The basic goal of a typical Posterior Lumbar Interbody Fusion (“PLIF”) procedure is to remove a problematic disc, and insert a prosthetic fusion device (such as a cage or a mesh) into the empty disk space created by removal of the natural disc. However, the pathophysiology of an intervertebral disc is such that the disc space in which the disc sits is typically collapsed (e.g., 30-50% of the time) prior to disc removal. Once the natural disc is removed (but prior to implant insertion), the annulus and soft tissue surrounding the disk space tend to force the adjacent vertebrae to come even closer together, thereby increasing the extent of disk space collapse. Since one goal of the surgery is to restore the patient's anatomic disc space to the extent possible, there is a need to spread apart these collapsed vertebrae. In one conventional PLIF procedure, a flat Spreader (which resembles a butter knife) is inserted with a horizontal disposition into the collapsed disk space and then rotated 90 degrees to vertically distract the adjacent vertebrae and restore the patient's physiologic disc space. The distracted endplates are essentially parallel to each other after the Spreader is rotated.
In addition, it is further desirable that the implanted device be secure within the disk space. However, since the geometry of the disk space varies from patient to patient, and the implants are typically manufactured in only a few shapes, the implants do not typically fit congruently into the distracted disk space. Accordingly, in one conventional PLIF procedure, congruence between rectangular implant shapes and the distracted disc space height is achieved by forming rectangular channels of known dimension in the adjacent endplates.
However, the current PLIF procedure for forming substantially rectangular channels in the endplates is a time-consuming three-step process. After the full discectomy and careful distraction of the disk space by the Spreaders described above, the surgeon must first insert a Reamer into the disk space and rotate it to create rounded grooves in both the superior and inferior endplates. In a second step, the surgeon then must insert the leading edge of a Pilot Broach into the disc space and axially impacts it to create a rectangular channel on the posterior side of the endplates. In the third step, the surgeon inserts a Finish Broach into the disc space and axially impact it to complete the anterior portion of the rectangular channel. Further details of the three-step Reamer—Pilot Broach—Finish Broach procedure and conventional instrument shapes can be found in a Brantigan et al. “Posterior Lumbar Interbody Fusion Techniques Using the Variable Screw Placement Spinal Fixation System” 6(1) in Spine: State of the Art Reviews. January 1992, pp. 175-200.
The Pilot Broach noted above has a body portion, a rectangular shaver portion extending distally from the body portion, and a cylindrical spreader portion extending from the shaver. The larger axial silhouette of the shaver portion relative to the cylindrical spreader portion defines shaving corners. The leading edge of the cylindrical spreader portion has a flat. Cylindrical spreader portion also includes an upper surface and a lower surface each of which bear upon the endplates. A crown is situated at the proximal end of the Pilot Broach and is used to engage a complimentary engagement connection.
Although the PLIF procedure using the Pilot Broach has been popular with surgeons, there have also been requests for improved instrumentation. In particular, surgeons have requested a quicker, easier 1-step method of preparing the rectangular channel in the endplates prior to implantation.
FIGS. 11b and 11c of U.S. Pat. No. 6,096,038 (“Michelson”) discloses a combined distractor-cutter having a distracting portion (102 in FIG. 11b and 260 in FIG. 11c) and a rotary shaving portion (270 in FIG. 11b and 250 in FIG. 11c). The distracting portion distracts the vertebral bodies while the rotary cutting portion prepares a bore shaped for the insertion of the threaded circular fusion cage.
Since each of these devices uses a rotary cutting device to prepare the endplates, the channels formed thereby are not substantially rectangular. In addition, cannulated technology (which protects the internal organs from the rotary cutting devices) is often needed when drilling devices are used, thereby increasing the complexity of the procedure.
FIGS. 25 and 25a-d of U.S. Pat. No. 6,174,311 (“Branch”) disclose a chisel having i) distracting portions 272, 273 for centering the chisel between the vertebrae and ii) upper and lower shavers 268, 270 for forming a rectangular channel in the distracted vertebrae. Arms 267 and 269 define a cavity 276 for receipt of bone chips and shaving debris. FIGS. 37a-c and 38 of Branch disclose a second chisel substantially similar to the chisel of FIG. 25.
One weakness of the Branch chisel lies in the disposition of both arms 267,269 and non-cutting edges 272, 273 at the lateral edges of the device. Because these arms and edges are disposed laterally, their effective widths essentially equal the entire width of the cutting edges, and thereby interrupt the surgeon's sightlines into the disk space.
U.S. Pat. No. 5,722,977 (“Wilhelmy”) discloses a combination osteotome and spacer guide. In use, as in FIG. 18, the spacer guide 8 is first inserted into the disc space 9. Next, the hollow osteotome 9 is slid over the outer dimension of the spacer guide 8 to its appropriate position. Lastly, driving head 49 of the osteotome is impacted by a mallet to drive the osteotome over the guide and into the vertebral bodies, and to cut and remove the desired amounts of bone.
One weakness of the Wilhelmy design lies in its need to slide the osteotome over the spacer guide in order to form the rectangular channel. Such sliding requires the maintence of close tolerances between the outer surface of the guide and the inner surface of the osetotome. This close tolerance may degrade with continued use. In addition, Wilhelmy teaches using separate osteotome and spacer guide instruments, thereby increasing complexity and cost. Another weakness of the Wilhelmy design lies in the relatively large width of the spacer. Since the width of the spacer must essentially equal the width of the osteotome to provide accurate cutting, the width of the spacer guide must be as large as possible. Accordingly, the surgeon's sightlines are interrupted by the device.
U.S. Pat. No. 4,697,586 (“Gazelle I”) discloses a chisel having a spreader portion and a chisel configured to slide over the spreader. The surgeon using the Gazelle I device first inserts the spreader into the intervertebral space. Next, the chisel portion of the device is slid along the outer surface of the spreader and its shaving portions cut rectangular channels into the endplates.
A publicly used device (“Gazelle II”) is somewhat similar to the Gazelle I device. Its main difference with Gazelle I is that the spreader of the Gazelle II device is rotatable. The surgeon using the Gazelle II device inserts the spreader into the intervertebral space and then rotates it 90 degrees to distract the disc space. Next, the chisel portion of the device is slid along the outer surface of the rotated spreader and its shaving portions cut rectangular channels into the endplates.
Like Wilhelmy, the Gazelle I and II devices require sliding the shaving portions over the distractor portion. In addition, the box nature of the chisel obscures sightlines. Lastly, the spreader has a height to width ratio of about 3:2, and so is is not relatively thin.
U.S. Pat. No. 4,736,738 (“Lipovsek”) discloses a shaving instrument for performing posterior lumbar interbody fusion, the instrument comprising a shaft adapted to be inserted into the intervertebral space and a chisel adapted to be slidably received within the shaft.
In sum, prior art procedures and devices used for endplate preparation suffer from:
In accordance with the present invention, there is provided a vertebral endplate chisel comprising:
This device allows preparation of the rectangular channel in one step. After a full discectomy has been performed and careful distraction of the disc space has been achieved, the surgeon places the inventive device against the posterior lip of the endplate, carefully aligns the instrument, and lightly impacts the device into the disc space to create the complete rectangular channel.
Since the width of the guide of the inventive device is less than the width of the upper shaving portion, the surgeon's sightlines into the disk space are not completely interrupted by the width of the guide as with the Branch device.
Since the shaving portions of the inventive device define substantially parallel planes (i.e., the shaving portion is not rotary), not only is a rectangular channel formed but also there is no need to use cannulated technology as with the Michelson device.
Lastly, since the guide of the inventive device is integrally connected to the base, shaving is performed by simply precisely locating the shaving portions at the desired depth of the vertebral surface and tapping the proximal end of the device with a hammer, and so does not require sliding the shaver over the guide as with the Gazelle and Wilhelmy devices.
a-4c disclose cross-sectional views through the base portion of three devices of the present invention.
Now referring to
Now referring to
Now referring to cross-sectional
Referring back to
Therefore, in some embodiments, as in
The I-beam-like shape includes the conventional I-beam shape, as shown in
The I-beam-like shape is advantageous because it minimizes the amount of material needed in the base section of the device, thereby maximizing debris pathway cross-section but without compromising the strength of the base section.
In some embodiments, upper 9 and lower 11 base portions do not contact the inner portion 470 of the intermediate portion, as in
Now referring to
In other embodiments, as in
Now referring to
Still referring to
Now referring to
Now referring to
Preferably, the guide is shaped so as to minimize interruption of the surgeon's sightlines. In some embodiments, the guide has a thin width. When the guide has such a thin width, the surgeon can more easily see the disc space. Preferably, the guide width WG is no more than 50% of the shaving portion width WSP, more preferably no more than 25%. In some embodiments, the guide is centered between the widths of the shaving portions. When the guide is so centered, the surgeon can see the disk space as easily from one side of the device as the other.
In some embodiments, the guide is sufficiently thin and centered so that the entire guide width is located within the middle one-third of the width WSP of the shaving portions. More preferably, the guide is sufficiently thin and centered so that the entire guide width is located within the middle one-fifth of the width of the shaving portions.
Now referring to
Still referring to
In some embodiments, as in
Now referring to
Although in preferred embodiments, the device is a single integral piece, in some embodiments, the device may be modular. For example, in some embodiments having a thin, centered guide, the shaving portions may be slidable over the outer surfaces of the guide.
Preferably, the device is made from either a metal or a ceramic material, or a composite of metals and ceramics. The device should be sterilized before use in a procedure. More preferably, the device is made of stainless steel.
Also in accordance with the present invention, there is provided a vertebral endplate chisel comprising:
Also in accordance with the present invention, there is provided a vertebral endplate chisel comprising:
Now referring to
The overall shape of guide 24 can be described as a pancake-like. Now referring to
In addition, the device of
In one method of using this device, once the disc space has been distracted by the Spreaders, the surgeon grips the Box Chisel by its proximal end and axially advances the distal end of the Box Chisel towards the distracted disc space. Since the disk space has already been distracted, tapered portions are the first portions of the tip to contact the vertebral endplates upon insertion into the disk space. If the disk space has been properly distracted, the flat leading edge portion of the tip should not contact the endplates. This initial contact between the tip tapers and the distracted endplates simply centers the Chisel Box relative to the adjacent vertebrae. Upon further axial advancement of the Box Chisel, tip contact with the endplates switches from the tapers to lands, and then finally to both lands and shavers. In this last mode, the shavers cut the endplates to form the desired channels of known dimension, such shaving being guided by the land-endplate contact.
In this embodiment, now referring to
Now referring to
Now referring to
Number | Name | Date | Kind |
---|---|---|---|
4586496 | Keller | May 1986 | A |
4697586 | Gazale | Oct 1987 | A |
4736738 | Lipovsek et al. | Apr 1988 | A |
4881534 | Uhl et al. | Nov 1989 | A |
5250050 | Poggie et al. | Oct 1993 | A |
5423825 | Levine | Jun 1995 | A |
5562736 | Ray et al. | Oct 1996 | A |
5571109 | Bertagnoli | Nov 1996 | A |
5649945 | Ray et al. | Jul 1997 | A |
5722977 | Wilhemy | Mar 1998 | A |
5803904 | Mehdizadeh | Sep 1998 | A |
5961522 | Mehzdizadeh | Oct 1999 | A |
6042582 | Ray | Mar 2000 | A |
6063088 | Winslow | May 2000 | A |
6096038 | Michelson | Aug 2000 | A |
6126664 | Troxell et al. | Oct 2000 | A |
6174311 | Branch et al. | Jan 2001 | B1 |
6200322 | Branch et al. | Mar 2001 | B1 |
6224607 | Michelson | May 2001 | B1 |
6228022 | Friesem | May 2001 | B1 |
6241729 | Estes et al. | Jun 2001 | B1 |
6241733 | Nicholson et al. | Jun 2001 | B1 |
6261293 | Nicholson et al. | Jul 2001 | B1 |
6436101 | Hamada | Aug 2002 | B1 |
6599291 | Foley et al. | Jul 2003 | B1 |
6610065 | Branch et al. | Aug 2003 | B1 |
6641582 | Hanson et al. | Nov 2003 | B1 |
20010010001 | Michelson | Jul 2001 | A1 |
20010010002 | Michelson | Jul 2001 | A1 |
Number | Date | Country |
---|---|---|
126647 | May 1996 | JP |
210316 | Aug 2000 | JP |
Number | Date | Country | |
---|---|---|---|
20030083664 A1 | May 2003 | US |