Patent Publication Number: US-2023147290-A1

Title: Spinal implant system and methods of use

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to medical devices for the treatment of spinal disorders, and more particularly to a surgical implant system including a bone fastener and a related method. 
     BACKGROUND 
     Spinal pathologies and disorders such as scoliosis and other curvature abnormalities, kyphosis, degenerative disc disease, disc herniation, osteoporosis, spondylolisthesis, stenosis, 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 deformity, pain, nerve damage, and partial or complete loss of mobility. 
     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 includes correction, fusion, fixation, discectomy, laminectomy 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 and bone fasteners can be delivered to a surgical site. The rods may be attached via the fasteners to the exterior of two or more vertebral members. This disclosure describes an improvement over these prior technologies. 
     SUMMARY 
     In one embodiment, a bone fastener is provided. The bone fastener comprises a first member defining an implant cavity and a plurality of adjacent grooves. A first band is configured for disposal within the grooves. A second band is configured for disposal within the grooves. A second member is configured to penetrate tissue and includes a head engageable with the first band to provisionally connect the members. The second band is moveable for disposal adjacent the first band to fix connection of the members. In some embodiments, implants, systems, instruments and methods are disclosed. 
     In one embodiment, the bone fastener comprises a first member that defines an implant cavity and a plurality of adjacent grooves. The grooves include a first portion and a second portion having a greater diameter than the first portion. A first band and a second band are configured for disposal within the grooves in an expanded configuration in the second portion and a contracted configuration in the first portion. A second member is configured to penetrate tissue and includes a head engageable with the first band to connect the members. A part is engageable with the second band to fix the second band adjacent the first band. In some embodiments, the first band is configured for disposal within the grooves in an expanded configuration while the second band is configured for disposal within the grooves in a contracted configuration. In some embodiments, the second band includes a free orientation that is expanded and the first band includes a free orientation that is contracted so that it provides a tactile audible indicia when moving the second member into the first member. 
     In one embodiment, the bone fastener comprises a first member that defines an implant cavity and a plurality of adjacent grooves. The grooves include a first groove, a second groove and a third groove. The second groove has a greater diameter than the first groove and the third groove. A first expandable band is configured for disposal within the grooves. A second expandable band is configured for disposal within the grooves. A second member is configured to penetrate tissue and includes a head engageable with the first band for translation from the first groove to the second groove to provisionally connect the members. A part is engageable with the second band for translation from the third groove to the second groove such that the second band prevents the first band from translating back into the second groove to fix connection of the members. In some embodiments; the second band engages the first band for translation to the second groove and restricts any further translation of the first band to fix connection of first member to second member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more readily apparent from the specific description accompanied by the following drawings, in which: 
         FIG.  1    is a side cross section view of components of one embodiment of a spinal implant system in accordance with the principles of the present disclosure; 
         FIG.  2    is a break away view of the components shown in  FIG.  1   ; 
         FIG.  3    is a side cross section view of the components shown in  FIG.  1   ; 
         FIG.  4    is a break away view of the components shown in  FIG.  1   ; 
         FIG.  5    is a break away view of the components shown in  FIG.  1   ; and 
         FIG.  6    is a break away view of the components shown in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments of a surgical system and related methods of use disclosed are discussed in terms of medical devices for the treatment of musculoskeletal disorders and more particularly, in terms of a spinal implant system including a bone fastener. In one embodiment, the present spinal implant system includes an implant comprising a bone fastener, such as, for example, a pedicle bone screw. In some embodiments, the systems and methods of the present disclosure are employed with a spinal joint fusion or fixation procedure, for example, with a cervical, thoracic, lumbar and/or sacral region of a spine. 
     In some embodiments, the present spinal implant system comprises a modular pedicle screw system including a double ring configuration. In some embodiments, the present spinal implant system comprises a mechanism to resist and/or prevent disengagement of a retainer of a modular screw system. In some embodiments, the present spinal implant system comprises a modular pedicle screw system including a screw shank, a receiver, a retainer and a compression insert. In some embodiments, the screw shank is inserted into the receiver and contacts the retainer translating the retainer from a first chamber to a second chamber. In some embodiments, the second chamber is oversized allowing for expansion of the retainer as the screw shank is translated further into the receiver. In some embodiments, the spinal implant system comprises a modular pedicle screw system having an additional expansion member configured to block the second chamber after the screw shank is engaged with the receiver. In some embodiments, blocking of the second chamber resists and/or prevents the retainer from migrating back into the second chamber and to resist and/or prevent disengagement of the components. 
     In some embodiments, the present spinal implant system comprises a modular assembly consisting of a receiver, expansion member, retainer and compression member. In some embodiments, the receiver includes first, second, and third chambers. In some embodiments, the first chamber is sized to be a close fit to a retainer member and the second chamber is oversized to allow expansion of the retainer. In some embodiments, the expansion of the retainer allows a screw shank to pass through the retainer. In some embodiments, a second expansion member is nested in an undersized third chamber, which causes the expansion member to collapse, such as, for example, by a reduction in diameter. The expansion member contains an outer groove, which mates with the receiver to prevent unintentional disengagement. In some embodiments, the expansion member in the relaxed state is sized with a diameter similar to the second chamber. In some embodiments, the spinal implant system includes a compression member positioned above the expansion member. 
     In some embodiments, the present spinal implant system is employed with a method of attaching a tulip assembly with a screw shank including the steps of translating the screw shank such that the retainer translates into the second chamber and expands then contracts to provisionally capture the screw shank. In some embodiments, the method includes the step of, once the screw shank is provisionally captured, the compression member being translated towards the expansion member forcing the expansion member into the second chamber. In some embodiments, when the expansion member is fully in the second chamber it is allowed to expand. As such, the expansion member allows for the compression member to pass through its inner diameter in the expanded state. In some embodiments, the expansion member is sized to prevent the retainer member from disengaging from the first chamber. In some embodiments, the retainer positioned in the first chamber resists and/or prevents the retainer from expanding and retains the screw shank in the tulip assembly. 
     In some embodiments, the spinal implant system comprises a modular system that includes a bone fastener including an array of members, such as, for example, bone screw shafts that can be selectively coupled to members, such as, for example, receivers. In some embodiments, the spinal implant system comprises a selectively coupled bone fastener that can be assembled on a surgical table or in-situ. In some embodiments, the bone fastener is selectively coupled with a non-instrumented assembly and/or manual assembly. In some embodiments, the non-instrumented assembly comprises manually engaging a screw shaft with a head/receiver of the bone fastener. In some embodiments, the non-instrumented assembly comprises manually engaging the screw shaft in a pop-on engagement with the head/receiver of the bone fastener. In some embodiments, a force required to manually engage a screw shaft with a head/receiver of the bone fastener in a non-instrumented assembly is in a range of 2 to 50 N. In some embodiments, a force required to manually engage a screw shaft with a head/receiver of the bone fastener in a non-instrumented assembly is in a range of 5 to 10 N. In some embodiments, this configuration provides manually engageable components of a bone fastener that are assembled without instrumentation, and subsequent to assembly, the assembled components have a selected pull-out strength and/or can be pulled apart, removed and/or separated with a minimum required force. 
     In some embodiments, the bone fastener is configured for assembly without the use of an instrument, such as, for example, a practitioner, surgeon and/or medical staff utilizes their hands for assembly. In some embodiments, the system requires minimal force to attach an implant receiver and a screw shaft assembly in-situ thereby reducing a pre-load on the vertebrae, such as, for, example, the pedicle. In some embodiments, the bone fastener includes an expandable ring. 
     In some embodiments, 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, tumor and fractures. In some embodiments, the present disclosure may be employed with other osteal and bone related applications, including those associated with diagnostics and therapeutics. In some embodiments, the disclosed spinal implant system may be alternatively employed in a surgical treatment with a patient in a prone or supine position, and/or employ various surgical approaches to the spine, including anterior, posterior, posterior mid-line, lateral, postero-lateral, and/or antero-lateral approaches, and in other body regions. The present disclosure may also be alternatively employed with procedures for treating the lumbar, cervical, thoracic, sacral and pelvic regions of a spinal column. The spinal implant system of the present disclosure may also be used on animals, bone models and other non-living substrates, such as, for example, in training, testing and demonstration. 
     The present disclosure may be understood more readily by reference to the following detailed description of the embodiments taken in connection with the accompanying drawing figures, which form a part of this disclosure. It is to be understood that this application is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting. In some embodiments, as used in the specification and including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” or “approximately” one particular value and/or to “about” or “approximately” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It is also understood that all spatial references, such as, for example, horizontal, vertical, top, upper, lower, bottom, left and right, are for illustrative purposes only and can be varied within the scope of the disclosure. For example, the references “upper” and “lower” are relative and used only in the context to the other, and are not necessarily “superior” and “inferior”. 
     As used in the specification and including the appended claims, “treating” or “treatment” of a disease or condition refers to performing a procedure that may include administering one or more drugs to a patient (human, normal or otherwise or other mammal), employing implantable devices, and/or employing instruments that treat the disease, such as, for example, microdiscectomy instruments used to remove portions bulging or herniated discs and/or bone spurs, in an effort to alleviate signs or symptoms of the disease or condition. Alleviation can occur prior to signs or symptoms of the disease or condition appearing, as well as after their appearance, Thus, treating or treatment includes preventing or prevention of disease or undesirable condition (e.g., preventing the disease from occurring in a patient, who may be predisposed to the disease but has not yet been diagnosed as having it). In addition, treating or treatment does not require complete alleviation of signs or symptoms, does not require a cure, and specifically includes procedures that have only a marginal effect on the patient. Treatment can include inhibiting the disease, e.g., arresting its development, or relieving the disease, e.g., causing regression of the disease. For example, treatment can include reducing acute or chronic inflammation; alleviating pain and mitigating and inducing re-growth of new ligament, bone and other tissues; as an adjunct in surgery; and/or any repair procedure. Also, as used in the specification and including the appended claims, the term “tissue” includes soft tissue, ligaments, tendons, cartilage and/or bone unless specifically referred to otherwise. 
     The following discussion includes a description of a surgical system including a bone fastener, related components and methods of employing the surgical system in accordance with the principles of the present disclosure. Alternate embodiments are also disclosed. Reference is made in detail to the exemplary embodiments of the present disclosure, which are illustrated in the accompanying figures. Turning to  FIGS.  1 - 6   , there are illustrated components of a spinal implant system  10 . 
     The components of spinal implant system  10  can be fabricated from biologically acceptable materials suitable for medical applications, including metals, synthetic polymers, ceramics and bone material and/or their composites. For example, the components of spinal implant system  10 , individually or collectively, can be fabricated from materials such as stainless steel alloys, commercially pure titanium, titanium alloys, Grade 5 titanium, super-elastic titanium alloys, cobalt-chrome alloys, superelastic metallic alloys (e.g., Nitinol, super elasto-plastic metals, such as GUM METAL®), ceramics and composites thereof such as calcium phosphate (e.g., SKELITE™), thermoplastics such as polyaryletherketone (PAEK) including polyetheretherketone (PEEK), polyetherketoneketone (PEKK) and polyetherketone (PEK), carbon-PEEK composites, PEEK-BaSO 4  polymeric rubbers, polyethylene terephthalate (PET), fabric, silicone, polyurethane, silicone-polyurethane copolymers, polymeric rubbers, polyolefin rubbers, hydrogels, semi-rigid and rigid materials, elastomers, rubbers, thermoplastic elastomers, thermoset elastomers, elastomeric composites, rigid polymers including polyphenylene, polyimide, polyimide, polyetherimide, polyethylene, epoxy, bone material including autograft, allograft, xenograft or transgenic cortical and/or corticocancellous bone, and tissue growth or differentiation factors, partially resorbable materials, such as, for example, composites of metals and calcium-based ceramics, composites of PEEK and calcium based ceramics, composites of PEEK with resorbable polymers, totally resorbable materials, such as, for example, calcium based ceramics such as calcium phosphate, tri-calcium phosphate (TCP), hydroxyapatite (HA)-TCP, calcium sulfate, or other resorbable polymers such as polyaetide, polyglycolide, polytyrosine carbonate, polycaroplaetohe and their combinations. 
     Various components of spinal implant system  10  may have material composites, including the above materials, to achieve various desired characteristics such as strength, rigidity, elasticity, compliance, biomechanical performance, durability and radiolucency or imaging preference. The components of spinal implant system  10 , individually or collectively, may also be fabricated from a heterogeneous material such as a combination of two or more of the above-described materials. The components of spinal implant system  10  may be monolithically formed, integrally connected or include fastening elements and/or instruments, as described herein. 
     Spinal implant system  10  includes a spinal implant, such as, for example, a bone fastener  180 . Bone fastener  180  comprises a member, such as, for example, a screw shaft assembly  12  and a member, such as, for example a head assembly  13 . Head assembly  13  includes a band, such as, for example, a retaining ring  36  configured for provisional capture of screw shaft assembly  12  and/or fixed connection of the components of bone fastener  180 , as described herein. Head assembly  13  includes a band, such as, for example, a ring  44  configured for disposal in a contracted orientation and an expanded interference orientation adjacent to ring  36  to facilitate fixed connection of the components of bone fastener  180 . In some embodiments, screw shaft assembly  12  and head assembly  13  are assembled in situ or prior to implant to form bone fastener  180 , as described herein. 
     Head assembly  13  includes a receiver  14 . Receiver  14  extends along and defines an axis X 1  Receiver  14  includes a pair of spaced apart arms  16 ,  18  that define an implant cavity  20  therebetween configured for disposal of a component of a spinal construct, such as, for example, a spinal rod (not shown). 
     Arms  16 ,  18  each extend parallel to axis X 1 . In some embodiments, arm  16  and/or arm  18  may be disposed at alternate orientations, relative to axis X 1 , such as, for example, transverse, perpendicular and/or other angular orientations such as acute or obtuse, coaxial and/or may be offset or staggered. Arms  16 ,  18  each include an arcuate outer surface extending between a pair of side surfaces. At least one of the outer surfaces and the side surfaces of arms  16 ,  18  have at least one recess or cavity therein configured to receive an insertion tool, compression instrument and/or instruments for inserting and tensioning bone fastener  180 . In some embodiments, arms  16 ,  18  are connected at proximal and distal ends thereof such that receiver  14  defines a closed spinal rod slot. In some embodiments, a spinal rod may be monolithically formed with receiver  14  or pre-assembled with receiver  14 . 
     Cavity  20  is substantially U-shaped. In some embodiments, all or only a portion of cavity  20  may have alternate cross section configurations, such as, for example, closed, V-shaped, W-shaped, oval, oblong triangular, square, polygonal, irregular, uniform, non-uniform, offset, staggered, and/or tapered. Receiver  14  includes an inner surface  22 . A portion of surface  22  includes a thread form  24  located adjacent arm  16  and a thread form  26  located adjacent arm  18 . Thread forms  24 ,  26  are each configured for engagement with a coupling member, such as, for example, a setscrew (not shown), to retain the spinal rod within cavity  20 . In some embodiments, surface  22  may be disposed with the coupling member in alternate fixation configurations, such as, for example, friction fit, pressure fit, locking protrusion/recess, locking keyway and/or adhesive. In some embodiments, all or only a portion of surface  22  may have alternate surface configurations to enhance engagement with the spinal rod and/or the setscrew, such as, for example, rough, arcuate, undulating, mesh, porous, semi-porous, dimpled and/or textured. In some embodiments, receiver  14  may include alternate configurations, such as, for example, closed, open and/or side access. In some embodiments, screw shaft assembly  12  is manually engaged with head assembly  13  in a non-instrumented assembly, as described herein, such that removal of head assembly  13  from screw shaft assembly  12  can withstand a clamp force applied from the coupling member. 
     Receiver  14  includes portion  28 , as shown in  FIG.  2   . Portion  28  includes a surface  30 . Surface  30  defines a cavity, such as, for example, a groove  34 . Groove  34  is configured for disposal of ring  36 . In some embodiments, groove  34  extends about all or a portion of surface  30 . Groove  34  includes a diameter D 1 . Ring  36  includes a circumference that defines an opening, such as, for example, a gap. In some embodiments, the gap is sized such that the gap has a thickness that is less than the height and the width. In some embodiments, the gap is sized to allow ring  36  to pass though a bottom of receiver  14  by contracting circumferentially. 
     Portion  28  includes a surface  40 , as shown in  FIG.  2   . Surface  40  defines a cavity, such as, for example, a groove  42 . Groove  42  is configured for disposal of ring  44 . Ring  44  includes a surface  46  that defines an outer groove  48  configured for engagement with a surface of groove  42 , as described herein. Ring  44  includes a circumference that extends between ends of ring  44 . In some embodiments, the ends define an opening, such as, for example, a gap. In some embodiments, the gap is sized such that the gap has a thickness that is less than the height and the width. In some embodiments, the gap is sized to allow ring  44  to engage surface  40  by contracting circumferentially. 
     Groove  42  includes a projection  50 . Projection  50  is configured for engagement with surface  46  of outer groove  48 . Projection  50  retains ring  44  within groove  42 , Projection  50  is configured to resist and/or prevent disengagement of ring  44  from groove  42 . Ring  44  is disengageable from groove  42  upon engagement with crown  80 , which causes surface  46  to disengage from projection  50  and drives ring  44  from groove  42 , as described herein. Groove  42  includes a diameter D 2 . In some embodiments, diameter D 1  is equal to diameter D 2 , as shown in  FIG.  2   . In some embodiments, diameter D 1  and diameter D 2  are different. In some embodiments, surface  40  retains ring  44  within groove  42  and groove  42  does not include projection  50 . 
     Receiver  14  includes a portion  60 , as shown in  FIG.  2   . Portion  60  includes a surface  62 , Surface  62  defines a cavity, such as, for example, a groove  64  configured for disposal of ring  36  and/or ring  44 . In some embodiments, groove  64  extends about all or a portion of surface  40 . Groove  64  includes a circumferential channel  66  that accommodates expansion of ring  36  and/or ring  44 , as described herein. Groove  64  includes a diameter D 3 . Diameter D 3  is greater than diameter D 1  and/or diameter D 2 . Diameter D 3  is sized to allow for expansion of ring  36  and/or ring  44  therein. Grooves  34 ,  42 ,  64  are disposed in a serial orientation along axis X 1 , as shown in  FIG.  2   , In some embodiments, grooves  34 ,  42 ,  64  are disposed in spaced apart relation. 
     A surface  68  is disposed between groove  64  and groove  34 . Surface  68  is disposed at an angle relative to axis X 1  to define a ramp  69 . Ramp  69  is selectively inclined to facilitate translation of ring  36  between groove  34  and groove  64 , as described herein. In one example, ring  36  is engaged with screw shaft assembly  12  for translation such that ring  36  slides along ramp  69 , which directs and/or guides ring  36  from groove  34  into groove  64 , and expands into a provisional capture orientation with screw shaft assembly  12 . In another example, ring  36  is engaged with ring  44  for translation such that ring  36  slides along ramp  69 , which directs and/or guides ring  36  from groove  64  into groove  34 , and contracts for fixed connection of the components of bone fastener  180  including permanent capture of head assembly  13  and screw shaft assembly  12 . In some embodiments, surface  68  is oriented substantially perpendicular to axis X 1 . 
     Ring  36  is resiliently biased to a contracted and/or capture orientation within groove  34 , as shown in  FIG.  3   , and expandable to an expanded orientation within groove  64 , as shown in  FIGS.  4  and  5   , for provisional capture of screw shaft assembly  12  with head assembly  13 , as described herein. Ring  36  is expandable from the contracted and/or capture orientation to the expanded orientation for assembly of screw shaft assembly  12  with head assembly  13 , as shown and described for example with regard to  FIGS.  3 - 6   . 
     Ring  44  is disposable in a contracted orientation within groove  42 , as shown in  FIGS.  3 - 5   , and resiliently biased to an expanded interference orientation within groove  64 , as shown in  FIG.  6   . In the interference orientation, ring  44  is disposed in channel  66  and adjacent to ring  36  for abutting and/or contacting engagement therewith to resist and/or prevent translation of ring  36  from groove  34  into groove  64 , and fixed connection of the components of bone fastener  180  including permanent capture of head assembly  13  and screw shaft assembly  12 , as described herein. 
     Receiver  14  includes a surface  70 . Surface  70  defines a slot  72 . Slot  72  is configured for disposal of a part, such as, for example a crown  80 . In some embodiments, all or only a portion of surface  70  may have alternate surface configurations, such as, for example, rough, arcuate, undulating, mesh, porous, semi-porous, dimpled and/or textured. 
     Crown  80  is configured for disposal within cavity  20  and slot  72 . Crown  80  includes a wall  82  having an end surface  84  and an end surface  86 . Surface  84  is configured to define at least a portion  88  of cavity  20 . Portion  88  is defined by an outer surface  90  that defines a curved portion of crown  80  configured for engagement with a spinal implant, such as, for example, a spinal rod. Surface  84  includes a circumferential flange  92 . Receiver  14  includes an undercut surface that defines a groove  94 . Flange  92  is configured for disposal with groove  94 , as shown in  FIG.  3   . Engagement of flange  92  with the undercut surface that defines groove  94  retains crown  80  with receiver  14  in a first orientation adjacent ring  44  when ring  44  is disposed in groove  42 . Translation of crown  80 , in a direction shown by arrow C and described herein with regard to  FIGS.  5  and  6   , into a second orientation moves ring  44  from groove  42 . In some embodiments, all or only a portion of surface  90  may have alternate cross section configurations, such as, for example, oval, oblong triangular, square, polygonal, irregular, uniform, non-uniform, offset, staggered, and/or tapered. In some embodiments, a part, as described herein, may include a crown, a sleeve and/or other component of head assembly  13 . 
     Crown  80  is configured for translation within slot  72  along surface  70 . Translation of crown  80  within slot  72  causes surface  86  to engage ring  44 . Surface  86  is disposed adjacent ring  44  such that axial translation of crown  80  causes crown  80  to displace ring  44  from groove  42 . Ring  44  is disengageable from groove  42  upon engagement with crown  80 , which causes surface  46  to disengage from projection  50  and drives ring  44  from groove  42 . As such, ring  44  is movable between the contracted orientation and the expanded interference orientation in groove  64 , as described herein, to prevent migration of ring  36  from groove  34  into groove  64  for fixed connection of the components of bone fastener  180 . Surface  86  is positioned with ring  44  to resist and/or prevent displacement of ring  44  from channel  66 . 
     Screw shaft assembly  12  includes shaft  181  and head  182 . Shaft  181  is configured to penetrate tissue, such as, for example, vertebral tissue. In some embodiments, shaft  181  includes an outer surface having an external thread form. In some embodiments, the external thread form may include a single thread turn or a plurality of discrete threads. Head  182  includes a tool engaging portion  184  configured to engage a surgical tool or instrument, as described herein. In some embodiments, portion  184  includes a hexagonal cross-section. In some embodiments, portion  184  may have alternative cross-sections, such as, for example, rectangular, polygonal, hexalobe, oval, or irregular. Head  182  includes a surface  186  that defines a plurality of ridges  188  to improve purchase of head  182  with crown  80 . In some embodiments, head  182  includes an outer surface  190  having planar surfaces or flats and/or arcuate surfaces. 
     In some embodiments, receiver  14  may be disposed with head  182  in alternate fixation configurations, such as, for example, friction fit, pressure fit, locking protrusion/recess, locking keyway and/or adhesive. In some embodiments, receiver  14  is configured for rotation relative to head  182  for multi-axial movement. In some embodiments, receiver  14  is configured for rotation in range of 360 degrees relative to head  182  to facilitate positioning of shaft  181  with tissue. In some embodiments, receiver  14  is configured for selective rotation in range of 360 degrees relative to and about head  182  such that shaft  181  is selectively aligned for rotation in a plane relative to receiver  14 . In some embodiments, receiver  14  may be disposed with head  182  in a uni-axial configuration or a sagittally adjustable configuration. 
     In some embodiments, screw shaft assembly  12  is manually engageable with head assembly  13  in a non-instrumented assembly, as described herein. In some embodiments, manual engagement and/or non-instrumented assembly of head assembly  13  and screw shaft assembly  12  includes coupling without use of separate and/or independent instrumentation engaged with screw shaft assembly  12  components to effect assembly. In some embodiments, manual engagement and/or non-instrumented assembly includes a practitioner, surgeon and/or medical staff grasping head assembly  13  and screw shaft assembly  12  and forcibly assembling the components. In some embodiments, manual engagement and/or non-instrumented assembly includes a practitioner, surgeon and/or medical staff grasping head assembly  13  and screw shaft assembly  12  and forcibly snap fitting the components together, as described herein. In some embodiments, manual engagement and/or non-instrumented assembly includes a practitioner, surgeon and/or medical staff grasping head assembly  13  and screw shaft assembly  12  and forcibly pop fitting the components together and/or pop fitting head assembly  13  onto screw shaft assembly  12 , as described herein. In some embodiments, a force in a range of 2-50 N is required to manually engage head assembly  13  and screw shaft assembly  12  and forcibly assemble the components. For example, a force in a range of 2-50 N is required to snap fit and/or pop fit assemble head assembly  13  and screw shaft assembly  12 . In some embodiments, a force in a range of 5-10 N is required to manually engage head assembly  13  and screw shaft assembly  12  and forcibly assemble the components. For example, a force in a range of 5-10 N is required to snap fit and/or pop fit assemble head assembly  13  and screw shaft assembly  12 . In some embodiments, this configuration provides manually engageable components that are assembled without instrumentation, and subsequent to assembly, the assembled components have a selected pull-out strength and/or can be pulled apart, removed and/or separated with a minimum required force. 
     In some embodiments, spinal implant system  10  comprises a spinal implant kit, as described herein, which includes a plurality of screw shaft assemblies  12  and/or head assemblies  13 . Screw shaft assembly  12  and/or head assembly is configured for selection such that the components of bone fastener  180  are interchangeable. 
     In assembly, operation and use, spinal implant system  10 , similar to the systems and methods described herein, includes a screw shaft assembly  12  for connection with a head assembly  13 , and is employed with a surgical procedure for treatment of a spinal disorder affecting a section of a spine of a patient, as discussed herein. Spinal implant system  10  is employed with a surgical procedure for treatment of a condition or injury of an affected section of the spine. 
     In some embodiments, a screw shaft assembly  12  is selected from a kit of a plurality of screw shaft assemblies  12  for interchangeable connection with head assembly  13  to comprise a bone fastener  180  having a selected movement, similar to those described herein. In some embodiments, the kit of screw shaft assemblies  12  includes a variety of screw shaft assemblies having different movement configurations when assembled with an interchangeable head assembly  13 , such as, for example, multi-axial movement, sagittal angulation movement, fixed axis movement, mono-axial movement and/or uni-planar movement. 
     In some embodiments, head assembly  13  includes receiver  14  assembled with crown  80 , ring  44  and ring  36 , as described herein. In some embodiments, ring  36  is initially disposed with groove  34  in a contracted orientation and ring  44  is initially disposed with groove  42  in a contracted orientation, as shown in  FIG.  3   . 
     Screw shaft assembly  12  is manually engageable, as described herein, with head assembly  13 , as shown in  FIGS.  3 - 6   . Head assembly  13  is assembled with screw shaft assembly  12  by translating receiver  14 , in a direction shown by arrow A in  FIG.  3   . Engagement of head  182  with receiver  14  causes ring  36  to translate, in a direction shown by arrow B in  FIG.  4   , such that ring  36  is positionable and allowed to expand into groove  64  to an expanded orientation, as described herein. Diameter D 3  of groove  64  is larger than diameter D 1  of groove  34  to allow ring  36  to expand into channel  66 . Engagement of head  182  with an inner surface of ring  36  causes ring  36  to expand and slide along ramp  69  into channel  66 . As head  182  translates further into receiver  14 , ring  36  passes over head  182  and resiliently contracts about head  182  within channel  66  to provisionally capture screw shaft assembly  12 , as shown in  FIG.  5   . 
     Crown  80  is manipulated, for example, via engagement by a surgical instrument to translate crown  80 , in a direction shown by arrow C in  FIG.  5   . Surface  86  engages ring  44  such that surface  46  disengages from projection  50  and ring  44  is displaced from groove  42 , as shown in  FIG.  6   . Ring  44  translates and engages ring  36  driving ring  36  from groove  64  into groove  34 . Ring  36  axially translates along receiver  14  and/or slides along ramp  69  into groove  34 . Ring  44  translates into groove  64  and resiliently expands into channel  66  to an expanded, interference orientation, as described herein. Ring  44  is oriented for abutting and/or contacting engagement with ring  36  to resist and/or prevent translation of ring  36  from groove  34  into groove  64 , and fixed connection of the components of bone fastener  180  including permanent capture of head assembly  13  and screw shaft assembly  12  in a selected movement configuration, for example, in a multi-axial movement configuration. Surface  86  is positioned with ring  44  to resist and/or prevent displacement of ring  44  from channel  66 . 
     In use, for treatment of a spinal disorder, bone fastener  180  including assembled screw shaft assembly  12  and head assembly  13  can be threaded and engaged with tissue. In some embodiments, bone fastener  180  is disposed adjacent vertebrae at a surgical site and is manipulated to drive, torque, insert or otherwise connect shaft  181  with vertebrae in connection with a surgical procedure, as described herein. 
     In some embodiments, spinal implant system  10  includes an agent, which may be disposed, packed, coated or layered within, on or about the components and/or surfaces of spinal implant system  10 . In some embodiments, the agent may include bone growth promoting material, such as, for example, bone graft to enhance fixation of the fixation elements with vertebrae. In some embodiments, the agent may be HA coating. In some embodiments, the agent may include one or a plurality of therapeutic agents and/or pharmacological agents for release, including sustained release, to treat, for example, pain, inflammation and degeneration. 
     In some embodiments, the use of microsurgical and image guided technologies may be employed to access, view and repair spinal deterioration or damage, with the aid of spinal implant system  10 . The components of spinal implant system  10  can be made of radiolucent materials such as polymers. Radiomarkers may be included for identification under x-ray, fluoroscopy, CT or other imaging techniques. 
     In some embodiments, spinal implant system  10  can include one or a plurality of bone fasteners  180  such as those described herein and/or fixation elements, which may be employed with a single vertebral level or a plurality of vertebral levels. In some embodiments, bone fasteners  180  may be engaged with vertebrae in various orientations, such as, for example, series, parallel; offset, staggered and/or alternate vertebral levels. In some embodiments, bone fasteners  180  may be configured as multi-axial screws, sagittal angulation screws, pedicle screws, mono-axial screws, uni-planar screws, fixed screws, anchors, tissue penetrating screws, conventional screws, expanding screws. In some embodiments, bone fasteners  180  may be employed with wedges, anchors, buttons, clips, snaps, friction fittings, compressive fittings, expanding rivets, staples, nails, adhesives, posts, connectors, fixation plates and/or post. 
     It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplification of the various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.