to be able to house the rest of the structural components.

Yet another approach is shown in US Patent No. 5,733,285 to Errico et al., In which a support is provided with a capped portion and a circular metal plate at the bottom on which a insert the head of a bone bolt. A sleeve is provided which slides around the circular metal plate to snap lock the portion of the metal plate around the head of the bone bolt. This apparatus is considered to be relatively bulky and unwieldy due to the external slide lock mechanism. It also depends on the fit of the outer sleeve and the relative strength of the metal plate and the bending and pressing components to securely lock the head of the bone bolt.

Therefore, there is still a need in the industry to achieve a bone anchor that can easily and securely engage an elongated element in any configuration, that is, soft, strong, corded or even screwed, that achieves improved angulation of the anchor. increased strength, reduced size, including profile and volume, of the components used to engage the bone anchor to the elongated element in any of a number of angular orientations.

DE 19720782 describes an apparatus for admitting and retaining components of a multiaxial bone anchoring system, according to the preamble of claim 1 attached hereto.

Summary of the invention

According to the invention, an apparatus is provided for admitting and retaining components of a multiaxial bone anchoring system, which consists of an element that defines an upper opening part and a lower opening part, a transverse channel that runs through and communicates the upper opening parts and lower opening parts, a groove around at least a part of said lower opening part and a C-shaped retaining element that is positioned around at least a part of a bone clamping anchor, bone clamping anchor and having a head, element retainer, placed under the head.

Brief description of the schemes

Fig. 1 is a side view of one embodiment of the multiaxial bone screw anchor assembly of the present invention.

Fig. 2 is an enlarged view of the embodiment of the invention shown in Fig. 1.

Fig. 3a is a side view of an embodiment of the receiving element of the embodiment of the invention illustrated in Fig. 2.

Fig. 3b is a front view of the incorporation of the receiving element illustrated in Fig. 3a.

Fig. 3c is a sectional view, taken along lines 3c-3c of Fig. 3a, and viewed in the direction of the arrows, of the receiver element incorporation illustrated in Fig. 3a.

Fig. 3d is a sectional view, taken along lines 3d-3d of Fig. 3b and viewed in the direction of the arrows, of the receiver element incorporation illustrated in Fig. 3a.

Fig. 4a is a side view of an embodiment of a bone anchor used in the embodiment of the invention illustrated in Fig. 2.

Fig. 4b is a sectional view, taken along lines 4b-4b of Fig. 4a and viewed in the direction of the arrows, of the bone anchor incorporation illustrated in Fig. 4a.

Fig. 4c is an enlarged view of a head incorporation of the bone anchor incorporation illustrated in Fig. 4a.

Fig. 5a is a top view of an embodiment of a crown element used in the embodiment of the present invention illustrated in Fig. 2.

Fig. 5b is a sectional view, taken along lines 5b-5b of Fig. 5a and viewed in the direction of the arrows, of the incorporation of the crown element illustrated in Fig. 5a.

Fig. 5c is a sectional view basically the same as Fig. 5b of another embodiment of a crown element used in the embodiment of the invention illustrated in Fig. 2.

Fig. 6a is a top view of an embodiment of a retainer used in the embodiment of the invention illustrated in Fig. 2.

Fig. 6b is a sectional view, taken along lines 6b-6b in Fig 6a and viewed in the direction of the arrows, of the incorporation of the retaining element illustrated in Fig. 6a.

Fig. 7 is an enlarged sectional view of the embodiment of the present invention illustrated in Fig.

1.

Description of preferred incorporation

In order to promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the schematics.

ES 2 250 201 T3 and specific language will be used to describe it. However, it should be understood that this is not intended to limit the scope of the invention by further alterations or modifications of the device shown and other applications of the principles of the invention illustrated herein, but rather to contemplate it as those skilled in the art would normally do. to which the invention is related.

Referring generally to Figures 1 and 2, an embodiment of a multiaxial bone anchor assembly 20 of the present invention is shown. In the embodiment shown, the assembly 20 includes a receiving element 30, a bone anchor 50, a crown element 70 and a retention element 90. The assembly 20 of the present invention is designed for use with an elongated element R ( Fig. 7) as a spinal bar, barbell, or other orthopedic structure, as described in more detail below.

Referring now generally to Figures 3a through 3d, one embodiment of the receptor element 30 of the present invention is shown. Receiver element 30 defines an upper aperture portion 31a and a lower aperture portion 31b, which in the embodiment shown form a single aperture 32 extending through receiver element 30, from upper aperture 33 at upper end 34 to a lower opening 35 at the lower end 36. The upper opening portion 31b of the opening 32, in a specific embodiment, includes a chamber 38 defined by a chamber wall 39. Alternatively, the upper and lower aperture portions 31a and 31b may have various configurations such as having one or the other. more sections of different diameters.

The aperture 32 is partially surrounded by a rounded or bevelled edge 40a at the upper end 34 of the receiver element 30 and is surrounded by a rounded or bevelled edge 40b at the lower end 36 of the receiver element 30.

In the vicinity of the lower end 36, the receiving element 30 defines a groove 41 and associated projection 41a around the opening 32. In the embodiment shown, the groove extends around the entire perimeter of the opening 32, although it can be seen that groove 41 may extend only in part around the perimeter of opening 32. Groove 41 has groove depth A (Fig. 7) and groove diameter B (Fig. 3a).

Receiver element 30 in the embodiment shown includes a pair of ascending limbs 42, 43 through which aperture 32 extends. Branches 42, 43 further define a transverse U-shaped channel 45 for aperture 32 communicating the upper part 31a and lower part 31b of opening 32, and which houses an elongated element R (Fig. 7). In a specific embodiment, internal threads 44 are formed on branches 42, 43, and branches 42, 43 are provided with indentations or holes 46, which allow the surgeon to fix the receiving element 30 with a suitable tool (not shown). . The internal thread 44 in a specific embodiment is a reverse angle thread, that is, a thread in which the front face is directed downward and towards the receiving element 30, as disclosed in US Patent No. 6,296,642. .UU., Common property, filed Nov. 9, 1998. Preferably, the upper part 47 of the receiver element 30 (which includes the branches 42, 43) is narrower than the lower part 48 of the receiver element 30, thus reducing the volume and profile of the receiver element.

Referring now generally to Figures 4a through 4c, an embodiment of a bone anchor 50 used in the present invention is shown. The bone anchor shown is a bone screw, which in one embodiment is essentially like the bone screw disclosed in US Patent No. 5,885,286.

Bone anchor 50 includes anchor portion 52 and head portion 54. Anchor portion 52 includes at least one thread 56, which may be a suppressed self-tapping thread. Head portion 54 is part of a sphere in the embodiment shown, although alternative curvature and other configurations may be used. Head 54 in one particular embodiment includes a series of ridges 58 to enhance grip with the interior of crown element 70 (described below). Head 54 may have alternate surface configurations to increase friction such as roughness or scoring. In addition, head 54 includes a tool drive impression 60, with which a tool (not shown) can be driven to drive the anchor portion 52 to a bone. Tool drive impression 60 is an internal impression in the embodiment shown, although an external impression can be used and can have one of several configurations, such as hexagonal, hexalobed, or other torque transfer configurations.

Other bone anchor 50 incorporations are contemplated as part of the scope of the present invention. For example, bone anchor 50 may be a bone hook rather than a screw. In such an embodiment, the anchor portion 52 would be configured with a hook rather than an elongated threaded section 56.

Head 54 of bone anchor 50 is shaped and sized to fit at least the bottom 31b of aperture 32 and chamber 38 of receiving element 30. Specifically, head 54 has a width less than the width of the lower opening part 31b and the chamber 38. As more fully described below, bone anchor 50 is inserted into receiving element 30, with head 54 entering lower opening portion 31b and chamber 38 through lower end 36 of receiving element 30.

Referring now to Figures 5a to 5b, an embodiment of the crown element of the present invention is shown. In such embodiment, the crown element 70 is in the form of a circular disc having an upper surface 72 with a beveled edge 74 and a lower surface 78. The lower surface 78 is configured to house the head 54 of the bone anchor 50 and, therefore Therefore, the shown embodiment of bottom surface 78 is in the shape of part of a sphere. Alternatively or additionally, the lower surface of the crown element 70 may have one or more additional shapes, such as a beveled or conical lower surface 78 (Fig. 5c). Bottom surface 78 may be provided with an enhanced friction or grip surface configuration (eg, roughness or ridges) to assist head 54 of bone anchor 50.

The embodiment shown of the crown element 70 also includes a hole 80.

ES 2 250 201 T3 hole 80 so that the head 54 and specifically the tool drive impression 60 of the bone anchor 50 can be accessed through the crown element 70. The crown element 70 is sized and shaped for fit at least the bottom 31b of the aperture 32 and the chamber 38 of the receiving element 30. Preferably, the external dimension of the crown element 70 will be slightly smaller than the internal dimension of the chamber 38 and the bottom 31b of the aperture 32, so that the crown element 70 can slide and rotate within the chamber 38 and opening 32. Furthermore, in the embodiment shown, the external dimension of the crown element is larger than the internal dimension of the upper opening part 31a, so that the crown element 70 cannot move within the upper opening part 31a.

Referring now to Figures 6a through 6b, an embodiment of the retainer 90 of the present invention is shown.

The retention element 90 is in the form of a C-shaped spring or in a clip defining a gap 91. The retention element 90 includes an upper surface 92 and a lower surface 94. In the embodiment shown, the retention element 90 also includes internal surfaces 96, 98, 100 that substantially surround aperture 102. In a specific embodiment, the inner surface 96 forms a part of a sphere with a radius sufficiently identical to the radius of the head 54 of the bone anchor 50, the inner surface 98 is cylindrical, and the inner surface 100 is conical and angled outward to allow a wider range of angular positioning of the bone anchor 50. In alternate embodiments , there may be single or multiple internal surfaces surrounding aperture 102, which surfaces may be cylindrical, conical, spherical, or of any other suitable configuration. The diameter of the opening 102 is smaller than the diameter of the head 54 of the bone anchor 50 and the diameter of the crown element 70.

The retainer 90 has a natural or unloaded external diameter D, that is, a diameter measured when the retainer 90 is not under any contractive (gap closing) or expansive (gap opening) stress. The diameter D of the retainer 90, in one embodiment, is less than the groove diameter B of the groove 41. Furthermore, the retainer 90 has a body width W that is considerably constant throughout the retainer 90. The body width W of the retainer 90 is greater than the groove depth A of the groove 41.

Referring generally to Figures 1, 2 and 7, assembly 20 is assembled as follows: bone anchor 50, crown element 70 and retention element 90 are inserted into receiving element 30 through lower end 36, so individually or essentially in one step. For example, crown element 70 may be inserted first, followed by bone anchor 50, and retention element 90 inserted last. In a particular embodiment, the retention element 90 is fitted around the bone anchor 50, directly below the head 54 prior to inserting the bone anchor 50 into the receiving element 30. The retention element 90 can be positioned around the bone anchor 50 by inserting the anchor portion 52 of the bone anchor 50 through opening 102 of the retainer 90 and moving the retainer 90 over the anchor portion 52 toward the head 54. Alternatively, the recess 91 of the retention element 90 may be pressed against the stem of the bone anchor 50 below the head 54, so that the recess 91 is widened to allow the placement of the bone anchor 50 within the opening 102 of the retention element. retention 90, wherein the receiving element 90 returns to its original size and shape. By positioning the crown element 70 on top of the head 54 of the bone anchor 50, so that the lower surface 78 of the crown element 70 is contiguous with the head 54 and securing the bone anchor 50 and the retention element 90 together as described above , simultaneous insertion of bone anchor 50, crown element 70, and retention element 90 into receiving element 30 can be accomplished.

Crown element 70 remains slidably and rotatably positioned in the lower position 3b of aperture 32 and / or chamber 38 of receiver element 30 and bone anchor 50 remains multiaxially movable relative to crown element 70 and the receiving element 30. The retaining element 90 is pushed up until it reaches the bottom 31b of the opening 32. The retainer 90 contracts, making the gap 91 smaller, as you push the retainer 90 against the bevelled edge 40b of the receiving member 30, until the outside diameter of the retainer 90 equals the diameter from the bottom 3b of the opening 32. The retention element 90 advances further into the opening 42 and into the groove 41, so that the retention element engages at least a part of the groove 41.

As noted above, in a particular embodiment, the groove diameter of groove 41 is less than the outer diameter D of retainer 90 in its natural (ie, unloaded) condition. Therefore, when the retainer 90 is within the groove 41, the retainer 90 presses against the walls of the groove 41. Alternatively, the groove diameter B of the groove 41 may be the same size or slightly larger than the natural external diameter D of the retainer 90. In this case, the lower surface 94 of the retainer 90 rests on the projection 41a. groove 41 and therefore holds retainer 90 within groove 41. The groove depth A of the groove 41 is less than the body width W of the retainer 90, so that when the retainer 90 engages the groove 41, a part of the retainer 90 projects into the lower opening portion 31b of opening 32.

When retaining ring 90 seats within groove 41, bone anchor 50 and crown element 70 are retained within opening 32 of receiving element 30. Crown element 70 abuts head 54 of the bone anchor 50 and head 54 abuts internal surface 96 of retainer 90. The retention element 90 is supported on the groove 41 and / or the projection 41a of the receiving element 30 and thus the bone anchor 50 and the crown element 70 will not pass through the retention ring 90 or leave the receiving element

ES 2 250 201 T3 when retaining ring 90 is within groove 41.

Preferably, assembly 20 is assembled (as described above) prior to use in a surgical procedure. Using the shown embodiment of assembly 20, bone anchor 50 of assembly 20 is screwed into a suitably prepared hole in bone (not shown). It should be understood that in alternative embodiments of the invention, for example, when bone anchor 50 is a bone hook, it may not be necessary to drill a hole in the bone and screw in the anchor. The threaded anchor portion 52 is inserted into the hole and a suitable screwing tool with tool drive impression 60 of the bone anchor 50 is used through the hole 80 in the crown element 70 and the bone anchor 50 is screwed into the bone. When bone anchor 50 is screwed into bone to the desired depth, receptor element 30 is positioned so that aperture 32 forms the desired angle with bone anchor 50, as shown in Fig. 1. In the embodiment shown , the angle 8 between the bone anchor 50 and the aperture 32 can have any value up to a maximum of 30 degrees in any direction. It will be seen that the maximum angle of bone anchor 50 relative to aperture 32 can be changed in various ways, for example, by fine-tuning the portion of bone anchor 50 located below head 54, providing a steeper angulation of bevelled edge 40b and / or or by placing the groove 41 as close as possible to the lower end 36 of the receiving element 30.

As described above, receptor element 30 can be angled as desired by the surgeon relative to bone anchor 50. An elongated element R, such as a spinal rod, connector, or other orthopedic surgical implant is attached to assembly 30. Elongated element R it is positioned in the channel 45 of the receiving element 30 and comes into contact with the upper surface 72 of the crown element 70. A compression element 120, such as a set screw or threaded plug, threads into the screws 44 of the receiver element and down into the elongated element R. The compression element 120, in one embodiment, is a set screw or a plug having external threads 122 and an imprint 124 to apply torque and, in a specific embodiment, is a cut-off set screw as shown in US Patent No. 5,885,286 to Sherman et al. In another embodiment, screw 122 is a reverse angle screw, as shown in US Patent No. 6,296,642, filed November 9, 1998, that is compatible with the reverse angle incorporation of the screw. 44 of receiver element 30, as described above. Alternatively, when receiving element 30 is externally threaded, compression element 120 may be an internally threaded nut.

As compression member 120 is tightened, elongated member R is pushed down against crown member 70, pushing crown member 70 down onto head 54 of bone anchor 50. Thereby, the head 54 is secured between retaining member 90 and crown member 70. In the embodiment of the invention where head 54 includes ridges 58, ridges 58 are pressed onto bottom surface 78 of crown member 70. In this way, the bone anchor 50 is locked in the desired angular position with respect to the elongated element R and the rest of the assembly 20.

Alternatively, assembly 20 can be assembled during the surgical procedure. The bone anchor 50, with the retaining ring 90 already positioned under the head 54, is inserted into the bone. The crown element is positioned over bone anchor 50 or in opening 32 in receiving element 30. Receiver element 30 is then pressed down on head 54 of bone anchor 50, forcing retaining ring 90 to contract, to enter opening 32 and seat in groove 41, as previously described. After mounting the assembly 20 in this way, an elongated element is loaded into the receiving element 30 and locked as described above.

Preferred materials for the present invention include stainless steel and titanium. It is recognized that any strong biocompatible material can be used to achieve the osteosynthesis and other orthopedic surgical goals of the present invention. In a specific embodiment, the crown element 70 may be made of a material somewhat softer than the material used for the ridges 58 of the head 54 of the bone anchor 50. This structure will allow the ridges 58 to penetrate somewhat more easily into the inner surface 78 of the crown element 70 during the locking of the assembly 20, thus providing a more definitive grip between the edges 58 and the crown element 70. In another specific embodiment, the crown element may be made of a somewhat softer material than the material used for the elongated element R. This structure will allow the upper surface 72 of the crown element 70 to deform into the shape of the elongated element during locking of the assembly 20, also providing a more secure locking of the implant.

Although the invention has been illustrated and described in detail in the schemes and the foregoing description, they should be considered as merely illustrative and not restrictive, it being understood that only the preferred embodiment has been shown and described and that the scope is defined by the claims.