U.S. patent application number 10/496215 was filed with the patent office on 2005-03-24 for intervertebral disc prosthesis.
Invention is credited to Wardlaw, Douglas.
Application Number | 20050065609 10/496215 |
Document ID | / |
Family ID | 9926028 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050065609 |
Kind Code |
A1 |
Wardlaw, Douglas |
March 24, 2005 |
Intervertebral disc prosthesis
Abstract
A flexible prosthetic cover (12) shaped to form a replacement
nucleus pulposis for an intervetebral disc comprises an aperture
for the introduction of filling material therein, and an elongate
introducer member (28) configured to pass into the aperture. The
cover has a strengthened portion (26) substantially opposite the
aperture for engaging the distal end (42) of the member, the
strenghtened portion and the said distal end being arranged to
interlock, for facilitating orientation of the cove, for example so
as to prevent relative rotation there between.
Inventors: |
Wardlaw, Douglas;
(Stonehaven, GB) |
Correspondence
Address: |
LICATLA & TYRRELL P.C.
66 E. MAIN STREET
MARLTON
NJ
08053
US
|
Family ID: |
9926028 |
Appl. No.: |
10/496215 |
Filed: |
November 8, 2004 |
PCT Filed: |
November 19, 2002 |
PCT NO: |
PCT/GB02/05210 |
Current U.S.
Class: |
623/17.12 ;
623/17.16 |
Current CPC
Class: |
A61F 2002/4627 20130101;
A61F 2/4611 20130101; A61F 2/441 20130101; A61F 2002/445
20130101 |
Class at
Publication: |
623/017.12 ;
623/017.16 |
International
Class: |
A61F 002/44; A61F
002/46 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2001 |
GB |
0127697.1 |
Claims
1. A flexible prosthetic cover shaped to form a replacement nucleus
pulposis for an intervertebral disc and comprising an aperture for
the introduction of filling material therein, and an elongate
introducer member configured to pass into the aperture, the cover
having a strengthened portion substantially opposite the aperture
for engaging the distal end of the member, the strengthened portion
and the said distal end being arranged to interlock, for
facilitating orientation of the cover.
2. The flexible prosthetic cover of claim 1 wherein the
strengthened portion and the distal end interlock so as to prevent
relative rotation there between.
3. The flexible prosthetic cover of claim 1, wherein the aperture
comprises an internal flap valve.
4. The flexible prosthetic cover of claim 1 wherein the
strengthened portion comprises a radio opaque marker for indicating
the orientation of the strengthened portion.
5. The flexible prosthetic cover of claim 1 wherein the introducer
member has an internal channel communicating with an aperture at or
adjacent the distal end therefore for allowing the injection of
filling material into the cover.
6. The flexible prosthetic cover of claim 1 wherein the aperture is
arranged to accept an introducer tube shaped to pass over the
introducer member and to form a channel there between after removal
of the introducer member for allowing the injection of filling
material into the cover.
7. The flexible prosthetic cover of claim 1 further comprising a
deformable porous body or mesh or coil shaped to fit within the
cover.
8. The flexible prosthetic cover of claim 1 further comprising an
edge portion being a resiliently deformable annular sleeve shaped
to fit within a disc annulus, the aperture and the strengthened
portion being provided in the edge portion.
9. The flexible prosthetic cover of claim 8 further comprising a
pair of opposed flexible central portions each joining an edge of
the sleeve.
10. The flexible prosthetic cover of claim 9, wherein the central
portions are arranged, when the cover is filled with a filling
material, to allow filling material to pass there 20 through.
11. The flexible prosthetic cover of claim 9 wherein the central
portions are formed of a material arranged to break under filling
pressure.
12. The flexible prosthetic cover of claim 9 wherein the central
portions are formed of a material which is absorbable by the
body.
13. The flexible prosthetic cover of claim 1 wherein the
strengthened portion comprises a shaped recess or protrusion, and
the distal end of the introducer rod is correspondingly shaped to
interlock therewith.
14. The flexible prosthetic cover of claim 1 wherein the aperture
comprises a valve structure formed of an imaging transparent
material.
15. The flexible prosthetic cover of claim 1 further comprising
obturating means operatively associated with the aperture.
16. A prosthetic cover for an intervertebral disc comprising an
edge portion being a resiliently deformable annular sleeve shaped
to fit within a disc annulus, and a pair of opposed flexible
central portions each joining an edge of the sleeve, the edge
portion including an aperture for the introduction of a filling
material.
17. The flexible prosthetic cover of claim 16 further comprising a
flexible balloon catheter shaped to fit within the cover when
inflated, and arranged to fit through the aperture when deflated.
Description
[0001] The present invention relates to an intervertebral disc
insert for containing filling material, hydrogel or a biological
replacement of a nucleus pulposis, in the form of a prosthetic
jacket or cover. Such a prosthesis may be used to perform interbody
fusion or to replace damaged nucleus pulposis with hydrogel or
cells and matrix as a biological replacement. Such devices are
useful to replace damaged disc nuclei, whether in the lumbar or
other region of the spine, for example using a percutaneous fusion
technique.
[0002] The normal intervertebral disc is a highly specialized joint
between the intervertebral bodies from the second cervical vertebra
to the first sacral vertebra in the human body. A disc is made up
of a strong outer ring called the annulus, which is strongly
attached to the intervertebral bodies above and below through
collagen fibers, and a central nucleus. The nucleus comprises a
mesh of collagen fibers to which is attached proteoglycan molecules
which are hygroscopic. It can therefore be said to consist of a
central portion and an intermediate zone. The central portion
comprises 90% proteoglycan and 10% collagen, and the intermediate
zone rather less proteoglycan and proportionately more collagen.
The annulus comprises 90% collagen with about 10% proteoglycan,
which proteoglycan acts to allow a sliding motion between adjacent
layers during normal daily use.
[0003] Like all other joints in the body, intervertebral discs,
particularly lumbar intervertebral discs, are subject to various
types of injury, degeneration and disease. Painful disc syndromes
can develop due to the destruction of the intervertebral disc
structure.
[0004] It is often the case that back pain emanating from an
intervertebral disc arises from a damaged annulus because the
outermost third of the annulus itself is the only part of the disc
structure which is innervated. In theory then, the insertion of a
prosthesis which has itself a finite structure with inherent
strength but at the same time is held in position by the annulus
would permit the annulus itself to heal with the commensurate
relief of pain.
[0005] Such a prosthesis has been suggested by the present
applicant in WO 99/02108. This provides an intervertebral disc
nucleus prosthesis generally comprising a transudative or ion
transport material extended over the inner face of a prosthetic
woven or porous fabric chosen for its strength and immunological
neutrality. With this design, tissue can grow over and incorporate
the outer fabric, while water and very low molecular weight
materials can pass through the prosthetic fabric and the
transudative membrane, thus eliminating, or at least substantially
alleviating, any immunological problems. This allows the anchoring
of the replacement nucleus pulposis within a disc space while
preventing the ingrowth of bony trabeculae, thereby providing a
more satisfactory long term solution.
[0006] An alternative arrangement generally comprises a three layer
cover, wherein the outer and inner layer are formed of a strong
material in a sandwich construction with a middle layer of a
transudative material of a small pore size. Very high pressures are
present in use within the normal disc nucleus. To counteract this
it is often necessary to introduce a hydrogel or other suitable
substance into the cover in a liquid or powdered state. Thus, the
hydrogel would have a tendency to escape through the cover were it
not so constructed as to combine strength with an ability to retain
the hydrogel which might otherwise leak out through the pores in
the cover. This alternative jacket construction addresses this
concern. Furthermore, materials have been developed which have both
strength and also function as a transducive membrane, e.g.
Goretex.
[0007] Another alternative arrangement is to have a cover of a
relatively impermeable material, for example polyurethane, which is
both strong and bio-compatible. In such arrangements, a hydrogel
and water mixture can be added in a pre-defined amount and ratio,
so as to produce a consistency which substantially replicates the
properties of the natural nucleus.
[0008] The various prosthetic arrangements described above remain
in position due to the snug fit within the annulus, and by virtue
of the prosthesis being considerably larger than the hole in the
annulus through which it was originally inserted. Also, adhesions
will develop between the prosthesis and the annulus over time.
[0009] Orientation of the prosthesis is facilitated by introducing
apparatus including a tubular external valve body which may be
internally screw threaded. An introducer rod is passed through the
body and may have an external screw thread for engagement
therewith. The rod thus serves as a stiffening device for
positioning the cover in the disc cavity. Where screw threads are
provided, rotation of the rod extends or retracts the distal end of
the rod further to facilitate orientation of the cover. The cover
preferably has a strengthened portion opposite the valve in which
the distal end of the rod may be seated.
[0010] According to the present invention, there is provided a
flexible prosthetic cover shaped to form a replacement nucleus
pulposis for an intervertebral disc and comprising an aperture for
the introduction of filling material therein, and an elongate
introducer member configured to pass into the aperture, the cover
having a strengthened portion substantially opposite the aperture
for engaging the distal end of the member, the strengthened portion
and the said distal end being arranged to interlock so as to
prevent relative rotation there between, for facilitating
orientation of the cover. The aperture preferably comprises an
internal valve such as a flap valve. Thus the cover may be
accurately seated within the disc space without the need for an
external valve body.
[0011] In one embodiment, the distal end of the introducer member
or rod may be cruciate or flat, and the strengthened portion may be
a seat having a correspondingly shaped slot or cross-shaped recess
for receiving it. Thus, the surgeon may extend the prosthesis into
the cavity between the adjacent vertebrae, using the introducer rod
as a temporary stiffening device. With the introducer rod seated in
the edge portion of the prosthesis, the cover is held in the
required orientation, and precise alignment may be achieved by
rotating the introducer rod.
[0012] Preferably, the strengthened portion comprises a
radio-opaque marker for indicating the position or orientation of
the strengthened portion, and thus of the cover.
[0013] The introducer member may have an internal channel and an
aperture at or adjacent the distal end therefore communicating with
the channel for allowing the injection of filling material into the
cover. Thus no further equipment will be required for injecting the
filling material. Alternatively, the aperture may be arranged to
accept an introducer tube shaped to pass over the introducer member
and to form a channel there between for allowing the injection of
filling material into the cover, after removal of the introducer
member.
[0014] The introducer member may comprise a balloon, such that when
the cover is inserted into a nuclear cavity in a rolled or folded
state, the balloon may be inflated to cause the cover to unfold and
fill the nuclear cavity. Such an arrangement may be important where
the cover is designed for a percutaneous fusion procedure, for
example as outlined below.
[0015] The cover may include a deformable porous body shaped to fit
within the cover, formed for example of a very fine mesh or very
loose roll or sponge of material. This may for example be made up
of very fine polypropylene or other material. The body is formed in
such a way that it may be inserted into the cover through the
aperture either before the cover is inserted into the disc nucleus
cavity, or when the cover is in place. The body may be attached to
the cover. Thus, once the filling material such as hydrogel is
introduced its properties may effectively be altered such that it
will not flow as a liquid, but will deform in a way more similar to
the natural disc nucleus.
[0016] Where the disc nucleus has degenerated to an extent beyond
that in which a prosthetic disc nucleus (as discussed above) can
usefully be inserted, then an alternative is to carry out a
percutaneous fusion on the affected intervertebral segment.
[0017] According to the present invention there is also provided a
prosthetic cover for an intervertebral disc comprising an edge
portion comprising a resiliently deformable annular sleeve, and a
pair of opposed central portions each joining an edge of the
sleeve, the edge portion including an aperture for the introduction
of a filling material.
[0018] Preferably, the central portions are arranged, when the
cover is filled with a filling material, to allow the filling
material to pass there through.
[0019] For example, the central portions may be formed of a weaker
material than that of the edge portion, which under pressure will
give to allow the filling material to burst through pores or
weakened layers in it. Advantageously the material of the central
portion may be made of a material which is not only weakened but
will reabsorb in time allowing replacement by bone or other
material so introduced. Alternatively, it may be made of an open
weave or such structure as will allows the filling material to
easily pass there through and come into contact with the bone of
the end plates. It may allow blood vessels from the adjacent end
plate bone to pass through it, and grow into the bone graft or
other material placed inside the cover, to allow vascularisation of
bone graft and conversion to solid bone.
[0020] Thus, the prosthetic cover may be inserted, in the form of a
substantially kidney shaped balloon, into the disc cavity following
removal of the nucleus in such a way that it fits the shape of the
cavity. The annular sleeve, generally in the shape of a car tyre,
fits within the disc annulus, with the thin central portions
adjacent the end plates of the superior and inferior vertebral
bodies. When a filling material is injected into the cover under
pressure, the material breaks the weakened central portions, or
bursts through the open weave, and pressurizes the annular sleeve
against the annulus, thereby preventing its escape through any
weaknesses or tears in the disc annulus that may be present.
[0021] The end plates of the vertebral bodies are preferably
prepared by creating holes in them. When the filling material,
which may be cement or bone substitute material, bursts through the
central portions, it may communicate directly with the prepared end
plates of the vertebral bodies, and "key" into holes created in
them.
[0022] Seating of the cover may alternatively be achieved by
insertion of a balloon catheter into the cover, which is inflated
to fill the inside thereof. After ensuring correct seating, the
balloon is deflated and an outer filling tube is passed over it
into the cover. The balloon may then be removed and the material
injected.
[0023] The aperture may be provided as part of a valve structure,
which is preferably formed of an imaging transparent material, for
example titanium, carbon fibre or a durable biocompatible plastics
material such as polypropylene. In one preferred embodiment, the
valve structure includes a one way valve arrangement which may be a
flap valve partially attached to an inside of the cover, such that
the valve structure will be in a closed state when an internal
pressure of the cover exceeds an exterior or injection pressure of
the hydrogel material. Alternatively, the one way valve arrangement
may be a conical nose with a narrower internal opening, again
directing the valve structure to a closed state under similar
circumstances. The conical configuration facilities insertion of
the introducer rod.
[0024] The valve structure may comprise a valve body with a
longitudinal bore therein, and obturating means associated with the
bore. The valve body is configured to be fluidly secured to the
edge portion of the prosthetic device. For example, an exterior
portion of the valve body may be attached to the edge portion of
the cover such that the longitudinal bore is in fluid communication
with an interior of the cover. The obturating means is configured
to selectively allow passage of filling material, such as hydrogel
through the longitudinal bore. The valve body may be generally
symmetrical and the longitudinal bore may extend axially within the
valve body.
[0025] Any suitable filling material may be used, for example
polyvinyl alcohol. The filling material may be hydrogel, for
example a polyvinyl alcohol material, such as HYPAN.RTM., developed
into a fluid or liquid form which will easily pass through the
valve structure and subsequently harden. Ideally, the swelling
pressure of the resultant hydrogel is in a range similar to, or as
close as possible to, a normal lumbar intervertebral disc. Ideally,
a hydrogel is used which has similar Theological properties to the
normal nucleus.
[0026] The prosthesis of the present invention is preferably sized
such that an internal surface area of a nuclear cavity is virtually
the same as the prosthesis. This will ensure that load distribution
within the resulting prosthesis is similar to that of a normal
intervertebral disc. The technology of hydrogels at the present
time means that the swelling pressure of hydrogel can only
approximate to one quarter or one third of a normal disc. So to
retain their ability to maintain disc height, it is preferable to
form the hydrogel as a solid or semi-solid material, or that the
hydrogel harden or cure following injection into the cover.
[0027] Alternatively, introduction of a mesh or loose coil or
sponge of a fine deformable material into the cover prior to
injection of the hydrogel may be carried out. This will have the
effect that when the hydrogel sets, the gel, mesh and cover will
form an integral structure with similar Theological properties to
the normal nucleus. In one alternative embodiment, a fine wire of a
radiolucent material is incorporated within the prosthesis to
demonstrate the position of a prosthesis in vivo.
[0028] In use, one preferred method of insertion of a prosthesis in
accordance with the present invention is as follows:--
[0029] A small skin incision is made with the point of a knife
adjacent a damaged intervertebral disc, including an annulus and a
nucleus, which has previously been extensively imaged by a Computer
Tomography or Magnetic Resonance Imaging. If necessary,
confirmation that it is the disc which is painful may be reached by
effecting provocative stress discography. This allows percutaneous
disc surgery to be carried out by a lateral approach whereby an
operating port and trochar is used to insert instruments laterally
between adjacent vertebrae in the spine through the paraspinal
musculature so entering the disc at the postlateral corner in the
safe triangle, inferior to the exiting nerve root. The trochar
creates a hole by spreading the fibres of the annulus and provides
for access to the nucleus portion of the intervertebral disc.
[0030] Chymopapain may be injected into the nucleus to digest the
proteoglycan structure thereof. Mechanical action as by a brush
with polypropylene bristles may be used to aid the breakdown of any
remaining collagen structure to enhance the effect of chymopapain
which may then be removed by suction. Subsequently an
intervertebral disc nucleus prosthesis in accordance with the
present invention is introduced through the disc annulus. The disc
annulus comprises an outer ring of strong collagenous fibrous
tissue. As previously described, the prosthesis preferably includes
a cover having an edge portion shaped to fit within the annulus,
and a valve structure. The valve structure, in one preferred
embodiment, includes the one-way valve arrangement (or conical
nose) and a body that may be knurled or fluted as appropriate. A
strengthening portion may be incorporated into the edge portion
immediately opposite the valve structure for receiving a distal end
of an introducer rod. This allows the relatively atraumatic
insertion of the prosthesis cover through the annulus into the
space created by the removed nucleus.
[0031] Prior to insertion, the external valve structure of the
prosthesis is preferably attached to an external introducer tube,
and the introducer rod is coaxially positioned within the external
introducer tube, and passes through the external valve structure.
The introducer rod serves as a temporary stiffening device,
allowing a surgeon to apply a pushing force on the cover. Thus,
with proper positioning of the introducer rod, engaged with the
strengthened portion in the edge portion of the cover, the surgeon
can extend the prosthesis cover into the cavity between adjacent
vertebrae. The function of the strengthened portion is to protect
the cover from damage by introducing the introducer rod. The
external introducer may then be rotated to precisely align the
strengthened portion of the cover within the annulus. The
introducer rod may be movable along its longitudinal axis, or may
be releasably attachable to the valve structure by a screw thread.
In one preferred embodiment, both the internal and external
introducers are attached to a prosthesis prior to insertion, and
the prosthesis is folded in such a way as to ensure its ease of
passage through the annulus into the nucleus. Such an arrangement
may be formed and inserted inside a delivery tube, which would in
turn be passed through the operating port to engage the hole in the
annulus, and ease passage of the cover into the nuclear cavity.
[0032] In a preferred embodiment, the cover preferably contains a
collapsible sponge, a mesh, or a fine coil which fills the cover,
and has a memory such that after insertion through the annulus into
the disc space, the sponge, mesh or coil will return to its
previous shape, i.e. the shape of the nucleus, and will expand
within the cover to fill the disc space. Once the prosthesis is
positioned within the disc space, the introducer rod is withdrawn.
Hydrogel material is then introduced into the prosthesis cover via
a syringe connected to the external introducer tube. In one
preferred embodiment, a distal end of the syringe is directed
through the external introducer tube and secured to the valve
structure. With this approach, the syringe has an internal seal, to
ensure that the hydrogel material passes through the valve
structure into the cover, and a locking mechanism to ensure a tight
seal with the valve structure. This may be achieved by an
arrangement, similar to the tubular spanner, in which the external
introducer tube is arranged to receive the syringe, and has grooves
to form a bayonet type fitting with pins provided on the
syringe.
[0033] The syringe of this embodiment further includes a tubular
piston rod and a piston that is selectively secured to a screw
configured to immediately close the valve structure after injection
of the hydrogel. In one embodiment, once a desired volume of
hydrogel has been injected into the cover of the prosthesis, and
the piston is at the bottom of the syringe, a screw driver may be
passed down a center of the piston to insert and tighten the screw
to the valve structure.
[0034] Alternatively, the screw and the screw driver may be
incorporated together into the piston, and the piston rod simply
turned to secure the screw to the valve structure. Alternatively,
the external introducer tube may be a cannula including two
proximal ports to facilitate injection of the hydrogel material.
With this configuration, a syringe is secured to one of the two
proximal ports. Hydrogel material is forced from the syringe into
the external introducer tube. The external introducer tube, in
turn, directs the hydrogel material to the valve structure and then
into the prosthetic cover. With the prosthesis filled adequately
with hydrogel material to a desired internal pressure, a screw is
then passed through the external introducer tube and secured to the
valve structure so as to retain the contents of the prosthesis. In
the event that the volume of hydrogel material needs to be
subsequently altered, this can be performed in a substantially
non-traumatic way by merely removing the screw and replacing the
contents of the prosthesic cover as necessary.
[0035] In an alternative embodiment, where an external valve
structure is not used, the introducer rod passes through a conical
valve and engages with the strengthened portion of the cover. In
this embodiment, the cover can lock with the introducer rod by way
of a cruciate flattened section at the distal end of the introducer
rod. Once the prosthesis is in position, a cannula is passed over
the introducer rod, which is then removed, leaving the cannula in
position within the cover. As mentioned hereinbefore, a sponge,
mesh or fine wire fill the cover, and may already be present within
the cover, or may be inserted through the introducer tube into the
cover. Once the cover is expanded in position, hydrogel is injected
to fill the cover, encompassing the sponge, or mesh, or coil,
before setting within the cover.
[0036] One aspect of the present invention will now be described in
detail by way of illustration only with reference to the
accompanying drawings.
[0037] FIG. 1A is a side sectional view of an intervertebral disc
nucleus prosthesis in accordance with the present invention;
[0038] FIG. 1B is a top sectional view of the prosthesis of FIG.
1A;
[0039] FIGS. 1C and 1D each show a side sectional view of the
prosthesis of FIG. 1B taken along the lines I-I, and a perspective
view of the distal end of the corresponding introducer rod, used
with the external valve structure is not used;
[0040] FIG. 2A is an enlarged side sectional view of the prosthesis
of FIG. 1A, including an introducer rod and external introducer
tube;
[0041] FIG. 2B is an enlarged, top sectional view of the
arrangement of FIG. 2A;
[0042] FIG. 3 shows in FIG. 3A a vertical section through an
intervertebral disc in the process of removal of a damaged nucleus
pulposis;
[0043] FIG. 3B shows the same view in transverse cross-section;
[0044] FIG. 4, shows in FIG. 4A a cross-section a prosthetic cover
in accordance with the present invention being introduced between
adjacent vertebrae, whereas FIG. 4B shows the same view of the
cover in accordance with the present invention being introduced in
transverse cross-section;
[0045] FIG. 5 shows in FIG. 5A the insertion of a hydrogel into the
prosthesis in accordance with the present invention in vertical
cross-section, whereas FIG. 5B shows the same view in transverse
section, and FIGS. 5C and 5D show cross-sectional views of a
syringe for use with the prosthesis;
[0046] FIG. 6 shows in FIG. 6A a vertical cross-section of the
completed prosthesis, while FIG. 6B shows the same view as FIG. 6A
in transverse cross-section; and
[0047] FIG. 7 shows in FIGS. 7A and 7B alternative embodiments of a
further prosthesis and introducer rod according to the
invention.
[0048] One embodiment of an intervertebral disc nucleus prosthesis
10 is shown in FIGS. 1A and 1B. The prosthesis 10 includes a cover
12, a filler material 14 and an aperture in the cover comprising a
valve structure 16. The cover 12 encompasses the filler material 14
and is sealed to a portion of the valve structure 16. In this
regard, the valve structure 16 is fluidly connected to an interior
of the cover 12. Notably, the prosthesis 10 is shown FIGS. 1A and
1B in an inflated state.
[0049] The cover 12 is generally in the form of a kidney shaped
balloon comprising an edge portion in the shape of an annular
sleeve 13, having a shape generally similar to that of a car tyre,
and two opposed central portions 15 joining each edge of the sleeve
13 to close the cover 12. The sleeve 13 is formed of a resilient
deformable material and is shaped to fit within the annulus of an
intervertebral disc following removal of the disc nucleus, as
described below. The central portions 15 are formed of a flexible
thin or weakened material, which allows the passage of the filler
material 14 there through under pressure. For example, the flexible
material may break or allow the filler material 14 to burst through
pores or weakened layers in it under filling pressure. For example,
the filler material may be a composite hydroxy apatite paste,
configured to harden within the cover 12 between vertebral bodies.
When injected under pressure, the filler material will key into
holes in the vertebral bodies. The composite hydroxy apatite paste
hardens to a cement composition which provides support for the
spine, and ingrowth of blood vessels from the vertebral end plates.
Eventually the structure will remodel into bone. The cover may
alternatively be filled by packing small fragments of a porous
hydroxyapetite, such as Apapore, into the cavity, which will absorb
blood and bone marrow from the vertebral end plates into its pores.
It thus forms a gelatinous semi-solid structure when the blood and
bone marrow clots, which will vascularise as previously described
and form into bone.
[0050] Alternatively, as described in WO 99/02108, the filler
material 14 may be a hydrogel material, which is flowable in a
first state and relatively rigid in a second state. In one
preferred embodiment, the hydrogel material is polyvinyl alcohol
based configured to transition from a liquid form in a first state
to a hardened or cured form in a second state. For example, the
hydrogel material 14 may be HYPAN.RTM., available from Hymedix
International, Inc. Preferably, the hydrogel material 14 has a
consistency and swelling pressure of a normal disc nucleus.
Additionally, as referred to hereinabove, the hydrogel material 14,
in an alternative embodiment, may be reinforced by introducing a
sponge, mesh or fine wire inside the cover 12, either before
introduction of the cover 12 into a disc space, or after via the
introducer tube, and injecting the hydrogel material 14 in a liquid
state into the cover 12 such that the hydrogel material 14 cures
around the mesh. The resulting structure would be more able to
resist stresses in a way similar to the normal disc nucleus. The
mesh would be introduced into the cover 12 prior to implant, and
may be a fine polypropylene thread. With this configuration, the
mesh would easily deform to facilitate insertion of the cover 12
into the nucleus, after which the mesh would spring out once again
to fill the cover 12.
[0051] The valve structure 16 preferably includes a one-way valve
18, and an extension body 20. The one-way valve 18 is integrally
formed with the extension body 20, the combination of which forms a
longitudinal bore 24 through the valve structure 16. The one-way
valve 18 is shown in FIGS. 1A and 1B as being a conical nose. With
this configuration, the conical nose restricts flow of the filler
material 14 from the cover 12 through the valve structure 16.
Alternatively, the one-way valve 18 may be a flap valve (described
in greater detail below) to further inhibit back flow of the
hydrogel material 14 out from the cover 12.
[0052] The filler material 14 may be a soup or growth medium
containing nuclear cells or cartilage cells which have been
previously removed from the patient, and grown in an artificial
medium until enough cells are present to fill the nuclear cavity,
These cells may then be injected into the nuclear cavity space so
as to substantially fill the cavity with this material, which will
allow the body to replicate and rebuild a nuclear structure. In
such embodiments, the cover may be made of a degradable plastics
material, which, when degraded, will be replaced by a collagen
structure which replicates the normal nucleus.
[0053] As shown in FIGS. 1A and 1B, the sleeve 13 is secured about
the one-way valve 18 portion of the valve structure 16, and the
extension body 20 extends from the sleeve 13. The cover includes a
shaped strengthened portion 26 positioned opposite the valve
structure 16 for providing a seat for the introducer rod. The
shaped portion 26 is formed at an interior of the sleeve 13, and
may assume a circular form, having a shape such as a slot to engage
with a distal end of an introducer rod, as described below.
Alternatively, the shaped portion 26 may have a cylindrical recess,
into which the distal end of the introducer rod may be rotatably
inserted.
[0054] The intervertebral disc nucleus prosthesis 10 is shown in
greater detail in FIGS. 2A and 2B. Notably, the prosthesis 10 is
shown in a deflated state, with the filler material 14 (FIGS. 1A
and 1B) removed from the cover 12. Additionally, the prosthesis 10
is shown in FIGS. 2A and 28 as being attached to an introducer rod
28 and an external introducer tube 40. The extension body 20 of the
valve structure 16 includes a proximal portion 32 and a distal
portion 34. In this regard, the proximal portion 32 is connected to
the one-way valve 18.
[0055] Use of the introducer rod 28 and the external introducer
tube 40 is described in greater detail below. Generally speaking
the external introducer tube 40 is an elongate tube having an
internal passage. The internal passage of the external introducer
tube 40 has a diameter approximating to an outer diameter of the
extension body 20. The introducer rod 28 is a relatively stiff
member having a diameter less than that of the internal passage of
the external introducer tube 40. Thus, the introducer rod 28 is
coaxially received in the external introducer tube 40. Further, the
introducer rod 28 includes a distal end 42 which is shaped, for
example cruciate, slotted, or cylindrical as required, to engage
with the shaped portion 26 of the cover. The introducer rod 28 has
a diameter approximating to that of the longitudinal bore 24 of the
valve structure 16 but has a diameter slightly less than the
longitudinal bore so as to be able to freely rotate therein.
Alternatively, the introducer rod 28 may be partially screw
threaded to engage the inside of the valve structure.
[0056] The distal end 42 of the introducer rod 28 may, for example,
be flattened and the shaped portion 26 of the cover 12 may have a
corresponding elongate slot or groove 27 as shown in FIG. 1C.
Alternatively, the distal end 42 may have another shape such as a
cruciate form, and the shaped portion 26 may have a corresponding
recess or groove 29 as shown in FIG. 1D.
[0057] A preferred method of implanting the intervertebral disc
nucleus prosthesis 10 is substantially as follows. A patient is
first extensively imaged by traditional means to obtain the level
and condition of a damaged disc 50, in the present case a damaged
lumbar disc, as shown in FIGS. 3A and 3B. The disc 50 is basically
comprised of an annulus 52 and opposing end plates 54 surrounding a
nucleus 56.
[0058] Following imaging, the nucleus 56 may be removed as is shown
in FIGS. 3A ands 3B. A preferred lateral percutaneous approach to
the disc 50 is used. An incision is made in the skin at the
appropriate point, and under imaging control a needle is passed to
the posterolateral point of the annulus. The tissues are then
dilated by a series of dilating tubes, and finally an operating
port 30 is passed down to the level of the annulus. The dilators
are then removed, leaving an operating channel. A hole 58 is
imparted to access the nucleus 56, and a needle (not shown) of
appropriate bore is used to enter the nucleus 56 via the hole 58
and chymopapain is injected to digest the proteoglycan of the
nucleus 56. This may be done either prior to the creation of the
hole 58 or through it. A polypropylene bristle brush (not shown)
may then be inserted to help break down any remaining structure of
the nucleus 56 and to aid the digestion of the nucleus 56, which
may be removed by suction. Additionally or alternatively, the
nucleus may be removed piecemeal by rongeurs.
[0059] Subsequently, the external introducer tube 40, otherwise
attached to the prosthesis 10 as previously described, is utilized.
It should be recalled that at this stage, the cover 12 is deflated
or empty. In this position, the longitudinal bore 24 of the valve
structure 16 is aligned with the internal passage of the external
introducer tube 40. The introducer rod 28 is then coaxially placed
through the internal passage and the longitudinal bore 24. The
distal end 42 engages the shaped portion 26 of the cover 12, such
that the flattened portion fits into the groove 27. Thus, the
introducer rod 28 can be extended within the cover 12 to define a
preferred diameter of the cover, approximately that of the disc 50
(FIG. 3A), and to hold the cover 12 in the correct orientation.
[0060] The surgeon then directs the external introducer tube 40 to
insert the cover 12 within the disc 50 as shown in FIGS. 4A and 4B.
More particularly, the cover 12 is directed through the hole 58 in
the annulus 52 to the area once occupied by the nucleus 56. The
introducer rod 28 acts as a stiffener, allowing the surgeon to push
or force the cover 12 through the annulus 52 and into the area
occupied by the nucleus 56. Rotation of the introducer rod 28
causes the sleeve 13 to rotate therewith. Thus the surgeon may
control the orientation of the cover to align the sleeve 13
precisely within the disc annulus 52.
[0061] Notably, the operating port 30 is shown in FIGS. 4A and 4B
as a cannula having two proximal ports 74 and 76. With this
configuration, the introducer rod 28 and the external introducer
tube 40 are positioned to extend outwardly from the first proximal
port 74.
[0062] Once the cover 12 has been properly positioned within the
space previously occupied by the nucleus 56, the introducer rod 28
is retracted from the external introducer tube 40. More
particularly, the introducer rod 28 is withdrawn both from the
longitudinal bore 24 of the valve structure 16 and towards the
first proximal port 74. The introducer rod 28 may be fully
withdrawn from the first proximal port 74 so long as a cap (not
shown) is used to prevent any back flow of the hydrogel material
14.
[0063] The filler material, which may be a composite ceramic paste,
or hydrogel material 14, is then injected into the cover 12, as
shown in FIGS. 5A and 5B which depict the prosthetic cover 12 in a
fully inflated state. This is achieved in two possible ways.
Firstly, a measured amount of the filler material 14 is introduced
into a specially designed syringe as shown in FIGS. 5C and 5D. The
syringe 80 is long and slender, having a seal 81 at the distal end
thereof, and is introduced into the external introducer tube 40 and
locks into it in such a way that it forms a seal with the valve
structure 16. This may be achieved by a locking mechanism, similar
to the tubular spanner arrangement as described previously, wherein
the syringe 82 inserted into the introducer tube has two opposed
locking grooves 84 for engaging opposed pins 86 provided on the
outside of the syringe 80, at the proximal end thereof, in the
manner of a bayonet fitting.
[0064] The filler material 14 is injected into the prosthesis cover
12 until a piston 88 of the syringe is adjacent the valve structure
16. In a preferred embodiment, the piston of the syringe includes a
locking screw 22 embedded in it which can be secured to the
proximal portion 32 of the external valve structure. Thus the
piston acts as a screw-driver such that after the hydrogel has been
injected, the screw engages the hole in the external valve and the
screw driver is turned to tighten it. The syringe may then be
withdrawn by releasing the pins 86 from the grooves 84.
[0065] The filler material 14 may be introduced via the second
proximal port 76 and flows down the internal passage 40 of the
external introducer tube 40 through the bore 24 in the valve
structure 16 and into the deflated prosthetic cover 12 so as to
inflate the same to the position shown in FIG. 5A. The introduction
of the filler material 14 is continued until the prosthetic cover
12 is adequately filled with the hydrogel material 14.
[0066] With reference now to FIG. 6, FIGS. 6A and 6B show sealing
of the valve structure 16. A screwdriver (not shown) having a set
screw 22 is introduced through the external introducer tube 40 and
pressed through any remaining the filler material 14 until the
screw thread on the sealing set screw 22 comes into contact with
the internal thread 38 in the extension body 20 of the valve
structure 16. The screw 22 is then rotated to close the bore 24.
With the screw 22 secured to the valve structure 16, the eternal
introducer tube 40 is disengaged from the prosthesis valve
structure 16.
[0067] The screw driver can freely rotate with the tubular
introducer, and engages with grooves in the valve so preventing
rotation of the valve by retaining the tubular screw driver against
rotation. The tubular introducer is then disengaged from the valve
structure whereupon the screw driver is removed.
[0068] In an alternative method of seating the cover, a balloon
catheter (not shown) is provided. This is inserted into the cover
and inflated to fill the inside and ensure correct positioning. The
balloon may then be deflated and an outer filling tube passed over
it into the cover. The balloon is then removed and the material
injected into the cover. In this case, the external valve structure
and introducer rod may not be required, and a simple flap may be
provided over the aperture to act as a one-way valve.
[0069] By means of the foregoing process, a replacement nucleus
pulposis can be inserted between adjacent vertebrae successfully
with the removal of pain and incapacity, and prevention of the
development of secondary degenerative changes in the disc due to
the replacement of damaged or degenerated intervertebral disc.
Where the disc has degenerated beyond repair, a percutaneous fusion
may be performed by injecting a hydroxy apatite cement into a cover
with a strengthened annular sleeve and weakened central portions
each joining an edge of the sleeve.
[0070] The invention relates therefore to the improved prosthetic
device, and to a method for its insertion.
[0071] In an alternative form of the prosthesis 10, the valve
structure 16 may allow passage of the introducer rod 28 through the
flap valve 18 to engage the strengthened portion 26. In this latter
case, the introducer rod 28 consists of a cannula with an internal
trochar having a shaped internal end which engages the strengthened
portion 26. The prosthesis 10 is inserted by pushing it into the
nuclear cavity whereupon the trochar is removed. A syringe,
containing the hydrogel material or a hydroxy apatite paste 14 is
then attached to the external end of the cannula and the hydrogel
material or hydroxy apatite paste 14 injected. Since the internal
pressure is greater than the injection pressure, the flap valve 18
will close on removal of the cannula. The hole (or operating port)
58 in the annulus 52 will tend to close as the fibres are
stretched, so that the prosthesis 10 which by this time is far
greater in size than the operating port 58 is easily retained in
position.
[0072] In another embodiment, as shown in FIGS. 7A and 7B, the
cover may be a simple flexible jacket 60 having a flap valve 62 as
previously described. In this case a radio-opaque marker is
provided in the strengthened portion 64 such that its position and
orientation may be visualized radiologically. Where no external
valve body is provided as in this example, the introducer rod not
only introduces the cover into the center of the disc, but also
acts as a means by which the filler material is injected into the
cover. Therefore, referring to FIG. 7A up to the point where it is
shaped at the distal end to engage the strengthened portion, the
introducer rod 66 is tubular. Filling material can be injected
through the tube into the cover through side openings 68
therein.
[0073] Alternatively, referring to FIG. 7B, an outer tube 70 may be
inserted over the rod 72 into the aperture of the cover 60. The
introducer rod 72 may or may not be removed, and the filling
material can be injected through the outer tube 70.
[0074] Such a flexible cover preferably includes the mesh structure
previously described.
* * * * *