U.S. patent application number 10/097711 was filed with the patent office on 2003-09-18 for two-part prosthetic nucleus replacement for surgical reconstruction of intervertebral discs.
Invention is credited to Lawson, Kevin Jon.
Application Number | 20030176921 10/097711 |
Document ID | / |
Family ID | 32926245 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030176921 |
Kind Code |
A1 |
Lawson, Kevin Jon |
September 18, 2003 |
Two-part prosthetic nucleus replacement for surgical reconstruction
of intervertebral discs
Abstract
A prosthetic nucleus replacement comprises a modular two-part
body formed into an oval disk. The top part has a domed surface
with a crest and is made of a high molecular weight polyethylene or
ceramic. The bottom part is made of biocompatible metal like
titanium and locks into an underlying vertebrae with a peg or brace
molding that extends down into a socket. The prosthetic nucleus
replacement is surgically implanted into the hollowed out
intervertebral space through a flap cut in the natural annulus
fibrosis. The lower vertebra is prepared to receive the peg by
clearing the material covering the top of the bone matrix. Bone
cement is used around the peg to ensure a tight fit and immobile
attachment of the disc to the lower vertebrae.
Inventors: |
Lawson, Kevin Jon; (Redding,
CA) |
Correspondence
Address: |
Robert Charles Hill
235 Montgomery Street #821
San Francisco
CA
94104
US
|
Family ID: |
32926245 |
Appl. No.: |
10/097711 |
Filed: |
March 13, 2002 |
Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61F 2002/30004
20130101; A61F 2/30767 20130101; A61F 2002/30354 20130101; A61F
2/442 20130101; A61F 2310/00407 20130101; A61F 2310/00179 20130101;
A61F 2310/00131 20130101; A61F 2250/0014 20130101; A61F 2220/0033
20130101; A61F 2310/00029 20130101; A61F 2310/00017 20130101; A61F
2310/00023 20130101; A61F 2002/444 20130101 |
Class at
Publication: |
623/17.11 |
International
Class: |
A61F 002/44 |
Claims
1. A prosthetic nucleus replacement for implanting within an
annulus fibrosis in one part of a human spine, comprising: a top
dome comprised substantially of a first biocompatible material, and
having a convex upper side for contacting and articulating with an
end-plate cartilage of a supported superior vertebrae; a base
mechanically fixed to and underneath the top dome and comprised
substantially of a second biocompatible material, and providing for
an immobile foundation on an underlying inferior vertebrae; and a
brace molding extending from a bottom side of the base and
providing for an immobilization to said underlying inferior
vertebrae; wherein, said first biocompatible material has a
relatively low coefficient of friction and slides easily when in
contact with natural cartilage; and wherein, said second
biocompatible material has a relatively high coefficient of
friction and fixes well to the bone of said inferior vertebrae.
2. The prosthetic nucleus replacement of claim 1, wherein: the base
has a porous bottom surface providing for a bone-growth fixation
with said inferior vertebrae.
3. The prosthetic nucleus replacement of claim 1, wherein: the base
has a textured bottom surface providing for a cement fixation with
said inferior vertebrae.
4. The prosthetic nucleus replacement of claim 1, wherein: the top
dome comprises ultra-high molecular-weight polyethylene.
5. The prosthetic nucleus replacement of claim 1, further
comprising: a radiograph marker placed within the top dome, and
that can assist a physician in determining the in stiu orientation
of said prosthetic nucleus replacement by non-invasive medical
imaging.
6. A method for surgically correcting a degenerated nucleus
pulposus by the implantation of a prosthetic in a human spine, the
method comprising: a flap technique incision of an annulus fibrosis
corresponding to an affected area of a spine; a diskectomy of a
degenerated nucleus pulposus in said affected area; curetting of
cartilage down to the bone of an inferior vertebrae adjacent to
said affected area and preparing said bone to receive a pin;
assembling a solid ellipsoidal body from interlocking ones of a
modular top dome of a first biocompatible material and a modular
base of a second biocompatible material, wherein the product
provides for replacement of a natural nucleus pulposus; inserting
said solid ellipsoidal body into said affected area through an
incision in said annulus fibrosis; immobilizing said solid
ellipsoidal body with respect to said inferior vertebrae; and
repairing incision in said annulus fibrosis; wherein, a permanent
articulation between said solid ellipsoidal body and a superior
vertebrae exists after surgery.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to surgical methods and
devices to treat back and leg pain and in particular to the
surgical insertion of prosthetic nucleus replacement within the
annulus fibrosis. The device replaces a portion of a damaged spinal
intervertebral disc to restore function.
[0003] 2. Description of Related Art
[0004] In the spine, the principal function of the disco-vertebral
joint is to transmit compressive loads and still allow flexibility.
Adjacent vertebrae are joined by a triple-joint complex. The
anterior complex or column is formed by the vertebral bodies which
are shaped like flattened cylinders with discoid shaped or ovoid
shaped intervertebral discs sandwiched between each vertebral body.
Facet joints in the rear of each vertebra have a smooth cartilage
surface, lubricating joint fluid, and a covering capsule. The facet
joints restrict the disc to small degrees of flexion and extension,
limit rotation, and protect against translational shear stress. The
disc itself comprises two principle parts, the nucleus pulposus at
the core, and the annulus fibrosis, which is a multilayer bias-ply
wrapping that surrounds the nucleus. The nucleus starts early in
life as eighty percent water, and slowly desiccates with age.
[0005] A damaged disc can cause nerve dysfunction and debilitating
pain in the back, legs and arms. Typical treatments that provide
relief and allow patients to function again include back braces,
medical treatment, physical therapy and surgery to remove the disc.
A conventional surgical solution removes the bad disc and promotes
new bone growth in the space to fuse the adjacent vertebrae
together.
[0006] Several different prosthetic intervertebral disc devices are
described by Casey K. Lee, et al., in "Prosthetic Intervertebral
Disc," Chapter 96, The Adult Spine: Principles and Practice, Raven
Press, Ltd., New York, .COPYRGT. 1991. The conclusion of Lee, et
al., is that "An appropriately designed and fabricated prosthetic
intervertebral disc may provide an improved alternative to
currently available surgical approaches to low back disorders."
Lee, et al., describe their work at the orthopedic research
laboratories at the New Jersey Medical School "to produce a
prosthetic intervertebral disc design that has biomechanical
characteristics similar to the natural disc." One result has been
the manufacture of a unit with a nucleus, annulus, and end plates
that are molded under heat and fused into a single prosthetic disc.
However, success of such a device depends on solid bone attachment.
Most prior concepts have been excessively complex and never
used.
[0007] A prosthetic nucleus replacement can be surgically implanted
within the annulus fibrosis. The natural attachments of the annulus
would therefore be able to produce the requisite tensile strength
of the repaired site. The prosthetic nucleus replacement would be
subject primarily to compressive forces.
[0008] Such a prosthetic nucleus replacement is described by the
present inventor, Kevin Lawson, in U.S. Pat. No. 6,146,422, issued
Nov. 14, 2000. But this device is composed of one homogeneous
material and thus its top and bottom sides exhibit identical
material characteristics. The described construction can also be
unnecessarily expensive to produce.
[0009] In general, the replacement nucleus top must be
biocompatible, exhibit a low coefficient of friction, have a smooth
surface, be resilient, and if possible radiolucent. It should help
produce clear easy to read x-ray, CAT, and/or MRI medical images,
e.g., to enable post-operative evaluations that are
non-invasive.
[0010] The bottom of the replacement nucleus must also be
biocompatible, but it should stay put. So a high coefficient of
friction is desirable, and maybe even cementable to the bone of the
underlying vertebrae.
[0011] No prior art replacement nucleus meets these apparently
conflicting criteria.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is to provide a
prosthetic nucleus replacement that is useful and functional.
[0013] Another object of the present invention is to provide a
prosthetic nucleus replacement that allows for medical images of
the spine to be taken for non-invasive postoperative
assessments.
[0014] Briefly, a prosthetic nucleus replacement embodiment of the
present invention comprises a modular two-part body formed into an
oval disk. The top part has a domed surface with a crest and is
made of a high molecular weight polyethylene or ceramic. The bottom
part is made of biocompatible metal like titanium and locks into an
underlying vertebrae with a peg or brace molding that extends down
into a socket or recess in the bone. The prosthetic nucleus
replacement is surgically implanted into the hollowed out
intervertebral space through a flap cut in the natural annulus
fibrosis. The lower vertebra is prepared to receive the peg by
clearing the material covering the top of the bone matrix. Bone
cement may be used around the peg to ensure a tight fit and
immobile attachment of the disc to the lower vertebrae as
necessary.
[0015] An advantage of the present invention is that a prosthetic
nucleus replacement is provided that supports the normal
compressive loads experienced by natural vertebrae.
[0016] Another advantage of the present invention is that a
prosthetic nucleus replacement is provided that fixes well to the
inferior vertebrae it sits upon.
[0017] A further advantage of the present invention is that a
prosthetic nucleus replacement is provided that slides easily under
the superior vertebrae it supports.
[0018] The above and still further objects, features, and
advantages of the present invention will become apparent upon
consideration of the following detailed description of specific
embodiments thereof, especially when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a diagram representing the spine of a patient with
a prosthetic nucleus replacement embodiment of the present
invention;
[0020] FIGS. 2A and 2B are an on-edge view and a bottom view of a
prosthetic nucleus replacement embodiment of the present invention
similar to that shown in FIG. 1; and
[0021] FIGS. 3A-F are lateral cross sectional diagrams of a variety
of implementations of spinal nucleus replacement prosthesis
embodiments of the present invention, similar to those shown in
FIGS. 1, 2A, and 2B.
DETAILED DESCRIPTION OF THE INVENTION
[0022] FIG. 1 illustrates a prosthetic spinal nucleus replacement
embodiment of the present invention, referred to herein by the
general reference numeral 100. A human spine 102 commonly comprises
a series of vertebrae 104-108 interdigitated with a corresponding
series of discs 110-113. Each natural disc comprises a nucleus
pulposus surrounded and contained by a corresponding annulus
fibrosis. Natural nucleus pulposus have jelly-like structures that
can absorb and dampen compressive shock loads. Natural annulus
fibrosis structures comprise multiple layers of bias-ply filaments
set at forty-degree angles that resemble the construction of an
automobile bias-ply tire carcass.
[0023] Disc 112, between vertebra 106 and 107, is assumed in FIG. 1
to be degenerated. The spinal nucleus replacement prosthesis 114 is
surgically embedded in the inter-vertebral space between vertebra
106 and 107, and inside an annulus fibrosis 116.
[0024] Prosthetic nucleus replacement embodiments of the present
invention comprise a two-part modular assembly that resembles a
flattened oval disk. The superior, or top part is domed and is made
of a biocompatible material that slides easily and articulates well
with the superior vertebrae 106. The inferior base part is made of
a different biocompatible material that can be fixed readily to the
bone of the inferior vertebrae 107. For example, a porous material
for bone in-growth, or a textured material for cementing. The
possible biocompatible materials include ceramics, polymers and
plastics, titanium, stainless steel, tantalum, chrome cobalt
alloys, etc. Ultra-high molecular-weight polyethylene is presently
preferred so that metal radiograph markers may be strategically
placed in the nucleus replacement prosthesis 114.
[0025] In general, prosthetic nuclei of the present invention are
implanted using a straight anterior or anterior lateral approach
with incision of the anterior longitudinal ligaments of the
annulus. Just before use, and after the implant site has been
evaluated, a prosthetic annulus is assembled from two modular
parts. E.g., a top dome and a base made of dissimilar materials. A
flap technique is used for the incision of the annulus, and such
tissues are closed back up with conventional sutures or suture
anchors to the bone. The endplate cartilage of the superior
vertebrae is preserved for permanent articulation with the
implanted nucleus prosthetic. The endplate cartilage of the
inferior vertebrae is curetted down to bone. The bone is prepared
to receive a peg embedded in the implanted nucleus prosthetic. Such
pinning and also cement are used to permanently immobilize this
interface. The whole assembly is carefully centered as far
posterior as possible to help reestablish natural kinematics of
flex-extension and lateral bending.
[0026] As shown in FIGS. 2A and 2B, a nucleus replacement
prosthesis 200 has a top half 202 that is domed and has a crest.
This interlocks for modular assembly with a base half 204. The
outside diameter of the nucleus replacement prosthesis 200 can
vary, e.g., in the range of twenty to thirty-six millimeters. The
overall height can also vary, e.g., in the range of eight to
sixteen millimeters. The actual dimensions required depend on the
size of the patient and the exact site to receive the implant. Such
required sizes are discernable from patient radiographs, CT-scans,
and MRI-scans.
[0027] A peg 206 extends down from the base 204. The peg 206 is
preferably two to four millimeters long, and is primarily used to
pin the nucleus replacement prosthesis 200 to the adjacent
underlying vertebrae, e.g., vertebrae 107 in FIG. 1. A pair of
metal radiograph markers 208 and 210 are placed so that radiographs
can be used to determine the position of the nucleus replacement
prosthesis 200.
[0028] The prosthetic nucleus replacement 200 is surgically
implanted into the hollowed out intervertebral space through a flap
cut in the natural annulus fibrosis. Such "hollowing out" is
commonly called a diskectomy. The lower vertebra is prepared to
receive the peg 206 by clearing the material covering the top of
the bone matrix. Bone cement can be used around the peg 206 to
ensure a tight fit and immobile attachment of the disc to the lower
vertebrae. Alternatively, a non-cement method can be used to
promote and receive bone growth that will eventually immobilize the
base 204.
[0029] FIGS. 3A-F show a variety of implementations of spinal
nucleus replacement prosthesis 114 and 200. In FIG. 3A, a spinal
nucleus replacement prosthesis 300 has a top dome 302 of ceramic
that interlocks with a titanium base 304. A porous titanium
bone-in-growth peg 306 is used to help immobilize the whole to an
underlying vertebrae.
[0030] In FIG. 3B, a spinal nucleus replacement prosthesis 310 has
a top dome 312 of polished titanium that interlocks with a textured
ceramic base 314. A tapered peg 316 and perimeter teeth 318 and 319
are used to help immobilize the whole to an underlying
vertebrae.
[0031] In FIG. 3C, a spinal nucleus replacement prosthesis 320
comprises a ceramic or polyethylene dome 322 that is jacketed on
the bottom by a metal base 324. Titanium or chrome-cobalt can be
used for the base 324. A pointed peg 326 is used to help immobilize
the whole to an underlying vertebrae.
[0032] In FIG. 3D, a spinal nucleus replacement prosthesis 330
includes a modular dome 332 interlocked onto a base 334 with a peg
336. Each part is made in a variety of sizes and shapes so the
surgeon can select a best fit for each situation.
[0033] In FIGS. 3E and 3F, a spinal nucleus replacement prosthesis
340 comprises a dome top 342 and a base 344 of dissimilar
biocompatible materials. An anti-pivot keel 346 is used to anchor
and positively prevent swiveling of the whole.
[0034] A surgical method embodiment of the present invention for
correcting a degenerated nucleus pulposus by the implantation of a
prosthetic in a human spine begins with a flap-technique incision
of an annulus fibrosis corresponding to an affected area of a
spine. Then a diskectomy of a degenerated nucleus pulposus is done
in the affected area. The cartilage is cut down to the bone of an
inferior vertebrae adjacent to the affected area and the bone is
prepared for anchoring to a modular annulus base. A solid
ellipsoidal body is then assembled from interlocking ones of a
modular top dome of a first biocompatible material and the modular
annulus base of a second biocompatible material. The assembly
provides for replacement of a natural nucleus pulposus. The
assembled solid ellipsoidal body is inserted into the affected area
through an incision in the annulus fibrosis. The solid ellipsoidal
body is immobilized with respect to the inferior vertebrae, e.g.,
using bone cement. And, then the incision in the annulus fibrosis
is closed. The result is a permanent articulation between the solid
ellipsoidal body and a superior vertebrae after surgery.
[0035] The present inventor's previous U.S. Pat. No. 6,146,422,
issued Nov. 14, 2000, is incorporated herein by reference.
[0036] Although particular embodiments of the present invention
have been described and illustrated, such was not intended to limit
the invention. Modifications and changes will no doubt become
apparent to those skilled in the art, and it was intended that the
invention only be limited by the scope of the appended claims.
* * * * *