Patent Application
20070179613
1. Field of the Disclosure
The present disclosure relates to the field of orthopedic surgery and has particular application to a total artificial joint and its post implantation performance.
2. Description of Related Art
Lubrication of a natural joint is a complex process that allows the joint to operate under a variety of conditions. Such conditions can include: maximum joint surface velocity and sudden and prolonged applied load. Articular cartilage is filled with synovial fluid that is squeezed from the surface upon loading. At high loads and low velocity, boundary lubrication is present as a means to protect the surfaces and minimize their contact. At higher velocities, fluid film lubrication is generated between the surfaces because of pressure build-up, which substantially completely separates the surfaces. Since cartilage is highly deformable under pressure, this deformation can enhance the thickness of the fluid film, a process which is typically termed elastohydrodynamic lubrication. Synovial fluid can act as a shock absorber, particularly under high loads when the synovial fluid's molecules undergo conformational changes. The energy of conformation is stored and released later. In contrast, the molecules serve as lubricants at low loads because they are flexible enough to maintain their conformation.
People who suffer from the pain and mobility loss associated with diseased joints may benefit from implants designed to improve their situation. Orthopedic implants made from metals, alloys, polymers, polymer blends and metal/polymer blends may alleviate the decreased motion in these diseased joints. Biocompatibility and bioresorbability of a material are often significant criteria for a successful implant. Wear occurring at the interface of surfaces within the joint can be a significant contributor to joint failure as well as to deleterious effects in collateral systems resulting from wear debris. The long-term performance of traditional prosthetic joints has suffered from, among other things, a lack of an effective, long-term lubrication mechanism, whether by effectively delivering a synovial fluid substitute or by replicating the delivery of natural fluids to joint articulation surfaces.
Accordingly, the present disclosure is directed to various embodiments of a passive lubricating intervertebral prosthetic implant, a prosthetic joint and a method of replacing intervertebral discs. In an exemplary embodiment an intervertebral prosthetic implant includes a pair of substantially rigid members configured to engage adjacent vertebrae and an articulation member configured to facilitate motion between the members. One of the members has at least one capillary channel configured to transport lubricious fluid proximate the articulation surface of the articulation member at least in part by capillary force.
In another exemplary embodiment, an intervertebral prosthetic implant includes a pair of substantially rigid members configured to engage adjacent vertebrae and an articulation member configured to facilitate motion between the members. One of the members has at least one fluid channel configured to allow lubricious fluid to flow proximate the articulation surface of the articulation member. A semi-permeable membrane is disposed proximate to the proximal end of at least one of the fluid channels.
In another exemplary embodiment, an intervertebral prosthetic implant includes a pair of substantially rigid members configured to engage adjacent vertebrae. One of the members includes an articulation member and at least one capillary channel configured to transport lubricious fluid to the articulation surface of the articulation member at least in part by capillary force.
In another exemplary embodiment, an intervertebral prosthetic implant includes a pair of substantially rigid members configured to engage adjacent vertebrae. One of the members includes an articulation member and at least one fluid channel configured to allow lubricious fluid to flow proximate the articulation surface of the articulation member. A semi-permeable membrane is disposed proximate to the proximal end of at least one of the fluid channels.
In another exemplary embodiment, a prosthetic joint includes a pair of substantially rigid members configured to engage first and second bones and an articulation member configured to facilitate motion between the pair of substantially rigid members. At least one of the substantially rigid members has one or more capillary channels configured to transport lubricious fluid to the articulation surface of the articulation member at least in part by capillary force.
In another exemplary embodiment, a prosthetic joint includes a pair of substantially rigid members configured to engage first and second bones and an articulation member configured to facilitate motion between the pair of substantially rigid members. At least one of the substantially rigid members has one or more fluid channels configured to allow lubricious fluid to flow proximate the articulation surface of the articulation member. A semi-permeable membrane is disposed proximate to the proximal end of at least one of the fluid channels.
In another exemplary embodiment, a method of replacing at least a portion of an intervertebral disc includes the steps of gaining access to the intervertebral disc; removing at least a portion of the intervertebral disc to create an intervertebral space; and inserting a prosthetic disc into the intervertebral space. The prosthetic disc includes a pair of substantially rigid members configured to engage adjacent vertebrae and an articulation member configured to facilitate motion between the members. At least one of the members has one or more capillary channels configured to transport lubricious fluid to the articulation surface of the articulation member at least in part by capillary force.
In another exemplary embodiment, a method of replacing at least a portion of an intervertebral disc includes the steps of gaining access to the intervertebral disc; removing at least a portion of the intervertebral disc to create an intervertebral space; and inserting a prosthetic disc into the intervertebral space. The prosthetic disc includes a pair of substantially rigid members configured to engage adjacent vertebrae and an articulation member configured to facilitate motion between the members. At least one of the members has one or more fluid channel configured to allow lubricious fluid to flow proximate the articulation surface of the articulation member. A semi-permeable membrane is disposed proximate the proximal end of at least one of the fluid channels and the articulation surface of the articulation member.
In another exemplary embodiment, an intervertebral prosthetic implant includes a pair of substantially rigid members configured to engage adjacent vertebrae and an articulation member configured to facilitate motion between the members. One of the members has at least one fluid channel configured to allow lubricious fluid to flow proximate the articulation surface of the articulation member. A semi-permeable membrane is disposed between the proximal end of at least one of the fluid channels and the articulation surface of the articulation member.
The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.
The use of the same reference symbols in different drawings indicates similar or identical items.
The teachings of the present application can find utility in various joint replacement situations, such as knee prosthetics, hip prosthetics and intervertebral prosthetic discs. With particular reference to intervertebral embodiments,
As shown in
As depicted in
In a particular embodiment, if one of the intervertebral lumbar discs 122, 124, 126, 128, 130 is diseased, degenerated, damaged, or otherwise in need of replacement, that intervertebral lumbar disc 122, 124, 126, 128, 130 can be at least partially removed and replaced with an intervertebral prosthetic disc according to one or more of the embodiments described herein. In a particular embodiment, a portion of the intervertebral lumbar disc 122, 124, 126, 128, 130 can be removed via a discectomy, or a similar surgical procedure, well known in the art. Further, removal of intervertebral lumbar disc material can result in the formation of an intervertebral space (not shown) between two adjacent lumbar vertebrae.
Referring to
As illustrated in
The vertebrae that make up the vertebral column have slightly different appearances as they range from the cervical region to the lumbar region of the vertebral column. However, all of the vertebrae, except the first and second cervical vertebrae, have the same basic structures, e.g., those structures described above in conjunction with
As shown in
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As illustrated in
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In various embodiments, the articulation member and the substantially rigid second member can be formed as a substantially monolithic structure. Alternatively, the articulation member can be at least partially attached to the second member or the articulation member can be at least partially attached to both members when motion restriction is desired. As shown in
Any of the substantially rigid components described herein can be formed of non-reactive polymers or biocompatible metals, alloys or ceramics. The polymers can include acrylonitrile polymers such as acrylonitrile-butadiene-styrene terpolymer, or the like; halogenated polymers such as polytetrafluoroethylene, polychlorotrifluoroethylene copolymer tetrafluoroethylene or hexafluoropropylene; polyimide; polysulfone; polycarbonate; polyethylene; polypropylene; polyvinylchloride-acrylic copolymer; polycarbonate-acrylonitrile-butadiene-styrene; polystyrene; as well as polyether materials such as polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyaryletherketone (PAEK), or the like. Exemplary metallic materials include stainless steel, titanium, platinum, tantalum, gold, and their alloys, as well as gold-plated ferrous alloys, platinum-plated ferrous alloys, cobalt-chromium alloys and titanium nitride coated stainless steel.
In further alternative embodiments, at least one of the first member or the second member has a plurality of fluid or capillary channels. As illustrated in
As exemplified in
The size and shape of a channel can affect its capillarity. In certain embodiments it may be desirable to configure the fluid channels such that some or all of them function as capillary channels, which, for purposes of this disclosure means a passageway through a member which is sized and shaped to facilitate movement of a target fluid by capillary forces through the passageway. In certain embodiments, the channel can be configured such that capillary force transports the target fluid from a source near the proximal end to a semi-permeable membrane. In certain embodiments, the channel can be configured such that capillary force transports the target fluid from a source near the proximal end through the length of the channel to the distal end. In other embodiments, the channel can be configured such that capillary force assists in transporting the target fluid away from a semi-permeable membrane and toward a point of use near or at an articulation surface. For purposes of this Description, the proximal end of a channel is the end nearest the bone being engaged by the implant/joint or nearest the surface of the implant/joint configured to engage a bone.
In certain embodiments, the cross-sectional size of at least one of the channels can vary along the length of the channel. For example, the cross-sectional size of at least one of the channels can increase along the length of the channel from the proximal end to the distal end. This configuration allows fluid to move from a portion of the channel where capillarity is relatively high to a portion of the channel where capillarity is lower. This configuration can find utility in embodiments incorporating a semi-permeable membrane within the channel or proximate the proximal end of the channel. In certain embodiments, the portion of the channel from the proximal end to the semi-permeable membrane can be narrower and have a greater capillarity than the portion of the channel between the semi-permeable membrane and the distal end. This difference in capillarity can substantially reduce the capillary force acting on the fluid at or near the semi-permeable membrane in order to allow for a more even draw of fluid in embodiments having multiple fluid channels with an uneven distribution of source fluid near the proximal ends of the channels. Furthermore, certain embodiments can benefit from a larger channel on the solute side of the semi-permeable membrane in order to increase osmotic potential on the solute side of the membrane.
In embodiments having a semi-permeable membrane, a solute can be disposed between the semi-permeable membrane and the articulation surface of the articulation member. The solute can be present in sufficient concentration to provide an effective amount of the lubricious fluid at the articulation surface of the articulation member in vivo. In this context, the term “effective amount” means that amount which will exhibit a lubricating effect on at lest a portion of the articulation surface. In alternative embodiments, at least a portion of the solute can be contained in a timed release delivery system, such as in one or more tablets and/or capsules that dissolve or otherwise deteriorate over time, in order to produce an extended or staged release of solute on the solute side of the membrane. Various embodiments can include tablets and/or capsules of various dissolution rates. In certain embodiments, the staged delivery of solute maintains an effective amount of the lubricious fluid at the articulation surface of the articulation member over a period of at least one year. In other embodiments, the effective amount of the lubricious fluid is maintained at the articulation surface of the articulation member for a period of at least five years.
In various embodiments, a solute is chosen that has a molecular weight sufficiently high to retard permeation of the solute through the semi-permeable membrane such that the effective amount of the lubricious fluid is maintained at the articulation surface of the articulation member over a period of at least one year. In other embodiments, the effective amount of the lubricious fluid is maintained at the articulation surface of the articulation member for a period of at least five years.
Lubricious fluid is passed across the semi-permeable membrane by osmosis and is transported to and/or maintained at an articulation surface on the solute side of the membrane by osmotic potential and/or osmotic pressure. Osmosis is the passage of a solvent through a semi-permeable membrane separating two solutions of different concentrations. A semi-permeable membrane allows passage of solvents and is selectively permeable to various solutes. There is a tendency for the separated solutions to become the same concentration as the solvent passes from lower concentration to higher concentration. Osmosis will stop when the two solutions become equal in concentration or when pressure is applied to the solution containing higher concentration. When the higher concentrated solution is in a substantially closed system, that is when system is of substantially constant volume, there is a build up of pressure as the solvent passes from low to high concentration (i.e., osmotic pressure). Osmotic pressure can be calculated from the formula TT=nRT/V, where n/V denotes the concentration of the solution in mol/L, R is the gas constant and T denotes absolute temperature. Thus an approx. 1% solution of sodium chloride on the solute side (corresponding to a concentration of approx. 0.3 mol/L) will result in a relatively high osmotic pressure of 7 to 8 bar across the membrane.
In alternative embodiments, the cavity between the semi-permeable membrane and the relevant articulation surface can be filled with a desired solution prior to implantation or subsequently through a suitable valve in communication with the cavity. The solution can be delivered through the insertion device or with another device after the insertion device is removed. Solution can also be allowed to pass into the cavity after implantation.
The solute can be chosen from a number of liquid-attracting agents used to drive the flow of a lubricious solvent, such as water, synovial fluid or the like. The solute may be an osmagent, an osmopolymer, or a mixture of the two. An osmagents is a nonvolatile species which is soluble in lubricious fluid and creates an osmotic potential which drives the osmotic inflow of lubricious fluid. A non-exclusive, exemplary listing of osmagents include magnesium sulfate, magnesium chloride, potassium sulfate, sodium chloride, sodium sulfate, lithium sulfate, sodium phosphate, potassium phosphate, d-mannitol, sorbitol, inositol, urea, magnesium succinate, tartaric acid, raffinose, and various monosaccharides, oligosaccharides and polysaccharides such as sucrose, glucose, lactose, fructose, and dextran, as well as mixtures of any of these various species. The solute may additionally contain a contrasting agent to make the implant opaque for X-rays. In certain embodiments, the contrasting agent can be introduced in a liquid state.
Osmopolymers are generally hydrophilic polymers that can swell upon contact with lubricious fluid and can be of plant or animal origin, or may be synthetic. A non-exclusive exemplary listing of osmopolymers include: poly(hydroxy-alkyl methacrylates) with a molecular weight of 30,000 to 5,000,000, poly(vinylpyrolidone) with a molecular weight of 10,000 to 360,000, anionic and cationic hydrogels, polyelectrolyte complexes, poly(vinyl alcohol) having low acetate residual—optionally cross-linked with glyoxal, formaldehyde or glutaraldehyde and having a degree of polymerization of 200 to 30,000, mixtures of methyl cellulose, cross-linked agar and carboxymethylcellulose, mixtures of hydroxypropyl methylcellulose and sodium carboxymethylcellulose, polymers of N-vinyllactams, polyoxyethylene-polyoxypropylene gels, polyoxybutylene-polyethylene block copolymer gels, carob gum, polyacrylic gels, polyester, gels, polyurea gels, polyether gels, polyamide gels, polypeptide gels, polyamino acid gels, polycellulosic gels, carbopol acidic carboxy polymers having molecular weights of 250,000 to 4,000,000, Cyanamer polyacrylamides, cross-linked indene-maleic anhydride polymers, polyacrylic acids having molecular weights of 80,000 to 200,000, starch graft copolymers, and acrylate polymer polysaccharides.
The semi-permeable membrane can be formed of a semi permeable material which allows passage of lubricious fluids, especially water, while limiting the passage of solutes. A non-exclusive listing of semi permeable materials include polyester elastomers, cellulose esters, cellulose ethers and cellulose ester-ethers, water flux enhanced ethylene-vinyl acetate copolymers, silicone, polyurethane, polycarbonate-urethane, silicone-polycarbonate-urethane or silicone-polyetherurethane. Any of the above can be provided with a coating or admixed with a material that reduces hydrophobic characteristics. The cellulosic polymers listed above can have a degree of substitution, D.S., on the anhydroglucose unit, from greater than 0 up to 3 inclusive. In this context, “D.S.” means the average number of hydroxyl groups originally present on the anhydroglucose unit comprising the cellulose polymer that are replaced by a substituting group. Representative materials include cellulose acylate, cellulose diacetate, cellulose triacetate, mono-, di-, and tricellulose alkanylates, mono-, di-, and tricellulose aroylates, and the like. Exemplary cellulosic polymers include cellulose acetate having a D.S. up to 1 and an acetyl content up to 21%; cellulose acetate having a D.S. of 1 to 2 and an acetyl content of 21% to 35%; cellulose acetate having a D.S. of 2 to 3 and an acetyl content of 35% to 44.8%, and the like. More specific cellulosic polymers include cellulose propionate having a D.S. of 1.8 and a propionyl content of 39.2% to 45% and a hydroxyl content of 2.8% to 5.4%; cellulose acetate butyrate having a D.S. of 1.8 and an acetyl content of 13% to 15% and a butyryl content of 34% to 39%; cellulose acetate butyrate having an acetyl content of 2% to 29%, a butyryl content of 17% to 53% and a hydroxyl content of 0.5% to 4.7%; cellulose acetate butyrate having a D.S. of 1.8, and acetyl content of 4% average weight percent and a butyryl content of 51%; cellulose triacylates having a D.S. of 2.9 to 3 such as cellulose trivalerate, cellulose trilaurate, cellulose tripalmitate, cellulose trisuccinate, and cellulose trioctanoate; cellulose diacylates having a D.S. of 2.2 to 2.6 such as cellulose disuccinate, cellulose dipalmitate, cellulose dioctanoate, cellulose dipentate; coesters of cellulose such as cellulose acetate butyrate and cellulose, cellulose acetate propionate, and the like. Any of the semi-permeable materials can be mixed with barium sulfate or the like to make them opaque for X-rays.
The concepts and features described herein also find utility in other prosthetic joints, such as hip and/or knee prostheses. Accordingly, another embodiment is directed to a prosthetic hip joint 1500, as shown in
In alternative embodiments, the fluid channels can be configured to transport lubricious fluid at least in part by capillary force. Further, at least one of the first or second members 1502, 1510 can have a plurality of capillary channels. At least one of the capillary channels can vary in cross-sectional size along its length, such as by increasing in cross-sectional size along its length from a proximal end 1520 to a distal end 1522. In various alternative embodiments, a semi-permeable membrane 1526 can be disposed proximate to the proximal end 1520 of at least one fluid channel 1524 or at any functional location between the proximal end 1520 and the articulation surface. As will be appreciated by the skilled practitioner, the substantially rigid members 1502, 1510 can be monolithic or can comprise multiple components as dictated by the situation.
Another embodiment is directed to a prosthetic knee joint 1600, as shown in
In alternative embodiments, the fluid channels can be configured to transport lubricious fluid at least in part by capillary force. Further, at least one of the first or second members 1602, 1610 can have a plurality of capillary channels. At least one of the capillary channels can vary in cross-sectional size along its length, such as by increasing in cross-sectional size along its length from a proximal end 1620 to a distal end 1622. In various alternative embodiments, a semi-permeable membrane 1626 can be disposed proximate to the proximal end 1620 of at least one fluid channel 1624 or at any functional location between the proximal end 1620 and the articulation surface. As will be appreciated by the skilled practitioner, the substantially rigid members 1602, 1610 can be monolithic or can comprise multiple components as dictated by the situation.
The prosthetic devices described herein can be implanted in any art-recognized method according to relevant indications and preferences of the surgeon. When the device is an intervertebral prosthetic implant, the method can include gaining access to the problematic disc and performing a discectomy to remove at least a portion of the disc thereby creating an intervertebral space for receiving the implant. One or more keel grooves may be cut into the cortical rim and cancellous bone to receive keel(s) if such is provided on the first and second members.
After installation, the members can be in direct contact with vertebral bone, e.g., cortical bone and cancellous bone. Consequently, the bone-contacting surface of the members can be coated with a bone-growth promoting substance, e.g., a hydroxyapatite coating formed of calcium phosphate. Additionally, the contact surface can be roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. In a particular embodiment, the roughening process can include acid etching; knurling; application of a bead coating, e.g., cobalt chrome beads; application of a roughening spray, e.g., titanium plasma spray (TPS); laser blasting; or any other similar process or method.
It will be understood that each of the elements described above, or two or more together, may also find utility in applications differing from the types described herein. While the invention has been illustrated and described as embodied in a passive lubricating prosthetic joint, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present invention. For example, multi-component end plates can be employed with the intervertebral embodiments of the present prosthetic when desired. Further, although many examples of various alternative biocompatible chemicals and materials have been presented throughout this specification, the omission of a possible item is not intended to specifically exclude its use in or in connection with the claimed invention. As such, further modifications and equivalents of the invention herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the invention as defined by the following claims.
