Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-10-01
2004-05-25
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S017150
Reexamination Certificate
active
06740117
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
Field of the Invention
This invention relates generally to a spinal implant assembly for implantation into the intervertebral space between adjacent vertebral bones to simultaneously provide stabilization and continued flexibility and proper anatomical motion, and more specifically to such a device which utilizes a spirally slotted belleville washer having a radially varying thickness profile as a restoring force generating element.
BACKGROUND OF THE INVENTION
The bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones coupled sequentially to one another by a tri-joint complex which consists of an anterior disc and the two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs. These more than 20 bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine, which comprises the top of the spine, up to the base of the skull, includes the first 7 vertebrae. The intermediate 12 bones are the thoracic vertebrae, and connect to the lower spine comprising the 5 lumbar vertebrae. The base of the spine is the sacral bones (including the coccyx). The component bones of the cervical spine are generally smaller than those of the thoracic spine, which are in turn smaller than those of the lumbar region. The sacral region connects laterally to the pelvis. While the sacral region is an integral part of the spine, for the purposes of fusion surgeries and for this disclosure, the word spine shall refer only to the cervical, thoracic, and lumbar regions.
The spinal column of bones is highly complex in that it includes over twenty bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Genetic or developmental irregularities, trauma, chronic stress, tumors, and degenerative wear are a few of the causes which can result in spinal pathologies for which surgical intervention may be necessary. A variety of systems have been disclosed in the art which achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back which needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, the interbody fusion cage has generated substantial interest because it can be implanted laparoscopically into the anterior of the spine, thus reducing operating room time, patient recovery time, and scarification.
Referring now to
FIGS. 1 and 2
, in which a side perspective view of an intervertebral body cage and an anterior perspective view of a post implantation spinal column are shown, respectively, a more complete description of these devices of the prior art is herein provided. These cages
10
generally comprise tubular metal body
12
having an external surface threading
14
. They are inserted transverse to the axis of the spine
16
, into preformed cylindrical holes at the junction of adjacent vertebral bodies (in
FIG. 2
the pair of cages
10
are inserted between the fifth lumbar vertebra (L
5
) and the top of the sacrum (S
1
). Two cages
10
are generally inserted side by side with the external threading
14
tapping into the lower surface of the vertebral bone above (L
5
), and the upper surface of the vertebral bone (S
1
) below. The cages
10
include holes
18
through which the adjacent bones are to grow. Additional material, for example autogenous bone graft materials, may be inserted into the hollow interior
20
of the cage
10
to incite or accelerate the growth of the bone into the cage. End caps (not shown) are often utilized to hold the bone graft material within the cage
10
.
These cages of the prior art have enjoyed medical success in promoting fusion and grossly approximating proper disc height. It is, however, important to note that the fusion of the adjacent bones is an incomplete solution to the underlying pathology as it does not cure the ailment, but rather simply masks the pathology under a stabilizing bridge of bone. This bone fusion limits the overall flexibility of the spinal column and artificially constrains the normal motion of the patient. This constraint can cause collateral injury to the patient's spine as additional stresses of motion, normally borne by the now-fused joint, are transferred onto the nearby facet joints and intervertebral discs. It would therefore, be a considerable advance in the art to provide an implant assembly which does not promote fusion, but, rather, which nearly completely mimics the biomechanical action of the natural disc cartilage, thereby permitting continued normal motion and stress distribution. It is, therefore, an object of the present invention to provide a new and novel intervertebral spacer which stabilizes the spine without promoting a bone fusion across the intervertebral space.
It is further an object of the present invention to provide an implant device which stabilizes the spine while still permitting normal motion.
It is further an object of the present invention to provide a device for implantation into the intervertebral space which does not promote the abnormal distribution of biomechanical stresses on the patient's spine.
Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.
SUMMARY OF THE INVENTION
The preceding objects of the invention are achieved by the present invention which is a flexible intervertebral spacer device comprising a pair of spaced apart base plates, arranged in a substantially parallel planar alignment (or slightly offset relative to one another in accordance with proper lordotic angulation) and coupled to one another by means of a spring mechanism. In particular, this spring mechanism provides a strong restoring force when a compressive load is applied to the plates, and may also permit limited rotation of the two plates relative to one another. While there are a wide variety of embodiments contemplated, two embodiments (and variations of both) are described herein as representative of preferred types. Each of these embodiments includes a spirally slotted and radially varying thickness belleville washer utilized as its restoring force providing element.
More particularly, with respect to the base plates, which are similar in all embodiments, as the assembly is to be positioned between the facing surfaces of adjacent vertebral bodies, and as such need to have substantially flat external surfaces which seat against the opposing bone surfaces. Inasmuch as these bone surfaces are often concave, it is anticipated that the opposing plates may be convex in accordance with the average topology of the spinal anatomy. In addition, the plates are to mate with the bone surfaces in such a way as to not rotate relative thereto. (The plates rotate relative to one another, but not with respect to the bone surfaces to which they are each in contact with.) In order to prevent rotation of a plate relative to the bone, the upper and lower plates may each further include outwardly directed spikes which penetrate the bone surface and mechanically hold the plates in place. It is further anticipated that the plates could include a porous coating into which the bone of the vertebral body can grow, however, it is not a limitation which is required of embodiments of the invention. (Note that this limited fusion of the bone to the base plate does not extend across the intervertebral space.)
While not preferred, it is possible, that between the base plates,
Ralph James D.
Tatar Stephen
Bortree, Esq. Timothy J.
Errico, Esq. Joseph P.
Pellegrino Brian E
Snow Bruce
SpineCore, Inc.
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