US20120232595A1

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Publication number: US20120232595A1
Application number: US13/042,074
Authority: US
Inventors: Tyler HOLSCHLAG
Original assignee: Individual
Current assignee: Atec Spine Inc
Priority date: 2011-03-07
Filing date: 2011-03-07
Publication date: 2012-09-13
Also published as: US20150080970A1; US10258387B2

Abstract

A fastener retention system for retaining fasteners within apertures of an orthopedic plate includes a first pocket disposed between two of the apertures in the plate, a blocking member disposed between the two apertures and including a second pocket that forms a cavity with the first pocket, and a spring that expands from a compressed configuration within the first pocket to a decompressed configuration within the cavity.

Description

FIELD

The present disclosure generally relates to the field of spinal orthopedics, and more particularly to fastener retention systems for spinal plates.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae include a hollow cavity and essentially stack one upon the other, forming a strong column for support of the cranium and trunk of the body. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. The intervertebral bodies, also known as intervertebral disks, include a fibrous ring filled with pulpy material. The disks function as spinal shock absorbers and also cooperate with synovial joints to facilitate movement and maintain flexibility of the spine. When one or more disks degenerate through accident or disease, nerves passing near the affected area may be compressed and consequently irritated. The result may be chronic and/or debilitating neck and/or back pain due to these spinal disorders.

One procedure for treating spinal disorders involves using substantially rigid plates for fixation of two or more vertebrae in desired spatial relationships and orientations relative to each other. During the procedure, the spine can be approached anteriorly or posteriorly. In either case, holes are drilled and tapped in at least two of the vertebrae to receive screws or other fasteners that secure the plate. The holes are positioned with reference to apertures formed in the plate. Typically the plate is curved about its longitudinal axis to facilitate contiguous surface engagement of the plate with the vertebrae. With the plate maintained against the vertebrae, the fasteners are driven into the vertebrae through the apertures in the plate. As a result, the plate maintains the attached vertebrae in a desired spacing and orientation with respect to each other.

Over time, some fasteners may gradually work loose from the vertebrae. Slight shock or vibration of the vertebrae, due to walking, climbing stairs or more vigorous activity by the patient following treatment increases this tendency, jeopardizing the integrity of fixation. Moreover, as the fasteners work loose, the outward protrusion of the heads over other components of the fasteners can be a source of discomfort and present the risk of trauma to adjacent and surrounding soft tissue. Some plates include a retention mechanism that prevents the screws from working loose after fixation.

Occasionally, the fasteners may not be inserted at a proper insertion angle during the fixation procedure. When the fastener is inserted at an improper angle, the retention mechanism may not be able to contact the fastener as the fastener backs away from the vertebra. The retention mechanism may increase the complexity of manufacturing and assembly. For example, the spinal plate may require features such as additional openings in the plate to assemble the retention mechanism. These openings may decrease the structural integrity of the plate. The retention mechanism may require various features that interact with springs or other compression members that bias the retention mechanism in one or more directions. Additional features such as stops that prevent the retention mechanism from moving too far relative to the plate or from over-compressing the springs may also complicate manufacture and assembly.

SUMMARY

In other features, the spring includes a height that is less than or equal to a depth of the first pocket when in the compressed configuration. The spring includes a height that is greater than a depth of the first pocket when in the decompressed configuration. The spring includes a plurality of flexible resilient members coupled by a plurality of hubs. The spring includes a radius of curvature in the decompressed configuration. The spring includes a central hub that contacts a surface of the first pocket in the compressed configuration and a surface of the second pocket in the decompressed configuration. The spring is further configured to bias the blocking member to protrude into at least one of the two apertures.

In still other features, the first pocket is disposed in a channel extending between the two apertures in the plate and includes a first depth D1. The blocking member is disposed in the channel and the second pocket includes a second depth D2. The spring is configured to compress to a first height H1 that is less than or equal to D1 when a first force is applied to the spring and expand to a second height H2 that is greater than D1 and less than or equal to the combined depth of D1 and D2 when the first force is released. The spring is further configured to engage with a portion of the blocking member when the first force is released and compress from a first length L1 to a second length L2 when a second force is applied to the blocking member.

A system for bone fixation includes an orthopedic plate having apertures configured to receive fasteners and a first pocket formed in a channel between two of the apertures, a blocking member that slides in the channel and includes a second pocket, wherein the first and second pockets form a cavity between the blocking member and the orthopedic plate, and a spring that expands from a compressed configuration, wherein a height of the spring is less than or equal to a depth of the first pocket, to a decompressed configuration, wherein the height of the spring is greater than the depth of the first pocket.

In other features, a first portion of the spring is configured to engage a wall of the second pocket in the decompressed configuration. A second portion of the spring is configured to engage a wall of the first pocket in the decompressed configuration. The spring biases the blocking member towards a top surface of the orthopedic plate in the decompressed configuration. The spring biases the blocking member towards a rest position substantially equidistant from the two apertures in the decompressed configuration. The spring includes a radius of curvature in the decompressed configuration that is less than a radius of curvature in the compressed configuration.

A method includes the steps of inserting a spring into a first pocket in a channel of a plate, inserting a blocking member having a second pocket into the channel of the plate, positioning the blocking member to align the second pocket and the first pocket forming a cavity, and expanding the spring to fill the cavity.

In other features, the method further comprises the steps of inserting a first screw into a first aperture adjacent to the first pocket to secure the plate to a vertebra, positioning the blocking member towards a second aperture that is opposite the first aperture and adjacent to the first pocket using the first screw, wherein the spring compresses, and decompressing the spring to bias the blocking member to align the second pocket and the first pocket.

In still other features, the method further comprises the steps of inserting a second screw into the second aperture to secure the plate to the vertebra, positioning the blocking member towards the first aperture using the second screw, wherein the spring compresses, and decompressing the spring to bias the blocking member to align the second pocket and the first pocket.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a spinal plate and a fastener retention system according to the principles of the present disclosure.

FIG. 2A is a partial perspective view of the spinal plate according to the principles of the present disclosure.

FIG. 2B is a partial perspective view illustrating assembly of the spinal plate and the fastener retention system according to the principles of the present disclosure.

FIG. 2C is a partial perspective view of the spinal plate and the fastener retention system according to the principles of the present disclosure.

FIG. 3 is a perspective view of a spring of the fastener retention system according to the principles of the present disclosure.

FIG. 4A is an elevational top view of the spring in a first decompressed position according to the principles of the present disclosure.

FIG. 4B is an elevational top view of the spring in a first compressed position according to the principles of the present disclosure.

FIG. 5 is an elevational side view of the spring according to the principles of the present disclosure

FIG. 6A is an elevational side view of the spring in a second decompressed position according to the principles of the present disclosure.

FIG. 6B is an elevational side view of the spring in a second compressed position according to the principles of the present disclosure.

FIG. 7A is a cross-sectional view of the spinal plate and the fastener retention system illustrating the spring in the second compressed position according to the principles of the present disclosure.

FIG. 7B is a cross-sectional view of the spinal plate and the fastener retention system illustrating the spring in the first and second decompressed positions according to the principles of the present disclosure.

FIG. 7C is a cross-sectional view of the spinal plate and fastener retention system illustrating the spring in the first compressed position according to the principles of the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.

Embodiments of the invention will now be described with reference to the Figures, wherein like numerals reflect like elements throughout. Embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the invention described herein. The words proximal and distal are applied herein to denote specific ends of components of the instrument described herein. For example only, a proximal end refers to the end of an instrument nearer to an operator of the instrument when the instrument is being used. A distal end refers to the end of a component further from the operator and extending towards the surgical area of a patient and/or the implant. Similarly, the words left and right, top and bottom, and upper and lower may denote opposite sides of a component.

Accordingly, a fastener retention mechanism for spinal plates of the present disclosure includes a blocking member and a spring that is compressible in multiple directions. The retention mechanism includes features that enable greater intrusion of the blocking member into the apertures to prevent fastener back-out from the vertebrae. The configuration of the spinal plate enables top-loading of the spring into a pocket of the spinal plate. The spring may be compressed in a first direction prior to insertion into the pocket of the plate. The blocking member may slide in place over the compressed spring. When the spring decompresses, the spring may fill the pocket and a cavity of the blocking member, thus enclosing the spring therebetween. The blocking member may slide towards a first one of two apertures to enable insertion of a fastener within a second one of the apertures. As the blocking member slides relative to the plate, the spring may compress in a second direction and bias the blocking member back to a rest position in which a portion of the blocking member intrudes upon the two apertures.

Referring now toFIG. 1, aspinal plate100 includesapertures102 that receive fasteners orbone screws104 for attachment to two or more vertebrae (not shown.) Theplate100 may be, for example, a cervical plate that is configured for attachment to three cervical vertebrae. Theplate100 may be formed from a variety of materials such as physiologically inert metals, alloys, and/or plastics. For example, theplate100 may be formed from a titanium and/or titanium-based alloy. Theplate100 is substantially symmetrical about acenter line106 that passes along a longitudinal axis of theplate100. A surgeon may position theplate100 over the vertebrae to be fixed and drill and tap holes in the vertebrae to receive thescrews104. In other examples, thescrews104 may be self-tapping. Eachhead108 of thescrews104 includes a driving feature such as hexagonal or star configuration that enables the surgeon to begin to drive thescrews104 into the vertebrae. As thescrews104 advance further into the vertebrae, theheads108 sink deeper into theapertures102.

Aretention mechanism110, disposed between afirst aperture102aand asecond aperture102b, may be used to prevent a correspondingfirst screw104aand a correspondingsecond screw104bfrom backing away from theplate100 should either become loose. As illustrated inFIG. 1, theapertures102 may be formed in pairs along thecenter line106. Each pair of theapertures102 may include a corresponding retention mechanism. When theretention mechanism110 is in a rest position or a locked position, as shown inFIG. 1, a portion of theretention mechanism110 intrudes upon both

apertures

102aand102b. Thus, if a screw should become loose and back away from the vertebra, thehead108 contacts theretention mechanism110 preventing the screw from backing out any further from the vertebra.

InFIG. 2A, achannel112 formed in theplate100 communicates with thefirst aperture102aand thesecond aperture102b. Thechannel112 may run perpendicular to thecenter line106. Thechannel112 may includegrooves114 that are configured to slidably receive a blockingmember116 as shown inFIGS. 2B and 2C. For example, each of thegrooves114 may include a cantilevered projection or edge that extends from atop surface118 of theplate100 and over a portion of thechannel112. The blockingmember116 may includebeveled edges120 that form a substantially trapezoidal cross-section. Thebeveled edges120 mate with thegrooves114 to prevent the blockingmember116 from exiting thechannel112 while allowing the blockingmember116 to slide substantially parallel to alateral line122 that is substantially perpendicular to thecenterline106.

Continuing withFIG. 2A, apocket123 may be formed in thechannel112. Thepocket123 may include a depression in thechannel112. Thepocket123 may include a length and width that form substantially a rectangular shape and include a depth D1 that is substantially less than an overall thickness of theplate100, as shown inFIG. 6B. Referring now toFIGS. 2B and 2C, the retention mechanism includes aspring124 that may be configured to rest within thepocket123. Thespring124 may be compressible in multiple directions. For example, thespring124 may include elements similar to an accordion spring that enable compression in a first direction along thelateral line122 when a first force F1 is applied as shown inFIG. 4B. Thespring124 may also include elements similar to a leaf spring that enable compression in a second direction along aperpendicular line126 that is perpendicular to both thecenter line106 and thelateral line122 when a force F2 is applied as shown inFIG. 6B.

Thespring124 may be formed from a variety of materials such as physiologically inert metals, alloys, and/or plastics. In other examples, thespring124 may be formed from other materials that may not be physiologically inert because thespring124 may be segregated from bone and/or tissue by thepocket122 and the blockingmember116 as described below with reference toFIGS. 7A-7C.

Continuing now withFIGS. 3-5, thespring124 may include various features that enable compression in the first direction that is substantially parallel to thelateral line122. For example, the shape of thespring124 may be substantially symmetrical about thelateral line122 and perpendicular to thelateral line122 along aright surface128 and aleft surface130 of acentral hub132. A leftupper rib134, a leftlower rib136, a rightupper rib138, and a rightlower rib140 extend from eachcentral hub132 in a symmetrical fashion aboutlateral line120. The ribs may be configured in a substantially linear fashion. Alternatively, the ribs may include some bends and/or some curvature. From left to right as depicted inFIG. 4A, each upperright rib138 is coupled with each adjacent upperleft rib134 to form anupper hub142, and each lowerright rib140 is coupled with each adjacent lowerleft rib136 to form alower hub144. The leftmost and rightmost upper and lower ribs may not couple with adjacent ribs and instead may form

end caps

146 and147 of thespring124.

Thus, eachcentral hub132 with a set of

ribs

134,136,138,140 may substantially form a resilient member that couples with an adjacent resilient member at the upper and

lower hubs

142 and144. For example, each resilient member may resemble an X-shaped member. In other examples, various suitably-shaped resilient members may be used to form various springs. For example, the spring may comprise substantially elliptically-shaped resilient members. Thespring124 may also comprise non-symmetrically-shaped resilient members. That is, the spring may comprise S-shaped resilient members, diagonal resilient members, and the like. In an uncompressed or decompressed configuration, such as when thespring124 biases the blockingmember116 to the rest position, thespring124 includes a length L1 that substantially fills thepocket123 as shown inFIG. 4A.

Referring now toFIG. 4B, as the force F1 is applied on theend cap146, thespring124 will deflect in a linear and consistent manner until it cannot bend any further, at a point where the entireright surface128 of onecentral hub132 may be in contact with the entireleft surface130 of the next adjacentcentral hub132. In this compressed configuration, thespring124 includes a length L2 that is less than L1. The stiffness of thespring124 may vary greatly as a function of the width, depth, thickness, material composition, and number of ribs and hubs within thespring124. Thus, thespring124 is compressible in a first direction that is substantially parallel to thelateral line122. Furthermore, thespring124 is self-limiting as theright surface128 and leftsurface130 contact one another thus preventing further compression due to the force F1. Thespring124 may include other self-limiting features, such asprojections148 on bottom portions of the end caps146 and147. Theprojections148 may contact the upper and

lower hubs

142 and144 when thespring124 is in the compressed configuration.

Referring now toFIGS. 6A-6B, the shape of thespring124 may include various features that enable compression in the second direction that is substantially parallel to theperpendicular line126. For example, thespring124 may include curvature of radius R applied to each resilient member. That is, theentire spring124 fromend cap146 to endcap147 may include curvature of radius R similar to a leaf spring as shown inFIG. 3. In other examples, each resilient member may include one or more curves or bends that substantially form a curved or angled profile. The curves or bends may be formed in a plane that is substantially parallel to a plane formed by theperpendicular line126 and thecenter line122.

Referring now toFIG. 6B, as a force F2 is applied to atop surface150 of thespring124, thespring124 will deflect in a linear and consistent manner until it cannot bend any further, at a point where abottom surface152 of thespring124 is substantially parallel to and/or contacts abase surface154 of thepocket123. In an uncompressed or decompressed configuration, thespring124 may include a height H1. As the force F2 is applied, thespring124 may be compressed to a height H2 that is less than H1.

Referring now toFIGS. 7A-7C, partial cross-sectional views of theplate100 andretention mechanism110 illustrate interaction of thespring124 with theplate100 and the blockingmember116. InFIG. 7A, thespring124 may be compressed to the height H2 so that the blockingmember116 may slide into place in thechannel112. For example, the force F2 may be applied to compress thespring124 until thebottom surface152 of thespring124 is substantially parallel to or in contact with thebase surface154 of thepocket123 as illustrated inFIG. 6B. That is, thespring124 may be compressed until the height H2 is less than or equal to the depth D1 of thepocket123. Once the blockingmember116 is centered over thepocket123, acavity156 may be formed by asecond pocket158 in the blockingmember116 and thefirst pocket123 of theplate100. Thesecond pocket158 may include a depth D2.

Referring now toFIG. 7B, as the force F2 decreases, thespring124 expands to fill thecavity156 until thetop surface150 of the spring contacts thepocket158 of the blockingmember116. That is, thespring124 may decompress until the height H2 is greater than the depth D1 and less than the combined depth D1 and depth D2. In another example, thespring124 may include material properties that enable thespring124 to be flattened prior to loading within thepocket123. For example, thespring124 may include the radius of curvature R at one temperature and be flattened by increasing or decreasing the temperature of thespring124 to a second temperature. That is, thespring124 may comprise materials such as nickel titanium, commonly referred to as nitinol, that include shape memory and super elastic properties based on the temperature of the materials. Once thespring124 has been flattened and loaded within thepocket122, the blockingmember116 may be slid into place above thepocket123 as described with reference toFIG. 7A. The temperature of thespring124 may then be increased or decreased as necessary to regain the curved shape such that thespring124 fills thecavity156.

InFIG. 7C, theretention mechanism110 moves to the first open position when the force F1 is applied, for example, by thehead108 of thefirst screw104abeing inserted into thefirst aperture102a(not shown). Anengagement portion160 of the blockingmember116 engages atop portion162 of theend cap146 of thespring124. Abottom portion164 of theend cap147 engages aside wall166 of thepocket122. Thus, as the force F1 is applied, thespring124 begins to compress in the second direction from length L1 to length L2. Similarly, the force F1 may be applied in the opposite direction, for example, by thehead108 of thesecond screw104bbeing inserted into thesecond aperture102b(not shown). Theretention mechanism110 moves to a second open position. As the force F1 decreases, thespring124 biases the blockingmember116 towards the rest or locked position and the length of thespring124 returns to length L1.

Example embodiments of the methods and systems of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments but should be defined only in accordance with the following claims and their equivalents. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.

Claims

1. A fastener retention system for retaining fasteners within apertures of an orthopedic plate, comprising:

a first pocket disposed between two of the apertures in the plate;

a blocking member disposed between the two apertures and including a second pocket that forms a cavity with the first pocket; and

a spring that expands from a compressed configuration within the first pocket to a decompressed configuration within the cavity.

2. The system ofclaim 1, wherein the spring includes a height that is less than or equal to a depth of the first pocket when in the compressed configuration.

3. The system ofclaim 1, wherein the spring includes a height that is greater than a depth of the first pocket when in the decompressed configuration.

4. The system ofclaim 1, wherein the spring includes a plurality of flexible resilient members coupled by a plurality of hubs.

5. The system ofclaim 1, wherein the spring includes a radius of curvature in the decompressed configuration.

6. The system ofclaim 1, wherein the spring includes a central hub that contacts a surface of the first pocket in the compressed configuration and a surface of the second pocket in the decompressed configuration.

7. The system ofclaim 1, wherein the spring is further configured to bias the blocking member to protrude into at least one of the two apertures.

8. The system ofclaim 1, wherein the first pocket is disposed in a channel extending between the two apertures in the plate and includes a first depth D1.

9. The system ofclaim 8, wherein the blocking member is disposed in the channel and the second pocket includes a second depth D2.

10. The system ofclaim 9, wherein the spring is configured to compress to a first height H1 that is less than or equal to D1 when a first force is applied to the spring and expand to a second height H2 that is greater than D1 and less than or equal to the combined depth of D1 and D2 when the first force is released.

11. The system ofclaim 10, wherein the spring is further configured to engage with a portion of the blocking member when the first force is released and compress from a first length L1 to a second length L2 when a second force is applied to the blocking member.

12. A system for bone fixation comprising:

an orthopedic plate having apertures configured to receive fasteners and a first pocket formed in a channel between two of the apertures;

a blocking member that slides in the channel and includes a second pocket, wherein the first and second pockets form a cavity between the blocking member and the orthopedic plate; and

a spring that expands from a compressed configuration, wherein a height of the spring is less than or equal to a depth of the first pocket, to a decompressed configuration, wherein the height of the spring is greater than the depth of the first pocket.

13. The system ofclaim 12, wherein a first portion of the spring is configured to engage a wall of the second pocket in the decompressed configuration.

14. The system ofclaim 12, wherein a second portion of the spring is configured to engage a wall of the first pocket in the decompressed configuration.

15. The system ofclaim 12, wherein the spring biases the blocking member towards a top surface of the orthopedic plate in the decompressed configuration.

16. The system ofclaim 12, wherein the spring biases the blocking member towards a rest position substantially equidistant from the two apertures in the decompressed configuration.

17. The system ofclaim 12, wherein the spring includes a radius of curvature in the decompressed configuration that is less than a radius of curvature in the compressed configuration.

18. A method comprising:

inserting a spring into a first pocket in a channel of a plate;

inserting a blocking member having a second pocket into the channel of the plate;

positioning the blocking member to align the second pocket and the first pocket forming a cavity; and

expanding the spring to fill the cavity.

19. The method ofclaim 18, further comprising:

inserting a first screw into a first aperture adjacent to the first pocket to secure the plate to a vertebra;

positioning the blocking member towards a second aperture that is opposite the first aperture and adjacent to the first pocket using the first screw, wherein the spring compresses; and

decompressing the spring to bias the blocking member to align the second pocket and the first pocket.

20. The method ofclaim 19, further comprising:

inserting a second screw into the second aperture to secure the plate to the vertebra;

positioning the blocking member towards the first aperture using the second screw, wherein the spring compresses; and