Abstract:
A spinal construct for implantation in a patient to provide stabilization to spinal structure with improved load sharing includes a flexible spinal rod having a first end and a second end, the spinal rod being configured to provide stabilization to spinal structure. It also includes a first bone fastener configured to securely attach to the flexible spinal rod and a second bone fastener configured to securely attach to the flexible spinal rod. The second bone fastener is a dynamic fastener arranged to provide motion in one direction more than another direction. The flexible spinal rod and the second bone fastener are oriented to cooperate in a manner that achieves load sharing by dynamically flexing under applied loads in a manner that distributes stresses and strains between the flexible spinal rod and the second bone fastener.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure is directed to stabilization constructs, and more particularly, to stabilization constructs with improved load sharing. 
       BACKGROUND 
       [0002]    Spinal disorders such as degenerative disc disease, disc herniation, osteoporosis, spondylolisthesis, stenosis, scoliosis and other curvature abnormalities, kyphosis, tumor, and fracture may result from factors including trauma, disease and degenerative conditions caused by injury and aging. Spinal disorders typically result in symptoms including pain, nerve damage, and partial or complete loss of mobility. 
         [0003]    Non-surgical treatments, such as medication, rehabilitation and exercise can be effective, however, may fail to relieve the symptoms associated with these disorders. Surgical treatment of these spinal disorders include discectomy, laminectomy, fusion and implantable prosthetics. As part of these surgical treatments, spinal constructs such as vertebral rods are often used to provide stability to a treated region. Rods redirect stresses away from a damaged or defective region while healing takes place to restore proper alignment and generally support the vertebral members. During surgical treatment, one or more rods may be attached via fasteners to the exterior of two or more vertebral members. 
         [0004]    Conventional stabilization constructs can be improved to reduce stress carried by I individual bone structures and implanted components. 
         [0005]    The fasteners and systems disclosed herein overcome one or more of the shortcomings of prior art devices. 
       SUMMARY 
       [0006]    In one exemplary aspect the present disclosure is directed to a spinal construct for implantation in a patient to provide stabilization to spinal structure with improved load sharing. The construct includes a flexible spinal rod having a first end and a second end, the spinal rod being configured to provide stabilization to spinal structure. It also includes a first bone fastener configured to securely attach to the flexible spinal rod and a second bone fastener configured to securely attach to the flexible spinal rod. The second bone fastener is a dynamic fastener arranged to provide motion in one direction more than another direction. The flexible spinal rod and the second bone fastener are oriented to cooperate in a manner that achieves load sharing by dynamically flexing under applied loads in a manner that distributes stresses and strains between the flexible spinal rod and the second bone fastener. 
         [0007]    In some aspects, the first bone fastener comprises a dynamic fastener arranged to provide motion in one direction more than another direction. The flexible spinal rod, the first bone fastener, and the second bone fastener are oriented to cooperate in a manner that achieves load sharing by dynamically flexing under applied loads in a manner that distributes stresses and strains between the flexible spinal rod and both the first and the second bone fasteners. 
         [0008]    In some aspects, the second bone fastener comprises a flexible bumper configured to dampen movement in at least one of flexion and extension. 
         [0009]    In another exemplary aspect, the present disclosure is directed to a spinal construct for implantation in a patient to provide stabilization to spinal structure with improved load sharing. The construct includes a flexible spinal rod having a first end and a second end, and being configured to provide stabilization to spinal structure. The spinal rod is configured in a manner that provides relatively more motion in a flexion and extension direction and relatively less motion in a lateral direction. The construct also includes a first bone fastener configured to securely attach to the flexible spinal rod. The first bone fastener being configured in a manner that provides relatively more motion in a flexion and extension direction and relatively less motion in a lateral direction. The flexible spinal rod and the first bone fastener are oriented to cooperate in a manner that achieves load sharing by dynamically flexing under applied loads in a manner that distributes stresses and strains between the flexible spinal rod and the first bone fastener. 
         [0010]    Further aspects, forms, embodiments, objects, features, benefits, and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings serve to exemplify some of the embodiments of this invention. 
           [0012]      FIG. 1  is an illustration of a portion of an exemplary vertebral column having exemplary spinal constructs attached thereto in accordance with one or more aspects of the present disclosure. 
           [0013]      FIGS. 2 and 3  are illustrations of an exemplary dynamic bone fastener for securing an dynamic spinal rod in accordance with one or more aspects of the present disclosure. 
           [0014]      FIG. 4  is an illustration of an exemplary dynamic bone fastener for securing an dynamic spinal rod having a bumper member in accordance with one or more aspects of the present disclosure. 
           [0015]      FIG. 5  is an illustration of an exemplary dynamic spinal rod for securing to a dynamic fastener in accordance with one or more aspects of the present disclosure. 
           [0016]      FIG. 6  is an illustration of an exemplary dynamic spinal rod having a bumper for securing to a dynamic fastener in accordance with one or more aspects of the present disclosure. 
           [0017]      FIG. 7  is an illustration of an exemplary spinal construct including a single dynamic bone fastener and a dynamic spinal rod for single level spinal stabilization in accordance with one or more aspects of the present disclosure. 
           [0018]      FIG. 8  is an illustration of an exemplary spinal construct including a two dynamic bone fasteners and a dynamic spinal rod for single level spinal stabilization in accordance with one or more aspects of the present disclosure. 
           [0019]      FIG. 9  is an illustration of an exemplary spinal construct including a dynamic bone fastener and a dynamic spinal rod for two-level spinal stabilization with a dynamic level and a fusion level in accordance with one or more aspects of the present disclosure. 
           [0020]      FIG. 10  is an illustration of an exemplary spinal construct including dynamic bone fasteners and a dynamic spinal rod for three-level spinal stabilization with two dynamic levels and a fusion level in accordance with one or more aspects of the present disclosure. 
           [0021]      FIG. 11  is an illustration of an exemplary spinal construct including two dynamic bone fasteners and a dynamic spinal rod for single level spinal stabilization where the bone fasteners are oriented in the same direction in accordance with one or more aspects of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The present disclosure relates generally to the field of implantable bone stabilization constructs, and more particularly to constructs having at least one dynamic bone fastener and a dynamic rod that cooperate together to achieve load sharing while providing stabilizing support to bone structure and tissue. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to embodiments or examples illustrated in the drawings, and specific language will be used to describe these examples. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alteration and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. 
         [0023]    The exemplary embodiments of the bone stabilization constructs are configured to provide stabilization to patient tissue, while at the same time distributing stresses and loads carried by the individual bone fastener and rod components. Distributed stresses result in increased resistance to wear and reduced stress and strain while maintaining or increasing the range of motion of conventional constructs. In addition, some embodiments are configured to provide increased directional motion in some directions, through particular fastener or rod designs, while maintaining or stabilizing directional motion in other directions. In some examples, in order to achieve a maximized directional motion, the bone fasteners and the rod work in concert to provide both maximized motion in some directions and more stabilized support in the other directions. 
         [0024]    The constructs and construct components in the present disclosure may be employed to treat spinal disorders such as, for example, degenerative disc disease, disc herniation, osteoporosis, spondylolisthesis, stenosis, scoliosis and other curvature abnormalities, kyphosis, tumors, and fractures, among other disorders. These constructs and construct components may be utilized using surgical treatments or techniques including open surgery and minimally invasive procedures, and may be used to treat, for example, discectomy, laminectomy, fusion, bone graft, implantable prosthetics and/or dynamic stabilization applications. It is contemplated that the present disclosure may be employed with other osteal and bone related applications, including those associated with diagnostics and therapeutics. It is further contemplated that the disclosed constructs may be employed in a surgical treatment with a patient in a prone or supine position, employing a posterior, lateral or anterior approach. The present disclosure may be employed with procedures for treating the lumbar, cervical, thoracic and pelvic regions of a spinal column. 
         [0025]      FIG. 1  shows exemplary spinal rod constructs  10  in place on a portion of a vertebral column V. Each exemplary construct  10  in  FIG. 1  includes two bone fasteners  20  connected by a longitudinally extending spinal rod  30 . In each construct  10 , a first bone fastener  20  is anchored to a first vertebra V 1  and a second bone fastener  20  is anchored to a second vertebra V 2 . The spinal rod  30  connects the fasteners to each other, providing stability to the vertebrae. As will be described below, the bone fasteners  20  are dynamic fasteners and the spinal rod  30  is a dynamic rod. As such, they each include at least one deformable or flexible section along the bone fastener  20  and at least one deformable section along the spinal rod  30 . Upon fixation of the spinal rod construct with vertebrae V, the bone fasteners  20  and spinal rod  30  each are configured to provide changing or a fixed level of resistance to movement during flexion, extension and/or torsion of the spine. Such constructs allow the overall strain and stress to be distributed between the rod and the fasteners in order to increase the level of load sharing, the dynamic behavior and/or the overall range of motion (ROM) of the construct while maintaining durability of the spinal implants and the bone-screw interface. 
         [0026]      FIGS. 2 and 3  show one example of a bone fastener  20  suitable for use in the constructs  10  in  FIG. 1 . The bone fastener  20  includes a fixation portion  102 , a connection portion  104 , and a flexible portion  106 . The fastener  100  includes a longitudinal axis  107 , shown for reference. The fixation portion  102  is configured to interface or engage with bone structure, such as the vertebrae V 1 , V 2  to secure the bone fastener  20  in place. In the embodiment shown, the fastener  20  is a bone screw and the fixation portion  102  comprises outwardly extending threads  108  configured to penetrate boney tissue. However, in other embodiments, the fixation portion is a hook, clamp, or other structure configured to interface or engage the bone structure. 
         [0027]    The connection portion  104  is configured to engage the spinal rod  30  shown in  FIG. 1 . In this embodiment, the connection portion  104  is a U-shaped receiver comprising a first arm  110  and a second arm  112 , spaced to receive the spinal rod  30 . The receiver includes a threaded inner surface  114  configured to threadably receive a set screw to secure the spinal rod in place in the receiver. Although shown as a U-shaped receiver, other embodiments of the connection portion  104  include bores or through holes, clamps, and other constructs and arrangements for receiving a spinal rod. 
         [0028]    The flexible portion  106  enables dynamic movement between the fixation portion  102  and the connection portion  104 , as indicated by the directional arrows in  FIG. 2 . It is configured to allow the connection portion  104  to pivot within a preestablished range at least in both a rearward and forward direction. It provides stability and structural integrity while reducing stress on spinal elements, the bone tissue engaged with the fixation portion  102 , the supporting structure  104 , and a spinal rod attached thereto. Here, the flexible portion  106  includes an arcuate C-shaped connecting portion  116  extending between and connecting the fixation portion  102  and the connection portion  104 . It is contemplated that the connecting portion  116  may have alternative configurations, such as U-shaped, V-shaped, or W-shaped, for example. The connecting portion  116  is disposed between the fixation portion  102  and the connecting portion  104  such that connecting portion  104  is longitudinally aligned with the fixation portion  102  along longitudinal axis  107 . The connecting portion  116  includes an inner surface  118  that defines a cavity  120  and an open end  122  such that the connecting portion  116  is configured to provide dampening. Here, the connecting portion  116  flexes as a result of elastic deformation. In this embodiment, because the connecting portion  116  is disposed to one side of the fastener  100 , the flexible portion  106  is arranged to flex about a point offset from the longitudinal axis  107  of the fastener  20 . Because the center of rotation is offset, the dynamic fastener provides a non-symmetrical rotational movement that may be desirable to treat spinal conditions. It is contemplated that the components of the bone fastener  20  may be monolithically formed, integrally connected or arranged with attaching elements. 
         [0029]    Because of its elastic nature, the connecting portion  116  provides biasing resistance to movement of the connecting portion  104  and the anchoring portion  102 . The connecting portion  116  has a first end  124 , a flexible joint portion  126 , and a second end  128 . The first end  124  and the second end  128  are flexible relative to a mid-point of the flexible joint portion  126 . The connecting portion  104  is connected with first end  124  and the anchor portion  102  is connected with second end  128 . It is contemplated that the connecting portion  116  may be structurally arranged to provide increasing, variable, constant and/or decreasing resistance. 
         [0030]    It is contemplated that the anchoring portion  102 , the connecting portion  104 , and the flexible portion  106  may be variously dimensioned, for example, with regard to length, width, diameter and thickness. It is further contemplated that the respective cross-sectional geometry or area of portions  102 ,  104 ,  106  may have various configurations, for example, round, oval, rectangular, irregular, consistent, variable, uniform and non-uniform. 
         [0031]    The connecting portion  116  may have a variable thickness t according to the requirements of the particular application. It is envisioned that thickness t of the connecting portion  116  may be in a range of 0.5 millimeters (mm) to 6.0 mm, and preferably 1.0 mm to 4.0 mm. The connecting portion  116  also has a width w. It is contemplated that the width w may be in a range 1 mm to 12 mm, and preferably 3 mm to 8 mm. In one embodiment, the connecting portion  116  is enlarged relative to anchoring portion  102  and the connecting portion  104  such that width w spans a greater distance than the profile of portions  102 ,  104 . 
         [0032]    Some embodiments of the connecting portion  116  have a wide, narrow, round, or irregular configuration. The connecting portion  116  can be variously configured and dimensioned with regard to size, shape, geometry and material. The connecting portion  116  may also have one or a plurality of elements connecting anchoring portion  102  and the connecting portion  104  such as spaced apart portions, staggered patterns and mesh. The connecting portion  116  may be fabricated from the same or alternative material to anchoring portion  102  and the connecting portion  104 . It may also have a different cross-sectional area, geometry or material property such as strength, modulus and flexibility relative to anchoring portion  102  and the connecting portion  104 . The connecting portion  116  may be connected to the anchoring portion  102  and the connecting portion  104  using various methods and structure including molding of a continuous component, mechanical fastening, adhesive bonding and combinations thereof. 
         [0033]    It is envisioned that the connecting portion  116  operates as a flexible hinge, which can be offset forward or backward relative to the axis  107  of the bone fastener  20  to modify the flexibility or stiffness of the spinal rod construct  10 . It is further envisioned that particular parameters of the bone fastener  20  may be selected to modulate the flexibility or stiffness of the spinal rod construct including the material modulus that may correlate to the hardness of a resistance member discussed below. For example, parameters may be selected to include a porosity level in a range of 1% to 75%, and preferably 5% to 50%, which may include a void volume in a range of 1% to 75%, and preferably 5% to 50%. These parameters allow modification of the properties or performance of bone fastener  20  such as strength, durability, flexibility (or stiffness), overall profile and the ability to employ a percutaneous approach, for a particular application. 
         [0034]    During movement of vertebrae V, for example, in flexion, extension and/or torsion, the connecting portion  104  moves relative to the anchor portion  102  to facilitate relative flexibility and/or movement of the rod  30  and/or other components of the spinal rod construct  10 . The first end  124  and second end  128  can flexibly expand, compress and/or rotate in torsion relative to the joint portion  126  such that the connecting portion  116  expands and compresses the cavity  120 . The open end  122  can also expand and compress. This configuration increases resistance during expansion, compression and/or rotation of the connecting portion  116 . The increase of resistance during flexion, extension and/or torsion provides limited movement of vertebrae V for load sharing and/or dynamic stabilization of the treated area of the spine. 
         [0035]    Because of the orientation of the connecting portion  116 , having a greater width w than thickness t, the bone fastener  20  is configured in a manner to provide directional movement, permitting more motion in the flexion and extension direction, and permitting less motion in the lateral directions. In some embodiments, the connecting portion  116  is designed to permit motion substantially only along a single plane. In such embodiments, due to the structural configuration, this planar motion is permitted substantially in the flexion and extension plane, aligned to extend through the longitudinal axis of the spinal rod  30 . 
         [0036]    In one embodiment, the cavity  120  is configured for disposal of a resistance member, such as, for example, a bumper  150 , as shown in  FIG. 4 . It is envisioned that the bumper  150  may be monolithically formed, integrally connected, employ fastening elements and/or adhesives for disposal within the flexible portion  106 . 
         [0037]    The bumper  150  is elastic and configured to provide variable resistance to movement of portions  102 ,  104 , and  106 . It is contemplated that the bumper  150  can provide increasing, variable, constant and/or decreasing resistance. The bumper  150  is disposed within the cavity  120  and in some embodiments, engages the surface  118  in a close fitting engagement. The bumper  150  can be variously configured with regard to size, shape, for example, round, oblong, rectangular, triangular, spherical, and irregular shapes. It is envisioned that the bumper  150  has a hardness in the range of 30 Shore A to 55 Shore D. The material of the bumper  150  can be solid or porous, homogeneous or heterogeneous, single polymer or a blend/composite of more than one polymer. It is contemplated that the resiliency of the bumper  150  can prevent creep and improve shape recovery of the spinal rod construct. It is envisioned that the bumper  150  is configured to prevent and/or resist closing of the open end  122 . It is further envisioned that bumper  150  is secured in place with the connecting portion  116 , and desirably mechanically secured therewith in a configuration to present migration and expulsion therefrom. In other embodiments, the bumper  150  can be textured, encapsulated, adhesively bonded and/or over molded with bone fastener  20 . The bumper  150  can be inserted within the cavity  120  for assembly, or formed in situ by, for example, a pouch, bag or balloon with the bumper configuration being inserted into cavity  120  and injected with a curable manner. 
         [0038]    Although the exemplary fasteners shown are mono-axial fasteners, in other embodiments, the fasteners are multi-axial type bone fasteners that include additional articulation, such as a ball and socket joint, between the fixation portion  102  and the connection portion  104 . Some examples of bone fasteners, including multi-axial type fasteners that may be used in the constructs described herein are found in U.S. patent application Ser. No. 12/762,421, filed Apr. 19, 2010, titled Load Sharing Bone Fastener and Methods of Use, incorporated herein by reference. 
         [0039]    The spinal rod construct  10  in  FIG. 1  includes the spinal rod  30 . An exemplary spinal rod  30  is described with reference to  FIG. 5 . The spinal rod  30  includes a first elongated section  202  that defines a first longitudinal axis  203  and a second elongated section  204  that defines a longitudinal axis  205 . It also includes an intermediate section  206  connected with sections  202 ,  204 , and disposed therebetween. The components of the spinal rod  30  may be monolithically formed, integrally connected, or arranged with attaching elements. Here, the intermediate section  206  is flexible relative to sections  202 ,  204 , and is configured to provide resistance to movement of sections  202 ,  204 . Depending on the embodiment, the intermediate section  206  may provide increasing, variable, constant, and/or decreasing resistance. It is contemplated that sections  202 ,  204 ,  206  can be variously dimensioned, for example, with regard to length, width, diameter and thickness. It is further contemplated that the respective cross-section of sections  202 ,  204 ,  206  may have various configurations, for example, round, oval, rectangular, irregular, uniform and non-uniform. Section  202  may have a different cross-sectional area, geometry, material or material property such as strength, modulus or flexibility relative to section  204 . 
         [0040]    The intermediate section  206  may have a variable thickness t according to the requirements of the particular application. In some embodiments, the thickness t of intermediate section  206  may be in a range of 1-10 mm, preferably in a range of 2-8 mm, and most preferably in a range of 3-5 mm. It is further envisioned that the cross-sectional geometry or area of intermediate section  206  can be uniform, non-uniform, consistent or variable. It may also have a width w, with the width w being greater than the thickness t. 
         [0041]    The intermediate section  206  may be configured as a flexible joint having a wide, narrow, round or irregular configuration. It is further envisioned that intermediate section  206  can be variously configured and dimensioned with regard to size, shape, thickness, geometry and material. The intermediate section  206  may also have one or a plurality of elements connecting sections  202 ,  204  such as spaced apart portions, staggered patterns, and mesh. It may be fabricated from the same or alternative material to sections  202 ,  204 . It may have a different cross-sectional area, geometry or material property such as strength, modulus and flexibility relative to sections  202 ,  204 . The intermediate section  206  may be connected to sections  202 ,  204  using various methods and structure including molding of a continuous component, mechanical fastening, adhesive bonding and combinations thereof. The intermediate section  206  may be a flexible hinge configuration, which can be offset forward or backward relative to a central axis of the rod  30  to modify the flexibility or stiffness of the spinal rod construct  10 . It is further envisioned that particular parameters may be selected to modulate the flexibility or stiffness of the spinal rod construct including the cross-sectional area (or thickness) of intermediate section  206 , material modulus that may correlate to the hardness of bumper  250  discussed below, modification of porosity in a range of 0-30 percent which may include modification of void volume in a range of 10 microns-1 mm, as well as rod material properties. These parameters allow modification of the properties or performance of the spinal rod construct such as strength, durability, flexibility (or stiffness), overall profile and the ability to employ a percutaneous approach, for a particular application. 
         [0042]    The intermediate section  206  includes a flexible joint member  208 , which has a C-shaped configuration and defines a corresponding shaped arcuate inner surface  210  and an open end  212 . It is contemplated that joint member  208  may have alternative configurations such as U-shaped, V-shaped or W-shaped. It is further contemplated that the spinal rod  30  may include one or a plurality of intermediate sections  206  spaced along the length of rod  30 , as discussed below. In embodiments including a plurality of sections  206 , the multiple sections  206  may be disposed in similar, or alternative orientations such as aligned, non-aligned, offset, open end facing or not facing vertebrae and alternate angular orientation. 
         [0043]    In this embodiment, because the joint member  208  is disposed to one side of the first and second rod sections  202 ,  204 , the joint member  208  is arranged to flex about a point offset from the longitudinal axes  203 ,  205  of the spinal rod  30 . Because the center of rotation is offset, the dynamic rod provides a non-symmetrical rotational movement that may be desirable to treat spinal conditions. 
         [0044]    The inner surface  210  defines a cavity  214 . The cavity  214  is configured to receive and house a resistance member, such as, for example, a bumper  250 , as shown in  FIG. 6 . The bumper  250  is elastic and configured to provide variable resistance to movement of sections  202 ,  204  and  206 . It is contemplated that the bumper  250  can provide increasing, variable, constant and/or decreasing resistance. The bumper  250  is disposed within cavity  214  and engages the surface  210  in a close fitting engagement. The bumper  250  can be variously configured with regard to size, shape, for example, round, oblong, rectangular, triangular, spherical, and irregular shapes. It is envisioned that the bumper  250  has a hardness in the range of 20 Shore A to 55 Shore D, and preferably between 70 and 90 Shore A. The material of the bumper  250  can be solid or porous, homogeneous or heterogeneous, single polymer or a blend/composite of more than one polymer. It is contemplated that the resiliency of the bumper  250  can prevent creep and improve shape recovery of the spinal rod construct. It is envisioned that the bumper  250  is configured to prevent and/or resist closing of the open end  212 . The bumper  250  can be inserted with cavity  214  for assembly, or formed in situ by, for example, a pouch, bag or balloon with the bumper configuration being inserted into cavity  214  and injected with a curable material. 
         [0045]    During flexion and extension of the spinal rod  30 , the first section  202  moves relative to the second section  204  from a first or neutral orientation to a second displaced orientation. In the first orientation, the first and second sections  202 ,  204  are disposed so that the longitudinal axis  203  is disposed at a first angle (including 0 degrees) relative to the longitudinal axis  205  about the flexible joint member  208 . In the second orientation, the first and second sections  202 ,  204  are disposed so that the longitudinal axis  203  and the longitudinal axis  205  are at a second angle relative to the first (including 0 degrees). The bumper  250  engagingly interacts with the intermediate section  206  in a configuration that provides increasing resistance to movement of sections  202 ,  204  from the first orientation to the second orientation. Movement of the components of the spinal rod construct between one or a plurality of orientations is contemplated and may include a range of increasing and decreasing levels of resistance of the components of the spinal rod construct. 
         [0046]    The first section  202  and second section  204  can flexibly expand, compress and/or rotate in torsion relative to the intermediate section  206  such that arm  36  expands and compresses cavity  40 . The joint member  208  can flexibly expand circumferentially about bumper  250  such that the first section  202  and second section  204  compress the bumper  250 ; or the joint member  208  can flexibly compress circumferentially about the bumper  250 . This configuration increases resistance during expansion and compression of the intermediate section  206 . The increase of resistance during flexion, extension and/or torsion provides limited movement of vertebrae V for load sharing and/or dynamic stabilization of the treated area of the spine. 
         [0047]    Because of the orientation of the joint member  208 , having a greater width w than thickness t, the spinal rod  30  is configured in a manner to provide directional movement, permitting more motion along a plane that includes the flexible joint member  208 , and permitting less motion in planar directions not along a plane including the flexible joint member  208 . In some embodiments, the joint member  208  is designed to permit motion substantially only along a single plane. 
         [0048]    In assembly, operation and use, the spinal construct  10  including bone fastener  20  and spinal rod  30  is employed with a surgical procedure for treatment of a spinal disorder affecting a section of a spine of a patient, as discussed herein. 
         [0049]      FIG. 7  shows one embodiment of an exemplary spinal rod construct  10  for treating a single level of a spinal structure. This embodiment includes a dynamic screw  20 , the dynamic spinal rod  30 , and a non-flexible conventional multi-axial screw  300 . Accordingly, the spinal rod construct in  FIG. 7  includes two cooperating dynamic structures that achieve load sharing by together absorbing loads resulting from flexion or extension. By distributing loads in both the dynamic screw  20  and the spinal rod  30 , stress and strain carried by each of the components individually is reduced, resulting in increased durability. In addition, the combination of a flexible fastener and flexible rod result in an increased dynamic nature of the construct, providing greater dynamic properties. Some embodiments have improved range of motion (ROM) over constructs using only a dynamic rod or dynamic screw. Because each component carries less stress and strain than it would if used alone, the reliability of the bone-screw interface may be increased, potentially reducing failure at those interfaces. In addition, reducing the stress and strain carried by each component individually increases reliability and durability of the component themselves, including reducing mid-shaft screw fractures. It should be noted that the bumpers  150 ,  250  in the spinal construct  10  are optional and that the construct may be formed of any flexible devices, with or without bumpers. 
         [0050]    In the embodiment shown, particular advantages are obtained due to the directional displacement achieved by the particular construct design. That is, as explained above, the bone fastener  20  is configured in a manner to provide directional movement, permitting more motion in the flexion and extension direction, and permitting less motion in the lateral directions. This is due to the nature and alignment of the flexible connecting portion  116 . In some embodiments, the connecting portion  116  is designed to permit motion substantially only along a single plane. In such embodiments, due to the structural configuration, this planar motion is permitted only in the flexion and extension plane, aligned to extend through the longitudinal axis of the spinal rod  30 . 
         [0051]    In addition, the spinal rod  30  is also configured to provide a cooperating advantage by permitting more motion in one direction and less direction in another. When oriented in the manner shown in  FIG. 7 , the rod provides more motion in the flexion and extension directions, and permits less motion in the lateral directions. It does this because the flexible sections of the fastener  20  and rod  30  are substantially aligned along a plane that extends through the fastener and rod axes  107 ,  203 ,  205 . Therefore, both the fastener  20  and rod  30  are arranged to permit more motion in flexion and extension and less motion in the lateral direction. By orienting the flexible fastener and rod as shown, so that the rod  30  and fastener  20  are aligned to contribute more to the flexion and extension movement and less to the lateral movement, the maximum range of stress distribution and maximum range of motion can be achieved. 
         [0052]    Here, both the fastener  20  and the spinal rod  30  include C-shaped flexible sections. Because the fastener and the spinal rod have matching dynamic capabilities, including a similar shaped motion-generating portion, and both using a bumper, the load-sharing benefits obtained by cooperating dynamic fasteners and dynamic rods can be maximized. In such embodiments that use bumpers, the fastener and rod may use bumpers formed of the same material. It is worth noting however, that the bumper materials can vary between components. 
         [0053]      FIG. 8  shows another embodiment of an exemplary spinal rod construct  10 . This embodiment includes two dynamic screws  20  and the dynamic spinal rod  30 . Because the construct  10  comprises three cooperating dynamic constructs, some of the load sharing advantages can be further capitalized. For example, because three dynamic constructs are used, there is an increased distribution of stress and strain under both flexion and extension. In addition, the construct  10  may provide a range of motion greater than the range of motion of the construct in  FIG. 7 . As described above, the orientation of the rod and fasteners is arranged to compensate for each other to maximize the range of motion. That is, each is arranged to provide a maximum ROM along the same plane. 
         [0054]      FIG. 9  shows another embodiment of an exemplary spinal rod construct, referred to by the reference numeral  310 . This embodiment is two level construct meaning it spans and provides support to two levels of the vertebral column. It includes a dynamic screw  20 , two multi-axial screws  300 , and a partially dynamic spinal rod  320 . Here, the spinal rod  320  includes the dynamic spinal rod features described above as in  FIG. 7 , but includes an extended rigid portion  312  configured for spanning a second vertebral level and for connecting to two conventional multiaxial screws  300 . Accordingly, the spinal rod construct  310  includes both a dynamic level  314  and a fusion level  316 . Therefore, all the advantages discussed above can be obtained at the dynamic level of the vertebral column, while still providing the opportunity to fuse a different level of the vertebral column. 
         [0055]      FIG. 10  shows another embodiment of an exemplary spinal rod construct, referred to by the reference numeral  340 . This embodiment is a three level construct meaning it spans and provides support to three levels of the vertebral column. It includes two dynamic screws  20 , two multi-axial screws  300 , and a partially dynamic spinal rod  350 . Here, the spinal rod  350  includes two ends  352 ,  354  having the dynamic spinal rod features described above as in  FIG. 7 . It also includes an extended rigid portion  356  between the two ends  352 ,  354 . Accordingly, the construct  350  includes a first dynamic level  358 , an intermediate fusion level  362 , and a second dynamic level  360 . Therefore, all the advantages discussed above can be obtained at the dynamic level of the vertebral column, while still providing the opportunity to fuse a different level of the vertebral column. These are just examples and it should be apparent that any number of levels and fusion or dynamic arrangements may be used. 
         [0056]      FIG. 11  discloses another example of the rod construct  10  arranged differently than the rod construct in  FIG. 8 . This embodiment includes two dynamic screws  20  and the dynamic spinal rod  30 . However, the orientation of the fasteners  20  is arranged to provide particular advantages to the construct that may not be obtained otherwise. For example, in this instance, the fasteners  20  are arranged so that the connecting portions  116  face the same direction, but the flexible connecting portions  116  are still maintained within substantially the same plane. This may provide particular motion by having the fasteners cooperate to achieve the desired ROM. For example, since the fasteners are arranged to face the same direction, the construct  10  may provide increased motion in one of extension or flexion, and less motion in the other of extension or flexion. The screws may be arranged in any desired orientation to achieve a particular result. 
         [0057]    The components of the construct  10  are fabricated from materials suitable for medical applications, including metals, polymers, ceramics, biocompatible materials and/or their composites, depending on the particular application and/or preference of a medical practitioner. For example, the bone fastener  20  and/or the rod  30  can be fabricated from materials such as commercially pure titanium, titanium alloys, Grade 5 titanium, super-elastic titanium alloys, cobalt-chrome alloys, stainless steel alloys, superelastic metallic alloys (e.g. Nitinol, super elasto-plastic metals, such as GUM METAL® manufactured by Toyota Material Incorporated of Japan), thermoplastics such as polyaryletherketone (PAEK) including polyetheretherketone (PEEK), polyetherketoneketone (PEKK) and polyetherketone (PEK), carbon fiber reinforced PEEK composites, PEEK-BaSO4 composites, ceramics and composites thereof such as calcium phosphate (e.g. SKELITE™ manufactured by Biologix Inc.), rigid polymers including polyphenylene, polyamide, polyimide, polyetherimide, polyethylene, polyurethanes of any durometer, epoxy and silicone. Different components may have alternative material composites to achieve various desired characteristics such as strength, rigidity, elasticity, compliance, biomechanical performance, durability and radiolucency or imaging preference. The components may also be fabricated from a heterogeneous material such as a combination of two or more of the above-described materials. 
         [0058]    In some examples, the bone fastener  20  and the spinal rod  30  are each formed of two or more materials. In one embodiment, different sections of portions the bone fastener  100  are be fabricated from carbon-reinforced PEEK and an intermediate section can be fabricated from PEEK. In one embodiment, the first and second sections are fabricated from PEEK and the intermediate section is fabricated from carbon-reinforced PEEK. In one embodiment, the fixation portion is fabricated from a first material, such as those described above, and the flexible portion is fabricated from a second material such as, for example, Nitinol, PEEK, carbon-PEEK, a titanium alloy and/or a cobalt-chrome alloy. In one embodiment, alternate materials may be employed in a radial direction of bone fastener  20  and the spinal rod  30  such that stiff materials such as metals or other composites are used in a core of the fastener sections and an outer sheet of lower modulus polymeric material is used in the outer radial portion of the fastener portions, or vice versa. 
         [0059]    As a further example, a resistance member, discussed below, of bone fastener  20  and the spinal rod  30  may be fabricated from materials such as silicone, polyurethane, silicone-polyurethane copolymers, polymeric rubbers, polyolefin rubbers, hydrogels, semi-rigid and rigid materials, and biocompatible materials such as elastomers, rubbers, thermoplastic elastomers, thermoset elastomers, elastomeric composites and plastics. It is envisioned that the components of the spinal rod construct can be manufactured via various methods. For example, bone fastener  20  and the spinal rod  30  can be manufactured and assembled via injection-molding, insert-molding, overmolding, compression molding, transfer molding, co-extrusion, pultrusion, dip-coating, spray-coating, powder-coating, porous-coating, machining, milling from a solid stock material, and their combinations. One skilled in the art, however, will realize that such materials and fabrication methods suitable for assembly and manufacture, in accordance with the present disclosure, would be appropriate. 
         [0060]    The bone fastener  20  may be employed as a bone screw, pedicle screw or multi-axial screw (MAS) used in spinal surgery. It is contemplated that bone fastener  30  may be coated with an osteoconductive material such as hydroxyapatite and/or osteoinductive agent such as a bone morphogenic protein for enhanced bony fixation to facilitate motion of the treated spinal area. The bone fastener  20 , the rod  30  and the bumpers  150 ,  250  can be made of radiolucent materials such as polymers. Radiomarkers may be included for identification under x-ray, fluoroscopy, CT or other imaging techniques. Metallic or ceramic radiomarkers, such as tantalum beads, tantalum pins, titanium pins, titanium endcaps and platinum wires can be used, such as being disposed at the end portions of rod  30  and/or along the length thereof adjacent the joint portion  46  or with bumper  150 . 
         [0061]    While the present invention has been illustrated by the above description of embodiments, and while the embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the invention to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general or inventive concept.