Method and device for fixing and correcting spondylolisthesis anteriorly

A method and apparatus for fixation and correction of spondylolisthesis anteriorly includes a disk cage which is inserted into the space between adjacent vertebrae, a drill guide for guiding and aligning a drill bit to angle an opening anteriorly between adjacent vertebrae, a distractor for temporarily aligning the vertebrae to position a disk cage and an elongated hollow screw positioned in said drilled opening through one vertebra, said disk cage and into said adjacent vertebra.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method and apparatus for fixation and reduction 
of spondylolisthesis, e.g., misalignment of the vertebrae comprising the 
spinal column. More specifically, the present invention relates to a disk 
cage positioned in the disk space between affected vertebra, and a screw 
through said vertebra, disk cage and other vertebra and a method utilizing 
that apparatus. 
2. Description of the Related Art 
Treatments for conditions involving subluxation of one vertebrae upon 
another, resulting in misalignment of the spinal column, involve the use 
of screws which extend through a plate and which are tightened to draw the 
misaligned vertebrae back into alignment. U.S. Pat. No. 5,531,747 to Ray 
(hereinafter "Ray") is an example of a plate and screw system for treating 
spondylolisthesis. Other approaches include insertion of an implant into 
the disk space between misaligned vertebrae such as shown in U.S. Pat. No. 
5,601,556 to Pisharodi (hereinafter "Pisharodi"). The Ray approach has its 
limitations as discussed in Pisharodi. That patent has a disadvantage in 
requiring removal of the disk and having multiple steps, that is, two 
implants are inserted into the disk space only to be substituted later 
with monolithic implants, Schafer et al., in U.S. Pat. No. 5,800,547 
discloses an angled block which is implanted into an intervertebral space. 
The block includes multiple openings through which securing pins extend 
after they are pushed into position by a camming mechanism inserted into 
another opening in the device. 
There is, therefore, a need for an improved method of treatment of 
conditions involving misalignment of the vertebrae of the spinal column, 
or spondylolisthesis, and it is a principal object of the present 
invention to provide such a method and an apparatus for use in connection 
with that method 
The art described in this section is not intended to constitute an 
admission that any patent, publication or other information referred to 
herein is "prior art" with respect to this invention, unless specifically 
designated as such. In addition, this section should not be construed to 
mean that a search has been made or that no other pertinent information as 
defined in 37 C.F.R. .sctn.1.56(a) exists. 
SUMMARY OF THE INVENTION 
The invention provides a means for correcting and fixing spondylolisthesis 
anteriorly. It involves using a distracting tool against adjacent vertebra 
to temporarily re-align the vertebrae and to open the disk space to allow 
insertion of a disk cage therewithin. The disk cage is then rotated to 
align an angled guide hole to the adjacent vertebrae and to space the 
vertebrae as desired. A drill guide is placed into the disk cage to 
provide a guide for accurately drilling a hole through one vertebra, 
through the angled guide hole of the disk cage and into the adjacent 
vertebra. A hollow, threaded screw is then threaded into the drill hole 
thus formed, connecting said vertebrae together through the disk cage. The 
disk cage and screw may be further bonded to the fused vertebrae by 
application of bone ingrowth medium into the disk cage and hollow screw to 
allow bone and fibrous fusions to form. The implant cross-links the disk 
cage and screw together to stabilize the spinal motion segment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the Figures, it will be seen that a typical misalignment, 
or spondylolisthesis of vertebrae occurs when one vertebra slides forward 
relative to another as best shown in FIG. 9. Typically, the L5 vertebra is 
pushed anteriorly from the desired position. This causes severe pain which 
can be alleviated by either fixation of the vertebrae or with correction 
of the alignment and fixation. 
FIGS. 1-4 show a disk cage 20 having one or more angled guide holes 22. As 
shown, the disk cage 20 preferably is substantially hollow, having an 
opening 24 therethrough, as well as numerous side openings 26 which 
increase the porosity of the device such that bone ingrowth may occur. As 
later described, opening 24 is required to receive tool 80 and does not 
need to pass through cage 20. As shown, disk cage 20 includes an upper 
surface 28 and a lower surface 30 through which the angled guide holes 22 
are positioned. In addition, surfaces 28, 30 may include threads 32 or 
other surface treatment to cause the surfaces to grip better to bone. FIG. 
4 shows a corner of cage 20 showing that the threads 32 may stop at the 
intersection of the sides 34, 36 at a notch 38. Cage 20 includes a ventral 
end 23 and a dorsal end 25. The opening 24 which functions as the tool 80 
receiving mechanism is in the ventral end 23. 
In order to use the disk cage, the disk 18 must be reamed out to 
accommodate the size of the disk cage 20. FIGS. 8-10 show an instrument 40 
used to both lift the adjacent vertebrae apart for reaming and to reduce 
the misalignment. Instrument 40 includes a pair of linked arms 42, 44 
having free ends 46, 48 which each include a sharp projection 50, 52 which 
may hold to the bone of a vertebra. Instrument 40 further includes a rod 
54 attached to the linked arms 42, 44 through opening 56 and to a slide 
member 60 which allows the slide member 60 to move up and down along the 
length of the linked arms. Instrument 40 includes a depth adjustment 
mechanism 62 which fixes the position of the slide member 60 to the linked 
arms 42, 44 at the position desired. A knob 64 may be held to control the 
instrument during adjustment. The slide member 60 includes a pair of 
spaced push members 66, 68 projecting opposite to the sharp projections 
50, 52. 
FIG. 9 shows the instrument 40 being used to increase the gap between 
adjacent vertebra 14, 16 and to correct the spondylolisthesis. As shown, 
the instrument is inserted on either side of the disk 18 and the sharp 
projections 50, 52 dig into the bone of vertebra 16. The slide member 60 
is adjusted down the linked arms 42, 44 by manipulating the adjustment 
mechanism 62 until the push members 66, 68 are firmly against the vertebra 
14. The instrument 40 may then be lifted up, causing the disk space to 
increase and for the spondylolisthesis to be reduced. While held up, the 
surgeon uses a reaming tool 70 as shown in FIG. 10 to prepare the disk 
space for a disk cage 20. The unique configuration of instrument 40 allows 
the surgeon to use a reamer while the instrument distracts the vertebrae. 
Once the disk space is prepared, the disk cage 20 is inserted. FIGS. 5, 6 
and 12 show that insertion may utilize a tool 80 which includes a head 82 
that may temporarily lock into opening 24 in the ventral end 23 of the 
disk cage 20. The tool 80 allows the surgeon to obtain leverage in 
inserting disk cage 20. Tool head 82 may include spring loaded, `recessed 
bearings 84 which may lock into side openings 26 as is common in socket 
wrenches. The disk cage 20 as shown has a narrower diameter across sides 
34, 36 than across upper and lower surfaces 28, 30. When so configured, 
the disk cage may be inserted into the disk space with a side 34, 36 up, 
making insertion easier. The surgeon may then simply rotate the tool 80 to 
twist the disk cage 20 such that the upper and lower surfaces 28, 30 
engage the bone of the vertebrae and the angled guide openings 22 are 
positioned as shown in FIGS. 13 and 14. This allows the tool 80 to be used 
as a distracting tool, but the surgeon determines whether the twist is 
needed or whether the disk cage 20 may simply be inserted without a need 
for rotation. 
Once in place, the disk cage is also used in conjunction with a drill guide 
90 as shown in FIGS. 7 and 13 to guide the formation of a hole 92 through 
the vertebra 14, 16. Drill guide 90 includes a head 94 configured as head 
82 to fasten to disk cage 20 and an angled guide tube 96 which is angled 
such that it will guide a drill bit 98 accurately through angled guide 
holes 22 of the disk cage 20. Hole 92 as drilled may be threaded or 
unthreaded. Drill guide 90 is then removed and a long, hollow screw 100 is 
threaded into hole 92 to fix the vertebrae 14, 16 together via the disk 
cage 20. 
As shown in FIG. 11, screw 100 is preferably hollow and includes threads 
102 to engage with the bone. A variety of bone growth inducing substances 
may be added to the disk cage 20 and screw 100 to foster bone ingrowth 
therethrough to make the fusion stronger. The screw 100 as shown has a 
hollow bore 104 and side openings 106 for bone ingrowth. 
As best shown in FIG. 14, the combination of the disk cage 20 and the screw 
100 fuses the vertebrae together with very few parts in a stable, solid 
fusion that keeps the correction of the spondylolisthesis as desired. The 
tools and instruments described function to ease the insertion of the 
combined system which reduces and fixes the corrected alignment of the 
vertebrae. 
While this invention may be embodied in many different forms, there are 
shown in the drawings and described in detail herein specific preferred 
embodiments of the invention. The present disclosure is an exemplification 
of the principles of the invention and is not intended to limit the 
invention to the particular embodiments illustrated. 
This completes the description of the preferred and alternate embodiments 
of the invention. Those skilled in the art may recognize other equivalents 
to the specific embodiment described herein which equivalents are intended 
to be encompassed by the claims attached hereto.