US20110184467A1 - Dynamic constructs for spinal stabilization - Google Patents

Abstract

Devices and methods for spinal stabilization include first and second anchors engageable to respective ones of first and second vertebrae and a connector assembly engageable with the anchors to provide a desired stabilization effect. The connector assembly can include a connecting element and a bumper element engageable to the first and second anchors.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• The present application is a divisional of U.S. patent application Ser. No. 11/483,330 filed on Jul. 7, 2006, which is incorporated herein by reference in its entirety.
BACKGROUND
• Elongated connecting elements, such as rods, plates, tethers, wires, cables, and other devices have been implanted along the spinal column and connected between two or more anchors engaged between one or more spinal motion segments. Such connecting elements can provide a rigid construct that resists movement of the spinal motion segment in response to spinal loading or movement of the spinal motion segment by the patient. Still other connecting elements are flexible to permit at least limited spinal motion while providing resistance to loading and motion of the spinal motion segment. Such flexible connecting elements can be considered to provide dynamic spinal stabilization since at least limited movement of the spinal motion segment is preserved after implantation of the connecting element.
• While prior connecting elements provide various spinal stabilization options, there remains a need for stabilization constructs that can provide dynamic resistance to forces and permit motion of the spinal column segment in different directions while maintaining stabilization of the spinal column segment and the structural integrity of the construct.
SUMMARY
• The present invention generally relates to constructs and methods for dynamically stabilizing a spinal column motion segment including at least two vertebrae by engaging the construct between the at least two vertebrae. The construct can be engaged to at least two anchors engaged to respective ones of the at least two vertebrae while permitting motion of the vertebrae relative to one another. The construct includes a bumper element extending between the anchors to resist movement of the anchors toward one another and a connecting element extending between the anchors to axially link the anchors to one another.
• According to one aspect, a spinal stabilization construct includes first and second anchors each including a proximal head and a distal portion engageable to respective ones of first and second vertebral bodies. The construct also includes a connector assembly extending along a longitudinal axis between the proximal heads of the first and second anchors. The connector assembly includes an elongated connecting element with a rigid body extending between opposites ends that are located in passages of respective ones of the proximal heads. The connector assembly also includes a flexible bumper element positioned about the connecting element with the bumper element extending between opposite ends in abutting engagement with the proximal heads to resist movement of the heads toward one another. The connector assembly also includes an engagement member coupled to the proximal head of the first anchor. The engagement member secures the respective opposite end of the connecting element in the passage of the proximal head of the first anchor. The other of the opposite ends of the connecting element is captured in the passage of the proximal head of the second anchor and is configured with the proximal head to move along the longitudinal axis relative to the second anchor in response to movement of the first and second vertebrae along the longitudinal axis.
• In another aspect, a spinal stabilization construct includes first and second anchors that each include a proximal head and a distal portion engageable to respective ones of first and second vertebral bodies. The construct also includes a connector assembly extending along a longitudinal axis between the proximal heads of the first and second anchors. The connecting assembly includes a bumper element extending along the longitudinal axis and positioned between the proximal heads in abutting engagement with the proximal heads to resist movement of the heads toward one another and an elongated connecting element including a band-shaped body extending along the longitudinal axis and around the proximal heads of the first and second anchors.
• In yet another aspect, a method for assembling a spinal stabilization construct comprises: engaging a first anchor to a first vertebra; engaging a second anchor to a second vertebra; measuring a distance between adjacent inner surfaces of proximal heads of the first and second anchors; selecting a bumper element having a length between opposite ends thereof greater than the distance measured; distracting the first and second anchors to separate the proximal heads; positioning the bumper element between the inner surfaces of the proximal heads; and compressing the proximal heads to secure the bumper element between the inner surfaces.
• In another aspect, a method for assembling a spinal stabilization construct comprises: engaging a first anchor to a first vertebra; engaging a second anchor to a second vertebra; positioning a bumper element around an elongated connecting element; engaging a first end of the connecting element to the first anchor; and slidably capturing the second end of the connecting element in the second anchor with the bumper element extending between the first and second anchors.
• According to another aspect, a spinal stabilization construct comprises first and second bone anchors and an elongated connecting element extending between the first and second bone anchors and a bumper element positioned around the connecting element between the first and second anchors. The connecting element includes a first end extending from the bumper element fixedly engaged with the first anchor and a second end extending from the bumper element movably engaged with the second bone anchor so that the second bone anchor is movable to translate along the connecting element and pivotal about the connecting element.
• In a further aspect, a spinal stabilization construct comprises first and second bone anchors and an elongated connecting element extending between the first and second bone anchors and a bumper element positioned around the connecting element between the first and second anchors. The connecting element includes a first end extending from the bumper element captured in the first bone anchor and a second end extending from the bumper element captured in the second bone anchor. Each of the first and second bone anchors are movable relative to the connecting element to translate along the connecting element and pivot about the connecting element.
• In another aspect, a spinal stabilization construct comprises first and second hone anchors and an elongated bumper element positioned between and abuttingly engaging the first and second bone anchors. The construct further comprises an elongated connecting element forming a band extending around the first and second anchors and along opposite sides of the bumper element.
• These and other aspects will be discussed further below.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a side view of a spinal column segment with a dynamic stabilization construct secured thereto.
• FIG. 2 is an elevation view of one embodiment of the stabilization construct ofFIG. 1.
• FIG. 3 is a perspective view of the stabilization construct ofFIG. 2.
• FIG. 4 is an exploded view of the stabilization construct ofFIG. 2.
• FIG. 5 is a perspective view of another embodiment bumper element useable with the stabilization construct ofFIG. 2.
• FIG. 6 is an elevation view of another embodiment of the dynamic stabilization construct ofFIG. 1.
• FIG. 7 is an exploded perspective view of the stabilization construct ofFIG. 6.
• FIG. 8 is a sectional view showing a connecting element of the stabilization construct engaged to a bone anchor.
• FIG. 9 is a perspective view of the stabilization construct ofFIG. 6.
• FIG. 10 is an elevation view of a portion of the stabilization construct ofFIG. 6 showing a first load distribution pattern.
• FIG. 11 is an elevation view of a portion of the stabilization construct ofFIG. 6 showing a second load distribution pattern.
• FIG. 12 is an elevation view showing a lordotic version of the stabilization construct ofFIG. 6.
• FIG. 13 is an exploded elevation view of a spinal column segment and a multi-level embodiment of the dynamic stabilization construct ofFIG. 6.
• FIG. 14 is an elevation view of another embodiment of the dynamic stabilization construct ofFIG. 1.
• FIG. 15 is an exploded perspective view of the stabilization construct ofFIG. 14.
• FIG. 16 is a perspective view of the stabilization construct ofFIG. 14.
• FIG. 17 is an elevation view of a portion of the stabilization construct ofFIG. 14 showing a first load distribution pattern.
• FIG. 18 is an elevation view of a portion of the stabilization construct ofFIG. 14 showing a second load distribution pattern.
• FIG. 19 is an elevation view showing a lordotic version of the stabilization construct ofFIG. 14.
• FIGS. 20A-20E show various steps of a method for assembling the stabilization construct ofFIG. 14.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
• For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates.
• Constructs and methods for providing dynamic stabilization of one or more spinal motion segments are provided. The constructs and methods include a connector assembly between two or more bone anchors that can be engaged to respective ones of at least two or more vertebral bodies of a spinal motion segment. The connector assembly extends along a longitudinal axis and includes a bumper element extending between the bone anchors to dynamically resist movement of the anchors toward one another and a connecting element that axially couples the anchors to one another.
• In one embodiment, one end of the connecting element is captured in at least one of the bone anchors with at least axial movement of the connecting element relative to the bone anchor permitted. In one form, the other end of the connecting element is fixed in the other bone anchor. In another form, the other end of the connecting element is captured in and can axially move in the other bone anchor. In another embodiment, the connecting element includes a band that extends around the bone anchors to axially limit or prevent the anchors from movement away from one another.
• In one embodiment, the connecting element can extend through the bumper element for engagement to the first and second bone anchors. In one form, the bone anchor includes a head with a pivoting ball arrangement through which an end of the connecting element extends. In another form, the ends of the connection element are slidably captured in heads of each of the bone anchors and extend to enlarged end elements that contact the respective bone anchor heads to limit movement of the bone anchors away from one another. In another embodiment, the connecting element extends around the bumper element. In one form, the bone anchors can include heads with flattened inner surfaces in abutting engagement with a respective end of the bumper element. In a further form, the outer perimeter of the heads of the bumper assembly can include a groove to receive the connecting element therein so that the connecting element extends around at least a portion of each of the bone anchor heads.
• The bone anchors discussed herein can be multi-axial or uni-axial in form, and can include an anchor member engageable to a vertebral body and a proximal head for receiving or engaging a respective end of the connector assembly. The multi-axial anchors allow the anchor member to be positioned at various angles relative to the head of the anchor. The uni-axial anchors can also provide a fixed positioning of the connector assembly to the bone anchor. The anchor member of the bone anchors can form a distal lower portion that is engageable to a vertebral body with the proximal head positioned adjacent the vertebral body. In one embodiment, the anchor member is in the form of a bone screw with a threaded shaft and a proximal head that is pivotally captured in the receiver. In other embodiments, the distal anchor member can be in the form of a hook, staple, cable, tether, suture anchor, interbody fusion implant, artificial disc implant, bolt, or other structure engageable to bony tissue. The proximal head can include a receiver with a U-shape, O-shape, or other shape that defines a passage that receives or engages the respective end of the connector assembly therein, thereon, therethrough, or thereover, for example. The connector assembly can extend from one or both of the bone anchors for securement to one or more additional vertebral bodies in multi-level stabilization constructs.
• FIG. 1 illustrates a dynamic stabilization construct20 engaged along a spinal column of a patient. More specifically, stabilization construct20 can be affixed to pedicles P of vertebrae V of the spinal column segment S from a posterior approach. Also contemplated are applications in posterior-lateral, lateral, antero-lateral and anterior approaches, and applications where the stabilization construct20 is engaged to other portions of the vertebrae V, such as the anterior body portion or any of the posterior elements. The spinal column segment S can comprise two vertebrae V as shown for a single level stabilization procedure or three or more vertebrae in multi-level stabilization procedures. The vertebrae V can be any one or combination of the sacral, lumbar, thoracic, and cervical vertebrae of the spinal column.
• Stabilization construct20 can include aconnector assembly22 extending along a longitudinal axis L betweenfirst bone anchor24 andsecond bone anchor26.Connector assembly22 can include abumper element28 positioned between bone anchors24,26 and in contact therewith to dynamically resist movement of bone anchors24,26 toward one another.Connector assembly22 can also include connectingelement30 extending along axis L and axially linking or connectinganchors24,26 to one another. Connectingelement30 can be engaged, captured or constrained withanchors24,26 to coupleconnector assembly22 toanchors24,26.Connector assembly22 can include an overall length along longitudinal axis L sized to extend between bone anchors24,26 when engaged to at least two vertebral bodiesV. Connector assembly22 can also be provided with a length sized to extend along three or more vertebrae with at least one bumper element between at least two adjacent vertebrae. The portions of theconnector assembly22 extending between the other vertebrae may include a bumper element, or may include a rod portion between the other vertebrae that provides rigid or dynamic stabilization without a bumper element.
• Instabilization construct20, bone anchors24,26 are affixed to various locations of the spinal column segment S, such as the pedicles P, and interconnected with one ormore connector assemblies22. Other procedures contemplateconnector assemblies22 may be employed at other locations about the spinal column, including anterior, antero-lateral, and lateral locations. Stabilization construct20 may also be employed in procedures where such locations are combined; e.g. to provide posterior and anterior stabilization. Stabilization construct20 may be used for, but is not limited to, treatment of degenerative spondylolisthesis, herniation, degeneration, arthritis, fracture, dislocation, scoliosis, kyphosis, spinal tumor, and/or a failed previous fusion.
• FIGS. 2-4 show various views of one embodiment of stabilization construct20 designated as stabilization construct40. Stabilization construct40 includes aconnector assembly42 extending between and engageable to afirst anchor44 and asecond anchor46.Connector assembly42 includes abumper element48 positioned between and abuttingly engaginganchors44,46 and a connectingelement50 extending between and engaged toanchors44,46.Bumper element48 and connectingelement50 extend along longitudinal axis L.
• Connectingelement50 includes an elongated rod-like body52 extending between afirst end54 and an oppositesecond end56.Body52 can have a circular cross-section as shown, or can include any other cross-sectional shape. The cross-section can further be constant along the length ofbody52 or be varying in size and shape.Body52 can be rigid so that when subjected to forces from spinal column loading it retains its shape and length.
• Bumper element48 includes an elongatedcylindrical body58 extending between afirst end60 and an oppositesecond end62 along longitudinalaxis L. Body58 can define acentral passage64 sized and shaped to receive connectingelement50 therethrough with ends54,56 extending axially from ends60,62, respectively.Cylindrical body58 andpassage64 can each define a circular cross-section as shown, or one or both may include any suitable non-circular cross-sectional shape along all or a portion of the length thereof.
• Bumper element48 can also include first andsecond spacer elements66,68 positioned adjacent respective ones of theends60,62.Spacer elements66,68 can includeaxial passages67,69, respectively, to receive connectingelement50 therethrough with ends54,56 extending axially therefrom.Spacer elements66,68 can be separate components frombody58 to allow the length and/or angulation of the ends ofbumper element48 relative to longitudinal axis L to be adjusted.
• Bone anchor44 can include anelongated shaft70 extending distally from aproximal head72.Shaft70 can be threaded as shown, or can be in the form of a hook or other suitable bone engaging structure.Shaft70 is shown fixed relative to head72, but can also be pivotal relative to head72 to allow adjustment in the angular orientation ofshaft70 relative to head72.Head72 can define apassage74 for receiving connectingelement50 therein.Passage74 is located between first andsecond arms76,78, which extend proximally from alower base portion80.Passage74 can define a U-shape or any other suitable shape.Arms76,78 can be internally threaded to threadingly receive anengagement member82.
• Engagement member82 can include a proximaltool engaging portion84 and adistal shaft portion86.Shaft portion86 can be in the form of a set screw to engagearms76,78.Tool engaging portion84 can be severable fromshaft86 upon application of a threshold torque toportion84 relative toportion86. Other forms forengagement member82 are contemplated, including nuts, caps, plugs, and sliding locking elements, for example. In the illustrated embodiment,engagement member82 can be threaded intopassage74 and into contact with connectingelement50 to secure it in position inhead72. When secured inhead72, connectingelement50 is fixed in position and translation along longitudinal axis L relative to anchor44 or pivoting relative to anchor44 is prevented or minimized.
• Bone anchor46 includes adistal shaft88 extending distally fromproximal head90.Shaft88 can be threaded as shown, or can be in the form of a hook or other suitable bone engaging structure.Proximal head90 includes a ring-like shape with apivotal coupling element92 pivotally captured therein. Couplingelement92 has a ball-like or spherical shape and defines apassage94 for receiving andslidable capturing end56 of connectingelement50 therethrough. The engagement relationship ofcoupling element92 with connectingelement50 allows connectingelement50 to axially translate relative to anchor46, as indicated byarrow96 inFIGS. 2 and 3. In addition,coupling element92 can universally pivot to at least some degree about connectingelement50 in response to movement of the vertebral body to whichanchor46 is engaged, as indicated byarrows98. Accordingly, construct40 provides a limited range of motion for the vertebrae to which it is engaged to move relative to one another, while providing limits to this motion when couplingelement92contacts connecting element50. Undesired movement, such as slippage or displacement of the vertebrae in the axial plane of the spinal column as indicated byarrow97, is resisted by each of theanchors44,46.
• InFIG. 5 there is shown another embodiment tobumper element48 designated asbumper element48′.Bumper element48′ can be identical tobumper element48, but includesholes49 extending throughbody58′ in communication withpassage64.Bumper element49′ can be made from a polymer material, such as PEEK, or other suitable material.Holes49 provide increased flexibility and compressibility. Any of the bumper embodiments could be made from PEEK or other polymer material, silicone material, polyurethane, elastomers, or other material providing the desired load resistance properties. In yet another form, the body of the bumper element can be made from a more rigid material, and the ends of the body or spacer elements at the end of the body can be made from a flexible material to allow some compression and thus limited movement of the vertebrae along the axis of the construct.
• Referring now toFIGS. 6 and 7, there is shown another embodiment of stabilization construct20 designated as stabilization construct110. Several elements in stabilization construct110 can be similar or identical to those discussed above with respect to construct40, and thus are designated with the same reference numerals.Stabilization construct110 includesconnector assembly112 extending between and engaged to first andsecond anchors44a,44b.Anchors44a,44bcan be identical to anchor44 discussed above, and are designate as “a” and “b” to indicate the anchors are separate anchors.
• Stabilization construct110 includes a connectingelement114 extending throughbumper element48. Connectingelement114 is positioned inpassages74a,74bofanchors44a,44band engaged therein with respective ones of theengagement members130a,130b.Bumper element48 andoptional spacer elements66,68 are positioned betweenheads72a,72bofanchors44a,44bin abutting engagement therewith.
• Connectingelement114 can include anelongated body116 extending between opposite ends118,120.Ends118,120 can include an enlarged, ball-like or spherical shaped extending outwardly frombody116. When secured toanchors44a,44b, ends118,120 are located axially adjacent to therespective head72a,72bon the side thereof opposite the respective adjacent end ofbumper element48.Engagement members130a,130bcan be engaged to respective ones of theheads72a,72bto capture connectingelement116 in therespective passages74a,74bwhile permitting axial movement of connectingelement114 and rotation of connectingelement114 inpassages74a,74b.
• FIG. 8 shows a sectional view ofhead72a,72bofanchor44a,44bwith connectingelement116 inpassage74a,74b.Engagement member130a,130bcan be similar toengagement member82 discussed above, and can include a distal threadedshaft portion134 and a proximaltool engaging portion136.Distal portion134 can engagehead72a,72binpassage74a,74b. However,proximal portion136contact head72a,72bto limit advancement ofdistal portion134 intopassage74a,74b. Whenproximal portion136 contacts heads72a,72b,distal end132 ofshaft portion134 is spaced from body16 of connectingelement114 by agap122. Accordingly,engagement members130a,130bcapture connecting element114 in theanchors44a,44bbut allow axial movement and rotation of the connectingelement114 and theanchors44a,44brelative to one another.
• Body116 of connectingelement114 can axially translate inpassages74a,74bto allow movement ofheads72a,72btoward one another and away from one another in response to spinal motion, as indicated byarrow96 inFIG. 9. For example, as shown inFIG. 6,bumper element48 can be compressed so that it is bulging radially outwardly in response to movement ofheads72a,72btoward one another, limiting movement ofheads72a,72band thus the adjacent vertebrae toward one another along axis L. Ends118,120 also contact heads72a,72bin response to movement ofheads72a,72baway from one another, and thus limit movement of the adjacent vertebrae away from one another along axis L. In addition, anchors44a,44bcan rotate and pivot relative to connectingelement114 at least until such rotation or pivoting is limited by contact between the anchor and the connecting element. Such translational, rotational and pivoting movement, indicated byarrows98aand98binFIG. 9, allows at least limited motion of the vertebrae to which stabilization construct110 is engaged while providing limits to that motion. Undesired movement, such as translation of the vertebrae in the axial plane of the spinal column, as indicated byarrow97, is prevented by contact between the connecting element and respective anchors and engagement members.
• FIGS. 10 and 11 shown loading ofbumper element48 in response to spinal extension and flexion, respectively, when stabilization construct110 is engaged to the pedicles of adjacent lumbar vertebrae, for example. InFIG. 10, extension movement of the posteriorly stabilized vertebrae results inshafts70a,70bpivoting away from one another as indicated byarrow137, pivoting the proximal ends ofheads72a,72btoward one another about connectingelement114 and into active engagement with theproximal side48aofbumper element48. This displacement ofheads72a,72band thus the extension of the vertebrae is dynamically resisted by compression ofbumper element48 alongproximal side48aas indicated byarrows128. The compression loading is greatest along the outermost portion ofbumper element48 and tapers toward longitudinal axis L and connectingelement114.
• InFIG. 11, flexion movement of the posteriorly stabilized vertebrae results inshafts70a,70bpivoting toward one another as indicated byarrow138, pivoting the proximal ends ofheads72a,72baway from one another about connectingelement114 so that the distal sides ofheads72a,72bactively engage thedistal side48bofbumper element48. This displacement ofheads72a,72band thus the flexion of the vertebrae is dynamically resisted by compression ofbumper element48 alongdistal side48bas indicated byarrows129. The compression loading is greatest along the outermost portion ofbumper element48 and tapers toward longitudinal axis L and connectingelement114.
• InFIG. 12 there is shown a lordotic version of stabilization construct110 designated as stabilization construct140. Stabilization construct140 can include several components that are identical to those ofstabilization construct110, and like components are designated with the same reference numerals. InFIG. 12, anchors44a,44bare oriented alongaxes45a,45b, respectively.Axes45a,45band thus anchors44a,44bare oriented to converge proximally at an angle A1.Connector assembly142 includes connectingelement114 as discussed above and abumper element148 extending about connectingelement114 betweenheads72a,72b.Bumper element148 includes abody150 extending betweenends152,154.Bumper element148 can further includeoptional spacer elements156,158 adjacent respective one of theends152,154.
• The ends of thebumper element148, whether defined bybody150 orspacer elements156,158, can be obliquely oriented to longitudinal axis L so as to extend generally parallel withaxes45a,45band thus abuttingly contact heads72a,72b. This provides the full surface area at the ends of thebumper element148 normally in contact withheads72a,72b. Resistance to both spinal extension and flexion of the vertebrae to which stabilization construct140 is engaged is thus provided bybumper element148 even when the axes ofanchors44a,44bare not parallel with one another.
• FIG. 13 shows a multi-level version of stabilization construct110 designated asmulti-level construct340. Construct340 includes an elongated connectingelement342 having a length to extend along at least three vertebrae V and anchors344,346,348 engaged to respective ones of the vertebraeV. Bumper elements350,352 are positioned about connectingelement342 and between respective pairs of theanchors344,346,348. Connectingelement342 can be slidably and rotatably captured in each of theanchors344,346,348 with a respective one of the engagement elements354,356,358. Alternatively, connectingelement342 can be rigidly engaged to one or more of theanchors344,346,348.
• Referring now toFIGS. 14 and 15, there is shown another embodiment of stabilization construct20 designated as stabilization construct200.Stabilization construct200 includes aconnector assembly202 extending between and engageable to afirst anchor204aand asecond anchor204b.Connector assembly202 includes abumper element208 positioned between and abuttingly engaginganchors204a,204band a connectingelement210 extending between and engaged to anchors204,206.Bumper element208 and connectingelement210 extend along longitudinal axis L.
• Connectingelement210 include an elongated band-like body212 extending between afirst end214 and an oppositesecond end216.Body212 can be made from metal or metal alloy such that it provides little or no stretching capability under normal spinal loading. Alternatively,body212 can be made from a flexible, resilient and elastic material that allows stretching movement of theanchors204a,204band thus the vertebrae to which construct200 is engaged.
• Bumper element208 includes an elongatedcylindrical body218 extending between afirst end220 and an oppositesecond end222 along longitudinalaxis L. Body218 can definecentral recesses224,225 sized and shaped to receive a portion of the respective anchor204,206 therein as discussed further below.Recesses224,225 can have a blind end inbody218. In another embodiment, recesses224,225 are connected by a central passage extending axially throughbody218.Cylindrical body218 can define a circular cross-section as shown, or may include any suitable non-circular cross-sectional shape along all or a portion of the length thereof.
• Bone anchors204a,204bcan be a mirror image of one another when implanted. Each includes anelongated shaft230a,230bextending distally from aproximal head232a,232b.Shaft230a,230bcan be threaded as shown, or can be in the form of a hook or other suitable bone engaging structure.Shaft230a,230bis shown fixed relative to head232a,232bbut can also be pivotal relative to head232a,232bto allow adjustment in the angular orientation ofshaft230a,230brelative to head232a,232b.Head232a,232bincludes aninner surface234a,234bhaving aprojection236a(FIG. 20A),236bextending therefrom along longitudinal axis L. The opposite,outer surface238a,238bofhead232a,232bincludes agroove240a,240bextending about thehead232a,232band in the direction of longitudinal axis L.
• When assembled,bumper element208 is positioned betweeninner surfaces234a,234bofheads232a,232b.Projections236a,236bcan be positioned in respective ones of therecesses224,225 ofbumper element208 to resist or prevent slippage from betweenheads232a,232b. Connectingelement210 is positioned ingrooves240a,240band around heads232a,232bandbumper element208. Since connectingelement210 extends aroundouter surfaces238a,238b, it couples theheads232a,232bto one another and can resist or prevent movement of theheads232a,232baway from one another along axisL. Connecting element210 can further securebumper element208 in position betweenheads232a,232bby compressing or maintaining compression of theheads232a,232bagainstbumper element208.
• Stabilization construct200 can be assembled to provide varying degrees of motion of the vertebrae to which construct200 is attached. For example, heads232a,232bcan be compressed toward one another to tightly gripbumper element208 therebetween, and then connectingelement210 secured aroundheads232a,232bto maintain the applied compression. Connectingelement210 can be relatively inelastic under spinal loading, preventing motion movement of the anchor heads232a,232baway from one another and thecompressed bumper element208 prevents movement of anchor heads232a,232btoward one another. Alternatively,bumper element208 can be rigid and relatively incompressible under spinal loading to prevent movement ofheads232a,232btoward one another.
• In another form shown inFIG. 16, connectingelement210 can be elastic under spinal loading and stretch when engaged aboutheads232a,232bto permit at least limited movement ofheads232a,232baway from one another along longitudinal axis L, as indicated byarrow96.Bumper element208 can be compressible under spinal loading to permit movement of the anchor heads232a,232btoward one another in response to movement of the vertebrae along longitudinal axis L as also indicated byarrow96. Furthermore, compressibility ofbumper element208 in response to spinal loading can permit pivoting and rotational movement of the vertebrae relative to one another, as indicated byarrows98a,98b.
• FIGS. 17 and 18 show loading ofbumper element208 in response to spinal extension and flexion, respectively, when stabilization construct200 is engaged to the pedicles of adjacent lumbar vertebrae, for example. InFIG. 17, extension movement of the posteriorly stabilized vertebrae results inshafts230a,230bpivoting away from one another as indicated byarrow246, pivoting the proximal ends ofheads232a,232btoward one another in active engagement withends220,222 ofbumper element208 adjacentproximal side208a. This displacement of theheads232a,232band thus the extension of the vertebrae is dynamically resisted by compression ofbumper element208 alongproximal side208aas indicated byarrows250. The compression loading is greatest along the outermost portion ofbumper element208 and tapers toward longitudinal axis L.
• InFIG. 18, flexion movement of the posteriorly stabilized vertebrae results inshafts230a,230bpivoting toward one another as indicated byarrow248, pivoting the proximal ends ofheads232a,232baway from one another so that theouter surfaces238a,238btension connecting element210 andinner surfaces234a,234bcontact the respective ends220,2222 to compress thedistal side208bofbumper element208. This displacement of theheads232a,232band thus the flexion of the vertebrae is dynamically resisted by compression ofbumper element208 alongdistal side208bas indicated byarrows252. The compression loading is greatest along the outermost portion ofbumper element208 and tapers toward longitudinal axis L.
• InFIG. 19 there is shown a lordotic version of stabilization construct200 designated as stabilization construct260. Stabilization construct260 can include several components that are identical to those ofstabilization construct200, and like components are designated with the same reference numerals. InFIG. 19, anchors204a,204bare oriented alongaxes205a,205b, respectively.Axes205a,205band thus anchors204a,204bare oriented to converge proximally at an angle A1.Connector assembly262 includes connectingelement210 as discussed above and a bumper element268 extending betweenheads232a,232bwith connectingelement210 positioned thereabout. Bumper element268 includes abody270 extending betweenends272,274.
• Inner surfaces234a,234bcan be angled relative toaxes205a,205bso that when anchors204a,204bare oriented alongaxes205a,205binner surfaces234a,234bare orthogonal to longitudinal axis L to contact similarly oriented ends272,274 ofbody270. in another arrangement, ends272,274 can be obliquely oriented to longitudinal axis L to contact similarly orientedinner surfaces234a,234bso that the surface area at the ends of the bumper element268 is fully in contact withheads232a,232b. Resistance to both spinal extension and flexion movement of the vertebrae to which stabilization construct260 is engaged is thus provided by bumper element268 even when the axes ofanchors204a,204bare not parallel with one another.
• Referring now toFIGS. 20A-20E, a method for assembling stabilization construct200 will be discussed. InFIG. 20A, anchors204a,204bare engaged to respective ones of first and second vertebrae. The distance X betweeninner surfaces234a,234bis measured. InFIG. 20B abumper element208 having length X+Y between ends220,222 is selected. The distance Y is selected to provide a desired tension in connectingelement210. InFIG. 20C, anchors204a,204bare distracted toseparate heads232a,232b. The selectedbumper element208 is positioned betweenheads232a,232bso thatprojections236a,236bcan be positioned in respective ones of therecesses224,225 ofbumper element208.
• InFIG. 20D, anchor heads232a,232bare compressed toward one another to bringinner surfaces234a,234bin contact with the respective ends220,222 and to accommodate placement of connectingelement210 aboutheads232a,232bingrooves240a,240b. In the compressed state,bumper element208 can bulge or flex outwardly. When connectingelement210 is in position, anchor compression can be released andbumper element208 pushes heads232a,232bapart totension connecting element210, maintaining the construct in an assembled condition. The distraction provided bybumper element208 can correspond to or be a function of the length increase Y determined inFIG. 20B.
• While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims (23)

1-14. (canceled)

15. A spinal stabilization construct, comprising:

first and second anchors, said first and second anchors each including a proximal head and a distal portion engageable to respective ones of first and second vertebral bodies;

a connector assembly extending along a longitudinal axis between said proximal heads of said first and second anchors, said connector assembly including:

a bumper element extending along the longitudinal axis and positioned between said proximal heads in abutting engagement with said proximal heads to resist movement of said heads toward one another; and

an elongated connecting element including a band-shaped body extending along the longitudinal axis and around said proximal heads of said first and second anchors.

16. The construct ofclaim 15, wherein said proximal heads include inner surfaces facing one another and outer surfaces facing away from one another, said bumper element being positioned in abutting engagement with said inner surfaces and said band-shaped body extending around said outer surfaces.

17. The construct ofclaim 16, wherein said outer surfaces each include a groove extending therearound along the longitudinal axis and said connecting element is positioned in said grooves.

18. The construct ofclaim 17, wherein said inner surfaces are flat and orthogonally oriented to the longitudinal axis.

19. The construct ofclaim 18, wherein each of said proximal heads includes a projection extending from said inner surface thereof along said longitudinal axis, said bumper element including opposite ends and a recess in each of said ends, said projections being received in respective ones of said recesses.

20. The construct ofclaim 15, wherein each of said proximal heads includes a projection extending therefrom along said longitudinal axis, said bumper element including opposite ends and a recess in each of said ends, said projections being received in respective ones of said recesses.

21. The construct ofclaim 15, wherein said bumper element is structured to prevent movement of said proximal heads toward one another and said connecting element is structured to prevent movement of said proximal heads away from one another.

22. The construct ofclaim 15, wherein said bumper element is compressible to permit movement of said proximal heads toward one another and said connecting element is elastic to permit movement of said proximal heads away from one another.

23. The construct ofclaim 15, wherein said distal portion of said first and second anchors includes a threaded shaft.

24. A method for assembling a spinal stabilization construct, comprising:

engaging a first anchor to a first vertebra;

engaging a second anchor to a second vertebra;

measuring a distance between adjacent inner surfaces of proximal heads of the first and second anchors;

selecting a bumper element having a length between opposite ends thereof greater than the distance measured;

distracting the first and second anchors to separate the proximal heads;

positioning the bumper element between the inner surfaces of the proximal heads;

compressing the proximal heads to secure the bumper element between the inner surfaces; and

positioning a connecting element around the proximal heads with the connecting element extending axially along opposite sides of the bumper element.

25. (canceled)

26. The method ofclaim 24, wherein positioning the connecting element include positioning the connecting element in grooves formed about the proximal heads.

27. The method ofclaim 26, wherein positioning the bumper element includes positioning projections extending from the proximal heads into recesses formed in opposite ends of the bumper element.

28. The method ofclaim 24, wherein the inner surfaces of the proximal heads are flat.

29. The method ofclaim 28, wherein positioning the bumper element includes positioning projections extending from the inner surfaces of the proximal heads into recesses formed in opposite ends of the bumper element.

30-41. (canceled)

42. A spinal stabilization construct, comprising:

first and second bone anchors and an elongated bumper element positioned between and abuttingly engaging said first and second bone anchors, and further comprising an elongated connecting element forming a hand extending around said first and second anchors and along opposite sides of said bumper element.

43. The construct ofclaim 42, wherein said first and second bone anchors each include a flat inner surface abuttingly engaging said bumper element and a projection extending from said inner surface into a recess in said bumper element.

44. The construct ofclaim 42, wherein said bumper element is compressible and said connecting element is elastic.

45. The construct ofclaim 42, wherein said bumper element is structured to prevent movement of said first and second anchors toward one another and said connecting element is structured to prevent movement of said first and second anchors away from one another.

46. The construct ofclaim 42, wherein said bumper element is compressible to permit movement of said first and second anchors toward one another and said connecting element is elastic to permit movement of said first and second anchors away from one another.

47. The construct ofclaim 42, wherein:

said first and second bone anchors each include a proximal head, said proximal heads including inner surfaces facing one another and outer surfaces facing away from one another;

said bumper element is positioned in abutting engagement with said inner surfaces and said band of said connecting element extends around said outer surfaces; and

said outer surfaces each include a groove extending therearound and said band of said connecting element is positioned in said grooves.

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