Spinal Fixation System

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.

BACKGROUND OF THE DISCLOSURE

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).

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.

BRIEF SUMMARY OF THE DISCLOSURE

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.

In another embodiment, 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. The friction plug may be a bilateral leaf spring. 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.

In yet another embodiment, 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.

In yet another embodiment, 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. In another embodiment, 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.

In yet another embodiment, 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 may apply a force to the head, and the friction plug may be a bilateral leaf spring.

In yet another embodiment, 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.

DETAILED DESCRIPTION

Particular embodiments 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 toFIGS.1A-2D, a polyaxial pedicle screw100in accordance with one embodiment of the present disclosure is shown. Polyaxial pedicle screw100includes a housing120, a friction plug130, an anvil140, a bone screw member160, and a compression ring or cap180.

Housing120defines a passage122formed therethrough that permits the reception other elements of screw100, along with a suitable driving instrument (not shown). The housing includes opposing arms120a,120bthat define a U-shaped channel110therebetween. Housing120also includes a collar124extending from a bottom of the housing, which is shown having a smaller diameter than the diameter defined by the opposing arms120a,120b. Collar124is adapted to facilitate the securement of compression ring or cap180to the housing120once the bone screw member160is seated within passage122. Collar124includes a cut out124athat provides a recess for the reception of a portion of the bone screw member160, namely a neck164(discussed further below). Housing120has one or more slots126a,126bpositioned above a shoulder defined on an inner surface of the housing120. The slots126a,126bextend continuously along opposing arms120a,120b.

Bone screw member160includes a head162and a threaded shaft166. The head162includes a first portion162aand a second portion162b. First portion162ais a cylindrical surface formed in the otherwise spherical head162(indeed second portion162bis spherical) that enables the head162to fit through the bottom of housing120and ultimately into passage122. Thus, in a position in which first portion162ais aligned with passage122, head162can be passed into the passage. In this position, neck164is received within cut out124a. Thereafter, upon rotation of the head within the passage and movement of the neck from the cut out, second portion162bmaintains head162within housing120. As shown, second portion162bincludes a surface texture in the form of serrations, which facilitate frictional engagement with other components of the assembly (e.g., anvil140).

Prior to the insertion of head162in passage122, anvil140is positioned in the passage. The placement of the head thereafter in fact captures the anvil within housing120. The anvil140includes protuberances142on opposite sides of an outer surface of the anvil140. These protuberances cooperate with slots (not shown) formed within passage122to 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 anvil140within housing120.

After the foregoing assembly steps, friction plug130is positioned in cutout124asuch that a portion of it abuts a portion of head162of bone screw member160. This abutment creates a frictional relationship (aided by the surface texture of second portion162b) created by the constant lateral force of the plug on the head162. This precludes the aforementioned “flop” often seen with pedicle screws.

With all other components in place, compression ring or cap180may be slid over shaft160and affixed (such as by friction, threading, bayonet mount, gluing, ultrasonic or other welding or the like) to collar124of housing120to further secure friction plug130and bone screw member160to housing120. The positioning of compression ring or cap180precludes bone screw member160from being positioned in a manner that would permit it to be removed from housing120.

FIGS.3A-3Fdepict friction plug130in more detail. As shown, friction plug130includes a base member132and a spring member134positioned within a recess133of base member132. Friction plug130also includes an inner surface130aand an outer surface130b, with the inner surface130ahaving a slight inward curve for engagement with head162and outer surface130bhaving a slight outward curve for engagement with compression ring or cap180.

Referring toFIGS.4A-F, spring member134is a leaf spring that includes an inner surface134aand an outer surface134b. Inner surface134ahas a slight inward curve and outer surface134bhas a slight outward curve for engagement with compression ring or cap180. Spring member134is positioned within recess133of base member132with inner surface134aaligned with inner surface130a, and outer surface134baligned with outer surface130b. Outer surface134bfrictionally engages with compression ring or cap180to provide a constant lateral force and cause inner surface130ato engage head162.

The interrelationships among the various components discussed above can be seen in the cross-sectional views ofFIGS.5A-6B. Specifically,FIG.5Bincludes an enlarged view of anvil140positioned in housing120prior to the bone screw member160and friction plug130being positioned in housing120.FIG.6B, on the other hand, includes an enlarged view of the fully assembled construct. As shown, inner surface130aof friction plug130is positioned to engage with head162, and outer surface130bis positioned to engage compression ring or cap180which further secures each component within housing120.

In the fully assembled state, friction plug130frictionally engages with head162to provide a constant lateral force. Spring member134, when positioned within recess133of base member132, flexes inward and its relationship with compression ring or cap180causes the constant force to ultimately be applied to head162by base member132which restricts movement of bone screw member160within housing120.

Another embodiment pedicle screw200is shown inFIGS.7-10with like reference numerals being utilized in connection with similar components to that of pedicle screw100, but within the200-series of numbers. For instance, pedicle screw200includes a housing220, a friction plug230, an anvil240, a bone screw member260, and a compression ring or cap280. In fact, the below discussion is focused on the only component that significantly differs from that of pedicle screw100-friction plug230.

FIGS.8A-Fdepict friction plug230in more detail. As shown, friction plug230is a bilateral leaf spring which includes an inner surface230aand an outer surface230b, with inner surface230ahaving a slight inward curve for engagement with head262and outer surface230bhaving a slight outward curve for engagement with compression ring or cap280. Inner surface230aand outer surface230bare joined at about their centers by a perpendicular support member232. Adjacent to either side of support member232and in-between inner and outer surfaces230a,230bare open spaces234a,234b.

The interrelationships among the various components discussed above can be seen in an enlarged view of the fully assembled construct in cross-sectional viewFIG.10B. As shown, inner surface230aof friction plug230is positioned to engage with head262, and outer surface230bis positioned to engage with compression ring or cap280which further secures each component within housing220.

In the fully assembled state, friction plug230frictionally engages with head262to provide a constant lateral force. Outer surface230bflexes outward when inner surface230ais engaged by head262. Outer surface230brelationship with compression ring or cap280causes constant force to ultimately be applied to head262by inner surface230awhich restricts movement of bone screw member260within the housing220.

Another embodiment pedicle screw300is shown inFIGS.11-14with like reference numerals being utilized in connection with similar components to that of pedicle screw100and200, but within the300-series of numbers. For instance, pedicle screw300includes a housing320, a friction plug330, an anvil340, a bone screw member360, and a compression ring or cap380. In fact, the below discussion is focused on the only component that significantly differs from that of pedicle screw100and200-friction plug330.

FIGS.12A-Fdepict friction plug330in more detail. As shown, friction plug330is bilateral leaf spring which includes an inner surface330aand an outer surface330b, with inner surface330ahaving a slight inward curve for engagement with head362and outer surface330bhaving a slight outward curve for engagement with compression ring or cap380. Inner surface330aand outer surface330bare joined at about their respective bottom portions by a base member332, with base member332having a slight inward curve for engagement with head362. In-between inner and outer surfaces330a,330bis open space334.

The interrelationships among the various components discussed above can be seen in an enlarged view of the fully assembled construct in cross-sectional viewFIG.14B. As shown, inner surface330aand base member332of friction plug330is positioned to engage with head362, and outer surface330bis positioned to engage with compression ring or cap380which further secures each component within housing320.

In the fully assembled state, friction plug330frictionally engages with head362to provide a constant lateral force. Outer surface330bflexes outward when inner surface330ais engaged by head362. Outer surface330brelationship with compression ring or cap380causes constant force to ultimately be applied to head362by inner surface330awhich restricts movement of bone screw member360within the housing320.

Another embodiment pedicle screw400is shown inFIGS.15-18with like reference numbers being utilized in connection with similar components of that of pedicle screws100,200, and300, but within the400-series of numbers. Pedicle screw400, however, does not include a friction plug but rather a modified anvil. For instance, pedicle screw400includes a housing420, an anvil440, a bone screw member460, and a compression ring or cap480. The below discussion is focused on the only component that significantly differs from that of pedicle screws100,200, and300-anvil440.

FIGS.16A-Cdepict anvil440in more detail. Anvil440includes a spring element444positioned within an inner surface446that fully encompasses the circumference of anvil440. Spring element444is a bilateral cantilevered spring as shown.

The interrelationships among the various components discussed above can be seen in the cross-sectional views ofFIGS.17A-18B.FIG.17Bincludes an enlarged view of anvil440positioned in housing420prior to bone screw member460being positioned in housing420.

FIG.18B, on the other hand, includes an enlarged view of the fully assembled construct. As shown, spring element444of anvil440is positioned to engage with head462and compression ring or cap480further secures each component within housing420.

In the fully assembled state, anvil440frictionally engages with head462to provide a constant force. When bone screw member460is positioned within anvil440, spring element444engages a second portion462bof the head462causing the spring element444to flex upward. The upward flex of the spring element444causes the constant force to ultimately be applied to head462by anvil440which restricts movement of bone screw member460within the housing420.

Another embodiment pedicle screw500is shown inFIGS.19-22with like reference numerals being utilized in connection with similar components to that of pedicle screws100,200,300and400, but within the500-series of numbers. Pedicle screw500, similar to pedicle screw400, does not include a friction plug but rather a modified anvil. Pedicle screw500includes a housing520, an anvil540, a bone screw member560, and a compression ring or cap580. The below discussion is focused on the only component that significantly differs from that of pedicle screws100,200,300, and400-anvil540.

FIGS.20A-Cdepict anvil540in more detail. Anvil540includes spring elements544positioned within an inner surface546that fully encompasses the circumference of anvil540. Spring elements544are bilateral cantilevered springs as shown.

The interrelationships among the various components discussed above can be seen in the cross-sectional views ofFIGS.21A-22B.FIG.21Bincludes an enlarged view of the anvil540positioned in housing520prior to bone screw member560being positioned in housing520.

FIG.22B, on the other hand, includes an enlarged view of the fully assembled construct. As shown, spring elements544of anvil540are positioned to engage head562and compression ring or cap580further secures each component within housing520.

In the fully assembled state, anvil540frictionally engages with head to provide a constant force. When bone screw member560is positioned within anvil540, spring elements544engages a second portion562bof the head562causing the spring elements544to flex upward. The upward flex of the spring element544causes the constant force to ultimately be applied to head562by anvil540which restricts movement of bone screw member560within the housing520.

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.

Alternative embodiments are also contemplated herein. For instance, the second portion of the bone screw member may include a surface texture in the form of knurling, while the friction plug can include a similar texture. It is also contemplated that different features of different embodiments can be utilized together, such as a design in which the spring elements are included both in the anvil and the friction plug.