Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2003-02-11
2003-12-30
O'Connor, Cary E. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S017160, C606S064000
Reexamination Certificate
active
06669729
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for the replacement of posterior vertebral elements, and more particularly to an apparatus and a method that replaces posterior vertebral elements while preserving spinal stability and mobility.
BACKGROUND OF THE INVENTION
The human spine
29
comprises individual vertebrae
30
that interlock with each other to form a spinal column, shown in FIG.
1
A. Referring to
FIGS. 1B
,
1
C, and
1
D, each vertebra
30
has a cylindrical bony body (vertebral body)
32
, two pedicles
48
extending from the vertebral body
32
, a lamina
47
extending from the pedicles
48
, three winglike projections (two transverse processes
33
,
35
extending from the pedicles
48
and one spinous process
34
extending from the lamina
47
), pars interarticularis
36
, two superior facets
46
extending from the pedicles
48
and two inferior facets
45
extending from the lamina
47
. The pars interarticularis
36
connects the superior
46
and inferior
45
facets on either side of the spinous process
34
. The bodies of the vertebrae
32
are stacked one on top of the other and form the strong but flexible spinal column. The spinous process
34
, lamina
47
, pars interarticularis
36
, superior facets
46
, inferior facets
45
, transverse processes
33
, and pedicles
48
are positioned so that the space they enclose forms a tube, i.e., the spinal canal
37
. The spinal canal
37
houses and protects the spinal cord and other neural elements. A fluid filled protective membrane, the dura
38
, covers the contents of the spinal canal. The spinal column is flexible enough to allow the body to twist and bend, but sturdy enough to support and protect the spinal cord and the other neural elements.
The vertebrae
30
are separated and cushioned by thin pads of tough, resilient fiber known as inter-vertebral discs
40
. Inter-vertebral discs
40
provide flexibility to the spine and act as shock absorbers during activity. There is a small opening (foramen)
42
between each vertebra
30
, through which nerves
44
pass and go to different body parts. When the vertebrae are properly aligned the nerves
44
pass through without a problem. However, when the vertebrae are misaligned or a constriction
45
is formed in the spinal canal, the nerves get compressed
44
a
and may cause back pain, leg pain or other neurological disorders. Disorders of the spine that may cause misalignment of the vertebrae or constriction of the spinal canal include spinal injuries, infections, tumor formation, herniation of the inter-vertebral discs (i.e., slippage or protrusion), arthritic disorders, and scoliosis. In these pathologic circumstances, surgery may be tried to either decompress the neural elements and/or fuse adjacent vertebral segments. Decompression may involve laminectomy, discectomy, or corpectomy. Laminectomy involves the removal of part of the lamina
47
, i.e., the bony roof of the spinal canal. Discectomy involves removal of the inter-vertebral discs
40
. Corpectomy involves removal of the vertebral body
32
as well as the adjacent disc spaces
40
. Laminectomy and corpectomy result in central exposure of the dura
38
and its contents. An exposed dura
38
puts the neural elements and spinal cord at risk from direct mechanical injury or scarring from overlying soft tissues. Scarring is considered a major cause for failed back syndrome in which patients continue to have back and leg pain after spinal surgery. Current methods to decrease the risk of developing this syndrome include covering the dura with fat harvested from the patient's subcutaneous tissues or using a synthetic material. However, no material as yet has been used that completely or significantly prevents scarring of the dura and nerve roots after spine surgery in humans.
Furthermore, laminectomy predisposes the patient to instability through the facet joints and may lead to post-laminectomy kyphosis (abnormal forward curvature of the spine), pain, and neurological dysfunction. Therefore the surgeon needs to stabilize the spine after laminectomy procedures and after corpectomy. One spine stabilization method is fusion. Fusion involves the fixation of two or more vertebrae. Fusion works well because it stops pain due to movement of the intervertebral discs
40
or facets
45
,
46
, immobilizes the spine, and prevents instability and or deformity of the spine after laminectomy or corpectomy. However, spinal fusion limits spinal mobility. Maintaining spinal mobility may be preferred over fusion in some cases to allow more flexibility of the spine and to decrease the risk of junction problems above and below the level of the fixation due to increased stress.
An arthritic facet joint may also cause back pain. Since the majority of the motion along the spine occurs at the facet joints, fusing the diseased facet would often relieve pain but again at a high cost of fusing across at least one spinal segment thus preventing motion and effectively increasing stresses at the adjacent facet joints. Increased stresses predispose facet joints to accelerated arthritis, pain, and instability requiring additional surgery to fuse these levels. This cyclic process results in an overall decreased mobility of the spine. Therefore, it is an attractive alternative to attempt to replace the diseased facet without resorting to fusion, thus avoiding significant limitation in mobility of the spine. The obvious solution would be to replace the opposing surfaces of each facet to preserve motion between the surfaces. Any efforts to replace the facets at their natural location necessitate destroying the facet capsule and risks producing an unstable joint. It would be desirable to achieve spine stabilization that preserves mobility, protects the contents of the spinal canal, does not cause tissue scarring, decreases pain in the facet joints, and does not always destroy the facet capsule.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features an orthopedic implantable device articulately connecting a first spinal vertebra to an adjacent second spinal vertebra. Each spinal vertebra includes a vertebral body, a pair of pedicles extending posteriorly from the vertebral body, a lamina extending from the pedicles, a pair of superior facets extending from the pedicles, a pair of inferior facets extending from the lamina, a pair of pars interarticularis connecting the superior and inferior facets, a spinous process extending from the lamina and a pair of transverse processes extending from the pedicles. The orthopedic implantable device includes a first component adapted to be attached to a posterior location of the first vertebra and a second component adapted to be attached to a posterior location of the second vertebra. The first component is articulately connected to the second component.
Implementations of this aspect of the invention may include one or more of the following features. The first component may be articulately connected to the second component along a posterior midline of the first and second vertebrae and/or along an axis medial to the facets of the vertebrae. The first component may comprise a body and at least one male articulation member attached to the first component body and the second component may comprise a body and at least one female articulation member attached to the second component body and the first component may be articulately connected to the second component by engaging the at least one male articulation member to the at least one female articulation member. The at least one male articulation member may comprise a hook and the at least one female articulation member may comprise a loop. The first component body may further comprise at least one female articulation member and the second component body may further comprise at least one male articulation member. The posterior locations of the first and second vertebrae are selected from a group including a pedicle, transverse processes, facets, lamina, pars interarticularis, and vert
AKC Patents
Collins Aliki K.
Melson Candice C.
O'Connor Cary E.
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