Instrumentation and method for facilitating insertion of spinal implant

A vertebral spacer apparatus includes an elongated member having proximal and distal end portions and defining a longitudinal axis and a vertebral spacer which is releasably mounted to the elongated member. The vertebral spacer includes an insertion end portion and a trailing end portion. The insertion end portion is configured to at least span an intervertebral space defined between adjacent vertebrae. The trailing end portion defines a dimension greater than a corresponding dimension of the insertion end portion and is sized to prevent entry thereof within the intervertebral space. The insertion end portion preferably includes first and second opposed support surfaces wherein a dimension defined between the first and second support surfaces at least spans the intervertebral space between adjacent vertebrae. A method for implanting a fusion implant with the vertebral spacer apparatus is also disclosed.

BACKGROUND 
1. Technical Field 
The present disclosure generally relates to a method and associated 
instrumentation for insertion of spinal implants to facilitate fusion of 
adjacent vertebral bodies and, more particularly, to a vertebral spacer 
utilized to maintain a predetermined spacial distance of adjacent 
vertebrae during the implant insertion. 
2. Background of the Related Art 
A large number of orthopedic procedures involve the insertion of either 
natural or prosthetic implants into bone or associated tissues. These 
procedures include, for example, ligament repair, joint repair or 
replacement, non-union fractures, facial reconstruction, spinal 
stabilization and spinal fusion. In a typical procedure, an insert, dowel 
or screw is inserted into a prepared bore formed in the bone or tissues to 
facilitate repair and healing. See, for example, U.S. Pat. No. 5,470,334 
to Ross et al.; U.S. Pat. No. 5,454,811 to Huebner; U.S. Pat. No. 
5,480,403 to Lee et al.; U.S. Pat. No. 5,358,511 to Gatturna et al.; and 
U.S. Pat. No. 4,877,020 to Vich. 
Some implants are particularly configured with cavities and bores to 
facilitate bony ingrowth and enhance anchoring of the implant at the 
insertion site. See, for example, U.S. Pat. No. 4,328,593 to Sutter et 
al.; U.S. Pat. No. 4,936,851 to Fox et al.; and U.S. Pat. No. 4,878,915 to 
Brantigan. Other specialized implants include fusion cages having internal 
cavities to receive bone growth stimulation materials such as bone chips 
and fragments. See, for example, U.S. Pat. No. 4,501,269 to Bagby; U.S. 
Pat. No. 4,961,740 to Ray et al.; U.S. Pat. No. 5,015,247 to Michaelson; 
and U.S. Pat. No. 5,489,307 to Kuslich et al. These types of implants are 
particularly well suited for intervertebral spinal fusion procedures 
necessitated by injury, disease or some degenerative disorder of the 
spinal disc. Subsequently, there may be progressive degeneration leading 
to mechanical instability between adjacent vertebrae necessitating direct 
fusion of the vertebrae while maintaining a pre-defined intervertebral 
space. This fusion may be accomplished by the insertion of one or more of 
the specialized implants as discussed above and also discussed in commonly 
assigned U.S. Pat. No. 5,026,373, the contents of which arc incorporated 
herein by reference. 
Both anterior (transabdominal) and posterior surgical approaches are used 
for interbody fusions of the lumbar spine. Fusions in the cervical area of 
the spine are performed using an anterior or posterior approach. 
Typically, an implant such as a plug, dowel, prosthesis or cage is 
inserted into a preformed cavity or drilled bone inside the interbody, 
interdiscal space. Since it is desirable in these procedures to promote a 
"bone to bone" bridge, connective tissue and at least a portion of the 
distal tissue is removed. Preferably, relatively deep cuts are made in the 
adjacent bones in order to penetrate into the softer, more vascularized 
cancellous region to facilitate bone growth across the implant. 
In many surgical implant techniques, two implants are inserted within the 
intervertebral space in side-by-side or lateral relation to fully support 
the adjacent vertebrae across the span of the intervertebral space. In 
accordance with these techniques, a first lateral side of the 
intervertebral space is prepared, e.g., by removing excess disc material 
and drilling/tapping a bore to receive the implant followed by insertion 
of the implant. Thereafter, the second lateral side is prepared for 
implant insertion in the same manner. During the initial preparation of 
the first lateral side of the intervertebral space, however, the adjacent 
vertebrae are subjected to displacement in both the lateral and 
longitudinal direction. This may cause additional movement of the 
vertebral portion disposed on the other (second) lateral side of the 
intervertebral space. 
U.S. Pat. No. 5,489,307 to Kuslich discloses a surgical method for 
implanting at least two spinal implants into a disc space utilizing a 
solid cylindrical distraction spacer which is inserted initially within 
one side of the disc space. The rigid distraction spacer is intended to 
act against the vertebral end plates of the adjacent vertebrae to urge the 
vertebra apart. The spacer is sized to be fully inserted such that it is 
either flush or slightly recessed within the disc space. 
The method and device disclosed in the Kuslich '307 patent is subject to 
several disadvantages which detract from its usefulness particularly in 
spinal surgery. For example, the Kuslich '307 distraction spacer is 
cylindrical thereby providing a limited area of surface contact with the 
adjacent vertebrae, which, consequently detracts from the stability 
provided to the adjacent vertebrae. Secondly, the distraction spacer is 
sized for complete entry within the intervertebral space, i.e., no 
provision is made to limit the insertion distance within the space. 
Consequently, over-insertion of the Kuslich distraction spacer may cause 
undesirable contact with, e.g., the aorta or dural nerve, depending on the 
surgical approach. Thirdly, the Kuslich '307 distraction spacer requires 
complete insertion within the intervertebral space which due to the 
concavity of the disc space, impedes attempts to subsequently remove the 
spacer after the operation. 
Accordingly, the present disclosure is directed to a novel method and 
associated instrumentation which overcomes the disadvantages of the prior 
art. The novel method and instrumentation of the present disclosure 
facilitates the introduction of a fusion implant by stabilizing the 
adjacent vertebrae and providing parallel vertebral endplate distraction 
so as to reestablish intervertebral disc space height during implant 
insertion and/or the performance of other spinal procedures. 
SUMMARY 
Generally, the present disclosure is directed to a vertebral spacer 
apparatus including an elongated member having proximal and distal end 
portions and defining a longitudinal axis and a vertebral spacer 
releasably mounted to the elongated member. The vertebral spacer includes 
an insertion end portion and a trailing end portion. The insertion end 
portion is configured to at least span an intervertebral space defined 
between adjacent vertebrae. The trailing end portion defines a dimension 
greater than a corresponding dimension of the insertion end portion and is 
sized to prevent entry thereof within the intervertebral space. 
In a preferred embodiment, the insertion end portion of the vertebral 
spacer includes first and second supporting surfaces for respectively 
engaging the adjacent vertebrae, wherein a dimension defined between the 
first and second supporting surfaces is sufficient to at least span an 
intervertebral space defined between adjacent vertebrae. The first and 
second supporting surfaces may be substantially planar and arc preferably 
in general parallel relation to the longitudinal axis of the elongated 
member. 
The trailing end portion may define a rectilinear cross-section. 
Alternatively, the insertion end portion may include first and second 
spacer arms extending in a general longitudinal direction and being 
dimensioned and configured such that each spacer arm at least spans an 
intervertebral space defined between adjacent vertebrae. Each spacer arm 
may define first and second supporting surfaces for respectively engaging 
the adjacent vertebrae. Preferably, each spacer arm defines a dimension 
between the first and second supporting surfaces sufficient to contact the 
opposed end faces of the adjacent vertebrae upon insertion thereof. 
The first and second supporting surfaces of each spacer arm are 
substantially planar and in general parallel relation to the longitudinal 
axis of the elongated member. 
A method for performing a surgical procedure adjacent an intervertebral 
space defined between adjacent vertebrae with the vertebral spacer 
apparatus is also disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
The preferred embodiments of the method and instrumentation disclosed 
herein are discussed in terms of orthopedic spinal fusion procedures and 
instrumentation. It is also envisioned, however, that the disclosure is 
applicable to a wide variety of procedures including, but, not limited to 
ligament repair, joint repair or replacement, non-union fractures, facial 
reconstruction and spinal stabilization. In addition, it is believed that 
the present method and instrumentation finds application in both open and 
minimally invasive procedures including endoscopic and arthroscopic 
procedures wherein access to the surgical site is achieved through a 
cannula or small incision. 
The following discussion will include a description of each instrument 
utilized in performing a spinal fusion method followed by a description of 
the preferred method for spinal fusion utilizing the instrumentation in 
accordance with the present disclosure. 
In the discussion which follows, the term "proximal", as is traditional, 
will refer to the portion of the structure which is closest to the 
operator, while the term "distal" will refer to the portion which is 
furthest from the operator. 
Referring now to the drawings in which like reference numerals identify 
similar or identical elements throughout the several views, FIG. 1 
illustrates in perspective view the spacer apparatus of the present 
disclosure. Spacer apparatus 10 includes spacer insertion instrument 12 
and a vertebral spacer 14 which is detachably mounted to the insertion 
instrument 12. In FIG. 1, a multitude of vertebral spacers 14 (e.g., 4) 
are shown with each spacer 14 being of different size thus representing a 
kit, i.e., the spacer apparatus may be packaged with at least four 
vertebral spacers 14 including four diameters (for example, 12 mm, 14 mm, 
16 mm and 18 mm) to correspond to the selected spinal implant size. 
With continued reference to FIG. 1, insertion instrument 12 includes handle 
16 and elongated portion 18 connected to the handle and extending distally 
therefrom. Handle 16 is generally disc-shaped as shown although other 
designs are contemplated as well. Elongated portion 18 defines collar 20 
and threaded portion 22 adjacent its distal end. Threaded portion 22 
functions in mounting vertebral spacer 14 to instrument 12. 
Referring now to FIGS. 2A-2C, each vertebral spacer 16 includes trailing 
end portion 24 and insertion end portion 26 extending distally from the 
trailing end portion 24. Trailing end portion 24 preferably defines a 
general circular cross-section which is enlarged relative to the dimension 
of the insertion end portion 26 and relative to the intervertebral space 
in which insertion end portion 26 is to be inserted. In particular, 
trailing end portion 24 defines a cross-sectional dimension or height "t" 
greater than the height of the intervertebral space, thus, precluding 
entry of the trailing end portion within the area of the intervertebral 
space. This prevents over insertion of vertebral spacer 14 within the 
intervertebral spacer, thereby precluding the possibility of undesired 
contact with the aorta and with the dural nerve. The enlarged 
configuration of trailing end portion 24 also facilitates removal of the 
vertebral spacer 14 subsequent to implant insertion. Trailing end portion 
24 further defines an internal threaded bore 28 which cooperatively 
engages the outer threaded portion 22 of insertion instrument 12 to 
releasably mount vertebral spacer 16 to the insertion instrument 12. Other 
means for mounting vertebral spacer 16 to insertion instrument 12 are 
envisioned as well such as a tongue and groove arrangement, a bayonet 
coupling, etc. 
Insertion end portion 26 preferably includes first and second diametrically 
opposed spacer arms 28. The outer surface 28a of each arm 28 is arcuate, 
i.e., defining a radius of curvature substantially equivalent to the 
radius of curvature of trailing end portion 24. Each arm 28 further 
defines first and second supporting surfaces 30, 32 which are in general 
parallel relation to each other and are preferably planar surfaces. The 
height "h" of each arm (i.e., the distance between supporting surfaces 30, 
32) preferably approximates the height of the intervertebral space in 
which the vertebral spacer 16 is to be implanted. For example, in spinal 
fusion, the height "h" of each arm may be 6 mm, 8 mm, 10 mm and 12 mm. The 
particular vertebral spacer size is selected dependent upon the 
intervertebral space in which it is to be inserted. Each arm 28 further 
includes tapered end portions 34 defining a generally V-shaped 
configuration. End portion 34 facilitates insertion of retractor arms 28 
within the operative site, e.g., within the intervertebral space. As noted 
above, the height "h" of spacer arms 28 is substantially less than 
corresponding height "t" (cross-sectional dimension) of trailing end 
portion 24, i.e., the diameter of trailing end portion 24 may be, e.g., 12 
mm, 14 mm, 16 mm and 18 mm, thus defining an abutment surface 36 at the 
juncture of the trailing and insertion end portions 24, 26. 
Referring now to FIG. 3, the various other instruments contemplated for use 
in the spinal fusion procedure are illustrated and consist of surgical 
retractor 100, surgical drill 200, surgical tap instrument 300, implant 
insertion instrument 400 with implant 500 and T-shaped handle 600. 
Surgical retractor 100 is disclosed in commonly assigned U.S. patent 
application Ser. No. 08/615,379, filed Mar. 14, 1996, the contents of 
which are incorporated herein by reference. Retractor 100 is configured 
for distracting adjacent vertebral bodies to facilitate the insertion and 
application of an implant, for providing a cannula for insertion of the 
instrument, and for ensuring proper alignment of the instrumentation and 
accurate insertion of the implant. Retractor 100 includes sleeve 102 with 
an enlarged head 104 at the proximal end of the sleeve 102. Sleeve 102 
includes first and second diametrically opposed retractor arms 106 having 
first and second parallel vertebrae supporting surfaces 108, 110. 
Drill instrument 200 is also disclosed in the '379 application. Drill 
instrument 200 includes drill shaft 202, extension shaft 204 and drill bit 
206 mounted at the distal end of the drill shaft. Extension shaft 204 has 
first and second collars 208, 210 which cooperate to control the depth of 
penetration of drill shaft 202 and drill bit 206 into the adjacent 
vertebrae. Drill shaft 202 includes a hexagonal-shaped head 212 at its 
proximal end to mount T-handle 600. 
Tap instrument 300 is also disclosed in the '379 application. Tap 
instrument 300 is utilized for forming an internal thread within the 
drilled bore formed by the drill instrument. Tap instrument 300 includes 
elongated member 302 having hex head 304 at its proximal end to engage 
T-shaped handle 600. Tap instrument 300 further includes distal tapping 
threaded portion 306. Distal tapping portion 306 includes a plurality of 
conveyance channels (one is shown) 308 extending longitudinally through 
the cutting thread. Each conveyance channel 308 has a directional 
component parallel to the longitudinal axis and a directional component 
transverse to the longitudinal axis. Each conveyance channel 308 
encompasses approximately an arc of about 1/3 the outer circumference of 
the tapping portion 306. Conveyance channels 308 are each dimensioned to 
receive bone material deburred by the cutting edges during the tapping 
procedure and to continually transmit the bone material proximally through 
the channel to avoid undesired material build up at the tapping site. In 
this manner, tapping instrument 300 may be used to completely tap the 
internal thread within the bore without interruption of the tapping 
procedure. It should be noted that the tap need not be used if a 
self-tapping implant is utilized. 
Implant insertion instrument 400 includes elongated member 402 having 
proximal mounting portion 404 for facilitating mounting to T-shaped handle 
600 and distal portion 406 which mounts implant 500. Distal portion 406 
includes cylindrical mount 408 which is received within the bore of the 
implant 500 and implant engaging ball 410 which is received within an 
aperture defined in the wall of the implant 500 to fix the implant to the 
instrument. 
Implant 500 is uniquely designed for use in spinal fusion procedures. This 
implant 500 is generally disclosed in U.S. Pat. No. 5,026,373 to Ray, the 
contents of which have been previously incorporated herein by reference, 
and is commonly referred to as a "fusion cage". 
Implant or fusion cage 500 includes a cylindrical cage body 502 having an 
internal cavity or hole for accommodating bone-growth inducing substances. 
One end 504 of cage body 502 is closed and defines a rounded or bull-nosed 
configuration to facilitate insertion of the fusion cage relative to one 
or more bony structures. The other end defines an opening which 
communicates with the internal cavity. The outer surface of the cage body 
502 includes a single continuous thread 506 (preferably V-shaped) having a 
plurality of raised turns with valleys defined between adjacent turns. 
A plurality of perforations 508 are disposed within the threads and extend 
through the outer surface of the cage body 502 to provide direct 
communication between the outer surface and internal cavity 504. The 
perforations 508 permit immediate contact between the bone growth inducing 
substances within the inner cavity and the bone structure when the cage 
body 502 is mated to the bone structure, e.g., adjacent vertebrae. An end 
cap (not shown) may be mountable to the open end of cage body 502 to 
enclose the bone-growth inducing substances within the interior cavity. 
T-shaped handle 600 includes mounting portion 602 defining hexagonal-shaped 
recess 604 which receives the corresponding structure of drill instrument 
200, tap instrument 300 and implant insertion instrument 400. 
Application of Instrumentation 
The use of the instrumentation in conjunction with the insertion of the 
fusion cage 500 into an intervertebral space defined between adjacent 
vertebrae will be described. The subsequent description will be 
particularly focused on an open posterior spinal fusion procedure, 
however, it is to be appreciated that an anterior approach is contemplated 
as well. 
The intervertebral space is accessed utilizing appropriate retractors, 
e.g., laminar retractors, dural extractors to expose the posterior 
vertebral surface. Thereafter, the desired-sized vertebral spacer 14 is 
selected and mounted to insertion instrument 12 by cooperation of 
corresponding threaded portions 22,28 of the instrument and the spacer. 
With reference to FIGS. 4-5, a first lateral side of the intervertebral 
space "i" is targeted. By manipulating insertion instrument 12, end 
portion 26 of vertebral spacer 14 is inserted within the intervertebral 
space "i" adjacent the first lateral side and advanced to a position 
whereby the abutment surface 36 adjacent trailing end portion 24 engages 
the posterior margin of the spinal column. As noted above, trailing end 
portion 24 is strategically sized to prevent entry thereof in the 
intervertebral space "i". A standard mallet may be utilized to impact 
handle 16 of instrument 12 to drive vertebral spacer 14 into the disc 
space. Vertebral spacer 14 is inserted in a manner such that first and 
second supporting surfaces 30, 32 of each spacer arm 28 respectively 
engage the opposed vertebral bodies "V.sub.1, V.sub.2 " as depicted in 
FIG. 5. The arms 28 distract the vertebral end plates in a parallel 
fashion. Once in position, insertion instrument 12 is removed from 
vertebral spacer 14 by rotating the instrument 12 to disengage the 
respective threaded portions 22, 28 thereby leaving the vertebral spacer 
14 within the intervertebral space. The spacer arms 28 of vertebral spacer 
14 are appropriately dimensioned to stabilize the desired lateral side of 
the intervertebral space. It is to be noted that vertebral spacer 14 may 
distract the adjacent vertebrae "v.sub.1 v.sub.2 " as desired to become 
firmly implanted within the intervertebral space "i". 
With reference now to FIG. 6, retractor 100 is inserted within the 
intervertebral space "i" adjacent the other lateral side thereof. 
Retractor 100 may be inserted by placing an impactor cap at the proximal 
end and impacting the retractor 100 into the intervertebral space "i". In 
the preferred procedure, retractor 100 is positioned within the 
intervertebral space "i" such that the first and second supporting 
surfaces 108, 110 of each retractor arm 106 respectively engage the 
opposed vertebral bodies "V.sub.1 V.sub.2 ". Upon insertion of retractor 
arms 106, the vertebral bodies "V.sub.1 V.sub.2 " are distracted whereby 
the retractor arms 100 become firmly lodged within the intervertebral 
space. The retractor 100 selected preferably corresponds in dimension to 
the implanted vertebral spacer 14 (i.e., the height of the retractor arms 
corresponds to the height of the spacer arms) to ensure parallel 
distraction of the adjacent vertebrae "V.sub.1, V.sub.2 " so as to 
maintain a predetermined spacial distance of the vertebrae across the span 
of the intervertebral space "i". 
Referring now to FIG. 7, the surgical drill instrument 300 is now utilized 
to prepare the disc space and vertebral end plates for insertion of the 
fusion implant. The cutting depth of drilling instrument is adjusted as 
desired (i.e., to correspond to the length of the fusion implant) by 
adjusting collars 208, 210. With the T-handle mounted to surgical drill 
instrument 300, the instrument is introduced into the axial bore of 
retractor 100 and advanced to contact the posterior surface of the 
vertebral bodies, "V.sub.1 V.sub.2 ". Drill 200 is advanced into the 
intervertebral space "i" by rotating T-handle 600 such that drill bit 200 
shears the soft tissue and cuts the bone of the adjacent vertebrae 
"V.sub.1 V.sub.2 " thereby forming a bore which extends into the adjacent 
vertebrae "V1 V.sub.2 ". Drill 200 is then removed from retractor 100. It 
is to be noted that during the bore forming process vertebral spacer 14 in 
conjunction with retractor 100 stabilize the adjacent vertebrae "V.sub.1 
V.sub.2 " (e.g., the first lateral side of the intervertebral space is 
stabilized by spacer 14 and the second lateral side is stabilized by 
retractor arms 106 of retractor 100) to minimize lateral and/or 
longitudinal movement of the bodies and also to facilitate the formation 
of a uniform bore within the end plates. 
Referring now to FIG. 8, tap instrument 300 is selected and attached to the 
T-handle 600. Tap instrument 300 is inserted into retractor 100 and 
positioned adjacent the drilled bore formed in the adjacent vertebrae 
"V.sub.1 V.sub.2 " by the surgical drill 200. With retractor 100 as a 
direct guide, T-handle 600 is rotated in the direction of the directional 
arrow of FIG. 8 while simultaneously applying sufficient downward pressure 
on the T-handle to advance the tap instrument 300 and promote even 
purchase into the endplates. Upon advancement of the tap instrument 300, 
the deburred bone chips collect within conveyance channel 308 of tapping 
head 306, and are conveyed proximally during rotational movement of the 
tapping head away from the tapping site. Tap instrument 300 is advanced 
into the bone until the desired depth has been achieved, which occurs when 
the distal end of tapping head 308 "bottoms out" on the bone. When tap 
instrument 300 reaches the appropriate depth, the tap instrument 300 is 
rotated via T-handle 600 in an opposite direction to back the instrument 
out of the bone. 
With reference now to FIG. 9, attention is focused on the insertion of 
fusion implant 500. Cage body 502 is mounted onto insertion instrument 400 
by positioning the cage body 502 onto mounting portion 408 of the 
instrument to permit mounting ball 410 to engage one of the apertures of 
the implant 500. This assembly is attached to T-handle 600. Insertion 
instrument 400 with mounted cage body 502 is inserted into retractor 100 
and the cage body 502 is positioned within the tapped bore by rotating 
insertion instrument 400 in the direction depicted in FIG. 9. Cage body 
502 is advanced until it is completely seated with the bore. An indicator 
line 414 (FIG. 3) on insertion instrument 400 assists the surgeon in 
determining when the cage is in proper position. Insertion instrument 400 
is then removed from retractor 100. 
At this point in the procedure, bone growth inducing substances may be 
harvested from, e.g., the iliac crest, and packed into the cage body 502 
of implant 500 until the cage body 502 is completely filled with bone 
growth inducing substances. An end cap may then be mounted to the cage 
body 202. Retractor 100 is then removed. 
With implant 500 appropriately positioned in the second lateral side of the 
intervertebral space "i", attention is directed to preparing the first 
lateral side for insertion of a second implant. Previously inserted 
vertebral spacer 14 is removed by insertion of spacer insertion instrument 
into the operative site and engagement of threaded portion 22 of the 
instrument with the internal threaded bore 28 of vertebral spacer 14. Once 
engaged, vertebral spacer 14 is removed by exerting a proximal force on 
insertion instrument 12. 
Thereafter retractor 100 is inserted into the intervertebral space "i" in 
the area previously occupied by vertebral spacer 14. A second bore is 
formed in this first lateral side with tapping, if desired, followed by 
insertion of the implant as effectuated in accordance with the methods and 
instruments described above in connection with FIGS. 3-8. 
FIG. 10 illustrates two lateral fusion implants 200 inserted within the 
intervertebral space. 
Referring now to FIGS. 11A-11C, an alternate embodiment of the vertebral 
spacer of the present disclosure is illustrated. Vertebral spacer 50 is 
implanted and utilized in a manner substantially similar to vertebral 
spacer described hereinabove and is inserted with the use of insertion 
instrument 12. Vertebral spacer 50 includes a solid vertebral spacer body 
52 having an insertion end 54 and a trailing end 56. The insertion end 54 
has a forward tapered portion 58 defining a generally V-shaped 
configuration to facilitate insertion within the adjacent vertebrae, and a 
rear supporting portion 60. The rear supporting portion 60 is of 
rectangular cross-section and defines upper and lower opposed support 
surfaces 62, 64 which are illustratively planar to increase surface area 
contact with the end plates of respective vertebrae upon insertion. The 
distance between the support surfaces 62,64 preferably approximates the 
height of the intervertebral space in which vertebral spacer 50 is to be 
implanted. The support surfaces 62,64 may be knurled, ridged etc. to 
facilitate retention between the adjacent vertebrae. 
Trailing end 56 of spacer body 52 has an enlarged cross-section relative to 
insertion end 54 to 1) prevent insertion of the trailing end 56 within the 
intervertebral space and possible undesired contact with, e.g., the aorta, 
dural nerve, and 2) enhance removal of the vertebral spacer 50 subsequent 
to implant insertion. 
Vertebral spacer body 52 further includes threaded bore 66 adjacent 
trailing end 56. Threaded bore 66 is engaged by threaded portion 22 of the 
insertion instrument 12 to mount the vertebral spacer 50 to the instrument 
12. 
While the above description contains many specifics, these specifics should 
not be construed as limitations on the scope of the disclosure, but merely 
as exemplifications of preferred embodiments thereof. For example, it is 
envisioned that a self-tapping implant may be utilized thus precluding the 
use of tap instrument 300. Those skilled in the art will envision many 
other possible variations that are within the scope and spirit of the 
disclosure as defined by the claims appended hereto.