Adjustable vertebral body replacement

Details Adjustable vertebral body replacement Adjustable vertebral body replacement

1998-05-05

2002-02-05

Milano, Michael J. (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

Reexamination Certificate

active

06344057

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns an implant for replacement of one or more vertebral bodies and their adjacent disks. More particularly, the vertebral body replacement is particularly well suited for implantation through an anterior approach.
The treatment of injuries to the spine has advanced significantly since the days of the first recorded surgical procedure for spinal cord injury in the late 7th Century. The techniques, instrumentation and implants have changed over the years and have been better adapted to address many forms of spinal injury and deformities that can occur due to trauma, disease or congenital effects. One type of spinal deformity, a kyphosis, involves a prolapse of the vertebral column towards the front of the body, often caused by the destruction of the vertebral body itself. This destruction can be in the form of a trauma type injury, such as a fracture or burst injury to the vertebral body, or a non-traumatic deformity caused by a tumor or a degeneration of the bone in the vertebral body.
Treatment of a kyphosis in the thoracic or lumbar spine appears now to be best achieved through an anterior approach, particularly in order to avoid some of the more severe complications associated with support or replacement of a damaged vertebral body. In most treatments of a kyphosis, a high degree of anterior reconstruction of the spine is required, most frequently involving total removal of the damaged vertebral body. In a typical anterior approach, partial or total ablation of the vertebral body and the two adjacent vertebral disks is carried out. The remaining space is then distracted to manipulate the spine to its correct orientation.
In many cases, the space is filled with a polymerizable paste or a bone graft which is frequently modeled to give it the shape of the destroyed vertebral body. Frequently, autologous bone, such as that extracted from the ilium, is used to bridge the space. The polymerizable paste can include a PMMA bone cement. Once the cavity remaining after the removal of the original vertebral body has been filled, an osteosynthesis instrument is positioned between the adjacent unaffected vertebrae to prevent any relative movement therebetween. The osteosynthesis device is essential to restabilize the vertebral column, to support the loads to which the thoracic or lumbar spine is exposed, and to enhance the likelihood and quickness of union of the bone graft material with the adjacent vertebral bodies. Once the bone graft and material is sufficiently solid, the osteosynthesis device normally is not subjected to any further mechanical stresses.
A known osteosynthesis device is depicted in U.S. Pat. No. 5,108,395 to Jean-Marie Laurain, the disclosure of which is incorporated herein by reference. This system is illustrated in
FIGS. 1 and 2
of the present application. Referring first to
FIG. 1
, it can be seen that a damaged vertebra V
3
includes a destroyed vertebral body C
3
. An interior implant
1
is provided for bridging between the two intact vertebrae V
2
and V
4
to permit removal of the damaged vertebra V
3
and its adjacent disks D
2
and D
3
. The anterior implant
1
includes a pair of clamps
2
which are engaged to the intact vertebral bodies by way of a number of spikes
3
. In addition, the clamps
2
are maintained in position by bone screws
5
extending through screw holes
11
, lateral lugs
8
of the clamps. The implant
1
also includes a plate
6
which is configured to span between the intact vertebrae and is strong enough to support the loads generated in the spinal column at that location.
Each clamp
2
includes a threaded post
12
projecting therefrom which is configured to pass through a corresponding opening
14
at each end of the plate
6
. A nut
7
is adapted to engage the threaded post
12
to fix the plate
6
to each of the clamps
2
. The surface of the clamps
2
include serrations
15
which mate with corresponding serrations
16
at each end of the plate
6
, thereby permitting differing angular orientations of the plate relative to each of the clamps. An opening
9
is provided through the threaded post
12
of the clamps to receive another bone screw
5
for firm fixation of the clamp with the healthy vertebral bodies V
2
and V
4
.
An important feature of the system described in the '395 patent is the provision of notches
18
in each of the clamps
2
. The notches are configured to receive the tips of a forceps
19
which is used to provide a distraction force between the two vertebrae V
2
and V
4
. As shown in
FIG. 2
, once the clamps
2
are fixed to the corresponding intact vertebrae, the forceps
19
are used to distract and permit room for placement of a bone graft G. Once the bone graft is in place, the anterior plate
6
can be attached to each of the clamps
2
in the manner previously described. Once the plate is in position, the distraction forceps
19
is removed and the nut
7
tightened to form a rigid construct.
The anterior construct shown in the '395 patent and in
FIGS. 1 and 2
of this application is one system for providing anterior fixation with the use of autologous or allogenic bone graft material. Other implants have been devised which rely upon an additional element interposed between the adjacent vertebra, in lieu of or in addition to the traditional bone graft material. One such device is shown in the patent to Harms et al. U.S. Pat. No. 4,820,305, which is sold as the “Harms Cage” by the Biedermann-Motech Company. This device contemplates a hollow cylindrical mesh which is inserted in the gap between adjacent vertebra, with bone graft material being disposed inside the hollow interior of the mesh.
The patent to Brantigan, U.S. Pat. No. 5,192,327, shows a device similar to the “Harms Cage” which is composed of a number of hollow oval-shaped implants within which bone graft material is disposed. European Patent No. 0 179 695 to Kehr shows a rigid inert body having a number of passageways extending between the intact vertebrae into which bone growth material can be implanted. In addition, the device shown in the Kehr European patent includes a plate spanning between the vertebrae having holes for receiving bone screws therethrough.
Another variety of implant devices particularly suited for replacement of vertebral bodies include components of generally solid construction which completely occupy the empty vertebral space. These devices are represented by the patents to Kapp et al., U.S. Pat. No. 4,554,914; Doty, U.S. Pat. No. 4,599,086; Ogilvie et al., U.S. Pat. No. 4,636,217; and Downey, U.S. Pat. No. 5,147,404. Each of these devices is provided with a spike or similar mechanism for engaging the endplates of the intact vertebrae to maintain the implant in position. A similar construction is followed in the U.S. Pat. No. 5,062,850 to MacMillan et al., although this device includes open space between support columns of the axially fixed vertebral body prosthesis.
In each of the former patents, the implant device requires separate distraction of the intact vertebrae prior to insertion of the device. The following patents show vertebral prosthesis which include some feature for expansion of the device in situ. For example, the Main et al., U.S. Pat. No. 4,932,975, and Barber U.S. Pat. No. 5,236,460 show prostheses that telescope through the admission of a hydraulic fluid. The patents of Rezaian, U.S. Pat. No. 4,401,112; Wu, U.S. Pat. No. 4,553,273 and Daher, U.S. Pat. No. 4,657,550 show devices that expand in situ the manipulation of a threaded component. In addition, the Rezaian patent shows a turnbuckle construct of this type with the addition of a spiked plate engaged in the opposite intact vertebrae to strengthen the construct.
In recent years, the application of anterior approaches to instrumenting the spine has become more prevalent. As these anterior approaches advance, it becomes of greater necessity to provide a vertebral body replacement that meets all of the benefits of anterior surgery without the detriments of the several pri

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