Patent Publication Number: US-2004059318-A1

Title: Instrument and method for surgical extraction

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This invention claims priority to the U.S. Provisional Application No. 60/412,183 filed Sep. 20, 2002, entitled “Surgical Instrument and Method for Extraction of an Implant”, which is incorporated herein by reference. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates generally to the field of surgical instrumentation and methods, and more particularly to instruments and methods for surgical extraction.  
       BACKGROUND  
       [0003] In the treatment of diseases, injuries or malformations affecting spinal motion segments, and especially those affecting the intervertebral disc, it has long been known to remove some or all of a degenerated, ruptured or otherwise failing vertebral tissue. In cases involving intervertebral disc tissue that has been removed or is otherwise absent from a spinal motion segment, corrective measures are typically used to ensure proper spacing between the adjacent vertebrae formerly separated by the removed disc tissue.  
       [0004] Various types and configurations of implants have been developed for maintaining proper spacing of the intervertebral disc space. For example, artificial disc devices have been developed for maintaining proper spacing of the intervertebral disc space while allowing a certain degree of relative movement between the adjacent vertebrae. Such devices usually include superior and inferior implant components that are engaged to respective upper and lower vertebrae with certain type of articular element disposed therebetween to allow the adjacent vertebrae to pivot, rotate and/or translate relative to one another.  
       [0005] In some instances, it may become necessary to remove or extract the spinal implant from the intervertebral disc space. For example, the spinal implant may require maintenance or possible replacement by a different type or configuration of implant. Thus, there is a general need in the industry to provide surgical instruments and methods for the extraction of a spinal implant from the intervertebral disc space. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.  
       SUMMARY  
       [0006] The present invention relates generally to instruments and methods for surgical extraction. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the several embodiments disclosed herein are described briefly as follows.  
       [0007] In one embodiment, a surgical instrument for extracting a prosthetic device includes a distal portion transitionable from an insertion configuration to an extraction configuration, wherein the insertion configuration is adapted for displacement along a portion of a prosthetic device, and the extraction configuration is adapted for engaging and extracting the prosthetic device, and a proximal portion connected to the distal portion.  
       [0008] In another embodiment, an instrument for surgical extraction includes at least one extraction prong wherein the at least one extraction prong comprises a transverse flange, and a mounting portion wherein the at least one extraction prong is secured to the mounting portion.  
       [0009] In a third embodiment, a method for surgical extraction includes inserting a surgical instrument having a distal portion transitionable from an insertion configuration to an extraction configuration; transitioning the distal portion to the extraction configuration; engaging the distal portion with an implant; and exerting an extraction force to extract the implant. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 is a side perspective view of a surgical instrument according to one embodiment of the present invention.  
     [0011]FIG. 2 is a perspective view of the distal end portion of the surgical instrument illustrated in FIG. 1.  
     [0012]FIG. 3 a  is a side cross-sectional view of the distal portion of the surgical instrument illustrated in FIG. 2 in an insertion configuration.  
     [0013]FIG. 3 b  is a side cross-sectional view of the distal portion of the surgical instrument illustrated in FIG. 2 in an extraction configuration.  
     [0014]FIG. 4 is a view of a mounting block according to one embodiment of the present invention.  
     [0015]FIG. 5 is an end view of the mounting block illustrated in FIG. 4.  
     [0016]FIG. 6 is a cross-sectional view of the mounting block illustrated in FIG. 4, as viewed along line  6 - 6  of FIG. 4.  
     [0017]FIG. 7 is a view of a first engaging member according to one embodiment of the present invention.  
     [0018]FIG. 8 is a side view of the first engaging member illustrated in FIG. 7.  
     [0019]FIG. 9 is a view of a second engaging member according to one embodiment of the present invention.  
     [0020]FIG. 10 is a side view of the second engaging member illustrated in FIG. 9.  
     [0021]FIG. 11 is a side perspective view of one embodiment of an implant suitable for extraction by the surgical instrument illustrated in FIG. 1.  
     [0022]FIG. 12 is a side perspective view of the distal end portion of the surgical instrument illustrated in FIG. 1 and the implant shown in FIG. 11.  
     [0023]FIG. 13 is a partial sectional view of the implant shown in FIG. 1 disposed between upper and lower vertebrae, with the distal end portions of the first and second engaging members positioned between first and second components of the implant in a compressed, insertion configuration.  
     [0024]FIG. 14 is a partial sectional view of the implant shown in FIG. 11 disposed between the upper and lower vertebrae, with the distal end portions of the first and second engaging members positioned adjacent posterior end surfaces of the implant in an expanded, extraction configuration. 
    
    
     DETAILED DESCRIPTION  
     [0025] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended, such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated herein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
     [0026] Referring now to FIG. 1, shown therein is a surgical instrument  20  according to one embodiment of the present invention for extraction of an implant. The surgical instrument  20  extends generally along a longitudinal axis L, and comprises a proximal portion, which may be an elongated portion  22 , and a distal portion  24 . The distal portion  24  is attached to the distal end of the elongated portion  22 , and is configured to engage an implant for subsequent extraction, the details of which will be described below. The surgical instrument  20  maybe useful in extracting a spinal implant from a vertebral space, and more specifically from an intervertebral disc space between adjacent vertebral bodies. It should be understood, however, that the surgical instrument  20  may also be used to extract implants from other portions of the spinal column or in applications outside of the spinal field. For example, it may be used to extract any type of implants, prosthetic devices, tissues, or organs from any anatomical region of an animal body.  
     [0027] In one embodiment of the invention, the elongated portion  20  includes a shaft member  30  and a handle member  32 . The shaft member  30  and the handle member  32  may comprise a substantially or partially rigid material, such as titanium, stainless steel or other medical grade materials. The shaft member  30  may comprise a variety of configurations, such as a generally linear, axial, angled or curvilinear configuration. The handle member  32  is removably coupled to the proximal end of the shaft member  30  by a coupling member  34 .  
     [0028] In one embodiment, the coupling member  34  is integrally formed with the shaft member  30 , and comprises an internally threaded sleeve configured to receive a threaded end portion  35  of the handle member  32  therein to removably attach the handle member  32  to the shaft member  30 .  
     [0029] In other embodiments, the shaft member  30  and the handle member  32  may be coupled together by other conventional connecting means, or may alternatively be integrally formed as a single-piece, unitary structure.  
     [0030] In one embodiment, the handle member  32  may comprise a gripping portion  36  and a connector portion  38 . The connector portion  38  is adapted for connecting various types of instruments or devices to the surgical instrument  20 . In one embodiment, the connector portion  38  is a Hudson-type connector; however, it should be understood that other types and configurations of connectors are also contemplated.  
     [0031] In one embodiment, the distal portion  24  of the surgical instrument  20  comprises a mounting portion  40  and an engaging portion  50 . The mounting portion  40  serves to couple the engaging portion  50  with the distal end of the shaft member  30 . As will be described in details below, the engaging portion  50  is transitionable from an insertion configuration adapted for displacement along a portion of an implant, to an extraction configuration adapted for engaging and extracting the implant from a vertebral space.  
     [0032] In one embodiment, the engaging portion  50  is transitioned from the insertion configuration to the extraction configuration via expansion or displacement of a distal end portion of the engaging portion  50  generally along the transverse axis T.  
     [0033] Referring now to FIG. 2, shown therein are additional details regarding the distal portion  24  of the surgical instrument  20 . In one embodiment, the mounting portion  40  generally comprises a mounting block  42  and a connector stem  44 . As will be described in greater details below, the mounting block  42  is adapted to support the engaging portion  50 , and includes a number of transverse openings  45   a - 45   c  extending therethrough and an axial slot  47  extending from the distal end of the block  42  and intersecting the transverse openings  45   a - 45   c . As will be discussed below, the connector stem  44  is adapted for engaging the shaft member  30  to secure the distal portion  24  of the surgical instrument  20  to the elongated portion  22 .  
     [0034] In one embodiment, the engaging portion  50  comprises first and second engaging members  60 ,  70 , each extending generally along the longitudinal axis L. The first engaging member  60  includes a first pair of extraction prongs  62   a ,  62   b  extending axially from a mounting plate  64 . The second engaging member  70  includes a second pair of extraction prongs  72   a ,  72   b  extending axially from a mounting plate  74 . It should be understood, however, that each of the first and second engaging members  60 ,  70  may include any number of extraction prongs, including a single extraction prong or three or more extraction prongs. It is also contemplated that the engaging portion  50  may comprise a fewer or greater number of engaging members.  
     [0035] In furtherance of the present example, the mounting plates  64 ,  74  of the respective engaging members  60 ,  70  are inserted within the axial slot  47  in the mounting block  45  in an overlapping relationship, with the second pair of extraction prongs  72   a ,  72   b  positioned intermediate the first pair of extraction prongs  62   a ,  62   b . In one embodiment, the engaging members  60 ,  70  are secured to the mounting block  42  via a number of pins or fasteners  80   a - 80   c  passing through corresponding ones of the transverse openings  45   a - 45   c  in the mounting block  42  and corresponding openings  65   a - 65   c ,  75   a - 75   c  extending through the mounting plates  64 ,  74 , respectively (FIGS. 7 and 9). In another embodiment, the pins  80   a - 80   c  may be replaced with various types of conventional fasteners, such as screws, bolts or rivets, to secure the engaging members  60 ,  70  to the mounting block  42 . In yet another embodiment, the engaging members  60 ,  70  may be directly attached to the mounting block  42  by any conventional means, such as by welding or by an adhesive. In still another embodiment, the engaging members  60 ,  70  may be integrally formed with the mounting block  42  to define a single-piece, unitary structure.  
     [0036] In one embodiment, the distal end portions of the extraction prong  62   a ,  62   b  may be turned or bent over to define a pair of transverse flanges or lips  66   a ,  66   b . Similarly, the distal end portions of the extraction prong  72   a ,  72   b  may be turned or bent over to define a pair of transverse flanges or lips  76   a ,  76   b . As will be discussed below, the transverse flanges  66   a ,  66   b  and  76   a ,  76   b  may each have a hook-shaped configuration or other shapes adapted to engaging a portion of an implant for subsequent extraction. In one embodiment, the first pair of transverse flanges  66   a ,  66   b  and the second pair of transverse flanges  76   a ,  76   b  extend in a generally opposite directions, the purpose of which will be discussed below.  
     [0037] The engaging members  60 ,  70  are at least partially formed of a relatively flexible, resilient material that is capable of being transitioned from a compressed, insertion configuration to an expanded, extraction configuration. In one embodiment, the engaging members  60 ,  70  comprise type 420 stainless steel. However, it should be understood that other materials are also contemplated, including but not limited to other types of stainless steel, titanium, elastomer, polymer, composite materials or shape memory alloys.  
     [0038] Referring now to FIGS. 3 a  and  3   b , shown therein is the distal portion  24  of the surgical instrument  20 , as illustrated in a compressed, insertion configuration and an expanded, extraction configuration, respectively.  
     [0039] Referring specifically to FIG. 3 a , the extraction prongs  62   a ,  62   b  of the engaging member  60  and the extraction prongs  72   a ,  72   b  of the engaging member  70  may be inwardly compressed (toward longitudinal axis L) in the direction of transverse axis T to define the compressed, insertion configuration. In that compressed configuration, the engaging members  60 ,  70  define a reduced transverse profile having a compressed height h1 to facilitate the insertion of the extraction instrument  20 .  
     [0040] Referring specifically to FIG. 3 b , when the compression force exerted on the extraction prongs  62   a ,  62   b  and  72   a ,  72   b  is released, the engaging members  60 ,  70  are outwardly displaced in the direction of transverse axis T to define the expanded, extraction configuration. In that expanded configuration, the engaging members  60 ,  70  define an increased transverse profile having an expanded height h2. The increased transverse profile facilitates engagement of the flange portions  66   a ,  66   b  of the engaging member  60  and the flange portions  76   a ,  76   b  of the engaging member  70  with a corresponding portion of the implant, the details of which will be described below.  
     [0041] As discussed above, the engaging members  60 ,  70  may comprise a shape-memory material, such as a shape-memory alloy (“SMA”), to aid in transitioning the engaging members  60 ,  70  from the insertion configuration (FIG. 3 a ) into the extraction configuration (FIG. 3 b ). More specifically, SMAs are known to exhibit a characteristic or behavior in which a particular component formed of an SMA is capable of being deformed from an initial “memorized” shape or configuration to a different shape or configuration, and then transitioned back toward the initial, memorized shape or configuration. If the engaging members  60 ,  70  comprise an SMA material and are compressed to the insertion configuration while at a temperature above the transformation temperatures of the SMA material, the engaging members  60 ,  70  will automatically recover or transition back toward the extraction configuration when the compression force is removed. This phenomenon is sometimes referred to a stress-induced martensitic (“SIM”) transformation. It will be understood that shape memory alloys and their properties are known in the art, and will only be briefly described herein.  
     [0042] While there are many alloys that exhibit shape-memory or SIM characteristics, one of the more common SMAs is an alloy formed of nickel and titanium. One such well-known SMA is Nitinol, which has proven to be highly effective for instruments and devices used in association with an animal body. Depending on its composition and treatment, transformation temperature range generally may fall between room temperature and normal human body temperature (i.e., about 35-40 degrees Celsius). Moreover, Nitinol has a very low corrosion rate and excellent wear resistance, thereby providing an additional advantage when used in association with the animal body. It should be understood, however, that SMA materials other than Nitinol are also contemplated for use in association with the present invention.  
     [0043] Referring now to FIGS.  4 - 6 , shown therein are additional details regarding the mounting portion  40  of the surgical instrument  20 . The mounting portion  40  may comprise a substantially rigid material, such as titanium, stainless steel or other substantially rigid medical grade materials. As discussed above, the mounting portion  40  generally comprises a mounting block  42  and a connector stem  44 .  
     [0044] In one embodiment, the mounting block  42  has a generally rectangular configuration; however, other shapes and configuration are also contemplated. The mounting block  42  includes three transverse opening  45   a - 45   c  extending therethrough which are sized to receive corresponding ones of the pins  80   a - 80   c  therein. In one embodiment, the openings  45   a - 45   c  are arranged in a triangular hole pattern. However, it should be understood that other hole patterns are also contemplated. It should also be understood that the mounting block  42  may define any number of transverse openings, including a single opening, two openings or four or more openings.  
     [0045] In furtherance of the embodiment, each of the transverse openings  45   a - 45   c  may have an inner diameter substantially equal to the outer diameter of each of the pins  80   a - 80   c . The pins  80   a - 80   c  are press fit into the openings  45   a - 45   c  to permanently engage the pins  80   a - 80   c  within the openings  45   a - 45   c , and to securely attach the engaging members  60 ,  70  to the mounting block  42 . Each end of the openings  45   a - 45   c  defines a chamber  46  opening onto the outer surface of the mounting block  42  to facilitate insertion of the pins  80   a - 80   c  and/or to aid in the press fitting process. The mounting block  42  may also include an axial slot  47  extending partially therethrough and intersecting each of the transverse openings  45   a - 45   c . The axial slot  47  may have a width sized to snuggly receive the mounting plates  64 ,  74  of the engaging members  60 ,  70  therein in an overlapping relationship (FIG. 6).  
     [0046] In one embodiment, the connector stem  44  extends perpendicularly from the mounting block  42  and has a generally cylindrical configuration; however, other shapes and configurations are also contemplated. In the illustrated embodiment, the connector stem  44  and the mounting block  42  are integrally formed to define a single-piece, unitary mounting portion  40 . However, it should be understood that the connector stem  44  and the mounting block  42  may be formed separately and attached together by various conventional methods, such as welding or fastening. In the illustrated embodiment, the connector stem  44  is removably coupled to the distal end of the shaft member  30  via a threaded connection. Specifically, the connector stem  44  defines a threaded passage  48  sized to receive a threaded end portion (not shown) of the shaft member  30  therein to removably couple the distal portion  24  of the surgical instrument  20  with the elongated portion  22  (FIG. 1). However, in other embodiments of the invention, the connector stem  44  and the shaft member  30  may be coupled together by other connecting means, or may alternatively be integrally formed as a single-piece, unitary structure.  
     [0047] Referring now to FIGS. 7 and 8, shown therein are additional details regarding the first engaging member  60  of the surgical instrument  20 . As discussed above, the first engaging member  60  includes a pair of extraction prongs  62   a ,  62   b  extending axially from the mounting plate  64 . The mounting plate  64  includes three openings  65   a - 65   c  extending therethrough that are arranged in a hole pattern corresponding to the hole pattern of the transverse openings  45   a - 45   c  extending through the mounting block  42 . In one embodiment, the openings  65   a - 65   c  have an inner diameter substantially equal to the outer diameter of the pins  80   a - 80   c . A close match between the openings  65   a - 65   c  and the pins  80   a - 80   c  (FIGS. 3 a  and  3   b ) provides relatively secure and rigid engagement between the first engaging member  60  and the mounting block  42 .  
     [0048] In one embodiment, each of the extraction prongs  62   a ,  62   b  may have a generally rectangular shape and be arranged in a substantially parallel relationship relative to the other. The extraction prongs  62   a ,  62   b  are offset from one another to define an open area therebetween having an inner width w1. In another embodiment, the distal end portions of the extraction prongs  62   a ,  62   b  are turned or bent over to define a respective pair of transverse flanges  66   a ,  66   b  each having a hook-shaped configuration. Each of the flanges  66   a ,  66   b  are arranged at an angle relative to the mounting plate  64 . In one embodiment, the angle falls within a range of about 30 degrees to about 90 degrees. In a specific embodiment, the angle α1 may be about 60 degrees. However, it should be understood that other angles of α1 are also contemplated, including angles less than 30 degrees or greater than 90 degrees. The engagement flanges  66   a ,  66   b  define inner bearing surfaces or edges  67   a ,  67   b , respectively, each facing toward the mounting plate  64 . The engagement flanges  66   a ,  66   b  also define end surfaces  68   a  and  68   b , respectively, each of which may be generally parallel to the mounting plate  64 . As will be described below, the flanges  66   a ,  66   b , and more specifically the bearing surfaces or edges  67   a ,  67   b , are adapted to engage a corresponding portion of an implant for subsequent extraction of the implant.  
     [0049] As discussed above, the engaging member  60  may comprise at least partially a relatively flexible, resilient material so as to facilitate transformation of the engaging member  60  from the compressed configuration illustrated in FIG. 3 a  to the expanded configuration illustrated in FIG. 3 b . In one embodiment, the extraction prongs  62   a ,  62   b  are outwardly biased toward the expanded configuration illustrated in FIG. 3 b . In order to further facilitate the transition from the compressed configuration to the expanded configuration, the extraction prongs  62   a ,  62   b  may include curved intermediate portions  63   a ,  63   b  having a bow-like or arcuate configuration. The intermediate portions  63   a ,  63   b  may function similar to that of a leaf spring, storing energy upon the imposition of a compression force onto the extraction prongs  62   a ,  62   b  and discharging the energy upon the release of the compression force to expand the extraction prongs  62   a ,  62   b . In one embodiment, the interface between each of the extraction prongs  62   a ,  62   b  and the mounting plate  64  defines a rounded corner  69 . The rounded corners  69  serve to strengthen the interconnection between the extraction prongs  62   a ,  62   b  and the mounting plate  64 , and minimize stress concentrations during compression and expansion of the extraction prongs  62   a ,  62   b  and/or to further facilitate transitioning of the extraction prongs  62   a ,  62   b  from the compressed configuration to the expanded configuration.  
     [0050] Referring to FIGS. 9 and 10, shown therein are additional details regarding the second engaging member  70  of the surgical instrument  20  according to one embodiment of the present invention. As discussed above, the second engaging member  70  may include a pair of extraction prongs  72   a ,  72   b  extending axially from the mounting plate  74 . The mounting plate  74  may include three openings  75   a - 75   c  extending therethrough, which are arranged in a hole pattern corresponding to the hole pattern of the transverse openings  45   a - 45   c  extending through the mounting block  42 . In one embodiment, each of the openings  75   a - 75   c  may have an inner diameter that is substantially equal to the outer diameter of each of the pins  80   a - 80   c . A close tolerance between the openings  75   a - 75   c  and the pins  80   a - 80   c  (FIGS. 3 a  and  3   b ) provides relatively secure and rigid engagement between the second engaging member  70  and the mounting block  42 .  
     [0051] In one embodiment, the extraction prongs  72   a ,  72   b  have generally rectangular shapes and are arranged in a substantially parallel relationship relative to one another. The extraction prongs  72   a ,  72   b  are offset from one another to define an open area therebetween. The extraction prongs  72   a ,  72   b  of the engaging member  70  define an outer width w2 that is sized somewhat less than the inner width w1 between the extraction prongs  62   a ,  62   b  of the engaging member  60 . In this manner, as illustrated in FIG. 2, the extraction prongs  72   a ,  72   b  may be positioned within the open area between the extraction prongs  62   a ,  62   b  to nest the inner extraction prongs  72   a ,  72   b  between the outer extraction prongs  62   a ,  62   b.    
     [0052] In another embodiment, the distal end portions of the extraction prong  72   a ,  72   b  are turned or bent over to define a respective pair of transverse flanges  76   a ,  76   b , each having a hook-shaped configuration. The transverse flanges  76   a ,  76   b  are arranged at an angle α2 relative to the mounting plate  74 . In one embodiment, the angle α2 falls within a range of about 30 degrees to about 90 degrees. In a specific embodiment, the angle α2 may be about 60 degrees. However, it should be understood that other angles α2 are also contemplated, including angles less than 30 degrees or greater than 90 degrees. The flanges  76   a ,  76   b  define inner bearing surfaces or edges  77   a ,  77   b , respectively, that face toward the mounting plate  74 . The engagement flanges  76   a ,  76   b  also define end surfaces  78   a ,  78   b  that may be arranged generally parallel with the mounting plate  74 . As will be described below, the flanges  76   a ,  76   b , and more specifically the bearing surfaces or edges  77   a ,  77   b , may be adapted to engage a corresponding portion of an implant for subsequent extraction of the implant from an intervertebral disc space.  
     [0053] As discussed above, the engaging member  70  may comprise at least partially a relatively flexible, resilient material to facilitate transformation of the engaging member  70  from the compressed configuration illustrated in FIG. 3 a  to the expanded configuration illustrated in FIG. 3 b . In one embodiment, the extraction prongs  72   a ,  72   b  are outwardly biased toward the expanded configuration illustrated in FIG. 3 b . In order to further facilitate transformation from the compressed configuration to the expanded configuration, the extraction prongs  72   a ,  72   b  may include curved intermediate portions  73   a ,  73   b , each having a bow-like or arcuate configuration. Like the intermediate portions  63   a ,  63   b  of the extraction prongs  62   a ,  62   b , the intermediate portions  73   a ,  73   b  may also function similar to that of a leaf spring, storing and releasing energy to facilitate transitioning of the extraction prongs  72   a ,  72   b  from the insertion configuration to the extraction configuration illustrated in FIG. 3 b . In one embodiment, the interface between the extraction prongs  72   a ,  72   b  and the mounting plate  74  defines a concave recess  79 . The concave recess  79  serves to strengthen the interconnection between the extraction prongs  72   a ,  72   b  and the mounting plate  74 , to minimize stress concentrations during compression and expansion of the extraction prongs  72   a ,  72   b  and/or to further facilitate transitioning of the extraction prongs  72   a ,  72   b  from the compressed configuration to the expanded configuration.  
     [0054] Referring to FIG. 11, shown therein is one embodiment of a spinal implant  100  suitable for extraction from a vertebral space by the surgical instrument  20 . The implant  100  is configured for implantation within an intervertebral disc space S between upper and lower vertebrae VU, VL (FIGS. 13 and 14) and includes a superior component  102  and an inferior component  104 . In one embodiment of the invention, the superior and inferior components  102 ,  104  comprise separate or discrete components of the implant  100 . However, it should be understood that the superior and inferior components  102 ,  104  may alternatively be integrally formed to define a single-piece, unitary implant  100 . In one embodiment, the superior and inferior components  102 ,  104  cooperate to form an articulating prosthetic joint. In a specific embodiment, the articulating joint is capable of providing relative pivotal and rotational movement between the adjacent vertebral bodies to maintain or restore motion substantially similar to the normal bio-mechanical motion provided by a natural intervertebral disc. However, it should be understood that other types of articulating or non-articulating implants are also contemplated for use in association with the present invention.  
     [0055] In one embodiment of the invention, the superior implant component  102  includes a support plate  110  having an inner surface  112 , an outer surface  114 , and anterior and posterior end surfaces  116 ,  118  extending between the inner and outer surfaces  112 ,  114 . Similarly, the inferior implant component  104  includes a support plate  120  having an inner surface  122 , an outer surface  124  and anterior and posterior end surfaces  126 ,  128  extending between the inner and outer surfaces  122 ,  124 . A spherical-shaped ball or projection  130  extends from the inner surface  122  of the inferior component  104  (FIG. 13), which is at least partially engaged within a spherical-shaped recess (not shown) extending from the inner surface  112  of the superior component  102 . The spherical-shaped projection  130  and the spherical-shaped recess (not shown) cooperate to allow the superior and inferior components  102 ,  104  to articulate relative to one another. The inner surfaces  112 ,  122  of the superior and inferior implant components  102 ,  104  are separated by a distance d so as to define a gap or passage  132  therebetween. As will be described below, the gap  132  is sized to allow for insertion of the engaging portion  50  of the surgical instrument  20  therein when the surgical instrument  20  is in the insertion configuration (FIGS. 3 a  and  13 ).  
     [0056] In furtherance of the example, the outer surfaces  114 ,  124  of the superior and inferior support plates  110 ,  120  are adapted to bear against the vertebral endplates of the upper and lower vertebrae VU, VL. In one embodiment, the outer surfaces  114 ,  124  are sized and shaped to extend substantially entirely across and along the intervertebral disc space S. In another embodiment, the outer surfaces  114 ,  124  are angled relative to the respective inner surfaces  112 ,  122  to accommodate for the particular lordotic angle between the upper and lower vertebrae VU, VL. In yet another embodiment, a flange member or keel  129 ,  139  extends from the respective outer surfaces  114 ,  124  of the superior and inferior support plates  110 ,  120 . The keels  129 ,  139  are sized and shaped for disposition within preformed slots or channels C formed through and along the endplates of the upper and lower vertebrae VU, VL (FIGS. 13 and 14) to stabilize the implant within the intervertebral disc space S. Each of the keels  129 ,  139  defines a number of openings extending therethrough to provide opportunity for bone through-growth to enhance fixation of the spinal implant  100  to the upper and lower vertebrae VU, VL.  
     [0057] Although a specific embodiment of a spinal implant  100  has been illustrated and described herein, it should be understood that other sizes, shapes and configurations of implants are also contemplated. For example, another embodiment of a spinal implant suitable for use in association with the present invention is illustrated and described in U.S. patent application Ser. No. 10/042,589 to Eisermann et al., entitled “Intervertebral Prosthetic Joint” and filed on Jan. 9, 2002, the contents of which are incorporated herein by reference.  
     [0058] Referring to FIG. 12, shown therein is the surgical instrument  20  engaged with the spinal implant  100  according to one embodiment of the present invention. As will be described below, the extraction prongs  62   a ,  62   b  and  72   a ,  72   b  of the respective engaging members  60 ,  70  are initially inwardly compressed toward one another to define the insertion configuration illustrated in FIG. 3 a . While in this reduced profile insertion configuration, the engaging members  60 ,  70  are displaced through the gap  132  between inner surfaces  112 ,  122  of the implant support plates  110 ,  120  generally along the longitudinal axis L in the direction of arrow A. Once the distal end portions of the engaging members  60 ,  70  pass beyond the posterior surfaces  118 ,  128  of the inferior and superior implant components  102 ,  104 , the engaging members  60 ,  70  will automatically transition to the expanded, extraction configuration illustrated in FIGS. 3 b  and  12 . During the transitioning, the transverse flanges  66   a ,  66   b  and  76   a ,  76  are outwardly displaced in generally opposite directions along the transverse axis T. As a result, the inner bearing surfaces  67   a ,  67   b  of the engaging member  60  are positioned adjacent the posterior end surface  128  of the inferior implant component  104 , and the inner bearing surfaces  77   a ,  77   b  of the engaging member  70  are positioned adjacent the posterior end surface  118  of the superior implant component  102 . The surgical instrument  20  is then displaced generally along the longitudinal axis L in the direction of arrow B to engage the bearing surfaces  77   a ,  77   b  and  67   a ,  67   b  securely against the posterior end surfaces  118 ,  128  of the inferior and superior implant components  102 ,  104 .  
     [0059] Referring to FIGS. 13 and 14, shown therein is the exemplary spinal implant  100  inserted within an intervertebral disc space S between the upper and lower vertebrae VU, VL, with the outer surfaces  114 ,  124  of the inferior and superior support plates  110 ,  120  engaged against the vertebral endplates and with the keels  129 ,  139  positioned within the channels C formed through and along the vertebral endplates.  
     [0060] In this example, the spinal implant  100  is positioned within the intervertebral disc space S with the superior and inferior implant components  102 ,  104  disposed in a vertical or stacked arrangement extending between the upper and lower vertebrae VU, VL. However, it should be understood other arrangements are also contemplated. For example, in another embodiment, the spinal implant may comprise a pair of bi-lateral implant components disposed in a horizontal or side-by-side arrangement within the intervertebral disc space S. In one such alternative embodiment, the spinal implant may comprise a pair of fusion cages or spacers positioned bi-laterally within the intervertebral disc space S and separated by a distance to define a gap or passage therebetween sized to receive the engaging members  60 ,  70  of the surgical instrument  20  therethrough when in the compressed, insertion configuration. It should be understood that other types, configurations and arrangements of implants are also contemplated for use in association with the present invention.  
     [0061]FIG. 13 illustrates the surgical instrument  20  as it is being axially displaced in a posterior direction along the gap  132  between the inferior and superior components  102 ,  104  of the implant  100  according to one embodiment of the present invention. FIG. 14 illustrates engagement of the surgical instrument  20  with the inferior and superior components  102 ,  104  for extraction of the implant  100  from the intervertebral disc space S in an anterior direction. In the illustrated embodiment of the invention, the surgical instrument  20  is used to extract the spinal implant  100  from the intervertebral disc space S via an anterior approach. However, it should be understood that the surgical instrument  20  may alternatively be used to extract the spinal implant  100  from the intervertebral disc space S via a posterior approach, a lateral approach, or other surgical approaches known to those skilled in the art.  
     [0062] Referring to FIG. 13, in one embodiment, prior to inserting the engaging members  60 ,  70  within the gap  132  between the inferior and superior implant components  102 ,  104 , the extraction prongs  62   a ,  62   b  and  72   a ,  72   b  may be inwardly compressed toward one another to the insertion configuration. When in the compressed configuration, the engaging members  60 ,  70  define a reduced profile having a compressed height h1 substantially equal to the distance d between the inner support plate surfaces  112 ,  122 . While in this reduced profile insertion configuration, the extraction prongs  62   a ,  62   b  and  72   a ,  72   b  may be displaced through the gap  132  in the direction of arrow A generally along the longitudinal axis L.  
     [0063] In furtherance of the example, during displacement along the gap  132 , the engaging members  60 ,  70  may be maintained in the compressed state via engagement of distal end surfaces  68   a ,  68   b  of the flanges  66   a ,  66   b  against the inner support plate surface  112 , and via engagement of distal end surfaces  78   a ,  78   b  of flanges  76   a ,  76   b  against the inner support plate surface  122 . Additionally, as the engaging members  60 ,  70  are displaced along the gap  132 , the spherical-shaped projection  130  extending from the inner support plate surface  122  may pass through the open area between the extraction prongs  72   a ,  72   b  of the engaging member  70 , thereby allowing the distal end portions of the engaging members  60 ,  70  to pass entirely through the gap  132 .  
     [0064] Referring to FIG. 14, in one embodiment, once the transverse flanges  66   a ,  66   b  and  76   a ,  76   b  of the respective engaging members  60 ,  70  are positioned beyond the posterior edges of the inner support plate surfaces  112 ,  122 , the engaging members  60 ,  70  may automatically transition to the expanded, extraction configuration. More specifically, when the flanges  66   a ,  66   b  and  76   a ,  76   b  are positioned beyond the support plates  110 ,  120 , the distal end surfaces  68   a ,  68   b  of the transverse flanges  66   a ,  66   b  and the distal end surfaces  78   a ,  78   b  of transverse flanges  76   a ,  76   b  will disengage the inner support plate surfaces  112 ,  122 . Since the engaging members  60 ,  70  are biased toward the extraction configuration, the prongs  62   a ,  62   b  and  72   a ,  72   b  will automatically expand in an outward direction along the transverse axis T. When in the expanded configuration, the engaging members  60 ,  70  define an increased profile having an expanded height h2 that is greater than the distance d between the inner support plate surfaces  112 ,  122 . As a result, the inner bearing surfaces  67   a ,  67   b  of the engaging member  60  will be positioned adjacent the posterior end surface  128  of the inferior implant component  104 , and the inner bearing surfaces  77   a ,  77   b  of the engaging member  70  will be positioned adjacent the posterior end surface  118  of the superior implant component  102 .  
     [0065] In furtherance of the example, once the engaging members  60 ,  70  are transitioned into the expanded configuration, an extraction force may be exerted onto the surgical instrument  20  in the direction of arrow B, which may be transmitted through the shaft member  30  to the engaging member  60 ,  70 , to extract the implant from the intervertebral disc space S. Notably, since the surgical instrument  20  engages both the superior and inferior implant components  102 ,  104 , the implant  100  may be extracted from the intervertebral disc space S as a single unit. Extraction of the entire implant  100  eliminates the requirement of having to distract the intervertebral disc space S to individually remove the inferior and superior implant components  102 ,  104 . Extraction of the implant  100  as a single unit also avoids stretching of the ligaments that extend between the upper and lower vertebrae VU, VL. However, it is understood that the inferior and superior implant components  102  and  104  may be extracted separately.  
     [0066] Referring back to FIG. 1, in one embodiment, the extraction force exerted onto the surgical instrument  20  may be generated by an impact or slap hammer (not shown) or another type of impact device. The slap hammer may be attached to the handle member  32  via the Hudson-type connector portion  38 . Alternatively, the handle member  32  may be removed from the instrument  20 , and the slap hammer may be connected to the shaft member  30  via the internally threaded coupling member  34 . Slap hammers are well known in the art and typically including a weight that freely slides along the length of a guide rod with a stop member secured to the end of the guide rod. Impacting the weight against the stop member in turn exerts a controlled force onto the shaft member  30 , which in turn is transmitted to the engaging members  60 ,  70  to exert an extraction force onto the spinal implant  100 . It should be understood, however, that other devices and techniques may be used to exert a force onto an implant to facilitate its removal. For example, in an alternative embodiment, a surgeon may manually grasp the handle member  32  and exert a pulling force in the direction of the axis L to extract the implant.  
     [0067] Although only a few exemplary embodiments of this invention have been described above in details, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Also, features illustrated and discussed above with respect to some embodiments can be combined with features illustrated and discussed above with respect to other embodiments. Accordingly, all such modifications are intended to be included within the scope of this invention.