US20120245691A1 - Expandable interbody spacer - Google Patents

Abstract

An expandable intervertebral spacer includes a body, a proximal end, and a distal end. The body includes quadrants that form a substantially cylindrical shape in a first configuration and a substantially cuboidal shape in a second configuration. Each quadrant includes a ramp portion with a ramp and a landing and a sliding portion with a sliding side and a foot. The ramp portion of a first quadrant engages the sliding portion of a second quadrant. The proximal end and the distal end couple with the plurality of quadrants and transfer an actuating force to expand the body from the first configuration to the second configuration.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application claims priority to U.S. Provisional Application No. 61/466,729, filed Mar. 23, 2011, and is incorporated herein by reference in its entirety.
FIELD
• The present disclosure generally relates to the field of spinal orthopedics, and more particularly to intervertebral implants and interbody devices.
BACKGROUND
• The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and stacked one upon the other, forming a strong hollow column for support of the cranium and trunk. 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. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders.
• The intervertebral fibro-cartilages are also known as intervertebral discs and are made of a fibrous ring filled with pulpy material. The discs function as spinal shock absorbers and also cooperate with synovial joints to facilitate movement and maintain flexibility of the spine. When one or more discs degenerate through accident or disease, nerves passing near the affected area may be compressed and are consequently irritated. The result may be chronic and/or debilitating back pain. Various methods and apparatus have been designed to relieve such back pain, including spinal fusion using an interbody spacer or suitable graft using techniques such as Anterior Lumbar Interbody Fusion (ALIF), Posterior Lumbar Interbody Fusion (PLIF), or Transforaminal Lumbar Interbody Fusion (TLIF) surgical techniques. The implants used in-these techniques, also commonly referred to as interbody spacers, are placed in the inter-discal space between adjacent vertebrae of the spine. Many times an exterior plate is used in conjunction with the interbody spacer to hold the adjacent vertebrae while the fusion occurs.
• Ideally, the interbody spacer should stabilize the intervertebral space and allow fusion of the adjacent vertebrae. Moreover, during the time it takes for fusion to occur, the interbody spacer should have sufficient structural integrity to withstand the stress of maintaining the space without substantially degrading or deforming and have sufficient stability to remain securely in place prior to actual bone fusion.
• Interbody spacers have been used successfully to fuse adjoining vertebral bodies to restore anatomical positioning and eliminate pain caused by a bulging disc. Spacers fit into the disc space and support the vertebral bodies allowing bone fusion to occur between the joint surfaces. The primary technical advances in this market have been in the methods of minimally invasive interbody delivery. Anterior delivery and more recently medial delivery have reduced morbidity and allowed faster patient rehabilitation.
• One major obstacle remaining in perfecting these procedures is reducing the displacement of soft tissue structures and the size of tissue dissections to place the relatively large interbodies necessary to properly support the spinal column during the bone remodeling process. Large interbodies also require extensive site preparation and sizing prior to placement. This site prep can cause increased trauma to surrounding structures as instrumentation is manipulated in the disc space.
SUMMARY
• An expandable intervertebral spacer includes a body, a proximal end, and a distal end. The body includes quadrants that form a substantially cylindrical shape in a first configuration and a substantially cuboidal shape in a second configuration. Each quadrant includes a ramp portion with a ramp and a landing and a sliding portion with a sliding side and a foot. The ramp portion of a first quadrant engages the sliding portion of a second quadrant. The proximal end and the distal end couple with the quadrants and transfer an actuating force to expand the body from the first configuration to the second configuration.
• In other features, the quadrants are integrally formed within the body. The ramp of the first quadrant engages a sliding side of the second quadrant in the first configuration. The landing of the first quadrant engages a foot of the second quadrant in the second configuration. A plurality of integral linking members couple the proximal and distal ends with the body. A plurality of integral linking members conform to the cylindrical shape in the first configuration and plastically deform when the body transforms to the second configuration. A tension member couples the first quadrant and the second quadrant. A tension member within the body includes a first length in the first configuration and a second length greater than the first length in the second configuration. An integral tension member within the body provides tension between the first quadrant with the second quadrant as the body expands from the first configuration to the second configuration. A threaded aperture is disposed within at least one of the proximal end and the distal end.
• An apparatus for expanding an intervertebral space includes a plurality of interlocking sections, a proximal end, and a distal end all integrally formed in a body. The plurality of interlocking sections integrally formed in the body is configurable between a first geometry and a second geometry. The proximal end and the distal end integrally formed in the body are configured to transfer an applied force to configure the body between the first geometry and the second geometry.
• In other features, a first of the interlocking sections slidably engages a second of the interlocking sections as the body transforms from the first geometry to the second geometry. The plurality of interlocking sections includes four quadrants that form a cylindrical arrangement in the first geometry and a cuboidal arrangement in the second geometry. At least one of the interlocking sections includes a sliding quadrant and at least one of the interlocking sections includes a ramp quadrant. A sliding side of a first interlocking section slides along a ramp of an adjacent second interlocking section as the applied force compresses the proximal and distal ends. A first of the interlocking sections includes a first sliding quadrant linked to a first ramp quadrant by a first bridge. A tension member integrally formed in the body links two of the interlocking sections. The first geometry fills a first volume and the second geometry fills a second volume greater than the first volume. One of the proximal and distal ends includes an attachment feature and the other of the proximal and distal ends includes an anti-rotation feature. A tension member linking two of the interlocking sections plastically deforms when the interlocking sections transform from the first configuration to the second configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of an expandable interbody spacer in a first configuration according to the principles of the present disclosure.
• FIG. 2 is a perspective view of the expandable interbody spacer begins to expand from the first configuration to a second configuration according to the principles of the present disclosure.
• FIG. 3 is a perspective view of the expandable interbody spacer prior to full expansion in the second configuration according to the principles of the present disclosure.
• FIG. 4 is a perspective view of the expandable interbody spacer in the second configuration according to the principles of the present disclosure.
• FIG. 5 is an elevational side view of the expandable interbody spacer in the second configuration according to the principles of the present disclosure.
• FIG. 6 is an elevational side view of the expandable interbody spacer illustrating deformation of a tension member of the interbody spacer according to the principles of the present disclosure.
• FIG. 7 is an elevational side view of the proximal end of the expandable interbody spacer in the first configuration according to the principles of the present disclosure.
• FIG. 8 is an elevational side view of the proximal end of the expandable interbody spacer in the second configuration according to the principles of the present disclosure.
DETAILED DESCRIPTION
• The use of a smaller interbody which may be expanded in-situ allows the possibility of performing the surgery percutaneously with minimal disruption to tissues surrounding the surgical site and intervening soft tissue structures. The expandable interbody spacer of the present disclosure includes features that reduce displacement of soft tissue and structures during placement of the interbody while providing support to the vertebrae while bone fusion occurs. The spacer includes a first configuration that may be a substantially cylindrical geometry with dimensions that allow percutaneous insertion of the spacer between the vertebrae. Once the spacer is positioned in a desired location between the vertebrae, the spacer may be expanded to a second configuration. The second configuration may be a substantially cuboidal geometry with dimensions that allow the spacer to fill the disc space and provide support to the adjacent vertebrae while bone fusion occurs. The second configuration provides rigid support between the adjacent vertebrae that withstands compressive forces.
• The expandable interbody spacer includes a system and method of expanding a compact cylindrical form into a cuboidal shaped implant which has the necessary structural integrity to support the load of the spinal column during bone remodeling and fusion. This design uses positive cam action of sections or quadrants as they slide pass one another to expand the implant. The use of cam action allows the precise control of the rate of expansion and ensures each segment deploys evenly.
• Embodiments of the invention will now be described with reference to the Figures, wherein like numerals reflect like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive way, simply because it is being utilized in conjunction with detailed description of certain specific embodiments of the invention. Furthermore, 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. 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.
• Referring now toFIGS. 1-8, anexpandable interbody spacer100 of the present disclosure includes a system of sections or quadrants and linking members that expand from a substantially cylindrical shape in a first configuration to a substantially cuboidal shape in a second configuration. The quadrants may be substantially rigid in construction and the linking members may be semi-rigid, flexible, and/or plastically deformable. Thespacer100 may include a substantially cylindrical shape to enable insertion through a circular, percutaneous surgical opening in a patient. For example, thespacer100 may include aproximal end102 having a circular profile, acylindrical body104, and adistal end106 also having a circular profile. Thebody104 may be segmented into the system of quadrants and linking members as described herein. The quadrants and linking members may be formed in thebody104 from a unitary construction. That is, the quadrants and linking members may be integral and continuous with thebody104. For example, the quadrants and linking members may be cut using laser cutting techniques or other methods in order to retain a unitary construction. In other examples, the quadrants and linking members may be joined together by other methods.
• FIG. 1 illustrates thespacer100 in the first configuration prior to percutaneous insertion into the patient. Thebody104 of thespacer100 may be described with reference to multiple sections or quadrants, each of which includes similar subsections or components. For example, a first quadrant of thebody104 includes a first slidingportion108 coupled with afirst ramp portion110 that together extend the length of thebody104. The first slidingportion108 and thefirst ramp portion110 include curved outer surfaces corresponding to the overall cylindrical shape of thespacer100 when in the first configuration. Thefirst ramp portion110 includes aramp112, alanding114, and acompressive side116. Thefirst ramp portion110 may include additional sides to form a substantially irregular pentagonal shape. Theramp112 may include anangle117 relative to the circumference of thebody104. The landing114 extends from theramp112 and substantially parallel to alongitudinal axis115 of thebody104. Thecompressive side116 extends from the landing116 substantially parallel to the circumference of thebody104. Acompressive linking member118 may flexibly couple thecompressive side116 to thedistal end106 of thespacer100.Various tabs120 may also extend from thecompressive side116 and towards thedistal end106.
• The first slidingportion108 includes a slidingside122, afoot124, and acentral side126. The first slidingportion108 may include additional sides that may also form a substantially irregular pentagonal or hexagonal shape. The slidingside122 includes thesame angle117 relative to the circumference of thebody104 and is substantially parallel to theramp112. Thefoot124 extends from the slidingside122 substantially parallel to theaxis115 of thebody104. Thecentral side126 extends from thefoot124 towards afirst bridge128. Thefirst bridge128 may link the first slidingquadrant108 to thefirst ramp portion110. Thefirst bridge128 may be substantially rigid to withstand compressive forces applied to thecompressive side116 of thefirst ramp portion110 so as not to buckle between the first slidingportion108 and thefirst ramp portion110. Thefirst bridge128 may be integral and continuous with the first slidingportion108 and thefirst ramp portion110.
• Continuing withFIG. 1, a second quadrant of thebody104 includes a second slidingportion208 coupled with asecond ramp portion210 that together extend the length of thebody104. The second slidingportion208 and thesecond ramp portion210 include curved outer surfaces corresponding to the overall cylindrical shape of thespacer100. Thesecond ramp portion210 includes aramp212, alanding214, and acompressive side216. Thesecond ramp portion210 may include additional sides and feet that may form a substantially irregular pentagonal shape. Theramp212 extends along the surface of thebody104 at a similar angle as theangle117 relative to the circumference of thebody104. The landing214 extends from theramp212 substantially parallel to theaxis115 of thebody114. Thecompressive side216 extends from the landing214 substantially parallel to the circumference of thebody214. Acompressive member118 couples thecompressive side216 to theproximal end102 of thespacer100.Various tabs120 may also extend from thecompressive side216 and towards theproximal end102.
• The second slidingportion208 includes a slidingside222, afoot224, and acentral side226. The second slidingportion208 may include additional sides that may also form a substantially irregular pentagonal or hexagonal shape. The slidingside222 extends along the surface of thebody104 at an angle similar to theangle117 and substantially parallel to theramp112. The slidingside222 is configured to slide relative to theramp112 when thespacer100 transforms from the first configuration to the second configuration. Thefoot224 extends from the slidingside222 substantially parallel to thelongitudinal axis115 of thebody104. Thecentral side226 extends from thefoot224 towards asecond bridge228. Thesecond bridge228 may link the second slidingportion208 to thesecond ramp portion210. Thesecond bridge228 may be substantially rigid to withstand compressive forces applied to thecompressive side216 of thesecond ramp portion210 so as not to buckle between the second slidingportion208 and thesecond ramp portion210. Thesecond bridge228 may be integral and continuous with the second slidingportion208 and thesecond ramp portion210.
• Afirst tension member130 extends from thefirst bridge128 to thesecond bridge228 and couples the first quadrant and the second quadrant of thebody104. Thetension member130 may be formed by thecentral sides126 and226 of the first slidingportion108 and the second slidingportion208 respectively. Thetension member130 may include flexible or semi-rigid regions that enable thetension member130 to elastically deflect, stretch, or bend as thespacer100 transforms from the first configuration to the second configuration as illustrated inFIGS. 2-4. Thetension member130 may provide resistive force or tension that provides an interference fit between the landings and feet as described herein. Once in the second configuration, thetension member130 may include rigid characteristics to withstand compressive forces associated with placement in the intervertebral disc space in the second configuration. For example, plastic deformation of thetension member130 may alter the physical characteristics of the constituent material and increase rigidity.
• Thebody104 may include additional quadrants having sliding portions and ramp portions similar to the first and second quadrants described above, such as a third quadrant and a fourth quadrant, that are substantially identical to and/or mirror images of the first and second quadrants. Each adjacent quadrant is linked by an additional tension member that extends from the bridge of one quadrant to the bridge of another quadrant. In the present example, four quadrants that each includes a sliding portion, a ramp portion, and a bridge may be linked by four tension members to expand from the cylindrical first configuration as illustrated inFIGS. 1 and 7 to form a substantially cuboidal second configuration as illustrated inFIGS. 4 and 8. Generally, the first configuration, such as the cylindrical arrangement, includes a first volume corresponding to the diameter D2 and length of the cylinder. The second configuration, such as the cuboidal arrangement, includes a second volume corresponding to the length of thespacer100 and an expanded width W and height H. The second volume is greater than the first volume.
• For purposes of expediency and clarity, actuation of thespacer100 will be described with reference to the first and second quadrants only. However, one skilled in the art may appreciate that the same interaction between sliding portions and ramp portions applies to the additional third and fourth quadrants. Furthermore, one skilled in the art may appreciate that any suitable number of sections may be included in thespacer100 to achieve various geometric configurations.
• Referring back toFIG. 1, in the first configuration, thefirst ramp portion110 and the second slidingportion208 are adjacent to one another and thesecond ramp portion210 and the first slidingportion108 are adjacent to one another. The outer surface of thebody104 may be substantially uniform as the sides of all the sections are substantially in alignment. Theproximal end102 of thespacer100 may include afirst aperture132 for insertion of a deployment tool, such as the exemplary deployment tool provided in U.S. Publication No. 2009/0318928, incorporated herein by reference. The deployment tool may pass through the center of thespacer100 and exit through thedistal end106 via asecond aperture136. Various attachment features of the deployment tool may couple with theproximal end102 and or thedistal end106 to enable percutaneous insertion into the patient. For example,threads138 on the proximal end andthreads140 on thedistal end104 may provide for attachment of the deployment tool. Once thespacer100 has been inserted and positioned within the intervertebral space between two vertebrae, the deployment tool may actuate to deploy and expand thespacer100 by applying a compressive force F1 to either or both ends of thespacer100 as shown inFIGS. 2 and 3.
• Continuing now withFIG. 2, as the force F1 acts on theends102 and106 of thespacer100, each of thecompressive members118 begins to push against the first and secondcompressive sides116 and216 of the first andsecond ramp portions110 and210 respectively. Theramp112 of thefirst ramp portion110 slidably engages with the slidingside222 of the second slidingportion208. Likewise, theramp212 of thesecond ramp portion210 slidably engages with the slidingside122 of the first slidingportion108. The compressive force F1 forces theends102 and106 towards each other and the sliding engagement of the sliding portions and ramp portions guides the movement of the first and second sections relative to each other. Thus, the second section begins to move away from the first section causing thespacer100 to expand. Thetension member130 may begin to elastically bend near thefirst bridge128 and thesecond bridge228. Thefoot224 of the second slidingportion208 begins to move away from thefirst bridge128 and thefoot124 of the first slidingportion108 begins to move away from thesecond bridge228.
• Continuing now withFIG. 3, as thefoot124 of the first slidingportion108 approaches the landing214 of thesecond ramp portion210, thetension member130 continues to deform. The tension member may provide some counterforce F2 that pulls the first slidingportion108 and thesecond ramp portion210 together. The counterforce F2 may cause some interference between thefoot124 of the first slidingportion108 and the landing214 of thesecond ramp portion210 as thespacer100 expands to the second configuration. For example, thetension member130 may elastically stretch while also resisting the movement of thesecond ramp portion210 away from the first slidingportion108. Similarly, as thefoot224 of the second slidingportion208 approaches the landing114 of thefirst ramp portion110, the counterforce F2 may pull the second slidingportion208 and thefirst ramp portion110 together. The counterforce F2 may cause some interference between thefoot224 of the second slidingportion208 and the landing114 of thefirst ramp portion110. For example, the interference between each foot and landing interface may require an increase in the force F1 applied to theproximal end102 anddistal end106 of thespacer100 in order to fully deploy thespacer100. The interference may provide tactile feedback to the surgeon as indication of full deployment.
• Referring now toFIG. 4, as thefeet124 and224 of each slidingportion108 and208 clear thelandings114 and214 of eachramp portion110 and210, the first and second sections of thebody104 may be fully expanded in the second configuration. Thus, thefeet124 and224 andlandings114 and214 mate to create a stable, 4-sided expanded structure in the second configuration. The alignment of each portion to a corresponding ramp portion provides stability and support to withstand compressive forces associated with inter-vertebral implantation. The supportingmembers130 may provide additional support to thespacer100 in the second configuration.
• Referring now toFIG. 5, a side view of thespacer100 in the second configuration illustrates additional features of the third and fourth quadrants of thespacer100. The third section of thespacer100 includes a third slidingportion308 coupled with athird ramp portion310 by athird bridge328. The fourth section includes a fourth slidingportion408 coupled with afourth ramp portion410 by afourth bridge428. Afoot424 of the fourth slidingportion408 contacts a landing314 of thethird ramp portion310. Afoot324 of the third slidingportion308 contacts a landing414 of thefourth ramp portion410. Contact between each pair of feet and landings provides rigid support to adjacent vertebrae after deployment within the intervertebral disc space. Atension member330 links thethird bridge328 with thefourth bridge428 and may provide additional support.Additional tension members230 and430 link the second bridge228 (not shown) with thethird bridge328 and thefourth bridge428 with the first bridge128 (not shown). InFIG. 6, another side view of the spacer in the second configuration illustrates how anothertension member330′ may deform during transition from the first configuration to the second configuration. For example, thetension member330′ may flex more than the tension members illustrated inFIGS. 1-5 and begin to resemble an “S” shape.
• Referring now toFIGS. 7 and 8, side views looking into theproximal end102 of thespacer100 illustrate the cylindrical first configuration and the expanded cuboidal second configuration in greater detail. InFIG. 7, thespacer100 is shown in the non-deployed first configuration. Thus, theproximal end102 and theaperture132 are the only visible features of thespacer100. Theaperture132 may include an inner diameter D1. The inner diameter D1 may be configured for attachment of the deployment tool or other suitable device. Thespacer100 may include an outer diameter D2 prior to deployment that is suitable for percutaneous insertion into the patient. Once thespacer100 has been inserted into the intervertebral disc space, the deployment tool (not shown) or other suitable device may be used to apply the force F1 as illustrated inFIGS. 2 and 3. InFIG. 8, thespacer100 expands to the deployed second configuration, and the slidingportions108 and308 andramp portions210 and410 thus radially expand away from the axial center of thespacer100. Once the slidingportions108 and308 andramp portions210 and410 reach the second configuration, thespacer100 may include a width W and a height H that are greater than the outer diameter D2 of thespacer100.
• In operation, thespacer100 may be inserted into the intervertebral disc space between two vertebrae using a deployment tool. An exemplary deployment tool may be found in commonly assigned U.S. Pub. No. 2010/0228301, entitled “Attachment Device and Methods of Use,” to Greenhalgh et al. which is incorporated herein by reference. In some cases, the disc space may include a degenerated disc or other disorder that may require a partial or complete discectomy prior to insertion of thespacer100. The deployment tool may engage with theproximal end102 and thedistal end106 of thespacer100. For example, the deployment tool may engage with thethreads138 and140 on at least one of theproximal end102 and thedistal end106 respectively. At one end, such as thedistal end106, the deployment tool may prevent rotation of thespacer100. At the other end, such as theproximal end102, the deployment tool may engage thethread138 to pull theproximal end102 anddistal end106 together. As the deployment instrument applies the force F1, thespacer100 gradually expands as described above. The deployment instrument may increase the amount of force F1 as interference between each foot and landing resists expansion of thespacer100. The increase in the force F1 may provide tactile feedback to the surgeon indicating near complete deployment of thespacer100. As each foot snaps onto its respective landing, the force F1 may decrease quickly providing additional feedback that thespacer100 is fully deployed and structurally rigid.
• 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.

Claims (20)

1. An expandable intervertebral spacer, comprising:

a body having quadrants that form a substantially cylindrical shape in a first configuration and a substantially cuboidal shape in a second configuration, wherein each quadrant includes

a ramp portion with a ramp and a landing; and

a sliding portion with a sliding side and a foot;

wherein the ramp portion of a first quadrant engages the sliding portion of a second quadrant, and

a proximal end and a distal end coupled with the quadrants and configured to transfer an actuating force to expand the body from the first configuration to the second configuration.

2. The spacer ofclaim 1, wherein the quadrants are integrally formed within the body.

3. The spacer ofclaim 1, wherein the ramp of the first quadrant engages a sliding side of the second quadrant in the first configuration.

4. The spacer ofclaim 1, wherein the landing of the first quadrant engages a foot of the second quadrant in the second configuration.

5. The spacer ofclaim 1, further comprising a plurality of integral linking members coupling the proximal and distal ends with the body.

6. The spacer ofclaim 1, further comprising a plurality of integral linking members that conform to the cylindrical shape in the first configuration and plastically deform when the body transforms to the second configuration.

7. The spacer ofclaim 1, further comprising a tension member coupling the first quadrant and the second quadrant.

8. The spacer ofclaim 1, further comprising a tension member within the body having a first length in the first configuration and a second length greater than the first length in the second configuration.

9. The spacer ofclaim 1, further comprising an integral tension member within the body that provides tension between the first quadrant with the second quadrant as the body expands from the first configuration to the second configuration.

10. The spacer ofclaim 1, further comprising a threaded aperture within at least one of the proximal end and the distal end.

11. An apparatus for expanding an intervertebral space, comprising:

a plurality of interlocking sections integrally formed in a body and configurable between a first geometry and a second geometry; and

a proximal end and a distal end integrally formed in the body and configured to transfer an applied force to configure the body between the first geometry and the second geometry.

12. The apparatus ofclaim 11, wherein a first of the interlocking sections slidably engages a second of the interlocking sections as the body transforms from the first geometry to the second geometry.

13. The apparatus ofclaim 11, wherein the plurality of interlocking sections includes four quadrants that form a cylindrical arrangement in the first geometry and a cuboidal arrangement in the second geometry.

14. The apparatus ofclaim 11, wherein at least one of the interlocking sections includes a sliding quadrant and at least one of the interlocking sections includes a ramp quadrant.

15. The apparatus ofclaim 11, wherein a sliding side of a first interlocking section slides along a ramp of an adjacent second interlocking section as the applied force compresses the proximal and distal ends.

16. The apparatus ofclaim 11, wherein a first of the interlocking sections includes a first sliding quadrant linked to a first ramp quadrant by a first bridge.

17. The apparatus ofclaim 11, further comprising a tension member integrally formed in the body links two of the interlocking sections.

18. The apparatus ofclaim 11, wherein the first geometry fills a first volume and the second geometry fills a second volume greater than the first volume.

19. The apparatus ofclaim 11, wherein one of the proximal and distal ends includes an attachment feature and the other of the proximal and distal ends includes an anti-rotation feature.

20. The apparatus ofclaim 11, further comprising a tension member linking two of the interlocking sections that plastically deforms when the interlocking sections transform from the first configuration to the second configuration.

Images