Patent Publication Number: US-2020281736-A1

Title: Intervertebral Implant Assembly and Instruments Therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/813,251, filed Mar. 4, 2019, the disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The spine is comprised of a plurality vertebrae that are cushioned by intervertebral discs. Such intervertebral discs can deteriorate or become damaged due to injury, disease, or extended wear which may result in significant back pain that limits a patient&#39;s mobility and quality of life. One method of treatment that has been widely utilized is spinal fusion, whereby an affected disc is partially or fully excised and vertebral bodies adjacent such disc are fused together through the use of interbody devices, such as spacers, cages, and the like. 
     The aforementioned devices are often packed with a bone growth promoting material, such as bone graft and/or any known combination of biologics. In addition, some interbody devices include porous surfaces that promote bone growth into the structure of the interbody device itself. However, it takes time for bone to grow into the interbody device and for bone to grow between adjacent vertebrae to fuse the same. In the meantime, interbody devices often include mechanical features that help maintain engagement between the interbody device and bone of the existing vertebrae. 
     In order to help stabilize the spine during fusion, plates and/or rods are commonly used in conjunction with the interbody device. Plates are typically connected to adjacent vertebrae via bone screws and are positioned so that they extend across the disc space that contains the interbody device. While such plates may help stabilize the vertebrae, the interbody device is still solely reliant on its mechanical features to maintain its position within the disc space, which may not be in and of itself sufficient to prevent movement which should be prevented to encourage bone growth. In addition, bone plates can introduce additional complications, such as screw back-out which can result in plate loosing and destabilization. Therefore, further improvements are desirable. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the present disclosure, a spinal fusion system includes an interbody device that includes a leading end, trailing end, and opposed bone contacting sides extending therebetween. The trailing end defines a threaded opening extending toward the leading end. The system also includes a bone plate that includes inner and outer surfaces and defines a first bone screw opening and connection screw opening extending therethrough. The system further includes a connection screw that includes a head and a threaded shaft. The head is positioned within the connection screw opening of the bone plate and is rotatably connected thereto such that the connection screw is rotatable about a longitudinal axis thereof but is prohibited from translational movement relative to the bone plate. The threaded shaft extends from the connection screw opening and is configured for threaded engagement with threaded opening of interbody device. 
     Additionally, the head of the connection screw may be snap-fit to the bone plate. The connection screw opening may include first and second sections thereof. The first section may be positioned closer to the outer surface than the second section and may have a cross-sectional dimension smaller than the second section such that a first shoulder is formed therebetween. The head of the connection screw may be at least partially positioned within the second section of the connection screw opening. The shoulder may prevent the connection screw from backing out of the connection screw opening. The head of the connection screw may include a plurality of flexible members that are movable radially inwardly from a first to a second position when the head is passed through the first section of the connection screw opening and then from the second to the first position when the flexible members are at least partially positioned within the second section. The flexible members may each include a flange extending radially outwardly therefrom. 
     Continuing with this aspect, the threaded shaft may include a right-handed outer thread, and the connection screw may define a threaded interior opening that includes a left-handed inner thread. The bone plate may include a second bone screw opening that extends therethrough. The first and second bone screw openings may be aligned with the connection screw opening along a longitudinal axis of the bone plate. The plate may further define a screw blocker opening positioned adjacent the bone screw opening, and the system may include a screw blocker rotatably positioned within the screw blocker opening. The screw blocker opening may define first and second grooves that extend along a length of the screw blocker opening, and the screw blocker may include a projection that is alternately engageable to the first and second grooves. The screw blocker may include a flexible arm and the projection may extend from the flexible arm. The flexible arm may be moveable inwardly when the screw blocker is rotated between the first and second grooves of the screw blocker opening. 
     In another aspect of the present disclosure, a bone plate assembly includes a bone plate that includes inner and outer surfaces and defines a first bone screw opening and first screw blocker opening. The first bone screw opening extends through the inner and outer surfaces. The first screw blocker opening is positioned adjacent the first bone screw opening and has first and second indentations circumferentially offset from each other about a longitudinal axis of the screw blocker opening. A first screw blocker is positioned within the first screw blocker opening and has a head and a body extending from the head. The body includes a projection extending radially outwardly therefrom and is alternately engageable with the first and second indentations of the screw blocker opening. 
     Additionally, the first and second indentations may each be semi-cylindrical grooves that extend along a portion of a length of the screw blocker opening. The screw blocker opening may include a first section that extends through the inner surface of the bone plate and may be conical and a second section that may be cylindrical. The indentations may be located within the second section. The body of the first screw blocker may have a post at a distal end thereof. The post may have a tool opening defined by a sidewall thereof. The sidewall may be radially expanded from a first configuration such that the first screw blocker is rotatable within the first screw blocker opening but is prohibited from translational movement relative to the bone plate. The screw blocker body may include a flexible arm that depends downwardly from the head and may be moveable inwardly as the screw blocker is rotated about a longitudinal axis thereof between the first and second indentations. The projection may extend from the flexible arm. The head of the first screw blocker may be asymmetric about a plane extending through the first screw blocker. The screw blocker opening may extend through a recessed portion of the bone plate such that the screw blocker head is positioned within the recessed portion and is moveable within the recess from an unblocked position to a blocked position in which a portion of the head is positioned over the bone screw opening. The assembly may further a second screw blocker. The bone plate may further define a second bone screw opening and second screw blocker opening adjacent the first bone screw opening. The second screw blocker may be positioned within the second screw blocker opening. 
     In a further aspect of the present disclosure, a method of spinal fusion of adjacent vertebrae of a mammalian subject includes connecting an interbody device to a first inner member of an insertion tool positioned within an outer member of the insertion tool; inserting the interbody device into an intervertebral disc space using the insertion tool; disconnecting the interbody device from the first inner member; removing the first inner member from the outer member; inserting a second inner member into the outer member; connecting a bone plate to the second inner member; inserting the bone plate into the mammalian subject adjacent the intervertebral disc space; and driving a bone screw through a bone screw opening of the bone plate and into a first vertebra. 
     Additionally, connecting the interbody device to the first inner member may include rotating the first inner member in a first direction, and connecting the bone plate to the second inner member may include rotating the second inner member in a second direction opposite the first direction. The method may further include connecting the bone plate to the interbody device while the interbody device is positioned within the disc space. Also, connecting the bone plate to the interbody device may include rotating the second inner member in the first direction. Connecting the bone plate to the interbody device may also include threadedly engaging a connection screw connected to the bone plate to the interbody device. Further, connecting the bone plate to the second inner member may include threadedly engaging a threaded tip of the second inner member to the connection screw. 
     Continuing with this aspect, the method may further include connecting an adapter to the outer member, connecting a slap hammer to the adapter, and removing the interbody device from the intervertebral disc space via the slap hammer Connecting the adapter to the outer member may include sliding the adapter over a knob of the first inner member. Connecting the adapter to the outer member may include pushing and rotating a knob of the adapter so that a threaded shaft of the adapter threadedly engages a threaded opening of the outer member. The outer member may include an angled shaft and the inner member may include an elongate shaft, a threaded tip, and a flexible portion disposed between the elongate shaft and threaded tip. The method may also include inserting the first inner member into a bore of the outer member such that a shoulder between the threaded tip and flexible portion is positioned in a facing relationship with a shoulder within the bore of the outer member. Even further, the method may include rotating a screw blocker from a first position to a second position so that a head thereof is positioned over the bone screw. 
     In a still further aspect of the present disclosure, a method of spinal fusion of adjacent vertebrae of a mammalian subject includes: connecting an interbody device to an insertion tool; inserting the interbody device into an intervertebral disc space using the insertion tool; disconnecting the interbody device from the insertion tool; and connecting a bone plate assembly to a second inner member. The bone plate assembly has a connection screw rotatably connected thereto such that the connection screw is rotatable about a longitudinal axis thereof but is prohibited from translational movement relative to the bone plate. The method also includes inserting the bone plate assembly into the mammalian subject adjacent the intervertebral disc space; and threadedly connecting a threaded shaft of the bone plate assembly to the interbody device while the interbody device is positioned within the disc space. 
     Additionally, the threadedly connecting step may be performed using the insertion tool. Connecting the interbody device to the insertion tool may also include rotating a first inner member of the insertion tool in a first direction, and connecting the bone plate assembly to the insertion tool may include rotating a second inner member of the insertion tool in a second direction opposite the first direction. Connecting the bone plate assembly to the interbody device may also include rotating the second inner member in the first direction. 
     In an even further aspect of the present disclosure, an insertion and extraction system for an interbody device includes an insertion tool that includes an outer member and an inner member, and an adapter that includes a body that defines a hollow compartment therein. The hollow compartment is configured to receive a portion of the outer and inner members. The adapter is connectable to the outer member. The system also includes a slap hammer connected to the adapter that has a sliding weight and a bumper for being bumped by the sliding weight. 
     Additionally, the inner member may include a knob extending from a proximal end of the outer member. The hollow compartment may be configured to receive the proximal end of the outer member and the knob. The adapter may include a threaded opening extending therein, and the slap hammer may have a threaded projection engageable with the threaded opening of the adapter. The adapter may include a spring and threaded shaft. The spring and threaded shaft may be disposed within a transverse opening extending into the body of the adapter and communicating with the hollow compartment. The spring and threaded shaft may be arranged such that the spring biases a threaded end of the threaded shaft away from the hollow compartment. The body of the adapter may include a post and the transverse opening that extends through the post, and the adapter may include a knob disposed over a portion of the post and may be connected to the inner shaft such that rotating the knob rotates the threaded shaft. The threaded shaft may include a collar extending radially outwardly therefrom and the spring may be arranged such that its bias pushes against the collar. Also, pushing on the knob may overcomes the bias of the spring to translate the threaded shaft from a first position in which the threaded end is disposed within the post and a second position in which the threaded tip is positioned within the hollow cavity. The outer member may also define a transverse threaded opening extending therein. When the insertion tool is received within the hollow cavity of the adapter, the threaded end of the threaded shaft may align with the transverse threaded opening of the outer member so that threaded member can be moved into engagement with the threaded opening over the bias of the spring. 
     In yet a further aspect of the present disclosure, a method of extracting an interbody device from an intervertebral disc space includes the steps of: sliding an adapter over a handle of an inserter; actuating a knob of the adapter to dispose a shaft of the adapter within a bore of the inserter; coupling a slap hammer to the adapter, the slap hammer including a sliding weight and a guide rod; and sliding the sliding weight along the guide rod to exert a force on the handle in a direction opposite the implant so as to transfer such force to the implant to remove it from the intervertebral disc space. 
     Additionally, the method may include connecting the adapter to the inserter by threadedly engaging a threaded shaft of the adapter with the bore of the inserter which is a threaded bore. Also, actuating the knob of the adapter may further include pushing on the knob to overcome a spring biasing the threaded shaft, and turning the knob to threadedly engage a threaded end of the threaded shaft and the bore. The inserter may include an outer member and an inner member. The inner member may have a threaded tip, an elongate shaft, and a flexible portion disposed between the threaded tip and elongate shaft. The outer member may include the handle, and sliding the adapter over the handle of the inserter may also include sliding the adapter over a knob of the inner member. The slap hammer may further include a threaded projection extending from a distal end surface and along a longitudinal axis of the slap hammer, and coupling the slap hammer to the adapter may further include threading the threaded projection into a threaded bore at a proximal surface of the adapter. The threaded bore may extend into the adapter along a longitudinal axis thereof. The method may further include aligning indicia on the adapter with indicia on the inserter prior to sliding the adapter onto the inserter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of fusion assembly according to an embodiment of the present disclosure. 
         FIG. 1B  is an exploded perspective view of the fusion assembly of  FIG. 1A . 
         FIG. 2A  is a rear perspective view of an intervertebral implant of the fusion assembly of  FIG. 1A . 
         FIG. 2B  is a front perspective view of the intervertebral implant of  FIG. 2A . 
         FIG. 3A  an exploded perspective view of a plate assembly of the fusion assembly of  FIG. 1A . 
         FIG. 3B  is a perspective view of the plate assembly of  FIG. 3A . 
         FIG. 3C  is a cross-sectional view of the plate assembly take along line C-C of  FIG. 3A . 
         FIG. 4A  is a perspective view of a screw blocker of the plate assembly of  FIG. 3A . 
         FIG. 4B  is a cross-sectional view of the screw blocker taken along line B-B of  FIG. 4A . 
         FIGS. 4C and 4D  are cross-sectional views of the screw blocker of  FIG. 4A  positioned within a plate of the plate assembly of  FIG. 3A . 
         FIG. 4E  is an enhanced view of a screw blocker opening within the plate of the plate assembly of  FIG. 3A . 
         FIG. 4F  is an enhanced view of the screw blocker of  FIG. 4A  in a first position within the plate of the plate assembly of  FIG. 3A . 
         FIG. 4G  is a cutaway view of the screw blocker and plate of  FIG. 4F . 
         FIG. 4H  is an enhanced view of the screw blocker of  FIG. 4A  in a second position within the plate of the plate assembly of  FIG. 3A . 
         FIG. 4I  is cutaway view of the screw blocker and plate of  FIG. 4H . 
         FIG. 5A  is a perspective view of a connecting screw of the plate assembly of  FIG. 3A . 
         FIG. 5B  is a cross-sectional view of the connecting screw of  FIG. 5A  taken along a midline thereof. 
         FIG. 5C  is a cross-sectional view of the connecting screw of  FIG. 5A  taken along a midline thereof and within the plate of the plate assembly of  FIG. 3A . 
         FIG. 6A  is a perspective view of the fusion assembly of  FIG. 1A . 
         FIG. 6B  is partial cross-sectional view taken along line B-B of  FIG. 6A . 
         FIG. 7A  is a perspective view of a plate assembly according to another embodiment of the present disclosure. 
         FIG. 7B  is a side view of a fusion assembly according to another embodiment of the disclosure including the plate assembly of  FIG. 7A . 
         FIG. 8  is a perspective view of an insertion/extraction system according to an embodiment of the present disclosure. 
         FIG. 9A  is a perspective view of an implant insertion configuration of the insertion/extraction system of  FIG. 8 . 
         FIG. 9B  is a perspective view of an outer member of the insertion/extraction system of  FIG. 8 . 
         FIG. 9C  is a perspective view of an inner member of the insertion/extraction system of  FIG. 8 . 
         FIG. 9D  is an enhanced cutaway view of a distal end of the outer member of  FIG. 9B . 
         FIG. 9E  is an enhanced cutaway view of a proximal end of the outer member of  FIG. 9B . 
         FIG. 9F  is an enhanced cross-sectional view of the inner member of  FIG. 9C  taken along a midline thereof. 
         FIG. 9G  is an enhanced cross-sectional view of an inner member according to another embodiment of the disclosure taken along a midline thereof. 
         FIG. 9H  is an enhanced view of a proximal end of the insertion/extraction system of  FIG. 8 . 
         FIG. 9I  is an enhanced cross-sectional view of the proximal end of  FIG. 9G  connected to the intervertebral implant of  FIG. 2A  taken along a midline thereof. 
         FIG. 10A  is a perspective view of an adapter of the insertion/extraction system of  FIG. 8 . 
         FIG. 10B  is an exploded view of the adapter of  FIG. 10A . 
         FIG. 10C  is a perspective view of the adapter being connected to the insertion configuration of the insertion/extraction system of  FIG. 9A . 
         FIGS. 10D and 10E  are cross-section views of the adapter in respective first and second configurations. 
         FIG. 11  is a perspective view of a slap hammer of the insertion/extraction system of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     When referring to specific directions in the following discussion of certain devices, it should be understood that such directions are described with regard to the device&#39;s orientation and position during exemplary application to the human body. Thus, as used herein, the term “proximal” means closer to the operator or in a direction toward the operator, and the term “distal” means more distant from the operator or in a direction away from the operator. The term “anterior” means towards the front part of the body or the face, and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body, and the term “lateral” means away from the midline of the body. The term “inferior” means toward the feet of the body, and the term “superior” means toward the head of the body. Also, as used herein, the terms “about,” “generally” and “substantially” are intended to mean that slight deviations from absolute are included within the scope of the term so modified. 
       FIGS. 1A-6B  depict a fusion assembly or system  100  according to an embodiment of the present disclosure. Fusion assembly  100  generally includes an intervertebral implant or interbody device  110  and a vertebral plate assembly  130 . 
     Interbody device  110 , as depicted in  FIGS. 2A and 2B , is particularly suited for a lateral approach. However, while interbody device  110  is described herein as being configured for a lateral approach, it is contemplated that other interbody devices may be used in fusion assembly  100 , such as interbody devices configured for an anterior approach, for example. Exemplary lateral and anterior interbody devices that can be used in fusion assembly can be found in U.S. Pat. No. 10,182,923, the disclosure of which is hereby incorporated by reference herein in in its entirety. 
     Interbody device  110  includes leading and trailing ends  112 ,  114 . Leading end  112  has a rounded, wedge nose to facilitate insertion into an intervertebral space, as shown in  FIG. 2B . Trailing end  114  defines a threaded opening  119  extending therein and extending toward leading end  112 , as shown in  FIG. 2A . Threaded opening  119  includes a right-handed thread and, in the embodiment depicted, communicates with a vertical graft window  111  closest to trailing end  114 . However, in other embodiments, threaded opening  119  may terminate before reaching graft window  111  such that threaded opening  119  is a blind opening. Trailing end  114  also defines smooth bores/openings  118  that extend partially into trailing end  114  such that smooth bores  118  are blind openings. Smooth bores  118  flank threaded opening  119  and are aligned with threaded opening  119  in a mediolateral direction. However, in some embodiments, smooth bores  119  may be positioned such that axes thereof are offset superiorly-inferiorly relative to the axis of threaded opening  119 . 
     Interbody device  110  also includes upper and lower bone contacting sides and lateral sidewalls  116  that extend between the leading and trailing ends  112 ,  114 . Vertical graft windows  111  extend in a superior-inferior direction entirely through interbody device  110  and through the upper and lower bone contacting sides. Horizontal graft windows or lateral windows  113  extend in the mediolateral direction entirely through interbody device  110  and through lateral sidewalls  116 . In the particular embodiment depicted, there are two vertical and two horizontal graft windows  111 ,  113 . However, more or less of the vertical and horizontal graft windows  111 ,  113  is contemplated, such as one or more than two of each graft window  111 ,  113 . Horizontal graft windows  113  intersect and are in communication with vertical graft windows  111  so that bone can grow vertically and horizontally through interbody device  110 . 
     To further facilitate bone growth, interbody device  110  includes a porous structure  117  that forms at least a portion of upper and lower bone contacting sides. In addition, porous structure  117  defines at least a portion of a perimeter of vertical and horizontal graft windows  111 ,  113 , as best shown in  FIG. 6B . Porous structure  117  has a porosity that facilitates bone growth. For example, porous structure  117  may have an average pore diameter of 100 to 1000 microns with a 30-80% porosity, but preferably a porosity of 55% to 65%. In addition, a depth of porous structure  117  may be 500 to 4500 microns, but preferably 500 to 1500 microns. Interbody device  110  also includes a solid, non-porous frame that helps provide strength to interbody device  110 . In particular, lateral sidewalls  116 , trailing end  114 , and leading end  112  comprise the solid frame and are thus made of a solid material. The solid frame and porous structure  117  can be made from any biocompatible metal, such as titanium and alloys thereof, and any biocompatible polymer, such as polyether ether ketone (“PEEK”), for example. 
     In addition to the solid frame, interbody device  110  also includes a plurality of solid serrations or teeth  115  that extend from the bone contacting sides. Such serrations  115  are configured to engage vertebral bodies to help limit movement of interbody device  110  while disposed within a disc space. In this regard, serrations  115  are made of a solid material, such as the same solid material that comprises the solid frame, to help provide sufficient strength to engage the bone and retain interbody device  110  relative to the vertebrae. However, in order to help maximize the volume of porous structure  117 , such serrations  115  are embedded in the porous structure  117  and extend therefrom. Such embedment can be achieved through an additive layer manufacturing (“ALM”) process, such as 3D printing, so that no separate connection mechanism is necessary to bring together any of the components of interbody device  110 . In some examples, ALM processes are powder-bed based and involve one or more of selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM), as disclosed in U.S. Pat. Nos. 7,537,664; 8,728,387; 9,180,010; and 9,456,901 as well as U.S. Patent Publication No. 2006/0147332, each of which is hereby incorporated by reference in their entireties herein. Other methods of ALM, which can be used to form the herein described implants, include stereolithography (SLA), fused deposition modeling (FDM), and continuous liquid interface production (CLIP). 
     Vertebral plate assembly  130 , as depicted in  FIGS. 3A and 3B , generally includes a bone plate  140 , screw blockers  160 , and a connection screw  170 . Plate  140  has a first side or bone contacting side and a second side or tool engagement side. The bone contacting side has a bone contacting surface or inner surface  144  that is concavely curved while the tool engagement side includes an outer surface  142  that is convexly curved so as to help conform plate  140  to the rounded outer surface of a vertebral body. The bone contacting side includes bosses or cylindrical projections  146  that extend from inner surface  144 . 
     Plate  140  defines a plurality of openings that extend into and/or through plate  140  from the tool engagement side to the bone contacting side. Such openings include bone screw openings  150   a - b , screw blocker openings  152   a - b , connection screw opening  154 , and smooth bores/openings  156 . Bone screw openings  150   a - b  extend through outer and inner surfaces  142 ,  144  and are configured to receive a bone screw  102  therein such that a head  101  of bone screw  102  is positioned beneath outer surface, as shown in  FIG. 1A . 
     Connection opening  154  is positioned between bone screw openings  150   a - b  and is aligned with bone screw openings  150   a - b  along a longitudinal axis of plate  140 . However, in some embodiments, first bone screw opening  150   a  may be offset medially from connection opening while second bone screw opening  150   b  may be offset laterally, and vice versa. As shown in  FIG. 3C , connection screw opening  154  is comprised of a plurality of sections  154   a - d . A first section  154   a  extends through inner surface  144  while a fourth section  154   d  extends through outer surface  142 . Second section  154   b  is adjacent to first section  154   a , and third section  154   c  is adjacent to fourth section  154   d  and second section  154   b . Second and third sections  154   b - c , or intermediate sections, each have larger cross-sectional dimensions than that of first and fourth sections  154   a ,  154   d . In addition, third section  154   c  has a larger cross-sectional dimension than second section  154   b . These differences in cross-sectional dimensions form shoulders within connection screw opening  154 . In particular, a first shoulder  141   a  is formed between first and second sections  154   a - b , and a second shoulder  141   b  is formed between third and fourth sections  154   c - d . First shoulder  141   a  faces toward outer surface  142  while second shoulder  141   b  faces toward inner surface  144 . In the embodiment depicted, sections  141   a - d  are cylindrical. However, in some embodiments one or more of such sections  141   a - d  may be conical. 
     Screw blocker openings  152   a - b  are each positioned adjacent to an associated bone screw opening  150   a - b  and extend through an associated recessed region  151  of plate  140 . Such recessed region  151 , as best shown in  FIGS. 4F and 4H , is shaped to accommodate a blocker head  162  of a screw blocker  160 , as described in more detail below, such that screw blocker head  162  at least partially resides within recessed region  151 . Screw blocker openings  152   a - b  each include first, second, and third sections  149   a - c , as best shown in  FIG. 4C . First section  149   a  extends through inner surface  144 , and third section  149   c  is adjacent to recessed region  151 . Second section  149   b  is intermediate first and third sections  149   a ,  149   c . Second and third sections  149   b - c  are cylindrical while first section  149   a  is conical. In addition, third section  149   c  includes two semi-cylindrical indentations/grooves  145   a - b  that extend along the length of third section  149   c  and are circumferentially offset from each other, as best shown in  FIG. 4E . Third section  149   c  also has a cross-sectional dimension greater than that of second section  149   b  which forms a shoulder  148  that faces toward outer surface  142  of plate  140 . It should be understood that in some embodiments, blocker openings  152   a - b  may only include first and third sections  149   a ,  149   c  as first section  149   a  may have a conical taper that intersects with the third section  149   c.    
     Smooth bores/openings  156  extend through outer surface  142  and partially into plate  140  such that smooth bores  156  are blind openings. Smooth bores  156  are aligned with connection screw opening  154  in a mediolateral direction. However, in some embodiments, smooth bores  156  may be positioned such that axes thereof are offset superiorly-inferiorly relative to an axis of connection screw opening  154 . Also, as shown in  FIG. 3C , each of bores  156  have an axis that coaligns with an axis of a corresponding boss  146 . 
     Screw blockers  160 , as depicted in  FIGS. 4A and 4B , each include a blocker head or proximal end  162  and a blocker body extending from head  162 . The blocker body includes an expansion post or distal end  166  and locking portion or intermediate portion  164 . Blocker head  162  defines a tool engagement opening  161  and is asymmetrically shaped or tear drop shaped so that it forms a lobe  131  that extends radially further from a longitudinal axis of screw blocker  160  than any other portion of blocker head  162  on an opposite side of the longitudinal axis from lobe  131 . 
     Intermediate portion  164  is positioned between blocker head  162  and expansion post  166 . Intermediate portion  164  is substantially cylindrical and is cut such that a recess extends through intermediate portion  164  so as to form a flexible arm or tab  163  that is cantilevered to blocker head  162 . Flexible arm  163  includes a lip or projection  165  that extends radially outwardly therefrom and is moveable in radially inwardly such that, when it is moved radially inwardly, flexible arm  163  is biased to its neutral position, as is shown. 
     Expansion post  166  extends distally from intermediate portion  164  and is substantially cylindrical. A tool opening  169  extends through post  166  toward and, in some embodiments, partially into intermediate portion  164 . A post sidewall  168  extends about tool opening  169  and is deformable such that post  166  is expandable from a cylindrical shape to a conical shape, as described in more detail below. 
     Connection screw  170 , as depicted in  FIGS. 5A and 5B , includes a head  172 , distal shaft  176 , and intermediate shaft  174 . Head  172  includes a tool opening  179  and a plurality of flexible members or tabs  178  that are circumferentially positioned about tool opening  179 . Such flexible members  178  are bendable radially inwardly toward a longitudinal axis of screw  170  but, when bent inwardly, are biased toward their neutral position, as is shown. Flexible members  178  each include a lip or flange  173  that extends radially outwardly therefrom and extends about a perimeter thereof. 
     Intermediate shaft  174  has a smooth outer surface that is substantially cylindrical and a threaded interior opening that includes a left-handed thread  175  that helically extends along the length of intermediate shaft  174 . The threaded interior opening is in axial communication with the tool opening of head  179 . An outer cross-sectional dimension of intermediate shaft  174  is smaller than an outer cross-sectional dimension of head  172  such that a distally facing shoulder  177  is formed therebetween. Distal shaft  176  extends from intermediate shaft  174  and includes a right-handed external thread  171  that helically extends along its length. Such thread  171  corresponds to that of threaded opening  119  of interbody device  110 . A major diameter of thread  171  is greater than a major diameter of inner thread  175  of intermediate shaft. 
     When fusion assembly  100  is fully assembled, bosses  146  are positioned within respective ones of smooth bores  118  of interbody device  110 , as best shown in  FIG. 6B . In addition, connection screw  170  extends through connection screw opening  154  of plate  130  and into interbody device  110  such that external threads  171  of distal shaft  176  threadedly engage threaded opening  119  of interbody device  110 . As shown in  FIGS. 5C and 6B , head  172  of connection screw  170  is snap-fit to plate within connection screw opening  154 . In this regard, when being loaded into plate  130 , flexible members  178  are pushed inwardly via lips  173  contacting the narrower fourth section  154   d  of opening  154 . When such lips  173  reach third section  154   c  of connection opening  154 , flexible members  178  snap outwardly to their neutral position. In this position, first shoulder  141   a  of opening  141  abuts shoulder  177  of screw  170  to prevent further distal movement of screw  170 , and second shoulder  141   b  of opening  141  abuts lips  173  to prevent further proximal movement of screw  170 . However, screw  170  remains rotatable relative to plate  130  for threaded connection to interbody device  110 . 
     Also in the fusion assembly  100 , screw blockers  160  are positioned in their respective blocker openings  152   a - d . More particularly, as shown in  FIG. 4C , expansion post  166  of each blocker  160  extends through second section  149   b  of blocker opening  152  and into first section  149   a , intermediate portion  164  is positioned within third section  149   c  of opening  152 , and head  162  is at least partially positioned within recessed region  151 . Screw blockers  160  are connected to plate  140  via deformation of expansion post  166 , which may be performed via a tool  104 , as shown in  FIG. 4D . When tool  104  is advanced into tool opening  169 , a tapered end  106  of such tool  104  causes sidewall  168  to expand outwardly and plastically deform such that post  166  generally conforms to the conical shape of first section  149   a  of blocker opening  152 . This deformation prevents each screw blocker  160  from being removed from their respective opening  152   a - b , but allows for such blockers  160  to be rotated therein. 
     When screw blockers  160  are positioned within their respective openings  152   a - b , such blockers  160  have first and second locked positions associated with indents  145   a - b . In this regard, when blockers  160  are in a first locked or unblocked position, as shown in  FIGS. 4F and 4G , head  162  is positioned within recessed region  151  of plate  140  so that lobe  131  resides in the recessed region  151  and does not cover a bone screw head  101 . In addition, when in the first locked position, lip  165  of flexible arm  163  is positioned in first indentation  145   a  of blocker opening  152 . When blockers  160  are in a second locked or blocked position, as shown in  FIGS. 4H and 4I , lip  165  is positioned within second indent  145   b  and lobe  131  is moved at least partially out of recessed region  151  so that it covers a portion of bone screw  102  head to prevent bone screw  102  from backing out of plate  140 . When transitioning from the first to the second position, or vice versa, an operator uses a tool/driver engaged to blocker head  162  via opening  161  to rotate blocker  160 . Once a predefined torque is achieved, flexible arm is cammed inwardly so that blocker  160  can be rotated to the next position. Once lip  165  reaches the next indentation  145   a  or  145   b , the bias of arm  163  snaps lip  165  into engagement with the other indentation  145   a  or  145   b  to lock blocker  160  in that position. This mechanism not only locks blocker  160  into a desired angular positions relative to bone screw  102 , but it also provides tactile feedback to the operator. Also, it should be understood that connection screw  170  and/or screw blockers  160  may be preloaded into plate  140  prior to delivery to the operating theater so that the operator does not have to assemble the plate during the procedure. 
       FIGS. 7A and 7B  depicts an alternative plate assembly  130 ′. Plate assembly  130 ′ differs from plate  130  in that it is configured to only be connected to one vertebra via a bone screw  102  rather than two. In this regard, plate assembly  130 ′, while including connection screw  170  and bosses (not shown) for connection to implant  110 , only includes one bone screw opening  150  and one associated screw blocker  160 . 
       FIGS. 8-11  illustrate an insertion/extraction system  10  according to an embodiment of the present disclosure. Insertion/extraction system  10  is configured to insert interbody device  100  into an intervertebral disc space and extract interbody device  100  therefrom. System  10  is also configured to insert plate assembly  130  into the patient/mammalian subject and connect plate assembly  130  to interbody device  100  in-situ, as described in more detail below. System  10  includes an inserter/extractor  200 , an adapter  300 , and a slap hammer  400 . 
     Inserter/extractor or insertion tool  200 , as depicted in  FIGS. 9A-9I , generally includes an outer member  210  and an inner member  250 . Outer member  210  includes a handle  202 , insertion end  220 , adaptor end  230 , and rigid shaft  214 . Insertion end  220  is positioned at a distal end of rigid shaft  214  and is crescent shaped such that it has a concave distal facing surface  221 , as best shown in  FIG. 9H . Insertion end  220  includes a pair of bosses  222  extending distally therefrom for insertion into smooth bores  118 ,  156  of interbody device  110  and plate  140 . Inserter/extractor  200 , as shown, is an angled inserter/extractor such that insertion end  220  is angled relative to rigid shaft  214 , as best shown in  FIG. 9D . In other words, in some embodiments rigid shaft  214  may be bent just proximal of insertion end  220  to allow for interbody device  110  to be inserted into an intervertebral space from certain locations relative to such disc space, while in other embodiments rigid shaft  214  may not be bent so that interbody device  110  can be inserted from other locations relative to disc space. 
     Handle  212  is located at a proximal end of rigid shaft  214  and generally has more girth than rigid shaft  214  so as to easily fit in an operator&#39;s hand. Adaptor end  230  is located at a proximal end of handle  212  and includes threaded openings  232  and spring-ball mechanisms  236 . Spring-ball mechanisms  236  each include a spring  238  and ball bearing  239  housed in adaptor end  230  and are positioned proximal of threaded openings  232 , although in some embodiments this may be reversed. Spring-ball mechanisms  236 , as well as threaded openings  232 , are positioned at opposite sides of a longitudinal axis of inserter/extractor  200 . A longitudinal bore  235  extends entirely through outer member  210  along the longitudinal axis thereof from adapter end  230  to insertion end  220  so that such bore  235  extends through concave surface  221 , even where outer member  210  is angled. However, bore  235  abruptly narrows in dimension just proximal of concave surface  221  of insertion end  220 . In other words, bore  235  has a first cross-sectional dimension greater than a second cross-sectional dimension of bore  235 . Bore  235  has the second cross-sectional dimension at a distal terminal end thereof where bore  235  extends through concave surface  221 . This difference in cross-section forms a shoulder  226 , as best shown in  FIGS. 9D and 9I . Ball bearings  239  of spring-ball mechanisms  236  communicate with bore  235  at a proximal end thereof, and threaded openings  232  extend from an exterior of adapter end  230  toward bore. 
     Inner member or first inner member  250  generally includes an elongate shaft  252 , knob  254 , and a connection end  260 . A longitudinal bore  268  may extend through connection end  260  and into elongate shaft such that inner member  250  can receive a guidewire, as best shown in  FIG. 9F . Knob  254  is located at a proximal end of elongate shaft  252  and is located adjacent a groove  253  on elongate shaft  214  that is configured to receive ball bearings  239  of the ball-spring mechanisms  236  of outer member  210  so as to form a ball-detent mechanism that allows inner member  250  to be removably connected to outer member  210 . Connection end  260  is located at a distal end of elongate shaft  252  and includes a threaded tip  264  and a flexible portion  262 , as best shown in  FIG. 9F . Flexible portion  262  is more proximal than threaded tip  264  and may be a coil, spring, goose neck, or the like so that threaded tip  264  can be angled relative to elongate shaft  252 . This allows inner member  250  to extend through bore  235  of outer member  210  even when outer member  210  is angled. Thus, in embodiments where outer member  210  is not angled, inner member  250  may not include flexible portion  262 . Elongate shaft  252 , including flexible member  262 , has a larger cross-sectional dimension than a minor diameter of threaded tip  264 , which forms a shoulder  266 . Threaded tip  264  also has threads  265  with a first major diameter which is particularly configured for threaded connection with threaded opening  119  of interbody device  110 . 
     A second inner member  250 ′ is shown in  FIG. 9G  and includes an alternative threaded tip  260 ′ that is particularly configured for threaded connection with threaded opening of connection screw  170 . In this regard, inner member  260 ′ has second major diameter smaller than that of inner member  260 . Also, threads  265 ′ of threaded tip  260 ′ are left-handed threads whereas threads  265  of first inner member  260  are right-handed threads. However, inner member is otherwise similarly configured such that it may include a flexible portion and shoulder  266 , as shown. 
     When inserter/extractor  200  is assembled, inner member  250  extends through bore  235  of outer member  210  so that threaded tip  264  of inner member  250  extends from insertion end  220  and is positioned between bosses  222 , as best shown in  FIG. 9H . Flexible portion  262  of inner member  250  allows inner member  250  to conform to the angled outer member  210 . In addition, shoulder  226  of outer member  210  provides a distal limit for inner member  250  such that shoulder  266  of inner member  250  abuts shoulder  226  before the entirety of threaded tip  264  can extend from bore  235 . Inner member  250  is removably connected via ball bearings  239  of spring-ball mechanisms  236  being positioned in groove  253  at the proximal end of elongate shaft  252 . However, this allows knob  254  to rotate inner shaft  252 . As such, interbody device  110  can be connected to inserter/extractor  200  by threadedly engaging threaded opening  119  via threaded tip  264  by rotating knob  254 . This pulls interbody device  110  into engagement with concave surface  221  and onto bosses  222  so that such bosses  222  are each positioned within a corresponding smooth bore  118  of interbody device  110  thereby providing anti-rotation. In addition to drawing interbody device  110  onto insertion end  220 , shoulders  226  and  266  are brought into firm contact. Such shoulder-to-shoulder contact helps protect threads  265  during insertion and flexible portion  262  during extraction of interbody device  110 . In particular, the flexible construction of flexible portion  262  is less robust than a rigid counterpart and is, therefore, prone to damage when stressed. However, the shoulder-to-shoulder contact mentioned above helps ensure undue stresses are not applied to flexible portion  262  during extraction, as described in more detail below. 
       FIGS. 10A-10E  illustrate an adapter  300  that can be coupled to inserter/extractor  200 . Adapter  300  has a body  302  with a hollow compartment  308  therein that is configured to receive the proximal end of inserter/extractor  200 , including knob  254 . Adapter  300  also includes a spring  312 , piston or threaded shaft  316 , washer or bushing  322 , and knob  304 . A post  306  extends from body  302  and has a transverse opening  305  in communication with hollow compartment  326 . In the embodiment shown, post  306  is substantially cylindrical. Post  306  is capped with knob  304 . However, spring  312 , threaded shaft  314 , and bushing  322  are positioned within post  306  such that spring  312  bears on an annular collar  318  of threaded shaft  314  and an inner shoulder  303  of post  306 . In addition, bushing  322  is positioned at one end of post opening  305  so that collar  318  is positioned between shoulder  303  and washer  322 . Thus, spring  312  exerts a biasing force on shaft  314  that biases collar  318  toward bushing  322  and, consequently, also biases a threaded end  316  of shaft  314  away from hollow compartment  308 . However, when this bias is overcome, threaded end  316  of shaft  314  can be moved into hollow compartment  308 . Threaded shaft  316  also includes a projection  320  at the opposite end of shaft  314  from threaded end  316 . In the embodiment shown, projection  320  has a “D” shape. In this regard, projection  320  couples shaft  314  to knob  304 , as knob  304  has an opening  307  of corresponding size and shape to that of projection  320 . Thus, the flat surface of the D-shaped projection  320  allows the shaft  314  to be engaged with knob  304  such that when knob  304  is rotated, shaft  314  will also rotate. The shape of projection  320  can be any shape, though, that allows for such rotation, such as star shaped, hex shaped, and the like. Thus, in other embodiments projection  320  may have a different shape. 
     Adapter  300  can be connected to inserter/extractor  200 . In this regard, adapter  300  is placed over knob  254  and adapter end  230  of outer member  210  such that the same is received within hollow compartment  308 , as best shown in  FIG. 10C . A laser mark or indicia  310  on handle  302  of adapter  300  and a corresponding laser mark on outer member  210  (not shown) allow for proper orientation of adapter  300 . This helps ensure that the threaded shaft  264  aligns with one of threaded openings  232  in inserter/extractor  200 . A corresponding taper of adapter end  230  of outer member  210  and hollow compartment  308  also allow threaded shaft  316  to align with threaded openings  232  in the proximal-distal direction. Once threaded shaft  314  is aligned with a threaded opening  232 , knob  304  can be pushed inwardly along the longitudinal axis of post  306  and in a direction towards hollow compartment  308  to overcome the bias of spring  312 . This causes knob  304  to advance threaded end  316  of shaft  314  into threaded opening  232  of inserter  200 . Knob  304  is then rotated, while the push force is exerted on it, in order to engage threaded end  316  with threads  234  of threaded opening  232 , as best shown in  FIGS. 10D and 10E . 
       FIG. 11  depicts an embodiment of slap hammer  400 . Slap hammer  400  includes a guide rod  406 , sliding weight  408 , and distal and proximal bumpers  404 ,  410 . Guide rod  406  is substantially cylindrical. Sliding weight  408  has a throughbore (not shown) extending along its longitudinal axis, the diameter of which is at least slightly larger than that of guide rod  406  so that weight  408  can slide on rod  406 . Guide rod  406  is positioned within the longitudinal throughbore of sliding weight  408  and extends past the proximal and distal end of sliding weight  408 . Bumpers  404 ,  410  are positioned at each end of guide rod  406  so that sliding weight  408  can slide proximally and distally along guide rod  406 , between bumper  404  and bumper  410 . Thus, as sliding weight  408  bumps into bumpers  406 ,  408 , a force is exerted on shaft  406 . A threaded projection  402  extends distally from distal bumper  404  and along the longitudinal axis of shaft  406 . Threaded projection  402  is configured to threadedly connect with a threaded opening  324  of adapter so that force caused by bumping weight  408  into proximal bumper  410  is transferred through adapter  300  when connected to slap hammer  400 . 
     In a method of implanting fusion assembly  100 , an operator accesses a target intervertebral disc between adjacent vertebrae and approaches such disc via a desired approach, such as a lateral or anterior approach, for example. The intervertebral disc is either completely are partially removed leaving a space available for the insertion of interbody device  110 . 
     Thereafter, interbody device  110  is connected to inserter/extractor  200 . This is achieved by inserting inner member  250  into bore  235  of outer member  210  such that threaded tip  264  extends from insertion end  220  of outer member  210  and such that ball-spring mechanisms  236  engage groove  253 . Threaded tip  264  is threaded into threaded opening  119  and bosses  222  are positioned within smooth bores  118 . It should be understood that interbody device  110  can be placed onto bosses  222  first and then threaded tip  264  is thereafter threaded to device  110 , in which case spring-ball mechanisms  236  engage groove  253  once interbody device  110  is fully seated against concave surface  221 . However, threaded tip  264  can thread into threaded opening  119  first after ball-detent mechanism is engaged so that interbody device  110  is drawn onto bosses  222  and into contact with concave surface  221 . 
     Once interbody device  110  is connected to inserter/extractor  200 , operator uses inserter/extractor  200  to insert interbody device  110  into the disc space. To assist in insertion, knob  254  of inner member  250  can be impacted at the proximal end thereof via a mallet or the like. Due to the abutment between shoulders  226  and  266  (see  FIG. 9G ) and connection of knob  254  to outer member  210 , the force from the impacts is transferred from inner member  250  to outer member  210  to interbody device  110 . In this regard, threads  265  are shielded from stresses imposed by such impacts. 
     After interbody device  110  is positioned within the disc space, it may be determined that interbody device  110  is not optimally positioned. In this regard, interbody device  110  can then be extracted from the disc space and reinserted. Removal of implant  100  includes aligning indicia  310  of adapter  300  with indicia on outer member  200 . This alignment ensures the alignment of the threaded portion  316  of shaft  314  with threaded opening  234  of adapter end  230 , thus allowing adapter  300  to be coupled to outer member  210 . Adapter  300  is then moved distally such that it slides over knob  254  and adapter end  230  of outer member  200 . Knob  254  and adapter end  230  are then located within hollow compartment  308 . An inward force is then exerted on knob  304 , compressing spring  312 , and inserting threaded portion  316  into threaded opening  232 , as best shown in  FIGS. 10D and 10E . Knob  304  is then rotated to engage threads  234  of threaded opening  232 , thereby coupling adapter  300  to outer member  210 . 
     Slap hammer  400  may then be coupled to adapter  300  by inserting threaded projection  402  into threaded opening  324  and engaging the threads therein by rotating guide rod  326 . Sliding weight  408  is then moved proximally along guide rod  406  and slammed against proximal bumper  410  to exert a force on system  10  to remove implant  100 . Again, due to abutment between shoulders  226  and  266  the force from the impact, however, is re-distributed away from inner member  250  and flexible portion  262  and exerted primarily on outer member  210  and adapter  300  thereby protecting flexible portion  262  from damage. In other words, without the shouldering feature (i.e., direct contact between shoulders  226  and  266 ), the pull force exerted by slap hammer  400  on outer member  210  would serve to move outer member  210  away from the disc space while compression of interbody device  110  within the disc space would provide an opposing force which would be applied to inner member  250  resulting in tension applied to flexible portion  262  of inner member  250  potentially damaging it. However, the shouldering feature transfers forces applied to inner member  250  to outer member  210  before such forces are transferred as tension to flexible member  262 . Thus, the shouldering feature shields flexible member  262  from potentially damaging stress during removal of interbody device via slap hammer  400 . Adapter  300  also helps shield flexible member  262  from damage by transferring pull forces from slap hammer  400  directly to outer member  210 . In other words, if slap hammer  400  were connected to inner member  250  instead of outer member  210  via adapter  300 , such as via knob  254 , then pull forces from slap hammer  400  would be transferred to inner member and, consequently, to flexible portion  262  potentially damaging the same. Thus, adapter  300  and the shouldering features help protect flexible portion  262  of inner member  262 . 
     Once interbody device  110  is removed from the disc space, slap hammer  400  may be disconnected from adapter  300  by unthreading it from adapter  300 . Adapter  300  is removed from outer member  210  by rotating knob  307  counterclockwise to disengage threaded shaft  314  from threaded opening  234  in outer member  210 . Spring  312  snaps threaded shaft  314  and knob  304  back to their neutral position after threads of threaded end  316  are fully disengaged which provides feedback to the operator that adapter  300  can then be slid off of the proximal end of inserter/extractor  200 . Adapter  300  is then removed from inserter/extractor  200 . Thereafter, interbody device  110  can be reinserted back into the disc space in the desired location via impacting inserter/extractor  200  as discussed above. 
     After interbody device  110  is positioned within the disc space, knob  254  can be rotated to disengage threaded tip  264  of inner member  250  from interbody device  110  and outer member  250  bosses  222  can be pulled clear from smooth bores  118 . First inner member  250  is then removed from outer member  210 , and second inner member  250 ′ is inserted into outer member  210 . Plate assembly  130  is placed adjacent to insertion end  220  of inserter/extractor  200 , bosses  222  are positioned within smooth bores  118  of plate  140 , threaded tip  264 ′ is inserted into tool opening  179  of connection screw  170 , and knob  254  is rotated counterclockwise to thread tip  264 ′ into connection screw  170 . 
     Thereafter, plate assembly  130  is guided to the disc space so that it is positioned adjacent trailing end of interbody device  110 . Plate assembly  130  is then connected to interbody device  110  by inserting bosses  146  of plate  140  into smooth bores  118  of interbody device  110  and rotating knob  254  clockwise which rotates connection screw  170  to threadedly engage distal shaft  176  of screw  170  with threaded opening  119 . Due to the snap-fit of connection screw  170  to plate  140 , plate  140  is drawn toward interbody device  110  and vertebrae so that bone screw openings  150   a - b  are each positioned adjacent a respective vertebra. Once a certain amount of torque is reached between connection screw  170  and interbody device  110 , threads  170  of distal shaft  176  begin to unthread from threaded opening  119  allowing inserter/extractor  200  to be disconnected from plate assembly  130 . This is made possible by the right-handed threads of interbody device  110  and threaded end  176  of connection screw  170  and the left-handed threads  265 ′ of second inner member  250 ′ and inner threads  175  of connection screw  170 . Once inserter/extractor  200  is fully disconnected from plate assembly  130 , a driver instrument (not shown) may then be used to further tighten the connection between plate assembly  130  and interbody device  110 . Bone screws  102  are inserted through respective bone screw openings  150   a - b . This can be done while plate assembly  130  is connected to inserter/extractor  200  or afterward. Either way, bosses  146  help maintain plate&#39;s orientation relative to vertebrae and interbody device  110  during bone screw insertion and tightening of connection screw  170 . Once bone screws  102  are fully seated, screw blockers  160  are operated to block bone screws  102  from back-out. This is achieved by engaging a driver to heads  162  of screw blockers  160  and rotating the same to overcome the bias of flexible arm  163  so that screw blockers  160  are rotated from the unblocked position to the blocked position in which lobe  131  of each blocker  160  is positioned over its respective screw head  101 . 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.