US20090210059A1 - Vertebral Disc Prosthesis - Google Patents

Vertebral Disc Prosthesis Download PDF

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Publication number
US20090210059A1
US20090210059A1 US11/887,984 US88798406A US2009210059A1 US 20090210059 A1 US20090210059 A1 US 20090210059A1 US 88798406 A US88798406 A US 88798406A US 2009210059 A1 US2009210059 A1 US 2009210059A1
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United States
Prior art keywords
prosthesis
radius
curvature
vertebrae
equilibrium
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Abandoned
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US11/887,984
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English (en)
Inventor
Peter Francis McCombe
William R. Sears
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Nuvasive Inc
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Individual
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Filing date
Publication date
Priority claimed from AU2005901682A external-priority patent/AU2005901682A0/en
Application filed by Individual filed Critical Individual
Assigned to WARSAW ORTHOPEDIC, INC. reassignment WARSAW ORTHOPEDIC, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MCCOMBE, PETER, SEARS, WILLIAM
Publication of US20090210059A1 publication Critical patent/US20090210059A1/en
Assigned to P & S MCCOMBE PTY LTD AS TRUSTEE FOR THE PETER MCCOMBE MEDICAL PTY LTD PRACTICE SUPERANNUATION FUND, HINTRON PTY LTD AS TRUSEE FOR THE HINTRON TRUST reassignment P & S MCCOMBE PTY LTD AS TRUSTEE FOR THE PETER MCCOMBE MEDICAL PTY LTD PRACTICE SUPERANNUATION FUND ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: WARSAW ORTHOPEDIC, INC.
Assigned to NUVASIVE, INC. reassignment NUVASIVE, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HINTRON PTY LTD AS TRUSTEE FOR THE HINTRON TRUST, P & S MCCOMBE PTY LTD AS TRUSTEE FOR THE PETER MCCOMBE MEDICAL PTY LTD PRACTICE SUPERANNUATION FUND
Assigned to BANK OF AMERICA, N.A., AS ADMINISTRATIVE AGENT reassignment BANK OF AMERICA, N.A., AS ADMINISTRATIVE AGENT SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: NUVASIVE CLINICAL SERVICES MONITORING, INC., NUVASIVE CLINICAL SERVICES, INC., NUVASIVE SPECIALIZED ORTHOPEDICS, INC., NUVASIVE, INC.
Abandoned legal-status Critical Current

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2/44—Joints for the spine, e.g. vertebrae, spinal discs
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2/44—Joints for the spine, e.g. vertebrae, spinal discs
    • A61F2/442—Intervertebral or spinal discs, e.g. resilient
    • A61F2/4425—Intervertebral or spinal discs, e.g. resilient made of articulated components
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
    • A61B34/10—Computer-aided planning, simulation or modelling of surgical operations
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
    • A61B34/10—Computer-aided planning, simulation or modelling of surgical operations
    • A61B2034/108—Computer aided selection or customisation of medical implants or cutting guides
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/08—Muscles; Tendons; Ligaments
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30621—Features concerning the anatomical functioning or articulation of the prosthetic joint
    • A61F2002/30649—Ball-and-socket joints
    • A61F2002/3065—Details of the ball-shaped head
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30621—Features concerning the anatomical functioning or articulation of the prosthetic joint
    • A61F2002/30649—Ball-and-socket joints
    • A61F2002/30654—Details of the concave socket
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30621—Features concerning the anatomical functioning or articulation of the prosthetic joint
    • A61F2002/30649—Ball-and-socket joints
    • A61F2002/30662—Ball-and-socket joints with rotation-limiting means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30621—Features concerning the anatomical functioning or articulation of the prosthetic joint
    • A61F2002/30649—Ball-and-socket joints
    • A61F2002/30663—Ball-and-socket joints multiaxial, e.g. biaxial; multipolar, e.g. bipolar or having an intermediate shell articulating between the ball and the socket
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2/30767—Special external or bone-contacting surface, e.g. coating for improving bone ingrowth
    • A61F2/30771—Special external or bone-contacting surface, e.g. coating for improving bone ingrowth applied in original prostheses, e.g. holes or grooves
    • A61F2002/30878—Special external or bone-contacting surface, e.g. coating for improving bone ingrowth applied in original prostheses, e.g. holes or grooves with non-sharp protrusions, for instance contacting the bone for anchoring, e.g. keels, pegs, pins, posts, shanks, stems, struts
    • A61F2002/30884—Fins or wings, e.g. longitudinal wings for preventing rotation within the bone cavity
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2/3094—Designing or manufacturing processes
    • A61F2/30942—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques
    • A61F2002/30943—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques using mathematical models
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2/44—Joints for the spine, e.g. vertebrae, spinal discs
    • A61F2/442—Intervertebral or spinal discs, e.g. resilient
    • A61F2/4425—Intervertebral or spinal discs, e.g. resilient made of articulated components
    • A61F2002/443—Intervertebral or spinal discs, e.g. resilient made of articulated components having two transversal endplates and at least one intermediate component

Definitions

  • the present invention relates to a prosthesis primarily for use as an artificial invertebral disk, predominantly, but not exclusively, for use in human spines.
  • a human invertebral disk maintains a linkage between adjacent vertebrae of the vertebral column. It must fulfil a number of important functions including load bearing and dampening of impact forces. Furthermore, it must permit a complex pattern of movements and resist various stresses, pure or combined, in the sagittal, coronal and axial planes. Assisted by musco-ligamentous structures surrounding the spine, the invertebral disk must also help to maintain the normal alignment of the vertebrae of the spinal column.
  • Typical failings of previous artificial disks have included loosening or dislodgement of vertebral fixation, premature materials wear or structural failure, poor replication of normal or physiological spinal segmental motion and predisposition to the loss of normal neutral vertebral alignment.
  • IAR instantaneous axis of rotation
  • the endoprosthesis described consists of a resilient body having a generally elliptical shape.
  • the endoprosthesis is affixed between adjacent upper and lower vertebrae through L-shaped supports each having confronting concave-convex legs for engaging the adjacent bone sectional thickness on one surface and retaining the resilient endoprosthesis therebetween.
  • the endoprosthesis is centrally located between the upper and lower vertebrae to allow central pivoting of the upper vertebrae relative to the lower vertebrae.
  • a gasket and seal are located at the anterior and posterior regions between the vertebrae to seal the endoprosthesis in its position between the upper and lower vertebrae.
  • U.S. Pat. No. 5,556,431 describes another type of invertebral disk endoprosthesis in which top and bottom plates are used instead of the L-shaped supports of the above identified US patent.
  • the endoprosthesis described includes a core which has spherical upper and lower surfaces which from drawings shown appear to be aligned with a central vertical axis through the upper and lower vertebrae.
  • the prosthesis core of this patent has an edge rim which limits the range of movement of the core and ensures even under extreme conditions cohesion of the prosthesis.
  • This patent also discloses displacement of the centre of articulation of the prosthesis towards the rear relative to the centre of the vertebral end plates so as to provide sufficient space in the ventral edge area of the prosthesis upper and lower plates so as to enable receipt of bone screws.
  • the present invention provides an alternative prosthesis which is aimed at mitigating at least some of the problems associated with prior art prosthesis.
  • a vertebral disk prosthesis which reproduces substantially similar kinematics of a human invertebral disk.
  • a process for analysing prosthesis performance is provided using a unique modelling method to describe motion of an artificial disk with a mobile core.
  • the process of analysis involves a combination of linear algebra and matrix transformations.
  • a prosthesis for a vertebral disk is provided with a mobile core in which the axis of rotation is able to vary, but which can more closely approximate the normal anatomical centre of rotation (ACR) of an existing prosthesis with a mobile core.
  • ACR anatomical centre of rotation
  • a disk prosthesis which minimises the adverse effects of abnormal tension in adjacent ligamentis structures.
  • a disk prosthesis which resists a tendency to adopt an abnormal position or orientation at rest.
  • a prosthetic disk which has a long life expectancy.
  • a prosthesis for a vertebral column comprising an upper part for attachment to an upper vertebrae, a lower part for attachment to a lower vertebrae and a middle part located between the upper and lower parts, wherein the upper part has a lower surface portion with a first radius of curvature, the middle part has an upper surface portion with a second radius of curvature and a lower surface portion with a third radius of curvature and the lower part has an upper surface portion with a fourth radius of curvature, wherein the centre of the radius of curvature for at least two surfaces is offset rearwardly with respect to a central vertical axis through the upper and lower vertebrae.
  • the centre of the fourth radius of curvature and/or the first radius of curvature is offset rearwardly of the central vertical axis.
  • centre of the radius of curvature of all of the surfaces is offset rearwardly with respect to the central vertical axis.
  • the centre of the radius of curvature for each of the surfaces is preferably located in the posterior third of the prosthesis.
  • the middle part may have a minor central axis and a major central axis, the minor central axis being located through the centre of the radius of curvature of the second and third surfaces.
  • the minor central axis may be inclined with respect to the vertical central axis.
  • the major axis is located through the centre of the posterior and anterior ends of the middle part.
  • the second and third surfaces may have a substantially similar radius of curvature.
  • At least one of the second and third surfaces may have one of a convex, concave, cylindrical surface.
  • the posterior and anterior ends may comprise flat surfaces.
  • the middle part has a convex upper surface and a concave lower surface.
  • the upper surface of the middle part is concave and the lower surface of the middle part is concave.
  • the radius of curvature of the upper surface of the middle part is greater than the radius of curvature of the lower surface.
  • the flat surfaces may be vertically oriented or slightly skewed in accordance with normal angulation of vertebrae.
  • the flat surfaces are vertically oriented parallel to the vertical axis plus or minus an angular offset.
  • the flat surfaces are parallel to the minor axis.
  • centre of the radius of curvature for the third surface is offset rearwardly with respect to the centre of the radius of curvature for the second surface.
  • the radius of curvature of the third surface has a centre on a line perpendicular to the major axis.
  • the radius of curvature of the third surface has a centre on a line coincident with the minor axis.
  • the radius of curvature of the second surface has a centre on a line at right angles/normal to the major axis.
  • the second surface has a radius of curvature with a centre on a line coincident with the minor axis.
  • the first and fourth surfaces have radii of curvature with a centre similar to that for the third and second surfaces respectively.
  • the centre of the radius of curvature of the second and/or third surfaces is substantially coincident with a vertical axis through the anatomical centre of rotation.
  • the length of the second and third surfaces may be substantially the same.
  • the length of the end surfaces of the posterior and anterior ends is different.
  • the posterior end surface may be larger than the anterior end surface if the second and third surfaces are convex.
  • the posterior end surface is smaller than the anterior end surface.
  • the second surface has a major portion located forward of the anatomical centre of rotation.
  • the third surface may have a major portion located forward of the anatomical centre of rotation.
  • each of the surfaces have a major portion located forward of the anatomical centre of rotation and the minor portion located rearwardly of it.
  • the middle part may be asymmetric.
  • a major portion of the middle part is located forward of the anatomical centre of rotation when the upper and lower vertebrae are substantially vertically aligned.
  • the minor axis of the middle part when in a vertical orientation close to its point of rest is as close as possible if not coincident with a vertical axis through the anatomical centre of rotation.
  • the upper part may comprise an axis of symmetry which is offset to the posterior end.
  • the axis of symmetry may coincide with the centre of radius of curvature of the first surface.
  • the axis of symmetry preferably passes through the anatomical centre of rotation.
  • the lower part may comprise an axis of symmetry which passes through the anatomical centre of rotation.
  • the first and second surfaces have substantially matching radii of curvature.
  • the third and fourth surfaces have substantially matching radii of curvature.
  • the upper part may comprise an anterior portion which is larger than a posterior portion relative to the axis of symmetry.
  • the lower part may comprise an anterior portion which is larger than a posterior portion relative to the axis of symmetry.
  • the middle part is movable relative to the upper and lower parts.
  • Movement of the middle part is preferably limited by stopping means located behind and in front of the middle part.
  • the stopping means may include end portions of the upper and lower parts.
  • the upper and lower parts may be fixed to the upper and lower vertebrae and configured to form a small gap between respective anterior end portions and a larger gap between respective posterior end portions.
  • the second and/or third surfaces include a curved surface portion.
  • the curved surface portion preferably has a substantially spherical profile with a radius of curvature.
  • the second and third surfaces have centres of radius of curvature which are vertically offset.
  • first and second surfaces have substantially similar radii of curvature of opposite sign.
  • the third and fourth surfaces may have substantially similar radii of curvature of opposite sine.
  • the second radius of curvature is different than the third radius of curvature.
  • the third radius of curvature is greater than the first or less than the first.
  • the third surface may be offset more than the second from the central vertical axis of the vertebrae.
  • the parts of the prosthesis are designed asymmetrically to correspond to the asymmetry of upper and lower vertebrae with which they are to be used.
  • the lower part and upper part include a stop surface at a rearward part to limit rearward movement of the middle part.
  • the length of one of the second/third surfaces may be greater than the other when measured front to back.
  • the fourth surface preferably includes a flat forward portion extending from a front end of a curved portion.
  • the curved portion preferably has a spherical cylindrical profile.
  • top and bottom surfaces are convex.
  • a device for linking bones comprising a band having first and second ends each with attachment portions for attachment to upper and lower bones and a plurality of filaments configured to provide a plurality of zones conducive to cellular growth.
  • the plurality of zones comprise spaces.
  • the plurality of filaments may be configured to form a matrix.
  • the plurality of zones comprise a plurality of interwoven portions.
  • the filaments may be woven together.
  • the band preferably comprises a gauze or mesh.
  • the band may have inherent stiffness.
  • the band is resiliently deformable.
  • the band is extendible and compressible.
  • the zones may comprise spaces between filaments.
  • the zones according to one embodiment include overlapping regions of filaments.
  • the spaces are formed by filaments.
  • the filaments are configured in parallel and perpendicular rows forming an intersecting grid pattern.
  • the device is used for linking upper and lower vertebrae.
  • the band is connected to an anterior portion of upper and lower vertebrae.
  • the band may be generally flat.
  • the band may be in the form of a flat strap.
  • the band may be composed of fabric, metal or a polymeric substance.
  • the band is made from a substance which dissolves in use.
  • the band preferably can concertina or lozenge.
  • the band provides axial support against a predetermined level of compression.
  • the band provides a predetermined level of resilient extension.
  • Each attachment portion may comprise a plate or strap with holes to allow fixing elements to be inserted therethrough.
  • a prosthesis for vertebrae having one or more of the features of the previously described prosthesis wherein the upper part when the prosthesis is attached to upper and lower vertebrae, closely simulates rotational and translational movements possible with an invertebral disk.
  • a method of producing a prosthesis for vertebrae comprising providing a model for designing a prosthesis used to simulate kinematics of an invertebral disk, using the model to produce a prosthesis comprising an upper part, a lower part and a middle part, which prosthesis simulates kinematics of an invertebral disk and wherein the upper part when the prosthesis is attached to upper and lower vertebrae simulates rotational and translational movements possible with an invertebral disk.
  • the simulation provided by the prosthesis includes tilting of the upper part relative to the anatomical centre of rotation of the lower vertebral disk.
  • the simulation provided by the prosthesis may include movement during rotation along an arc permissible with an invertebral disk.
  • the simulation provided by the prosthesis may include translational movement forward and back to an extent permissible for an upper vertebrae with an invertebral disk.
  • anatomical centre of rotation may vary for adjacent pairs of upper and lower vertebrae in a vertebral column.
  • the radius of curvature for the first and second surfaces is selected based on rotational movement possible for an upper vertebrae with respect to a lower vertebrae.
  • the third and fourth surfaces have a radius of curvature which is selected to simulate the amount of tilting possible for the upper vertebrae.
  • the angle of tilting permissible for the upper vertebrae and the angle indicative of the rotational movement of the upper vertebrae together closely approximate the angular displacement of an upper vertebrae with respect to a lower vertebrae with an invertebral disk between the upper and lower vertebrae.
  • a process for analysing performance of a prosthesis for use between upper and lower vertebrae comprising determining a first centre of radius of curvature for a lower surface of a middle part of a prosthesis, determining a second centre of radius of curvature for an upper surface of the middle part of the prosthesis, providing a link between the first centre of radius of curvature and second centre of radius of curvature, rotating the second centre of radius of curvature with respect to the first centre of radius of curvature by a degrees representing tilting of the upper vertebrae, rotating a portion of the first link by ⁇ degrees whereby the length of the portion corresponds to the length from the second centre of rotation of curvature to the centre of the lower surface of the upper vertebrae or upper surface of the upper part whereby ⁇ corresponds to angular movement of the upper part over the upper surface of the middle part, determining the anatomical centre of rotation, determining an angle ⁇ corresponding to the desired angle of rotation of an in
  • the link passes through the minor axis of the middle part.
  • the angle ⁇ corresponds to the angle between the upper centre of radius of curvature relative to a central vertical axis of the upper and lower vertebrae (prosthesis axis).
  • the angle ⁇ corresponds to the angle formed by moving the first link through an angle whereby the link coincides with a central point on the lower surface of the upper vertebrae when moved a maximum permissible amount relative to the anatomical centre of rotation.
  • the process includes determining the length of the first link and the length of a second link between the lower centre of radius of curvature and the centre point on the lower surface of the upper vertebrae.
  • the method involves converting a frame located at the anatomical centre of rotation to a global co-ordinate system and moving the frame by translational and rotational transformations to relocate the frame at either the centre of the lower surface of the upper vertebrae or a point on the lower surface of the upper vertebrae that lies on a vertical axis through the anatomical centre of rotation when the upper vertebrae is in rest above the lower vertebrae.
  • transformations involved include the algebraic and matrix transformations described in the preferred embodiment.
  • the process involves designing the prosthesis so that the maximal change in ligament length due to prosthesis malplacement is minimised.
  • Prosthesis malplacement can be defined by the value of the horizontal distance between the prosthesis axis and the patients centre of rotation (value Ldsk in FIGS. 5 a , 5 c and value L in FIGS. 19A and 19B ).
  • the process involves designing a mechanism such that the ligament is stretched in such a way as to be under more tension in flexion and extension and be under the least tension in the neutral position.
  • a mechanism will provide a restoring force that will tend to move the prosthesis back to a neutral position.
  • a modelling method for a prosthesis comprising:
  • l the distance of the CUPR from the ACR along an x axis
  • p the distance of the CUPR from the ACR along a y axis.
  • ⁇ is the angle of rotation of the CLPR in relation to the CUPR
  • T is a transformation matrix
  • ⁇ is the angle of rotation of a point B on an upper vertebrae relative to the CLPR
  • ⁇ normal rotation of an upper vertebrae relating to the ACR.
  • frames B6 and A3 are rotated by ⁇ ° about global reference frame A1 to produce new frames A4 and B7.
  • the step of comparing includes solving at least one of the following equations for a minimum value.
  • the step of comparing includes solving simultaneous equations for equivalent rows and columns of A4 and B7.
  • reference frame A1 is a global reference frame.
  • prosthesis is intended to cover any artificial insert having any number of components.
  • the modelling method used for analysing performance of a prosthesis preferably describes motion of an artificial disk that has a mobile core and is constrained by adjacent ligamentous structures.
  • the modelling method preferably can be used to optimise the various design parameters of a mobile core prosthesis so as to more accurately reproduce the location of the IAR of a normal disk and minimise the tendency to follow or adopt an abnormal path of motion during flexion/extension movements and/or an abnormal neutral alignment in the sagittal plane at rest.
  • the Mathematical Process can be used to optimize a disc mechanism consisting of curved upper and lower articulations where the arc centres are below the disc base but where the radii are unequal. This may permit variation in the vertical location of the prosthesis axis of rotation but restrict it to below the disc base. Such a prosthesis would not have the ability to achieve certain undesirable positions that would be readily apparent to someone skilled in the art.
  • the Mathematical Process may be used to design a prosthesis which will minimize the effect of abnormal tension in the adjacent ligamentous structures
  • the prosthesis may optimally be further supported by the placement of an artificial ALL, attached to anterior aspect of the vertebral bodies and separate from the disc prosthesis.
  • the prosthesis may not function correctly without appropriate tension in the adjacent ligamentous structures.
  • the placement of constraints within the disk prosthesis will strain the prosthesis/vertebral interface and may predispose to loosening of the prosthesis.
  • the mathematical process may be used to design a prosthesis which will minimise the effect of abnormal tension in the adjacent ligamentous structures, the prosthesis may optimally be further supported by the placement of an artificial ALL, attached to anterior aspect of the vertebral bodies and separate from the disk prosthesis.
  • FIG. 1 shows a schematic diagram of a prior art prosthesis between upper and lower vertebrae
  • FIG. 2 shows a dual linkage model of a prosthesis in accordance with an embodiment of the present invention
  • FIG. 3 shows a schematic of motion of a normal invertebral disk about an anatomical centre of rotation
  • FIG. 4 shows a schematic diagram of upper and lower vertebrae with attached global reference frame in accordance with a preferred embodiment of the present invention
  • FIGS. 5A and 5C show a schematic diagram of a prosthesis (convex/concave and biconcave core respectively) and upper and lower vertebrae showing translational characteristics of a model according to the preferred embodiment of the invention
  • FIGS. 5B and 5D show rotational characteristics of the model shown in FIGS. 5A and 5C ;
  • FIG. 6 shows a schematic of a bi-convex core prosthesis with an upper vertebrae in kyphosis
  • FIG. 7 shows a schematic of a convex/concave core prosthesis with the upper vertebrae in kyphosis
  • FIG. 8 shows a schematic diagram of a biconvex prosthesis with the upper vertebrae under the constraint of maximum ligament stretch (MLS);
  • FIG. 9 shows a schematic diagram of a prosthesis with a core having a convex upper surface and concave lower surface, with the upper vertebrae under the constraint of maximum ligament stretch (MLS);
  • MLS maximum ligament stretch
  • FIG. 10A shows a prosthesis according to another embodiment with upper and lower vertebrae in rest positions
  • FIG. 10B shows the prosthesis shown in FIG. 10A with the upper vertebrae rotated by 10°;
  • FIG. 11 shows a prosthesis according to another embodiment of the present invention with the upper vertebrae and lower vertebrae at rest;
  • FIG. 12 shows the prosthesis shown in FIG. 11 with the upper vertebrae rotated by 10°;
  • FIG. 13A shows a top view of a prosthesis according to another embodiment of the present invention.
  • FIG. 13B shows a cross-sectional view of the prosthesis of FIG. 13A taken along sectional lines A-A;
  • FIG. 13C shows a cross-sectional view of the prosthesis shown in FIG. 13A taken along sectional lines B-B;
  • FIG. 13D shows a top view of the prosthesis shown in FIG. 13A ;
  • FIG. 13E shows a rear view of the prosthesis shown in FIG. 13A ;
  • FIG. 13F shows a side view of the prosthesis shown in FIG. 13A with the left hand side representing the posterior end;
  • FIG. 14 shows an angled view of a prosthesis according to another embodiment of the present invention.
  • FIG. 15A shows a side schematic view of a prosthesis according to another embodiment of the invention with upper and lower vertebrae in a rest position;
  • FIG. 15B shows the prosthesis in FIG. 15A with the upper vertebrae rotated 10°
  • FIG. 16 shows a schematic side view of a prosthesis according to another embodiment of the present invention.
  • FIG. 17 shows a schematic side view of a prosthesis according to a further embodiment of the present invention.
  • FIG. 18 shows a front view of a ligament band of the present invention according to one embodiment
  • FIG. 19A shows a schematic cross-sectional end view of a prosthesis in an equilibrium position according to another embodiment of the invention.
  • FIG. 19B shows the prosthesis of FIG. 19A in an unstable position
  • FIGS. 20A and 20B show a three dimensional graphical analysis of different positions of a prosthesis having a core with a convex upper surface and convex lower surface in accordance with an embodiment of the present invention
  • FIG. 21 shows a 2D graphical representation of a the prosthesis analysed in FIG. 20 ;
  • FIG. 22 shows a 3D graphical analysis of a bi-convex prosthesis
  • FIG. 23 shows a 2D graph of ligament length vs angular movement for a dual convex prosthesis
  • FIG. 24A and 24B show a 3D graphical analysis of a Bi-concave prosthesis according to different embodiments of the present invention.
  • FIG. 1 shows a prosthesis with a bi-convex core representing a prior art prosthesis as shown for example in U.S. Pat. No. 5,674,296 to Bryan.
  • the upper vertebrae 10 can rotate relative to the core 11 and the core 11 can rotate relative to the lower vertebrae 12 .
  • Incremental normal rotation in the sagittal plane occurs around an instantaneous centre of rotation. When measured over larger angles this ICR moves somewhat, although in both the lumber and cervical spines it is always in the posterior one half of the lower vertebrae.
  • motion of the upper vertebrae 10 can be described by analysing it as a dual linkage with links 14 and 15 as shown in FIG. 2 .
  • Point CUPR remains fixed in global co-ordinates.
  • the motion can be considered as sequential movements of the links 14 and 15 .
  • upper vertebrae 10 , the core 11 and the point CLPR rotate by ⁇ degrees around the point CUPR.
  • the lower vertebrae 12 then rotate by ⁇ degrees around the newly rotated position of CLPR (CLPR 1 ).
  • the minor axis (not shown) of the core 11 remains at right angles to link A which itself passes through the minor axis of the core 11 .
  • Core 11 therefore moves in the same direction to upper vertebrae 10 . In flexion core 11 will anteriorly, in extension core 11 will move posteriorly.
  • FIG. 3 shows motion of a normal disk, (invertebral disk) with the approximation of a fixed centre of rotation (ACR). All points on vertebrae 10 move to corresponding points on vertebrae 18 and the transformation that describes the movement of any arbitrary point from the position of upper vertebrae 10 to upper vertebrae 16 is rotation by angle ⁇ around ACR. Lines 17 and 18 both exhibit positional information and angular information. These characteristics are defined as position and orientation.
  • Position and orientation of objects in two dimensional space are conveniently describe by the use of linear algebra.
  • a coordinate system can be attached to the object. This coordinate system is called a frame. All points on the moving object have fixed coordinates in the new frame and the frame is considered to move within another coordinate system—usually the global or ‘world’ coordinate system.
  • FIG. 4 shows a Frame FR1 attached to the moving vertebrae in FIG. 3 . The origin of this frame is displaced from the origin of the global frame G by position vector p.
  • the orientation of frame FR1 is given by the unit vectors n for the x axis and o for the y axis of FR1.
  • n x x coordinate of unit vector n
  • n y y coordinate of unit vector n
  • ⁇ x x coordinate of unit vector ⁇
  • ⁇ y y coordinate of unit vector ⁇
  • Any point with coordinates x,y attached to frame FR1 can be converted to global coordinates by premultiplying matrix FR1 by the vector of the coordinates of the point in FR1
  • Any frame such as FR1 can be transformed by multiplying by a transformation matrix T with the following characteristics.
  • Matrix M is premultiplied by Frame FR1 frame FR1 will be rotated around the fixed global reference frame origin and translated in the direction of the global reference frames axes. If Matrix M is postmultilpied by FR1, FR1 is rotated around the origin of the moving frame (FR1) and translated in the direction of the moving (FR1) frames axes.
  • FIGS. 5A to 5D show a hypothetical prosthesis with a convex upper surface and a concave lower surface.
  • a mechanical linkage consisting of line segment AD rotating around point A and a further link consisting of line segment DB.
  • DB is rigidly attached to the upper vertebrae and upper prosthetic end plate.
  • a reference frame has been attached at point ACR.
  • a further reference frame has been attached at point A.
  • BFR 1 should have the following value—expressed in the global reference frame AFR 1 .
  • FIG. 1 alpha is negative considering the normal convention of positive rotation being anticlockwise.
  • BFR ⁇ ⁇ 2 BFR ⁇ ⁇ 1 ⁇ R ⁇ [ 1 0 0 0 1 - Bdsk 0 0 1 ]
  • BFR ⁇ ⁇ 3 BFR ⁇ ⁇ 2 ⁇ R ⁇ [ 1 0 0 0 1 Cdsk 0 0 1 ]
  • BFR 3 is now attached to the upper vertebrae at point B and has the orientation of the upper vertebrae.
  • BFR 3 (1,3) (row 1, column 3) contains a function f(alpha,Beta) that represents the x coordinate of point B and BFR 3 (2,3) contains a function g(alpha, Beta) that represents the y coordinate of point B.
  • BFR 3 (1,1) contains a function k (alpha,Beta) that represents the cosine of the angle made by the top vertebrae with the global reference frame.
  • BFR ⁇ ⁇ 4 BFR ⁇ ⁇ 3 ⁇ [ 1 0 - Ldsk 0 1 0 0 0 1 ]
  • the equivalent functions f, g and k now represent the coordinates of point E and the (unchanged) angle of orientation of the upper vertebrae.
  • AFR ⁇ ⁇ 1 [ 1 0 0 0 1 0 0 0 1 ]
  • a frame APFR 2 can be derived by rotation by angle gamma (the desired rotation of the normal disc) of frame AFR 1 to produce AFR 1 R
  • AFR ⁇ ⁇ 1 ⁇ R AFR ⁇ ⁇ 1 ⁇ [ cos ⁇ ⁇ ⁇ - sin ⁇ ⁇ ⁇ 0 sin ⁇ ⁇ ⁇ cos ⁇ ⁇ ⁇ 0 0 0 1 ]
  • Frame AFR 1 R can now be translated by value Adsk along the y axis of AF 1 R to produce frame AFR 2
  • AFR ⁇ ⁇ 2 AFR ⁇ ⁇ 1 ⁇ R ⁇ [ 1 0 0 0 1 Adsk 0 0 1 ]
  • AFR ⁇ ⁇ 2 [ cos ⁇ ⁇ ⁇ - sin ⁇ ⁇ ⁇ - sin ⁇ ⁇ ⁇ ⁇ Adsk sin ⁇ ⁇ ⁇ cos ⁇ ⁇ ⁇ cos ⁇ ⁇ ⁇ Adsk 0 0 1 ]
  • AFR 2 (1,3) should now contain the x coordinates of point E and AFR 2 (2,3) should now contain the y coordinates of point E.
  • Equations 6 and 7 represent 2 simultaneous equations with two variables. In order for the mechanism to exactly simulate the movement of the normal disc, it also follows the AFR 2 and BFR 4 must be equal.
  • AFR2 BFR4 (8)
  • FIG. 6 represents the effect of an attempt to flex an existing prosthesis with a biconvex core by 10 degrees with the constraint (constraint 1) being that point E is the same as the normal prosthesis.
  • the solution to equations 6, 7 and 8 result in a equalling ⁇ 10.72° and ⁇ equalling ⁇ 18.26°.
  • the dashed line represents a real disk rotating by 10° about .ACR, this position represents the kyphotic solution to keep points E with the same co-ordinates.
  • FIG. 7 represents the effect of an attempt to flex a prosthesis with a core with a convex uppersurface and a concave lower surface by 10 degrees with the constraint (constraint 1) being that point E is the same as the normal prosthesis.
  • the solution to equations 6, 7 and 8 result in a equalling 5.71° and ⁇ equalling ⁇ 7.71°.
  • the dashed line represents a real disk rotating by 10° about .ACR, this position represents the kyphotic solution to keep points E with the same co-ordinates, Though the position of kyphosis is significantly less than the biconvex core prosthesis.
  • This position is the position of zero ligament stretch (ZLS).
  • FIG. 7 the effect of attempting to extend a prosthesis by 10° is shown. Solutions to equations 6, 7 and 8 result in ⁇ equalling ⁇ 1.55° and ⁇ equalling 4.75°.
  • the dashed representation of the upper vertebrae again represents a real disk rotating by 10° about .ACR. This position represents the Lordotic solution to keep points E with the same co-ordinates. This position represents the 0 ligament stretch position (ZLS).
  • the other useful constraint is to constrain the lower end plate of the upper vertebrae to be parallel with the lower end plate of the upper vertebrae in the ‘normal’ situation and to minimize the distance between them. This can be achieved by rotating frames BFR 4 and AFR 2 by gamma degrees about the global reference frame AFR 1 to produce two new frames AFR 3 and BFR 5
  • AFR ⁇ ⁇ 3 [ cos ⁇ ⁇ ⁇ - sin ⁇ ⁇ ⁇ 0 sin ⁇ ⁇ ⁇ cos ⁇ ⁇ ⁇ 0 0 0 1 ] ⁇ AFR ⁇ ⁇ 2
  • BFR ⁇ ⁇ 5 [ cos ⁇ ⁇ ⁇ - sin ⁇ ⁇ ⁇ 0 sin ⁇ ⁇ ⁇ cos ⁇ ⁇ ⁇ 0 0 0 1 ] ⁇ BFR ⁇ ⁇ 4
  • FIG. 8 shows the effect of adding this constraint (constraint 2) to an existing prosthesis with a biconvex core and attempting to match a 10 degree of flexion from a ‘normal’ motion segment. It can be seen that with this constraint that the two upper vertebrae cannot superimpose and that a ligament joining points ACR to E must be stretched beyond its normal length. With the constraint that the end plates are parallel, solutions to equation 6, 7 and 8 result in a equalling ⁇ 1.61° and ⁇ equalling ⁇ 8.39°. The dashed lines represent the real disk rotating by 10° about .ACR and the resultant position represents the solution to keep points with the end plates parallel and with minimum distance between them. This constraint is therefore termed Maximal Ligament Stretch (MLS).
  • MLS Maximal Ligament Stretch
  • the posterior longitudinal ligament is much tougher.
  • the lumbar spine therefore would preferentially attempt to stretch the ligament ACR-E by using the constraint MLS.
  • the annulus fibrosis would rarely allow this and the theory would suggest that flexion would be limited.
  • the real constraints in a given disc space will be a combination of the constraints ZLS and ALS.
  • the difference in the angle achieved by the vertebrae and the desired angle (Gamma ⁇ (alpha+beta)) in the ZLS situation (Delta A) will be a measure of the prostheses inability to match the normal motion required.
  • the difference between the length of ligament ACR-E and the desired length (Delta L) will also be a measure of the prostheses inability to match the normal motion required.
  • Delta A is minimized to virtually nil by reducing variable Ldsk to zero. This has the effect of moving the prosthetic axis posteriorly so that the ACR lies on the Prosthetic Axis. In this position Delta A remains very small for all positions of the ACR that lie at or below the disk space on the prosthetic axis.
  • Delta A is minimized when the radii of the upper and lower prosthetic articulations are approximately equal.
  • Delta A is minimized when the radii of the articulations are larger and Delta A gets larger with smaller radii.
  • Delta A is between 3 and 5°.
  • the translation of the Core is larger when the Prosthetic Radii are larger and the translation is smaller when the radii are smaller.
  • the disclosed prosthesis therefore seeks to. Move the prosthetic axis to the posterior one third of the disc.
  • the core of the prosthesis is no longer symmetrical and was it to rotate, it may impinge on the spinal canal.
  • the prosthesis consists, briefly, of two end plates, an intermediate mobile core and a separate anterior band for attachment to the upper and lower vertebrae.
  • FIGS. 13A to 13E show another embodiment of the invention in which the prosthesis consists of a core 50 having concave upper and lower surfaces 51 , 52 .
  • An upper plate 53 has a convex lower surface 54 and lower plate 55 has an upper convex surface 56 .
  • the lower surfaces 52 , 56 are cylindrical from one side to the other (rotational and translational movement) rather than completely spherical, whereas the top surfaces 51 and 54 are completely spherical allowing for universal movement as opposed to backwards and forward movement as with the lower surfaces.
  • an additional feature of the prosthesis 49 shown in these figures is the provision of upper and lower vertical ridges 57 , 58 which are centrally located and adapted to fit into grooves created in the bottom surface of the upper vertebrae and the upper surface of the lower vertebrae.
  • the core 50 and upper plate 53 and lower plate 55 have the prosthetic axis 60 moved to the posterior 1 ⁇ 3 of the prosthesis so that the centre of the upper radius of curvature (CUPR) A and the centre of the lower radius of curvature (CLPR) D are aligned on the vertical axis through the ACR.
  • CUPR upper radius of curvature
  • CLPR lower radius of curvature
  • a major portion 61 is located forward of the axis 60 and a minor portion 62 is located behind it.
  • the minor axis of the core 50 is aligned with the vertical axis 61 .
  • the anterior and posterior vertical edges of the core 50 are flat and aligned in parallel with the minor axis 64 .
  • FIG. 12 an upper vertebrae 65 rotated through angles ⁇ and ⁇ are almost coincident with vertebrae 66 represented in dash line and corresponding to rotation by 10° ( ⁇ ) about the ACR.
  • This position represents the solution to keep points with the end plates parallel and with minimum distance between them. This corresponds to the position of maximum ligament stretch (MLS).
  • MLS maximum ligament stretch
  • the core of a bio-concave prosthesis as shown in FIGS. 11 and 12 move anteriorly in flexion. The amount of ligament stretch required to do this is less than when the prosthetic axis is at the mid point of the prosthesis and has therefore a design as shown in FIG. 10A and FIG. 10B .
  • FIG. 10B again shows the effect of moving upper vertebrae 71 through angles ⁇ and ⁇ compared to an upper vertebrae rotating by 10° relative to the ACR. It can be seen that movement possible by upper vertebrae 71 does not approximate movement of a real vertebrae 74 as well as prosthesis as designed with a prosthetic axis/minor axis coincident with the vertical axis through the ACR.
  • FIG. 14 shows an angled view of the prosthetic device 49 with core 50 , upper plate 53 and lower plate 55 .
  • FIGS. 15A and 15B show an alternative embodiment of the invention in which a prosthesis is provided with a core 75 with upper plate 76 and lower plate 77 .
  • the core 75 has an upper convex surface 78 and a lower concave surface 79 .
  • the minor axis 80 the prosthetic axis coincides with the vertical axis through the ACR of the lower vertebrae 81 .
  • the lower surface 79 is convex it is significantly smaller than the upper convex surface 78 .
  • the lower surface of the upper plate 76 is concave and has a matching configuration to surface 78 .
  • the lower plate 77 has a convex upper surface which is longer than the matching concave surface 79 to allow movement by the core 75 there over backwards or forwards.
  • FIG. 15B shows how rotation of the upper vertebrae 82 results in relative movement between upper plate 76 and core 75 as well as relative movement between core 75 and lower plate 77 .
  • the prosthetic axis is asymmetric and a major portion of the core 75 is located forward of the prosthetic axis.
  • FIG. 16 shows a side view of another prosthesis 83 consisting of a core 84 having an upper convex surface 85 which has a lower radius of curvature compared to a lower concave surface 86 .
  • both the upper and lower surfaces 85 , 86 have centres of radius of curvature which are located below the core 84 .
  • Upper plate 87 has a lower concave surface matching that of surface 85 and lower plate 88 has an upper convex surface 89 which is much longer than the length of the surface 86 to allow reasonable travel backwards and forwards.
  • the convex surface 89 of the lower plate 88 extends into a straight horizontal flat surface 90 . This effectively prevents forward travel of the core 84 beyond the end of the convex surface 89 .
  • FIG. 17 shows a prosthesis 91 which is similar to prosthesis 83 except that the upper surface 92 has a greater radius of curvature than the lower surface 93 .
  • the lower surface of the upper plate 93 is concave and longer in length than its co acting upper surface 91 .
  • Lower plate 95 has a convex surface which is longer in length than the co-acting concave surface 92 .
  • an upwardly angled straight section 98 is provided as a method of stopping movement of the core 99 beyond the end of the convex surface 96 .
  • the forward end of convex surface 96 also extends into a horizontal straight section 97 which serves to prevent the core 99 moving beyond the front end of the curved surface 96 .
  • the prostheses 83 , 91 are more realistically represented in FIGS. 16 and 17 as being interposed between upper and lower vertebrae which have a more trapezoidal shape rather than a rectangular shape.
  • surfaces 90 and 97 and previously described surfaces have been described as being horizontal, in fact they are slanted and instead are generally parallel to the general orientation of the upper and lower faces of the upper and lower vertebrae. It should also be noted that surfaces 90 and 97 can be angled upwardly or even downwardly as long as they prevent forward movement of the core 84 , 99 .
  • An additional component useful for a prosthesis designed to emulate characteristics of an invertebral disk include a band 100 shown in FIG. 18 which is designed to closely simulate actions of ligature and in one embodiment also provides a stop for forward movement of a prosthetic core.
  • the band 100 consists of a woven fabric 101 consisting of filaments of wafts and wefts creating a weave with a grid like pattern.
  • Upper and lower ends 102 , 103 are provided with connecting plates 104 , 105 each with holes 106 for screws to be inserted through for attachment to upper and lower vertebrae respectively.
  • the woven fabric 101 is preferably designed to encourage cellular growth in the interstitial spaces between the threads/filaments and to ultimately result in ligatures growing between the upper and lower vertebrae.
  • the band is in the form of a prosthetic ligament made from a woven and absorbable material of appropriate stiffness.
  • the woven material is designed to allow ingrowth of fibrous tissue to replace the function of the prosthetic ligament as it is reabsorbed.
  • the band is in the form of a gauze made of wire or polymeric material.
  • the band is able to elongate or contract in a similar fashion to a ligament.
  • the end plates may be made from a metal such as titanium, cobalt-chromium steel or a ceramic composite. Typically they have a roughened planar surface which abuts against the adjacent surface of the vertebrae. To assist with fixing the plates to the vertebrae, they may be provided with a fin or ridge as described in the embodiment shown in FIGS. 13 and 14 or they may be provided with curved surfaces for bearing on an adjacent vertebral body end plate.
  • the upper and lower surfaces of the core as well as the adjacent curved surfaces of the upper and lower end plates are preferably smooth to enhance articulation.
  • the central core may be made from similar materials to those used for the end plates, but may also be made from a plastic such as UHMW polyethylene or polyurethane composite.
  • each of the curved surfaces of the prosthesis is in the range of 5 to 35 mm.
  • the foot print of the prosthesis end plates may be of a variety of shapes but will be optimised to minimise the risk of subsidence into the adjacent vertebral bone.
  • co acting surfaces of the core and the lower plate could be ellipsoid instead of cylindrical to provide restricted relative movement therebetween.
  • x( ⁇ , ⁇ ) ⁇ (sin ⁇ cos ⁇ +cos ⁇ sin ⁇ ) ⁇ Ldsk+(cos ⁇ cos ⁇ sin ⁇ sin ⁇ ) ⁇ Cdsk ⁇ cos ⁇ Bdsk+Pdsk
  • Constants define the size and functional type of the prosthesis.
  • Equations 1-3 describe the kinematics of these 4 prosthesis.
  • ⁇ is the angular displacement of the upper part relative to the middle part
  • ⁇ is the angular displacement of the middle part relative to the lower part
  • l is the ligature joining a part of the upper part with the centre of rotation of the skeletal structure (or prosthesis) when in use and where x( ⁇ , ⁇ ) and y( ⁇ , ⁇ ) are different functions.
  • ligature includes any elongate member particularly one with a degree of extension of stretch and contraction or compression.
  • alpha and beta can be calculated that produce a minimum value for l.
  • l can be considered to be the lateral ligament of the spinal motion segment. As this is elastic it can be seen that it will behave as a spring and consequently will have the lowest elastic potential energy when l is smallest.
  • An equilibrium position can be calculated when l is either a minimum or a maximum. Mathematically this can be defined as the gradient vector being zero:
  • prostheses 1) and 4) have unstable equilibrium positions. This situation occurs when matching an on axis or off axis COR. By increasing the radii of the upper and lower articulations the value of the gradient vector will be less negative and the tendency to adopt a position of maximum flexion or extension will be diminished.
  • Prostheses 2) and 3) however, have the property of having a positive second partial derivative of l.
  • Prostheses 2) and 3) therefore have stable equilibrium positions and are self correcting or self centering.
  • FIG. 20A shows a graphical plot in three dimensions of the ligament length l versus ⁇ and ⁇ for a prosthesis core with a convex upper surface and a concave lower surface where the radius of curvature of the upper surface of greater than that of the lower surface.
  • the upper radius is 36 mm compared to 12 mm for the lower radius.
  • FIG. 20A It can be seen from FIG. 20A that the three dimensional graph shown indicates a minimum ligament length as represented by a trough in the graph.
  • FIG. 20B shows the effect of introducing a value for L of 1 mm for the same type of prosthesis shown in FIG. 20A .
  • the equilibrium position moves in the opposite direction to L.
  • the mathematical method can be used to optimise this change in equilibrium position and make the prosthesis less sensitive to changes in Y offset (L) or X offset (moving the patient's CR inferiorly).
  • FIG. 21 shows a two dimensional view of the change in ligament length with angle of flexion for the prosthesis referred to in FIG. 20A .
  • this Figure it can be seen that there is a clear trough around the centre of rotation represented by angle of flexion extension 0.
  • This graph clearly shows that any movement of the prosthesis away from the centre of rotation results in extension of the ligament length and therefore a natural tendency for the ligament to want to return to its minimum length at the centre of rotation.
  • FIG. 22 A graphical solution to the mathematical equation outlined above is shown in FIG. 22 for a biconvex core. It should be apparent from this graphical analysis that there is no minimum ligament length which provides a point of equilibrium. In fact the two dimensional graphical representation shown in FIG. 23 shows how the point of equilibrium is located about the centre of rotation of the biconvex core and shows that any movement of the core away from the centre of rotation results in a decrease in the ligaments length and therefore a tendency for the core to move away from the point of equilibrium.
  • FIG. 24A shows another embodiment of the invention in which the prosthesis has a biconcave core.
  • the prosthesis has a biconcave core.
  • This point of equilibrium corresponds to the minimum ligature length and hence provides a natural tendency for the core to return to the point of equilibrium if there is movement away from the centre of rotation.
  • FIG. 24B shows the variation in ligament length for a biconcave prosthesis with the upper radius equal to 36 mm and the lower radius equal to 36 mm with Y offset and X offset being zero. It can thus be seen that with equal radius the graphical representation of the mathematical model shows there is no tendency for movement of the prosthesis away from the equilibrium position to result in a movement back to the equilibrium position.
  • the two dimensional graphical representation which is not shown has a similar appearance to FIG. 21 .
  • All prostheses are able to match a COR that is on axis.
  • the COR When the COR is off axis they can only match by either stretching or shortening the lateral ligament (Delta L) or by adopting abnormal orientation (Delta A). Delta A and Delta L, for a given offset can be reduced by making the Radii Larger.
  • Prosthesis 2 does so with loss of disc height.
  • Prosthesis 3 does so with a gain in disc height.
  • the Ideal prosthesis has
  • the preferred embodiment is 3) with as large radii as possible. This has the added advantage of resistance to pure translation (because the soft tissues would need to lengthen)
  • the second preferred embodiment is 2) this has the advantage of relatively unrestricted translation.
  • the ratio of radii for prosthesis 3 can be set so that under a COR match to a physiologically normal centre of rotation there is equal arc travel between the top and bottom articulation. This can be achieved by
  • alpha and beta can be calculated for the CR match.
  • a capacity to calculate alpha and beta allows the prosthesis to be drafted.
  • the preferred radii are 5 mm and 50 mm.
  • Prosthesis 2 does not allow the travel on each articulating surface to be equal.
  • the mathematical model will be used for this prosthesis to allow an optimum choice of ratio of radii based on any desirable parameter such as the desired ratio of angles ⁇ and ⁇ .
  • the ideal ratio is 2:1-1:2.
  • the preferred radii are between 8-40 mm for each radii.
  • the preferred radii are between 6-30 mm
  • FIGS. 10A to 11B and 13 A to 13 F show a prosthesis having a biconcave profile.
  • FIGS. 15A , 15 D, 16 and 17 show a prosthesis with an upper convex surface and a lower concave surface. It is preferred that the version of the prosthesis shown in FIG. 17 is utilised as the radius of curvature of the upper surface is larger than that of the lower concave surface. It is also preferred that the lower surface of the upper plate has a matching profile to the upper surface of the prosthesis and the upper surface of the lower plate has a matching profile to the lower surface of the prosthesis. It should be understood however that this does not mean that the entire lower surface of the upper plate and upper surface of the lower plate have the matching profiles. Thus a reference to FIG.
  • FIG. 19A shows one preferred configuration of a prosthesis having the preferred upper and lower surface profiles identified above.
  • the prosthesis 110 shown is symmetrical about a central vertical axis and has smooth curved outer upper and lower edges.
  • the prosthesis is shown offset rearwardly and hence with its core 113 retained within a rearward region of the upper and lower plates 111 , 112 .
  • the upper surface of the lower plate 112 has a rearward portion having a convex shape of matching configuration to the opposing concave profile of the core 113 .
  • the apex of the convex region is offset rearwardly with respect to the centre of prosthesis.
  • the convex region is symmetrical about its offset central vertical axis and on either side extends into a concave trough with the result that the overall profile of this region has the appearance of part of a sinusoidal curve.
  • Each of the troughs extend into upwardly curved surfaces on either side of the convex region and provide rearward and forward detents to limit forward and backward movement of the prosthesis relative to the lower plate.
  • the upper plate 111 has a rearwardly offset concave lower surface with a rearmost downwardly extending edge which is configured to limit rearward movement of the core 113 relative to the upper plate 111 .
  • the radius of curvature of the lower surface of the upper plate is larger than the radius of curvature of the upper surface of the lower plate.
  • the radius of curvature has a common origin which is located on the central vertical axis of the prosthesis at a virtual point below the prosthesis.
  • FIG. 19A also shows the core 113 in a stable equilibrium position aligned with the central vertical axis 114 which is rearwardly offset to the anatomical central axis.
  • a lateral ligament 115 is shown connected between upper and lower vertebrae 116 , 117 .
  • the ligament 115 is offset by a distance L from the axis 114 .
  • FIG. 19B shows how the prosthesis 112 is effected by backward rotational movement of the upper vertebrae 116 with respect to the lower vertebral disk 117 .
  • the lateral ligament 115 rotates about the centre of rotation (CR) and the upper plate 111 and core 113 rotate to an unstable position. Because of the difference in radius of curvature of the upper surface of core 113 and the lower surface the ligament 115 is stretched and there is a natural tendency for it to return to the equilibrium position shown in FIG. 19A . The difference in radius of curvature also means that the upper vertebral disk 116 will rotate and translate with respect to the lower vertebral disk 117 .
  • the further the central vertical axis of the prothesis is offset from the centre of rotation of the skeletal structure, the larger the radius of curvature of the upper surface of the prosthesis.
  • the radius of curvature of the upper surface of the prosthesis is between 30 and 50 mm in the lumbar spine and 20 and 40 mm in the cervical spine.
  • the ratio of the radius of curvature of the upper surface of the prosthesis compared to the lower surface of the prosthesis is within a predetermined range an increase in the radius of curvature of the upper surface of the prosthesis will result in a corresponding increase in radius of curvature of the lower surface of the prosthesis.
  • the length of the convex region of the upper surface of the lower plate (when measured from front to rear) is determined in accordance with typical travel allowed for a vertebral disk in a typical vertebral column.
  • all embodiments of the prostheses have a prosthetic axis that is set in the posterior h of the disc to as closely as possible match the normal physiological centre of rotation.

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  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Orthopedic Medicine & Surgery (AREA)
  • Neurology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • Veterinary Medicine (AREA)
  • Public Health (AREA)
  • Heart & Thoracic Surgery (AREA)
  • General Health & Medical Sciences (AREA)
  • Cardiology (AREA)
  • Vascular Medicine (AREA)
  • Transplantation (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Surgery (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Robotics (AREA)
  • Medical Informatics (AREA)
  • Molecular Biology (AREA)
  • Prostheses (AREA)
US11/887,984 2005-04-06 2006-04-06 Vertebral Disc Prosthesis Abandoned US20090210059A1 (en)

Applications Claiming Priority (3)

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AU2005901682 2005-04-06
AU2005901682A AU2005901682A0 (en) 2005-04-06 A prosthesis
PCT/AU2006/000457 WO2006105603A1 (en) 2005-04-06 2006-04-06 Vertebral disc prosthesis

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PCT/AU2006/000457 A-371-Of-International WO2006105603A1 (en) 2005-04-06 2006-04-06 Vertebral disc prosthesis

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US14/032,143 Continuation US9138329B2 (en) 2005-04-06 2013-09-19 Vertebral disc prosthesis

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US20090210059A1 true US20090210059A1 (en) 2009-08-20

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US11/887,984 Abandoned US20090210059A1 (en) 2005-04-06 2006-04-06 Vertebral Disc Prosthesis
US14/032,143 Active US9138329B2 (en) 2005-04-06 2013-09-19 Vertebral disc prosthesis
US14/827,972 Active US9375322B2 (en) 2005-04-06 2015-08-17 Vertebral disc prosthesis
US15/166,098 Active US10226354B2 (en) 2005-04-06 2016-05-26 Prosthesis

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US14/032,143 Active US9138329B2 (en) 2005-04-06 2013-09-19 Vertebral disc prosthesis
US14/827,972 Active US9375322B2 (en) 2005-04-06 2015-08-17 Vertebral disc prosthesis
US15/166,098 Active US10226354B2 (en) 2005-04-06 2016-05-26 Prosthesis

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US (4) US20090210059A1 (ko)
EP (1) EP1865890B1 (ko)
JP (1) JP2008534180A (ko)
KR (1) KR101360150B1 (ko)
CN (1) CN101222887B (ko)
BR (1) BRPI0608666A2 (ko)
CA (1) CA2604128A1 (ko)
MX (1) MX2007012258A (ko)
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US8252058B2 (en) * 2006-02-16 2012-08-28 Amedica Corporation Spinal implant with elliptical articulatory interface
US20140052257A1 (en) * 2010-12-10 2014-02-20 Jeff Bennett Spine Stabilization Device and Methods
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US11197765B2 (en) * 2019-12-04 2021-12-14 Robert S. Bray, Jr. Artificial disc replacement device
US11839554B2 (en) 2020-01-23 2023-12-12 Robert S. Bray, Jr. Method of implanting an artificial disc replacement device

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WO2018087692A1 (en) * 2016-11-09 2018-05-17 Exponential Medical Technologies (Proprietary) Limited Artificial intervertebral disc
KR102402225B1 (ko) * 2020-12-23 2022-05-26 (주)헬스허브 경추 인공 디스크 시술을 위한 시뮬레이션 장치 및 그 방법

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US11839554B2 (en) 2020-01-23 2023-12-12 Robert S. Bray, Jr. Method of implanting an artificial disc replacement device

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CN101222887A (zh) 2008-07-16
US20160346094A1 (en) 2016-12-01
CA2604128A1 (en) 2006-10-12
KR101360150B1 (ko) 2014-02-11
MX2007012258A (es) 2007-12-07
EP1865890A4 (en) 2010-05-05
ZA200708495B (en) 2008-11-26
JP2008534180A (ja) 2008-08-28
US9375322B2 (en) 2016-06-28
US20160038303A1 (en) 2016-02-11
US20140094915A1 (en) 2014-04-03
US10226354B2 (en) 2019-03-12
KR20080007238A (ko) 2008-01-17
CN101222887B (zh) 2012-11-07
WO2006105603A1 (en) 2006-10-12
EP1865890A1 (en) 2007-12-19
EP1865890B1 (en) 2018-11-21
BRPI0608666A2 (pt) 2010-01-19
US9138329B2 (en) 2015-09-22

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