US20090240341A1

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Publication number: US20090240341A1
Application number: US12/017,430
Authority: US
Inventors: Ashish Diwan; Zoran Milijasevic; Johnathon Choi; Sandra Fisher
Original assignee: Columna Pty Ltd
Current assignee: Kunovus Pty Ltd
Priority date: 2005-08-15
Filing date: 2008-01-22
Publication date: 2009-09-24
Also published as: CN101242791A; KR20080043836A; AU2006281991A1; CA2617820A1; ZA200801247B; EP1915108A1; WO2007019631A1; US9216092B2; US20120290095A1; JP2009504279A; US20120330221A1

Abstract

A tissue prosthesis100 comprises an envelope38 of a biologically inert, elastically deformable material capable of being expanded to conform to an interior surface of a cavity36 formed at a site10 in a patient's body. A filler material60 is received in a fluent state in the envelope38. The filler material60 is of the same class of material as the envelope38 to form, when cured, together with the envelope38, a unified structure.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/AU2006/001176, filed on Aug. 15, 2006, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/708,670, filed on Aug. 15, 2005, the full disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION1. Field of the Invention

This invention relates generally to the repair of tissue in a body and, more particularly, to a method of, and equipment for, forming a tissue prosthesis in situ and to a tissue prosthesis. The invention has particular, but not necessarily exclusive, application in the field of minimally invasive intervertebral disc nucleus repair.

Joints of the musculoskeletal system of the human or animal body rely on the presence of healthy cartilaginous tissue for proper operation. Cartilaginous tissue can degenerate due to a number of causes, eg. age or injury. Degradation of the tissue can reach a point where movement can cause severe discomfort and pain.

In the case of the spinal column, it comprises a series of 26 mobile vertebral bones or vertebrae connected by 75 stable articulations that control motion. The vertebrae are generally divided into posterior and anterior elements by thick pillows of bone called pedicles. The anterior element of the vertebra is a kidney shaped prism of bone with a concavity directed posteriorly and has flat superior and inferior surfaces called end plates. An intervertebral disc is sandwiched between adjacent pairs of vertebrae forming a joint between the adjacent pair of vertebrae. These discs are viscoelastic structures comprising a layer of strong deformable soft tissue. The intervertebral discs are subjected to a considerable variety of forces and moments resulting from the movements and loads of the spinal column. Each intervertebral disc has two components being the annulus fibrosis circumscribing a nucleus pulposus. The intervertebral disc cooperates with the end plates of the vertebrae between which it is sandwiched.

The primary function of the nucleus pulposus of the disc is to give the disc its elasticity and compressibility characteristics to assist in sustaining and transmitting weight. The annulus fibrosis contains and limits the expansion of the nucleus pulposus during compression and also holds together successive vertebrae, resisting tension and torsion in the spine. The end plates of the vertebrae are responsible for the influx of nutrients into the disc and the efflux of waste products from within the disc.

With age or injury, a degenerative process of the disc may occur whereby its structures undergo morphological and biological changes affecting the efficiency with which the disc operates. Thus, the nucleus pulposus may reduce in volume and dehydrate resulting in a load reduction on the nucleus pulposus, a loss in intradiscal pressure and, hence, additional loading on the annulus fibrosis. In a normally functioning disc, the intradiscal pressure generated results in deformation of the end plates of the adjacent vertebrae generating the natural pumping action which assists in the influx of the nutrients and the efflux of waste products as stated above. A drop in intradiscal pressure therefore results in less end plate deformation. The nutrients supplied to the discal tissue is reduced and metabolic wastes are not removed with the same efficiency. This contributes to a degenerative cascade.

Radial and circumferential tears, cracks and fissures may begin to appear within the annulus fibrosis. If these defects do not heal, some of the nuclear material may begin to migrate into the defects in the annulus fibrosis. Migration of the nuclear material into the annulus fibrosis may cause stretching and delamination of layers of the annulus fibrosis resulting in back pain due to stimulation of the sinu-vertebral nerve. An intervertebral disc without a competent nucleus is unable to function properly. Further, since the spine is a cooperative system of elements, altering the structure and mechanics at one location of the spinal column may significantly increase stresses experienced at adjacent locations thereby further contributing to the degenerative cascade.

In the past, operative intervention has occurred to relieve lower back pain arising from intervertebral disc degeneration. Most of this operative intervention has been by way of a discectomy where leaking nuclear material is removed or, alternatively, fusion. The primary purpose of a discectomy is to excise any disc material that is impinging on the spinal nerve causing pain or sensory changes. Fusion means eliminating a motion segment between two vertebrae by use of a bone graft and sometimes internal fixation. Biomechanical studies show that fusion alters the biomechanics of the spine and causes increased stresses to be experienced at the junction between the fused and unfused segments. This promotes degeneration and begins the degenerative cycle anew. Clearly, being an invasive operative procedure, fusion is a risky procedure with no guarantee of success.

Due to the minimal success rate of the previous two procedures, as well as their inability to restore complete function to the spinal column, alternative treatments have been sought in the form of artificial disc replacements. Theoretical advantages of artificial disc replacement over a fusion procedure include preservation or restoration of segmental motion in the spine, restoration of intervertebral architecture and foraminal height, sparing of adjacent segments of the spine from abnormal stresses and restoration of normal biomechanics across the lumbar spine. The established artificial disc replacement procedure consists of techniques that require a surgical incision on the abdomen, retraction of large blood vessels, a total excision of the anterior longitudinal ligament, anterior and posterior annulus along with the nucleus and near total removal of the lateral annulus and implantation of an articulated prosthesis. This is a major spinal column reconstruction operation.

There is therefore a need for a surgical procedure which, as far as possible, restores the biomechanics of joints such as those between adjacent vertebrae of the spine by the provision of a tissue prosthesis mimicking natural, healthy cartilaginous tissue.

BRIEF SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

According to a first aspect of the invention, there is provided a tissue prosthesis which comprises:

- an envelope of a biologically inert, elastically deformable material capable of being expanded to conform to an interior surface of a cavity formed at a site in a patient's body; and
- a filler material received in a fluent state in the envelope, the filler material being of the same class of material as the envelope to form, when cured, together with the envelope, a unified structure.

The envelope may be of an elastomeric material capable of expanding to up to 100 times its relaxed state. Further, the filler material may be of an elastomeric material capable of absorbing shock and withstanding compressive, tensile, bending and torsional forces. The envelope may be expanded to be stretched and retained under tension after being charged with the filler material.

In this specification, the term “expanded” and its variations is to be understood as meaning “stretched elastically”.

Both the envelope and the filler material may be of an elastomeric material having a Shore Hardness in the range of between about 5 to 90 A. Preferably, the envelope and the filler material are of a silicone rubber material. However, to promote bonding between the envelope and the filler material, the envelope and the filler material may be of different grades of silicone rubber material and may be pre-treated in different ways prior to use.

The envelope may include a neck portion, the neck portion defining a zone of weakness for facilitating separation of the envelope from a delivery device. Further, the envelope may include a flow control device arranged at an inlet opening to the envelope for inhibiting back flow of the filler material from the envelope. In an embodiment, the prosthesis may include a flow control defining member, the flow control defining member being separate from the envelope and being arranged at the inlet opening to the envelope.

The envelope may carry a marker arrangement on an exterior surface for enabling the envelope to be used to assess dimensions and a shape of the cavity and positioning of the envelope in the cavity.

According to a second aspect of the invention, there is provided a tissue prosthesis which comprises:

- an envelope of a foraminous, chemically inert material shaped to conform to an interior surface of a cavity formed at a site in a patient's body in which the envelope is to be placed; and
- a filler material received in a fluent state in the envelope, the filler material being of an elastomeric material which, prior to being cured, is urged into foramens of the envelope to form an integrated structure which inhibits relative movement between the envelope and the filler material, in use, and once the filler material has cured.

The envelope may be of a knitted biological or synthetic polymeric material. More particularly, the envelope may be of a knitted polyester material, such as polyethylene terephthalate (PET). Further, the envelope may be coated with a material of the same class as the filler material.

Once again, the envelope may include a flow control device arranged at an inlet opening to the envelope for inhibiting back flow of the filler material from the envelope. The prosthesis may include a flow control defining member, the flow control defining member being separate from the envelope and being arranged at the inlet opening to the envelope.

According to a third aspect of the invention, there is provided a method of forming a tissue prosthesis in situ at a site in a patient's body, the method comprising:

- accessing the site in the patient's body;
- if necessary, removing tissue from the site to form a cavity;
- inserting an envelope of a biologically inert, elastically deformable material into the cavity;
- charging a filler material, in a fluent state, into the envelope to cause the envelope to expand and conform to the shape of the cavity; and
- allowing the filler material to cure, the filler material being of the same class of material as the envelope so that, when the filler material has cured, a unified prosthesis is formed.

The method may include accessing the site by inserting an introducer through an aperture formed in tissue associated with the site and removing nuclear tissue, if required, from the site. The nuclear material may be removed by mechanical, ultrasonic, laser, Argon gas or radio frequency ablation, or the like, in combination with suction and irrigation. For example, mechanical removal may be effected by using a reaming-type tool.

Once the nuclear tissue has been removed, the method may include checking dimensions of the cavity so formed. Thus, the method may include using the envelope, containing suitable markers, to check the dimensions of the cavity. This may be effected by inflating the envelope using a suitable fluid such as a water/saline solution. Instead of using the envelope with markers, the method may include using a flexible wire fed down the introducer and checking the position of the wire using a fluoroscopic x-ray technique once the wire is in position. In yet a further way of checking the dimensions of the cavity, the method may include deploying a jacket of similar dimensions to the envelope in the cavity, inflating the jacket with the water/saline solution and, using a fluoroscope, detecting the periphery of the jacket by radio opaque markers on an outer surface of the jacket.

Once the envelope has been placed in position, the method may include checking the integrity of the envelope, i.e. to ensure that the envelope does not have any leaks or other defects. This may be effected by filling the envelope with the water/saline solution.

The method may include evacuating an interior of the envelope to inhibit the formation or entrapment of fluid bubbles in the filler material. Instead, the method may include commencing filling of the envelope from a distal end of the envelope and progressively filling the envelope towards a proximal end of the envelope (by withdrawing a filler tube or allowing the material buoyancy to lift the filler tube) to inhibit the formation or entrapment of fluid bubbles in the filler material. In the latter case, either a delivery device by which the envelope is introduced into the cavity or the envelope may define a formation allowing the escape of air as the envelope is charged with the filler material.

The method may include, once filling of the envelope has been completed and a filler element withdrawn, occluding the aperture in the tissue of the site. Occluding the aperture may comprise closing it off by a non-return valve or by crimping closed a neck portion of the envelope. A removable tube may be nested over the delivery device and may be propelled distally to remove the envelope and valve from the delivery device.

The method may include attaching the envelope to a distal end of a tubular delivery device and everting the envelope on the distal end prior to insertion of the delivery device into the introducer for delivery of the envelope into the cavity of the site.

Preferably, the method includes accessing the site percutaneously in a minimally invasive surgical procedure. Hence, the method may be used to perform minimally invasive intervertebral disc nucleus replacement and may comprise:

- forming an aperture in an annulus fibrosis of the disc percutaneously;
- extracting a nucleus pulposus of the disc to form a disc cavity bounded by the annulus fibrosis of the disc and end plates of vertebrae between which the disc is located;
- inserting the envelope, in a relaxed state, into the cavity through the aperture;
- charging the filler material into the envelope to cause the envelope to expand and conform to the shape of the disc cavity;
- allowing the filler material to cure to form, together with the envelope, the unified prosthesis; and
- occluding the aperture.

Preferably, the method includes expanding and stretching the walls of the envelope and retaining the envelope under tension after charging it with filler material.

According to a fourth aspect of the invention, there is provided equipment for forming a tissue prosthesis in situ at a site in a patient's body, the equipment comprising:

- a delivery device displaceably receivable in a lumen of an introducer, the delivery device defining a passageway;
- an envelope carried at a distal end of the delivery device, the envelope being of a biologically inert, elastically deformable material capable of being expanded to conform to an interior surface of a cavity formed at the site; and
- a supply of a filler material chargeable in a fluent state into the envelope through the passageway of the delivery device, the filler material being of the same class of material as the envelope to form, when cured, together with the envelope, a unified prosthesis.

The equipment may include an aperture forming element to form an aperture into the site, the aperture forming element being receivable through the introducer for delivery to the site. The aperture forming element may, for example, be a trocar.

Further, the equipment may include a tissue removal mechanism insertable through the aperture for removing tissue, if required, to form the cavity. As indicated above, the tissue removal mechanism may comprise mechanical, ultrasonic, laser, Argon gas or radio frequency ablation mechanisms, or the like in combination with suction and irrigation. For example, the tissue removal mechanism may be a reaming-type tool.

The envelope may be of an elastomeric material capable of expanding to up to 100 times its relaxed state. The envelope is preferably expanded to be stretched and retained under tension after being charged with the filler material.

The envelope may include a neck portion, the neck portion defining a zone of weakness for facilitating separation of the envelope from the delivery device. Further, the envelope may includes a flow control device arranged at an inlet opening to the envelope for inhibiting back flow of the filler material from the envelope. The equipment may include a flow control defining member, the flow control defining member being separate from the envelope and being arranged at the inlet opening to the envelope.

The filler material may be of an elastomeric material capable of absorbing shock and withstanding compressive, tensile, bending and torsional forces. More particularly, the envelope and the filler material may be of an elastomeric material having a Shore Hardness in the range of about 5 to 90 A. The envelope and the filler material may be of a silicone rubber material.

The equipment may include a dispenser containing the supply of filler material.

Further, the equipment may include a sensing arrangement configured to sense a parameter of the filler material charged into the envelope. The sensing arrangement may comprise a pressure sensor for sensing the pressure of filler material charged into the envelope, a temperature sensor for sensing the temperature of the filler material charged into the envelope, be configured to sense the quantity of filler material charged into the envelope and/or comprise a flow rate sensor for sensing the rate of flow of the filler material into the envelope. Further, the sensing arrangement may be configured to sense the presence of air bubbles in the filler material charged into the envelope.

According to a fifth aspect of the invention, there is provided equipment for forming a tissue prosthesis in situ at a site in a patient's body, the equipment comprising:

- a tubular delivery device, the delivery device defining a passageway, an envelope of the prosthesis being mountable to a distal end of the delivery device to be received in a cavity at the site;
- a filler member receivable in the passageway of the delivery device, the filler member being receivable with clearance in the passageway to define a gap to enable fluid to be evacuated at least from the envelope; and
- a removal mechanism carried by the delivery device for enabling the envelope to be removed from the delivery device after the envelope has been charged with filler material via the filler member.

The equipment may include a tubular introducer and an aperture forming element, such as a trocar, to form an aperture at the site, the aperture forming element being receivable through the introducer for delivery to the site.

Further, the equipment may include a tissue removal mechanism insertable through the aperture for removing tissue, if required, to form the cavity.

The introducer and the delivery device may include a retaining arrangement for retaining the delivery device with respect to the introducer.

In addition the equipment may include a supply of filler material attachable to a proximal end of the filler member. The filler material may be a mixture of a plurality of parts and the supply of filler material may comprise a dispenser defining a plurality of chambers in each of which one part of the filler material is received prior to use. The dispenser may further comprise a mixer arranged intermediate an outlet of the dispenser and the proximal end of the filler member for mixing the filler material prior to charging it into the envelope.

A proximal end of the delivery device may carry a connector for connection to an evacuating mechanism such as an evacuation pump.

The equipment may include the envelope, the envelope being of an elastomeric material capable of expanding to up to 100 times its relaxed state. Preferably, the envelope is expanded to be stretched and retained under tension after being charged with the filler material. The envelope may include a neck portion, the neck portion defining a zone of weakness for facilitating separation of the envelope from the delivery device.

Further, the envelope may include a flow control device arranged at an inlet opening to the envelope for inhibiting back flow of the filler material from the envelope. The equipment may include a flow control defining member, the flow control defining member being separate from the envelope and being arranged at the inlet opening to the envelope.

A distal end of the filler member may carry an engaging member which engages the flow control device to at least partially open the flow control device and to allow the interior of the envelope to be evacuated prior to being charged with the filler material.

The filler material may be of an elastomeric material capable of absorbing shock and withstanding compressive, tensile, bending and torsional forces. The envelope and the filler material may be of an elastomeric material having a Shore Hardness in the range of about 5 to 90 A. Preferably, the envelope and the filler material are of a silicone rubber material.

The equipment may include a sensing arrangement configured to sense a parameter of the filler material charged into the envelope. The sensing arrangement may comprise a pressure sensor for sensing the pressure of filler material charged into the envelope, a temperature sensor for sensing the temperature of the filler material charged into the envelope, be configured to sense the quantity of filler material charged into the envelope and/or comprise a flow rate sensor for sensing the rate of flow of the filler material into the envelope. Further, the sensing arrangement may be configured to sense the presence of air bubbles in the filler material charged into the envelope.

According to a sixth aspect of the invention, there is provided equipment for forming a tissue prosthesis in situ at a site in a patient's body, the equipment comprising:

- a tubular delivery device, the delivery device defining a passageway, an envelope of the prosthesis being mountable to a distal end of the delivery device to be received in a cavity at the site;
- a stiffening element arranged to project from a distal end of the delivery device with the envelope, in use, being received over the stiffening element to be supported by the stiffening element; and
- a removal mechanism carried by the delivery device for enabling the envelope to be removed from the delivery device after the envelope has been charged with filler material via the filler member.

In one embodiment, the stiffening element may be an elongate element, such as a rod or tube, receivable with clearance in the passageway of the delivery device to define a gap to enable fluid to be evacuated at least from the envelope to enable fluid to be withdrawn from the envelope to collapse the envelope on to a distal end of the elongate element projecting from the distal end of the delivery device.

The equipment may include a filler member receivable in the passageway of the delivery device after removal of the stiffening element, the filler member being receivable, after removal of the stiffening element, with clearance in the passageway to define a gap to enable fluid to be evacuated at least from the envelope.

In another embodiment, the equipment may include a tubular filler member receivable in the passageway of the delivery device, the filler member being receivable with clearance in the passageway to define a gap to enable fluid to be evacuated at least from the envelope and the stiffening element being an elongate element receivable through the passage of the filler member.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are now described by way of example only with reference to the accompanying drawings in which:

FIGS. 1-8 show schematic illustrations of various steps of a method, in accordance with an embodiment of the invention, for forming a tissue prosthesis in situ at a site in a patient's body;

FIG. 9 shows a schematic illustration of a delivery device for use in the method;

FIG. 10 shows a schematic, sectional side view of part of equipment, in accordance with another embodiment of the invention, for forming a tissue prosthesis, in situ at a site in a patient's body;

FIG. 11 shows a schematic, sectional side view of another embodiment of the equipment;

FIG. 12 shows a schematic, side view and end view of part of the equipment;

FIG. 13 shows a sectional side view of an envelope, attached to a delivery device, the envelope forming part of a tissue prosthesis, in accordance with yet a further embodiment of the invention;

FIG. 14 shows a sectional side view of another mounting of the envelope on the delivery device;

FIGS. 15-17 show different shapes of envelopes for use in the tissue prosthesis;

FIG. 18 shows a plan view of another embodiment of equipment for forming a tissue prosthesis, in situ, at a site in a patient's body;

FIG. 19 shows a sectional side view taken along line XIX-XIX inFIG. 18;

FIG. 20 shows, on an enlarged scale, a sectional side view of the part of the equipment encircled by circle ‘A’ inFIG. 19;

FIG. 21 shows, on an enlarged scale, a sectional side view of the part of the equipment encircled by circle ‘B’ inFIG. 19;

FIG. 22 shows a sectional side view of yet a further embodiment of equipment for forming a tissue prosthesis, in situ, at a site in a patient's body;

FIG. 23 shows on an enlarged scale, a sectional side view of the part of the equipment encircled by circle ‘C’ inFIG. 22; and

FIG. 24 shows on an enlarged scale, a sectional side view of the part of the equipment encircled by circle ‘D’ inFIG. 22.

DETAILED DESCRIPTION OF THE INVENTION

While this invention has been developed specifically for the field of minimally invasive intervertebral disc nucleus replacement, it will readily be appreciated that the invention has applications in other fields requiring tissue prostheses. However, for ease of explanation, embodiments of the invention will be described below with reference to minimally invasive intervertebral disc nucleus replacement.

Anintervertebral disc10 is arranged between

adjacent vertebrae

12 and14. Thedisc10 comprises anannulus fibrosis16 made up of concentric layers of fibrous tissue. Theannulus fibrosis16 circumscribes anucleus pulposus18 of thedisc10, thenucleus pulposus18 being of soft tissue. Thedisc10 is sandwiched betweenend plates20 of the

vertebrae

12 and14. Relative movement between the

vertebrae

12 and14 causes compression of thenucleus pulposus18 by theend plates20. This serves to assist in the influx of nutrients into thedisc10 and the efflux of waste products from within thedisc10.

In a method of forming a tissue prosthesis, in situ, in accordance with an embodiment of the invention, a damaged nucleus pulposus18 of thedisc10 is removed and is replaced by an artificial prosthesis. Thus, in an initial step as shown inFIG. 1 of the drawings, anintroducer22 is inserted percutaneously into abutment with thedisc10. An aperture forming element in the form of atrocar24 is inserted into alumen26 of theintroducer22. Apoint28 of the trocar pierces theannulus fibrosis16 of thedisc10 forming an aperture30 (FIG. 2) in theannulus fibrosis16 of thedisc10.

After the formation of theaperture30 thetrocar24 is removed from theintroducer22. Once thetrocar24 has been removed, a nucleotomy is performed on thedisc10. The nucleotomy involves the removal of nuclear tissue constituting thenucleus pulposus18. While various methods of removing the nucleus pulposus can be used, the example shows the use of amechanical device32. Themechanical device32 comprises a reamingtool34. Themechanical device32 is inserted through thelumen26 of the introducer and theaperture30 in theannulus fibrosis16 of thedisc10 into thenucleus pulposus18. The reamingtool34 is operated to remove the nucleus pulposus as shown inFIG. 4 of the drawings so that acavity36 remains. Thecavity36 is bounded by theannulus fibrosis16 and theend plates20 of the

vertebrae

12 and14.Residue64 of thenucleus pulposus18 remains resulting in thecavity36 having irregular walls.

Anenvelope38 of an elastomeric material, more particularly, a silicone rubber material is mounted on a distal end of atubular delivery device40. Thetubular delivery device40 defines apassageway42. Theenvelope38 is made from the silicone rubber material which is biologically inert and which can elastically deform up to 100 times the size of theenvelope38 in its relaxed state.

In one embodiment, as shown in greater detail inFIG. 10 of the drawings, theenvelope38, in its relaxed, or deflated, state, is a snug fit over adistal end44 of thedelivery device40. Afirst sleeve46 is arranged coaxially over thedelivery device40 adjacent thedistal end44 of thedelivery device40. Thissleeve46 has a plurality ofopenings48 defined in it. Theseopenings48 cooperate withopenings50 at thedistal end44 of thedelivery device40. Afurther sleeve52 is mounted coaxially about thesleeve46 and communicates with an evacuation device (not shown) via an evacuatingtube54. Proximal ends of the

sleeves

46 and52 are sealed against an outer surface of thedelivery device40 via seals56. Afurther seal58 is arranged between a distal end of thesleeve52 and thesleeve46.

When filler material, referenced generally by thereference numeral60, is injected into theenvelope38, a low pressure is, simultaneously or prior to injection, imparted to the distal end of thedelivery device40 to evacuate fluid, more particularly, air, from within theenvelope38. This assists in airless mixing and ensures that the formation of air bubbles in thefiller material60 is inhibited. Evacuation of air also inhibits entrapment of air within theenvelope38 by theincoming filler material60 and facilitates the flow of thefiller material60 into theenvelope38. As thefiller material60 is charged into theenvelope38 through the fillingopenings50, air is drawn out of theenvelope38 by operation of the evacuation device via theevacuation tube54. The air is received between the outer surface of thedelivery device40 and thesleeve46. This air passes through theopenings48 in thesleeve46 and through theevacuation tube54.

Thefiller material60 is also of a silicone rubber material which is able to absorb shocks and withstand compressive, tensile, bending and torsional forces imparted to it by movement of the

vertebrae

12 and14. In addition, due to the fact that thefiller material60 is the same class or type as the material of theenvelope38, once the filler material has cured in theenvelope38, a unified or single, integrated structure is formed which is resistant to delamination and relative movement between theenvelope38 and thefiller material60.

Theenvelope38 is made from a silicone rubber material having the following characteristics:

- a Shore hardness (A scale) in the range from about 20-50;
- a tensile strength in the range from about 2700 kPa to 11000 kPa;
- an elongation of between about 400% and 800%; and
- a tear strength of between about 1700 kg/m and 4500 kg/m.

Thefiller material60 is also of a silicone rubber material which, prior to use, is stored in two separate parts. Thefiller material60, comprising the combined parts, when mixed in a ratio of 1:1 and cured, has the following characteristics:

- a Shore hardness (A scale) in the range from about 20 to 40, more particularly, about 25 to 30 and, optimally, about 28;
- a tensile strength in the range form about 7000 kPa to about 9500 kPa, more particularly, about 8000 kPa to about 9000 kPa and, optimally, about 8500 kPa;
- an elongation in the range from about 550% to 700%, more particularly, about 600% to 650% and optimally, about 640%; and
- a tear strength in the range from about 1000 to 2000 kg/m, more particularly, about 1250 kg/m to 1750 kg/m and, optimally, about 1500 kg/m.

One example of a suitable material for the filler material has the following characteristics after mixing the parts in a 1:1 ratio and after curing:

- a Shore hardness (A scale) of 28;
- a tensile strength of 8439 kPa;
- an elongation of 639%; and
- a tear strength of 1500 kg/m.

Thefiller material60 is treated to contain 5%, by volume, barium sulphate to appear radio-opaque under X-ray, CT, fluoroscopy and MRI. In addition, thefiller material60 contains a catalyst and has a scorch time of between about 1.5 to 2.5 minutes with a curing time of about 5 minutes. When thefiller material60 is charged into theenvelope38 it causes inflation or expansion of theenvelope38 in an elastically deformable manner. Expansion of theenvelope38 can occur to such an extent that, where necessary, the expandedenvelope38 distracts the

vertebrae

12 and14 to restore the original spacing between the

vertebrae

12 and14. By using radio-opacity in thefiller material60, distraction of the

vertebrae

12 and14 can be monitored in real time using a fluoroscope or the similar equipment.

Further, theenvelope38 conforms to the shape of thecavity36. Because theenvelope38 expands within thecavity36 and conforms closely to the shape of thecavity36, theenvelope38 self anchors within thecavity36 and “extrusion” of aunified prosthesis100, comprising theenvelope38 and thefiller material60, formed through theaperture30 previously formed in theannulus16 of the disc is inhibited.

The material for the envelope may, depending on the grade or class of material used, be post cured for a period of time. This is effected by placing the mouldedenvelope38 into an oven, for example, for a period of about 1 to 4 hours at a temperature of about 150° C. to 180° C.

By having the material of theenvelope38 and thefiller material60 of the same type, but different grades or classes, chemical bonding between the materials is enhanced which encourages the formation of theprosthesis100.

Thefiller material60 is dispensed from a dispensing source such as adispenser62.

As described above, when thenucleus pulposus18 has been removed, aresidue64 remains about the inner surface of the annulus fibrosis and on theend plates20 of the

vertebrae

12 and14. Thisresidue64 is of an irregular shape. Therefore, in charging theenvelope38 with thefiller material60, it is necessary to monitor the charging of thefiller material60 into theenvelope38. This is done by a sensing arrangement. In one embodiment of the invention, the sensing arrangement comprises apressure sensor66 at an inlet to theenvelope38. In another embodiment, the sensing arrangement comprises avolume sensor68 arranged at an outlet of thedispenser62 for monitoring the volume offiller material60 dispensed. The sensing arrangement could, in addition or instead, be a flow rate sensor which monitors the rate of flow of thefiller material60.

Yet a further method of monitoring filling of theenvelope38 is monitoring back flow offiller material60 from between theenvelope38 and the distal end of thedelivery device40. As thefiller material60 oozes out it may loosen theenvelope38 allowing thedelivery device40 to be removed.

It is also necessary to monitor the shape and size of thecavity36 taking theresidue64 into account. This can be achieved in a number of ways. One of the ways in which this can be achieved is by having radioopaque markers70 arranged on theenvelope38. Prior to charging theenvelope38 with thefiller material60, theenvelope38 can be expanded to conform to the shape of thecavity36 by means of a water/saline solution or a radio opaque solution. Themarkers70, being radio opaque, are monitored under a fluoroscope to determine the shape and size of thecavity36.

Other methods of assessing the size of thecavity36 include the use of a flexible wire inserted down thelumen26 of theintroducer22, the wire being monitored by a fluoroscope. Yet a further way of monitoring the shape and size of thecavity36 is by use of a dedicated jacket, of similar dimensions to thecavity36, which is inserted into thecavity36 and inflated using the water/saline solution or the radio opaque solution. The jacket carries radio opaque markers which are monitored by a fluoroscope.

After the shape and size of thecavity36 have been determined, thefiller material60 is dispensed from thedispenser62 and is monitored via the

sensing arrangements

66 or68, as the case may be. As illustrated inFIG. 7 of the drawings, thefiller material60 causes elastic expansion or inflation of theenvelope38 so that theenvelope38 conforms to the shape of thecavity36 and bears against theresidue64 of the nucleus pulposus remaining in thecavity36. Theenvelope38, having been elastically expanded by thefiller material60, remains under tension around thefiller material60 while conforming to the shape of thecavity36.

Backflow filler material

60 from the interior of theenvelope38 is controlled either by avalve72 as shown inFIG. 13 of the drawings or by aclamping device74 as shown inFIG. 7 of the drawings. Thevalve72 is a duckbill valve and acts as a one way valve so that backflow offiller material60 from theenvelope38 is inhibited.

Once theenvelope38 has been filled and has expanded so that it conforms closely to the shape of thecavity36 and is received snugly in thecavity36, thefiller material60 is allowed to cure for a predetermined period of time of, for example, about 10 minutes. After curing of thefiller material60, thedelivery device40 is removed leaving theaperture30 occluded as shown at76 inFIG. 8 of the drawings. Theunified tissue prosthesis100 so formed is fully cured after about 24 hours.

To facilitate removal of thedelivery device40 from theenvelope38, theenvelope38 has a zone of weakness in the form of a circumferential groove78 (FIG. 14) formed at a proximal end. As thedelivery device40 is withdrawn, when its distal end comes into register with thegroove78, thedelivery device40 is twisted relative to the envelope to cause a break at thegroove78 to form theocclusion76 in theaperture30 of theannulus fibrosis16 of thedisc10.

FIG. 12 shows another way of delivering theenvelope38 into thecavity36. In this embodiment of the invention, theenvelope38 is everted to lie within the distal end of thedelivery device40 to facilitate its insertion into thecavity36. A similar arrangement is shown inFIG. 9 andFIG. 14 of the drawings.

InFIG. 11 of the drawings, another embodiment of equipment for forming thetissue prosthesis100 is shown. In this embodiment, afiller tube80 is used. Thetube80 is received in thepassageway42 of thedelivery device40. Asleeve82 is arranged coaxially about thedelivery device40. A first displacement device, such as a trigger,84 is provided for controlling relative movement between thedelivery device40 and thetube80. A second displacement device, which may also be in the form of a trigger,86 controls relative movement between thedelivery device40 and thesleeve82.

The equipment, as shown inFIG. 11 of the drawings, is for use where an evacuating device is not used. Thus, to fill theenvelope38, thetube80 is urged towards the distal end of theenvelope38 and charging of thefiller material60 into theenvelope38 commences at the distal end of theenvelope38. Filling of theenvelope38 progresses from its distal end towards its proximal end. Thus, asfiller material60 is charged into theenvelope38, thetube80 is slid proximally relative to thetube40 by manipulating thetrigger84 or slides back through buoyancy of the filler material. Once theenvelope38 is in its fully inflated state, theenvelope38 is urged off the distal end of thedelivery device40 by manipulating thetrigger86. As thetube80 is withdrawn from thevalve72 and theenvelope38 is removed from the distal end of thedelivery device40, thevalve72 closes to form theocclusion76.

To facilitate expulsion of air when an evacuating system is not being used, theenvelope38 has a bead88 (FIG. 12) formed along that portion which seats on the distal end of thedelivery device40 to createpassages90 through which air can be discharged as theenvelope38 is charged with thefiller material60.

As described above, theenvelope38 is of a silicone rubber material which can be inflated up to 100 times its relaxed size without rupturing. In another embodiment, theenvelope38 is of a less expansible material such as a biological or a synthetic polymeric material. A suitable synthetic polymeric material may, for example, be a polyester such as polyethylene terephthalate (PET). Theenvelope38 is of a knitted PET material so that, when thefiller material60 is charged into theenvelope38, the filler material fills foramens or interstices in theenvelope38 to form an integrated structure which resists relative movement between thefiller material60 and theenvelope38. Alternatively, the knitted PET material may be coated with silicone allowing thefiller material60 to integrate with the coating.

FIGS. 15 to 17 show different shapes ofenvelopes38 which can be used depending on whichintervertebral disc10 is to have its nucleus pulposus18 replaced.

Referring now toFIGS. 18 to 21 of the drawings, yet a further embodiment of equipment for forming a tissue prosthesis, in situ, at a site in a patient's body is illustrated. With reference to the previous drawings, like reference numerals refer to like parts, unless otherwise specified.

In this embodiment, theequipment110 comprises a delivery device in the form of anenvelope tube112. Theenvelope tube112 carries theenvelope38 at its distal end.

A filler member in the form of afiller tube114 is slidably received within apassage116 of theenvelope tube112. As illustrated more clearly inFIG. 21 of the drawings, thefiller tube114 has a smaller outer diameter than an inner diameter of theenvelope tube112 to form anannular gap118 between thefiller tube114 and theenvelope tube112.

A removal mechanism in the form of a push-offtube120 is a snug fit on the outer surface of theenvelope tube112.

In this embodiment, theenvelope38 is of a two part construction comprising a sleeve122 (FIG. 21) to which anenvelope defining member124 is adhesively bonded as shown by an annularadhesive layer126. Thesleeve122 defines thevalve72.

A distal end of thefiller tube114 carries an engagingmember128 which engages and opens thevalve72 so that theannular gap118 is in flow communication with an interior130 of theenvelope38. A distal end of the push-offtube120 terminates short of a proximal end of thesleeve122 of theenvelope38. However, it is also to be noted, as will be described in greater detail below, that theenvelope tube112 is displaceable relative to the push-offtube120 in the direction ofarrow132.

Instead of the engagingmember128, thevalve72 could have a small opening (not shown) in it. The size of the opening in thevalve72 is selected to allow the passage of air through it but is sufficiently small that the viscosity of the filler material will inhibit the passage of the filler material through it.

Yet a further way of evacuating theinterior130 of theenvelope38 is to insert thefiller tube112 into theinterior130 of theenvelope38 and to have a slit (not shown) in thefiller tube114 upstream of thevalve72. Thus, if thevalve72 seals about thefiller tube112, air can still be drawn from theinterior130 of theenvelope38 into thegap116 via the slit when the evacuation device is operated.

A proximal end of theenvelope tube112 carries aconnector134. Theconnector134 is a Y-connector having aprimary member136 and asecondary member138 projecting from theprimary member136. Theenvelope tube112 is fast with theprimary member136 of theconnector134. Thesecondary member138 of theconnector134 is in flow communication with thepassage116 of theenvelope tube112 and, hence, in use with thegap118 between theenvelope tube112 and thefiller tube114. Thesecondary member138 is connectable to an evacuation device (not shown) such as an evacuation pump for creating a low pressure in thegap118 and, via the engagingmember128 opening thevalve72, theinterior130 of theenvelope38 prior to filler material being charged into theinterior130 of theenvelope38.

As shown more clearly inFIG. 20 of the drawings, theconnector134 includes aretaining mechanism140 for retaining theenvelope tube112 in position relative to theintroducer22. Theretaining mechanism140 comprises a receivingformation142 carried at a proximal end of theintroducer22. Theretaining mechanism140 further includes aclip portion144 forming the distal end of theconnector134 which clips into the receivingformation142 to retain theenvelope tube112 in position relative to theintroducer22.

A proximal end of the push-offtube120 carries agripping formation146 which is accessible externally of theretaining mechanism140 for enabling the push-offtube120 to be held while theenvelope tube112 is moved in the direction of thearrow132 after charging of theenvelope38 with the filler material.

Theequipment110 further includes adispensing device148 for dispensing filler material. Thedispensing device148 includes adispenser150 feeding into a mixing device in the form of astatic mixer152. A distal end of thestatic mixer152 carries thefiller tube114. ALuer lock arrangement154 is arranged at the distal end of thestatic mixer152 and connects the dispensingarrangement148 to theconnector134.

The filler material is of a silicone rubber, as indicated above. To inhibit curing of the filler material prior to its being charged into theenvelope38, the filler material is retained in two, separate parts. Thus, thedispenser150 includes tworeservoirs156 in each of which a part of the filler material is initially received. Eachreservoir156 has aplunger158 associated with it for dispensing the parts from thereservoirs156 into thestatic mixer152 where the parts are mixed prior to being charged into theenvelope38. It is to be noted that theplungers158 are displaceable together with each other via a suitable displacing device (not shown) such as a pneumatic gun.

Thus, in use, the filler material to be charged into theenvelope38 is provided in the dispensingarrangement148. The dispensingarrangement148 is connected to theconnector134 via theLuer lock154. Anenvelope38, in a deflated condition, is mounted on theenvelope tube112. After the nucleotomy has been performed on thedisc10, theenvelope tube112 with theenvelope38 on its distal end is inserted through theintroducer22 so that theenvelope38, in its deflated condition, is received within thecavity36 of thedisc10. Thefiller tube114 is inserted into the interior of thefiller tube112 so that the engagingmember128 engages thevalve72 and opens thevalve72. By opening thevalve72, theinterior130 of theenvelope38 is placed in fluid communication with thegap118 between theenvelope tube112 and thefiller tube114.

An evacuation device (not shown) is attached to thesecondary member138 of theconnector134 and a vacuum is drawn. This creates a low pressure within thegap118 and theinterior130 of theenvelope38 and inhibits the formation of air bubbles in theprosthesis100 as the filler material is charged into theenvelope38.

The filler material is dispensed from thedispensing device148 into thefiller tube114 and into theinterior130 of theenvelope38. This causes theenvelope38 to expand elastically to conform to the shape of thecavity36 of thedisc10 with theenvelope38 being retained under tension by the filler material.

After charging of the filler material into theinterior130 of theenvelope38, thefiller tube114 is withdrawn. Withdrawal of thefiller tube114 causes withdrawal of the engagingmember128 allowing thevalve72 to close to inhibit leakage of filler material from theinterior130 of theenvelope38.

After curing, theenvelope tube112 is moved relative to the push offtube120 in the direction of thearrow132 by holding the push offtube120 using thegripping device146. This urges thesleeve122 of theenvelope38 off the end of theenvelope tube112 as theenvelope tube112 is withdrawn relative to the push offtube120. Thevalve72 occludes the opening to theenvelope38 and theaperture30 previously formed in theannulus fibrosis16 of thedisc10. Theequipment110, including theintroducer22, is then withdrawn from the patient's body and the procedure is complete.

Referring now toFIGS. 22 to 24 of the drawings, still a further embodiment of equipment for forming a tissue prosthesis, in situ, at a site in a patient's body is illustrated. Once again, with reference to the previous drawings, like reference numerals refer to like parts, unless otherwise specified.

In this embodiment, theequipment110 includes a stiffening element in the form of a stiffening rod ortube160. Prior to insertion of thefiller tube114 into theenvelope tube112, the stiffeningrod160 is inserted into thepassage116 of theenvelope tube112. Adistal end162 of the stiffeningrod160 projects beyond a distal end of theenvelope tube112 and terminates at a distal wall in theinterior130 of theenvelope38. Agap161 is created between theenvelope tube112 and thestiffening rod160. Thegap161 and theinterior130 of theenvelope38 are evacuated by operation of the evacuation device to cause theenvelope38 to collapse on to thedistal end162 of the stiffeningrod160. This facilitates insertion of theenvelope38 into theintroducer22 and into thecavity36 of thedisc10.

Once theenvelope38 has been located within thecavity36, the evacuation device is turned off to release theenvelope38 from thedistal end162 of the stiffeningrod160 and this allows the stiffeningrod160 to be withdrawn. Thefiller tube114 can then be inserted into theenvelope tube112, as described above, to enablefiller material60 to be charged into theenvelope38.

In another embodiment (not illustrated), the stiffeningrod160 is dimensioned to fit in the interior of thefiller tube114. With this arrangement, thegap118 between theenvelope tube112 and thefiller tube114 is evacuated, as described above, with the stiffeningrod160 projecting through the distal end of theenvelope tube112 and theenvelope38 being collapsed over thedistal end162 of the stiffeningrod160.

Aproximal end164 of the stiffening rod carries acap connector166 which connects to theY connector134 to retain thestiffening rod160 in position relative to theenvelope tube112 and/or thefiller tube118, as the case may be. Thecap connector166 seals hermetically against a proximal end of the Y connector to enable thegap161 and theinterior130 of theenvelope38.

It is an advantage of the invention that a method and equipment are provided which facilitates minimally invasive formation of a tissue prosthesis in situ. In addition a tissue prosthesis is provided which is resistant to delamination. In particular, in the case where the tissue prosthesis has an envelope and filler material of the same class of material, a unified, integrated structure is provided which is resistant to delamination and relative movement between the envelope and the filler material. The unified structure and the fact that the envelope is elastically deformed and is retained under tension also renders the envelope resistant to creasing increasing the operational efficiency of the prosthesis by being better able to distribute forces to the annulus fibrosis of the disc.

In addition, the use of a silicone rubber envelope is particularly advantageous due to the fact that, when a nucleotomy has been performed, residue remains behind which is irregular in shape. It is beneficial to have a prosthesis which expands and conforms as closely as possible to the shape of the cavity in order that compressive, tensile, bending and torsional forces can be accommodated by the disc. In addition, the provision of a tissue prosthesis expanding and closely conforming to the shape of the cavity results in an improvement in stimulation and deformation of the end plates of the vertebrae and thereby aiding in restoration of the natural pumping action which assists in the influx of nutrients and the effluxion of waste products from within the disc.

It is yet a further advantage of the invention that the tissue prosthesis can be formed in situ in a minimally invasive manner. The need for invasive surgical procedures is therefore obviated and there is the added advantage of more rapid post-operative recovery and the reduced need for a prolonged period in hospital.

The equipment of the invention further provides an efficient, easy to use manner of forming the tissue prosthesis. By having the tubes etc nested, a clinician is more easily able to manipulate the equipment to place and form the tissue prosthesis.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.