Patent Description:
The present disclosure relates to spinal fixation devices and, more particularly, to pedicle screw fixation assemblies.

The spinal column is a complex system of bones and connective tissues that provides support for the body while protecting the spinal cord and nerves. The spinal column includes a series of vertebral bodies stacked on top of one another, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces exerted upon the spinal column, as well as maintains proper spacing of the bodies with respect to each other. A vertebral canal containing the spinal cord and nerves is located behind the vertebral bodies.

There are many types of spinal column disorders including scoliosis (abnormal lateral curvature of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnormal backward curvature of the spine, usually in the lumbar spine) and spondylolisthesis (forward displacement of one vertebra over another, usually in a lumbar or cervical spine), for example, that are caused by abnormalities, such as disease or trauma, and that are characterized by misalignment of the spinal column. When the spinal column is misaligned, one or more of the misaligned vertebral bodies can "pinch" or apply pressure to the underlying spinal cord and nerves, which often results in debilitating pain and diminished nerve function. For this reason, the forgoing conditions regularly require the imposition and/or maintenance of corrective forces on the spine in order to return the spine to its normal alignment.

A surgical technique, commonly referred to as spinal fixation, utilizes surgical implants for fusing together and/or mechanically immobilizing two or more vertebral bodies of the spinal column. Spinal fixation may also be used to alter the alignment of adjacent vertebral bodies relative to one another so as to change the overall alignment of the spinal column.

One common spinal fixation device utilizes spinal rods placed generally parallel to the spine and fixation devices, such as pedicle screw assemblies, interconnected between the spinal rods and selected portions of the spine. In some instances, the spinal rods can then be connected to each other via cross-connecting members to provide a more rigid support and alignment system.

Pedicle screw assemblies typically include a bone screw and a housing or coupling element for coupling the bone screw to the spinal rod. Pedicle screws generally come in two forms: a polyaxial pedicle screw (which allows the housing to freely rotate relative to the head of the screw) and a uniplanar pedicle screw (which restricts movement of the housing relative to the screw head to a single plane). Examples of polyaxial screw devices are disclosed in <CIT> and <CIT>.

In both types of screws, unrestricted movement of the coupling element with respect to the screws is not preferable. This is often referred to as "flop," and can complicate the handling of the pedicle screw during a surgical procedure. Many different structures and techniques have been developed to combat this problem, but a need still exists for simple and easy assemblies that prevent the issue.

According to the present invention, there is provided a polyaxial pedicle screw as defined in appended claim <NUM>. Other advantageous embodiments are provided as defined in the corresponding dependent claims.

According to the present invention, a polyaxial pedicle screw comprises.

Further, the present disclosure is directed to a polyaxial pedicle screw including a housing, a friction plug, an anvil, a bone screw member, and a compression ring or cap. The housing includes opposing arms, a collar at a bottom portion of the housing, a cutout, and a passage. The anvil is positioned in the passage. The bone screw member includes a head and a threaded shaft extending from the head along a shaft axis, wherein the head is configured to be positioned in the passage. The friction plug is positioned in the cutout, wherein the friction plug applies a force to the head. The compression ring or cap is positioned over the collar and the friction plug.

The friction plug includes a base member and a spring member positioned within the base member. An inner surface of the base member has a slight inward curve for engagement with the head of the bone screw member, and an outer surface of the base member has a slight outward curve for engagement with the cap. Further, an inner surface of the spring member has a slight inward curve, and an outer surface of the spring member has a slight outward curve for engagement with the compression ring or cap. The inner surfaces of the base member and spring member are generally aligned, as are the outer surfaces of the base member and spring member. When the inner surface of the base member is engaged by the head of the bone screw member, the spring member flexes inward and its relationship with the compression ring or cap causes a constant lateral force to be applied to the head of the bone member. The force applied to the head of the bone member restricts movement of the bone screw member within the housing.

According to the invention, the friction plug includes an inner surface and an outer surface joined by a perpendicular support member. An inner surface has a slight inward curve for engagement with the head of the bone screw member, and an outer surface has a slight outward curve for engagement with the cap. When the inner surface is engaged by the head of the bone screw member, the outer surface flexes inward and its relationship with the compression ring or cap causes a force to be applied to the head of the bone member. The force applied to the head of the bone member restricts movement of the bone screw member within the housing. The head of the bone screw member may have a first portion and a second portion, wherein the second portion includes a surface texture, and the friction plug may include a surface texture for increased frictional engagement with the second portion.

Further, the inner surface and the outer surface of the friction plug may be joined at their respective centers by the perpendicular member. A first opening may be located adjacent to a first side of the perpendicular member between the inner surface and the outer surface, and a second space may be located adjacent a second side of the perpendicular member between the inner surface and the outer surface. Furthermore, the inner surface and the outer surface of the friction may have substantially semi-obround shapes, and a bottom portion of the inner and outer surfaces may be substantially planar.

According to yet another aspect of the disclosure, the friction plug includes an inner surface and an outer surface that are joined by a base member at a bottom portion of both the respective inner and outer surfaces. An inner surface has a slight inward curve for engagement with the head of the bone screw member, and an outer surface has a slight outward curve for engagement with the cap. Further, the base member has a slight inward curve for engagement with the head of the bone screw member. When the inner surface of the friction plug is engaged by the head of the bone screw member, the outer surface of the friction plug flexes inward and its relationship with the compression ring or cap causes a force to be applied to the head of the bone screw member. The force applied to the head of the bone screw member restricts movement of the bone screw member within the housing.

According to yet another aspect of the disclosure, the polyaxial pedicle screw includes a housing, a bone screw member, and an anvil. The housing includes opposing arms, a collar, and a passage. The bone screw member includes a head and a threaded shaft extending from the head along a shaft axis, wherein the head has a first portion and a second portion, the second portion having a surface texture. The anvil is positioned in the passage, wherein the anvil includes a spring element positioned in an inner portion of the anvil, wherein the spring element frictionally engages with the second portion of the head and provides a constant force to a top portion of the head. The spring element is a bilateral cantilevered spring positioned along a circumference of the inner portion of the anvil. According to another aspect of the disclosure, the spring element is comprised of multiple bilateral cantilevered springs individually positioned and spaced apart along a circumference of the inner portion of the anvil.

According to the invention, a polyaxial pedicle screw includes a housing, a friction plug, an anvil, a bone screw member, and a compression ring or cap. The housing includes opposing arms, a collar at a bottom portion of the housing, a cutout, and a passage. The anvil is positioned in the passage. The bone screw member includes a head and a threaded shaft extending from the head along a shaft axis, wherein the head is configured to be positioned in the passage. The friction plug includes an inner surface and an outer surface joined by a perpendicular support member. The friction plug is positioned in the cutout and the inner surface is configured to engage the head and the outer surface is configured to engage the cap. The compression ring or cap is positioned over the collar and the friction plug. The friction plug applies a force to the head, and the friction plug is a bilateral leaf spring.

According to yet another aspect of the disclosure, a polyaxial pedicle screw includes a housing, a friction plug, an anvil, a bone screw member, and a compression ring or cap. The housing includes opposing arms, a collar at a bottom portion of the housing, a cutout, and a passage. The anvil is positioned in the passage. The bone screw member includes a head and a threaded shaft extending from the head along a shaft axis, wherein the head is configured to be positioned in the passage. The friction plug includes an inner surface and an outer surface joined by a perpendicular support member. The friction plug is positioned in the cutout and restricts movement of the bone screw member within the housing. The compression ring or cap is positioned over the collar and the friction plug. The friction plug may engage the head of the bone screw member and restrict movement of the head within the passage. Further, the friction plug may restrict polyaxial movement of the shaft relative to the shaft axis, and the friction plug may be a bilateral leaf spring.

Particular embodiments and unclaimed examples of the present disclosure will be described herein with reference to the accompanying drawings. As shown in the drawings and as described throughout the following description, and as is traditional when referring to relative positioning on an object, the term "proximal" should be understood as referring to the portion of a structure that is closer to a clinician during proper use and the term "distal" should be understood as referring to the portion of a structure that is farther from the clinician during proper use. Also, as used herein, the terms "substantially," "generally," and "about" are intended to mean that slight deviations from absolute are included within the scope of the term so modified.

Referring to <FIG>, a polyaxial pedicle screw <NUM> in accordance with an unclaimed example of the present disclosure is shown. Polyaxial pedicle screw <NUM> includes a housing <NUM>, a friction plug <NUM>, an anvil <NUM>, a bone screw member <NUM>, and a compression ring or cap <NUM>.

Housing <NUM> defines a passage <NUM> formed therethrough that permits the reception other elements of screw <NUM>, along with a suitable driving instrument (not shown). The housing includes opposing arms 120a, 120b that define a U-shaped channel <NUM> therebetween. Housing <NUM> also includes a collar <NUM> extending from a bottom of the housing, which is shown having a smaller diameter than the diameter defined by the opposing arms 120a, 120b. Collar <NUM> is adapted to facilitate the securement of compression ring or cap <NUM> to the housing <NUM> once the bone screw member <NUM> is seated within passage <NUM>. Collar <NUM> includes a cut out 124a that provides a recess for the reception of a portion of the bone screw member <NUM>, namely a neck <NUM> (discussed further below). Housing <NUM> has one or more slots 126a, 126b positioned above a shoulder defined on an inner surface of the housing <NUM>. The slots 126a, 126b extend continuously along opposing arms 120a, 120b.

Bone screw member <NUM> includes a head <NUM> and a threaded shaft <NUM>. The head <NUM> includes a first portion 162a and a second portion 162b. First portion 162a is a cylindrical surface formed in the otherwise spherical head <NUM> (indeed second portion 162b is spherical) that enables the head <NUM> to fit through the bottom of housing <NUM> and ultimately into passage <NUM>. Thus, in a position in which first portion 162a is aligned with passage <NUM>, head <NUM> can be passed into the passage. In this position, neck <NUM> is received within cut out 124a. Thereafter, upon rotation of the head within the passage and movement of the neck from the cut out, second portion 162b maintains head <NUM> within housing <NUM>. As shown, second portion 162b includes a surface texture in the form of serrations, which facilitate frictional engagement with other components of the assembly (e.g., anvil <NUM>).

Prior to the insertion of head <NUM> in passage <NUM>, anvil <NUM> is positioned in the passage. The placement of the head thereafter in fact captures the anvil within housing <NUM>. The anvil <NUM> includes protuberances <NUM> on opposite sides of an outer surface of the anvil <NUM>. These protuberances cooperate with slots (not shown) formed within passage <NUM> to prevent rotation of the anvil within the housing. Likewise, upper surfaces of the anvil abut the above-discussed shoulders formed with the passage to prevent further upward movement of anvil <NUM> within housing <NUM>.

After the foregoing assembly steps, friction plug <NUM> is positioned in cutout 124a such that a portion of it abuts a portion of head <NUM> of bone screw member <NUM>. This abutment creates a frictional relationship (aided by the surface texture of second portion 162b) created by the constant lateral force of the plug on the head <NUM>. This precludes the aforementioned "flop" often seen with pedicle screws.

With all other components in place, compression ring or cap <NUM> may be slid over shaft <NUM> and affixed (such as by friction, threading, bayonet mount, gluing, ultrasonic or other welding or the like) to collar <NUM> of housing <NUM> to further secure friction plug <NUM> and bone screw member <NUM> to housing <NUM>. The positioning of compression ring or cap <NUM> precludes bone screw member <NUM> from being positioned in a manner that would permit it to be removed from housing <NUM>.

<FIG> depict friction plug <NUM> in more detail. As shown, friction plug <NUM> includes a base member <NUM> and a spring member <NUM> positioned within a recess <NUM> of base member <NUM>. Friction plug <NUM> also includes an inner surface 130a and an outer surface 130b, with the inner surface 130a having a slight inward curve for engagement with head <NUM> and outer surface 130b having a slight outward curve for engagement with compression ring or cap <NUM>.

Referring to <FIG>, spring member <NUM> is a leaf spring that includes an inner surface 134a and an outer surface 134b. Inner surface 134a has a slight inward curve and outer surface 134b has a slight outward curve for engagement with compression ring or cap <NUM>. Spring member <NUM> is positioned within recess <NUM> of base member <NUM> with inner surface 134a aligned with inner surface 130a, and outer surface 134b aligned with outer surface 130b. Outer surface 134b frictionally engages with compression ring or cap <NUM> to provide a constant lateral force and cause inner surface 130a to engage head <NUM>.

The interrelationships among the various components discussed above can be seen in the cross-sectional views of <FIG>. Specifically, <FIG> includes an enlarged view of anvil <NUM> positioned in housing <NUM> prior to the bone screw member <NUM> and friction plug <NUM> being positioned in housing <NUM>. <FIG>, on the other hand, includes an enlarged view of the fully assembled construct. As shown, inner surface 130a of friction plug <NUM> is positioned to engage with head <NUM>, and outer surface 130b is positioned to engage compression ring or cap <NUM> which further secures each component within housing <NUM>.

In the fully assembled state, friction plug <NUM> frictionally engages with head <NUM> to provide a constant lateral force. Spring member <NUM>, when positioned within recess <NUM> of base member <NUM>, flexes inward and its relationship with compression ring or cap <NUM> causes the constant force to ultimately be applied to head <NUM> by base member <NUM> which restricts movement of bone screw member <NUM> within housing <NUM>.

An embodiment pedicle screw <NUM> is shown in <FIG> with like reference numerals being utilized in connection with similar components to that of pedicle screw <NUM>, but within the <NUM>-series of numbers. For instance, pedicle screw <NUM> includes a housing <NUM>, a friction plug <NUM>, an anvil <NUM>, a bone screw member <NUM>, and a compression ring or cap <NUM>. In fact, the below discussion is focused on the only component that significantly differs from that of pedicle screw <NUM> - friction plug <NUM>.

<FIG> depict friction plug <NUM> in more detail. As shown, friction plug <NUM> is a bilateral leaf spring which includes an inner surface 230a and an outer surface 230b, with inner surface 230a having a slight inward curve for engagement with head <NUM> and outer surface 230b having a slight outward curve for engagement with compression ring or cap <NUM>. Inner surface 230a and outer surface 230b are joined at about their centers by a perpendicular support member <NUM>. Adjacent to either side of support member <NUM> and in-between inner and outer surfaces 230a, 230b are open spaces 234a, 234b.

The interrelationships among the various components discussed above can be seen in an enlarged view of the fully assembled construct in cross-sectional view <FIG>. As shown, inner surface 230a of friction plug <NUM> is positioned to engage with head <NUM>, and outer surface 230b is positioned to engage with compression ring or cap <NUM> which further secures each component within housing <NUM>.

In the fully assembled state, friction plug <NUM> frictionally engages with head <NUM> to provide a constant lateral force. Outer surface 230b flexes outward when inner surface 230a is engaged by head <NUM>. Outer surface 230b relationship with compression ring or cap <NUM> causes constant force to ultimately be applied to head <NUM> by inner surface 230a which restricts movement of bone screw member <NUM> within the housing <NUM>.

An unclaimed example pedicle screw <NUM> is shown in <FIG> with like reference numerals being utilized in connection with similar components to that of pedicle screw <NUM> and <NUM>, but within the <NUM>-series of numbers. For instance, pedicle screw <NUM> includes a housing <NUM>, a friction plug <NUM>, an anvil <NUM>, a bone screw member <NUM>, and a compression ring or cap <NUM>. In fact, the below discussion is focused on the only component that significantly differs from that of pedicle screw <NUM> and <NUM> - friction plug <NUM>.

<FIG> depict friction plug <NUM> in more detail. As shown, friction plug <NUM> is bilateral leaf spring which includes an inner surface 330a and an outer surface 330b, with inner surface 330a having a slight inward curve for engagement with head <NUM> and outer surface 330b having a slight outward curve for engagement with compression ring or cap <NUM>. Inner surface 330a and outer surface 330b are joined at about their respective bottom portions by a base member <NUM>, with base member <NUM> having a slight inward curve for engagement with head <NUM>. In-between inner and outer surfaces 330a, 330b is open space <NUM>.

The interrelationships among the various components discussed above can be seen in an enlarged view of the fully assembled construct in cross-sectional view <FIG>. As shown, inner surface 330a and base member <NUM> of friction plug <NUM> is positioned to engage with head <NUM>, and outer surface 330b is positioned to engage with compression ring or cap <NUM> which further secures each component within housing <NUM>.

In the fully assembled state, friction plug <NUM> frictionally engages with head <NUM> to provide a constant lateral force. Outer surface 330b flexes outward when inner surface 330a is engaged by head <NUM>. Outer surface 330b relationship with compression ring or cap <NUM> causes constant force to ultimately be applied to head <NUM> by inner surface 330a which restricts movement of bone screw member <NUM> within the housing <NUM>.

Another unclaimed example pedicle screw <NUM> is shown in <FIG> with like reference numbers being utilized in connection with similar components of that of pedicle screws <NUM>, <NUM>, and <NUM>, but within the <NUM>-series of numbers. Pedicle screw <NUM>, however, does not include a friction plug but rather a modified anvil. For instance, pedicle screw <NUM> includes a housing <NUM>, an anvil <NUM>, a bone screw member <NUM>, and a compression ring or cap <NUM>. The below discussion is focused on the only component that significantly differs from that of pedicle screws <NUM>, <NUM>, and <NUM> - anvil <NUM>.

<FIG> depict anvil <NUM> in more detail. Anvil <NUM> includes a spring element <NUM> positioned within an inner surface <NUM> that fully encompasses the circumference of anvil <NUM>. Spring element <NUM> is a bilateral cantilevered spring as shown.

The interrelationships among the various components discussed above can be seen in the cross-sectional views of <FIG> includes an enlarged view of anvil <NUM> positioned in housing <NUM> prior to bone screw member <NUM> being positioned in housing <NUM>.

<FIG>, on the other hand, includes an enlarged view of the fully assembled construct. As shown, spring element <NUM> of anvil <NUM> is positioned to engage with head <NUM> and compression ring or cap <NUM> further secures each component within housing <NUM>.

In the fully assembled state, anvil <NUM> frictionally engages with head <NUM> to provide a constant force. When bone screw member <NUM> is positioned within anvil <NUM>, spring element <NUM> engages a second portion 462b of the head <NUM> causing the spring element <NUM> to flex upward. The upward flex of the spring element <NUM> causes the constant force to ultimately be applied to head <NUM> by anvil <NUM> which restricts movement of bone screw member <NUM> within the housing <NUM>.

Another unclaimed example pedicle screw <NUM> is shown in <FIG> with like reference numerals being utilized in connection with similar components to that of pedicle screws <NUM>, <NUM>, <NUM> and <NUM>, but within the <NUM>-series of numbers. Pedicle screw <NUM>, similar to pedicle screw <NUM>, does not include a friction plug but rather a modified anvil. Pedicle screw <NUM> includes a housing <NUM>, an anvil <NUM>, a bone screw member <NUM>, and a compression ring or cap <NUM>. The below discussion is focused on the only component that significantly differs from that of pedicle screws <NUM>, <NUM>, <NUM>, and <NUM> - anvil <NUM>.

<FIG> depict anvil <NUM> in more detail. Anvil <NUM> includes spring elements <NUM> positioned within an inner surface <NUM> that fully encompasses the circumference of anvil <NUM>. Spring elements <NUM> are bilateral cantilevered springs as shown.

The interrelationships among the various components discussed above can be seen in the cross-sectional views of <FIG> includes an enlarged view of the anvil <NUM> positioned in housing <NUM> prior to bone screw member <NUM> being positioned in housing <NUM>.

<FIG>, on the other hand, includes an enlarged view of the fully assembled construct. As shown, spring elements <NUM> of anvil <NUM> are positioned to engage head <NUM> and compression ring or cap <NUM> further secures each component within housing <NUM>.

In the fully assembled state, anvil <NUM> frictionally engages with head to provide a constant force. When bone screw member <NUM> is positioned within anvil <NUM>, spring elements <NUM> engages a second portion 562b of the head <NUM> causing the spring elements <NUM> to flex upward. The upward flex of the spring element <NUM> causes the constant force to ultimately be applied to head <NUM> by anvil <NUM> which restricts movement of bone screw member <NUM> within the housing <NUM>.

As can be appreciated, any portion of any of the presently disclosed polyaxial pedicle screws can be formed of titanium, titanium alloy, stainless steel, cobalt chrome, or other metal or polymeric materials. In this regard, it is also appreciated that utilizing a combination of compatible materials in the screw assembly may be advantageous. Thus, it is contemplated that the housing could be made of a harder or stiffer material such as cobalt chrome, while the screw and anvil and set screw may be made of another, compatible material such as titanium or titanium alloy. Further, components of any of the presently disclosed embodiments may be press fit, staked, pinned, or welded together.

Claim 1:
A polyaxial pedicle screw (<NUM>) comprising:
a housing (<NUM>) including opposing arms, a collar at a bottom portion of the housing (<NUM>), a cutout through a portion of the collar, and a passage extending through the housing (<NUM>);
an anvil (<NUM>) positioned in the passage; and
a bone screw member (<NUM>) including a head (<NUM>) and a threaded shaft extending from the head (<NUM>) along a shaft axis, wherein the head (<NUM>) is configured to be positioned in the passage adjacent to the anvil (<NUM>),
characterized by further comprising a friction plug (<NUM>) including a bilateral leaf spring member positioned in the cutout, wherein the friction plug (<NUM>) includes an inner surface (230a) and an outer surface (230b) joined by a perpendicular support member (<NUM>), and wherein the friction plug (<NUM>) applies a force to the head (<NUM>); and
a cap (<NUM>) positioned over the collar and the friction plug (<NUM>).