WO2014015262A1 - Implants orthopédiques hybrides, composites, métalliques - Google Patents

Implants orthopédiques hybrides, composites, métalliques Download PDF

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Publication number
WO2014015262A1
WO2014015262A1 PCT/US2013/051281 US2013051281W WO2014015262A1 WO 2014015262 A1 WO2014015262 A1 WO 2014015262A1 US 2013051281 W US2013051281 W US 2013051281W WO 2014015262 A1 WO2014015262 A1 WO 2014015262A1
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WO
WIPO (PCT)
Prior art keywords
core
metal
mold
over
bone
Prior art date
Application number
PCT/US2013/051281
Other languages
English (en)
Inventor
Darren J Wilson
Henry B. Faber
Joseph M. Ferrante
Gene E. Austin
David L. Evans
Original Assignee
Smith & Nephew, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Smith & Nephew, Inc. filed Critical Smith & Nephew, Inc.
Publication of WO2014015262A1 publication Critical patent/WO2014015262A1/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
    • A61B17/56—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor
    • A61B17/58—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor for osteosynthesis, e.g. bone plates, screws, setting implements or the like
    • A61B17/68—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin
    • A61B17/72—Intramedullary pins, nails or other devices
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/02—Inorganic materials
    • A61L27/04—Metals or alloys
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/28—Materials for coating prostheses
    • A61L27/34—Macromolecular materials
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
    • A61B2017/00526—Methods of manufacturing

Definitions

  • metal orthopaedic implants are typically used to either repair broken bones or reconstruct diseased joints in a patient. These metal orthopaedic implants are commonly made from cobalt chrome, titanium-64 and stainless steel. High strength composites provide an alternative material for manufacturing orthopaedic devices and offer advantages in terms of improved visualization and interpretation of the healing site, accelerated healing, improved patient comfort, and reduced volume of metal.
  • the commercial motivation to switch to a fully compositized structure has been tempered due to higher manufacturing and raw material costs, coupled with the risks associated with the introduction of a new technology into the market place at a cost premium.
  • Hybrid orthopedic implants made of plastic and metal present advantages by combining the benefits of each material and avoiding their disadvantages.
  • the material that is strongest or is easiest to manufacture or shape into complex or thin sections can be selectively used for different portions of the implant.
  • metal implants present the advantage of malleability, i.e. the surgeon can permanently change the shape of the implant to suit his needs by bending or twisting during application.
  • these devices offer the opportunity of being shaped intra-operatively by either bending or twisting operations due to the malleability of the metal core component while their size and shape can be modified by either cutting with scissors or shaving with a scalpel.
  • plastic is more elastic and therefore contours to the unique shape of a patient's bone, if made thin enough and pressed or molded onto the bone surface.
  • a key issue in manufacturing metal-polymer composite hybrid systems is the transitive region that joins the two dissimilar materials.
  • There are a variety of methods to secure the metal portion to the composite portion For example, certain physical or chemical etching or anodization pretreatment processes, which produce oxide films on the metal surfaces which, because of their porosity and microscopic roughness, mechanically interlock with the polymer forming much stronger bonds than if the surface were smooth.
  • machined features are added to the metal core component, e.g. grooves, dovetails and pins to interlock the over-mold component onto the metal surface.
  • FIGS 1-20 illustrate various embodiments of the invention.
  • the metal core component can be tapered or non-tapered and solid or cannulated with or without the inclusion of design features, e.g. screw holes, slots, key- ways, Figure 2.
  • the inner diameter of the core is typically 4.8 mm whereas the outer diameter of the core ranges from 7.3 mm up to 10.5 mm.
  • This part is fabricated by conventional metal working techniques and may consist of any of a wide variety of metals, the most preferred being stainless steel, cobalt-chrome alloy, and titanium alloy.
  • tapered, stainless steel core component designed specifically to clone the distal and proximal sections of a standard commercially available "all metal" tibial intramedullary nail for an 8.5 mm, 10 mm, 11.5 and 13 mm are illustrated in Figure 4(a-d) respectively.
  • the tapered core component can be formed by turning down the distal section to a specified outer diameter with a known bending stiffness.
  • the over-mold component can be a polymer (e.g. injection mold grade PEEK) or a composite (e.g. 30 % w/v short carbon fiber reinforced PEEK).
  • the theoretical bending stiffness of the metal hybrid composite intramedullary nail for both the tapered and non-tapered design can be determined from the product of the Young's modulus and the second moment of inertia. For comparative purposes, the bending stiffness's of the "all metal" tibial intramedullary nail in the distal and proximal section are indicated in Table 1.
  • the bending stiffness can reach up to 70% of the theoretical bending stiffness measured for an "all metal" tibial intramedullary nail of equivalent outer diameter, Table 1. This assumes that the core and over-mold components selected are cobalt chromium alloy and PEEK respectively. For the non-tapered hybrid nail design, the bending stiffness mismatch is lower.
  • Titanium-64 core 8.9 OD/4.8 ID 8.9 OD/4.8 ID 32.2 32.2
  • the surface of the metal core is either physically or chemically textured or grooved to help key-in the over-mold material.
  • the core consists of a plurality of pins or ridges extending axially or radially or a combination of both from the surface or is equipped with dovetails located at the distal and proximal ends of the core, as indicated in Figures 5(a) and (b) respectively.
  • the over-mold component is typically 0.5 mm - 3.0 mm thick.
  • the matrix is preferably selected from polysulfone, polyaryletherketone including but not limited to polyether-ether-ketone, polyether-ketone-ketone, polyimide, polyacetal, epoxy, polyethylene and polycyanate.
  • the optional composite portion for increased stiffness comprises of one or more filaments disposed about a longitudinal axis and within a polymer matrix.
  • the reinforcement agent can be either a tow or a fiber, e.g. glass, carbon or aramid fibers or high strength fiber drawn polyester.
  • the two parts may also be connected via an adhesive joint, or a shrink fit joint.
  • the metal portion may be received within the composite portion and secured thereto. Pre-heating the metal core might be necessary to bring its surface temperature closer to the melt temperature of the over-mold ( ⁇ 350°C) so at to reach optimum bond strength.
  • filament winding which is an automated process of wrapping filaments in a helical pattern over the metal core.
  • the advantages of this method include precise fiber orientations, high fibre-to-resin ratios, straight uncrimped fibre paths, high consistency and reproducibility.
  • This method comprises the steps of first filament winding a tow circumferentially around a metal core at various angles with respect to the longitudinal axis to form an outer-layer comprising one or more layers.
  • Each layer may contain fibers oriented at a constant angle along the longitudinal axis or fibers oriented at a changing angle with the longitudinal axis to provide additional resistance to torsional forces.
  • the angles used are selected to give desired mechanical properties both globally and locally in the structure. Consequently, the compositized over-mold layer can be engineered to provide a variable modulus along the length of the core due to the use of either filament winding or braiding techniques.
  • FIG. 6 Another method of making the device is using a hybrid injection molding process outlined in Figure 6.
  • a thin wall tapered metal tube is placed in the injection- molding tool/mold.
  • the design features located in the metal core are shut off using a series of metal inserts (1-8).
  • the tool closes and is then filled with a polymer resin at the open end.
  • the molten polymers flows into the empty cavity left between the core and the mold, referred to hereafter as the "gate” using a standard injection molding process.
  • polymer flows through the openings left by the inserts and surrounds the edges of the metal frame profile filling the gate, Figure 6. Solidification of the polymer creates a mechanical, interlocked connection between both materials producing a single unified component.
  • the composite structure ejects from the tool as a hybrid product, Figure 7.
  • Secondary operations include laser etching the over mold component, cleaning, inspection, sterilisation and packaging.
  • the polymer can be molded separately and can then be pressed with the metal core in a secondary operation.
  • Different additives can be added to the polymer to provide benefits such as conductivity, radiopacity, therapeutic effects, toughness, crystallinity, etc.
  • a 3D model acquired from the non-tapered core and molding tool, which also requires minimal inserts to seal off the design features on the implant is given in Figure 8.
  • a 3D model acquired form the final over-molded product is given in Figure 9.
  • the design features required on the core can be introduced after the injection molding process eliminating the need for extensive metal inserts within the molding process, Figure 10.
  • the core is surrounded by nitrogen/argon or subjected to vacuum to minimize oxidation of the surface of the core to enhance adhesive bonding between the metal core and the polymer.
  • the malleability of a hybrid device is suitable for the thermoplastic component minimising the risk of delamination and flaking.
  • 3D filling analyses can be used to determine the mold filling characteristics of the short (18 cm) and long (44 cm) straight and tapered core designs in terms of (a) optimum process conditions, (b) gate positions, (c) fill patterns, (d) weld lines, (e) clamp forces, (f) pressure and (g) temperature distribution across the mold, Figures 11- 14. These analyses assume that the over-mold component is non-reinforced PEEK, and the mold and melt temperature are 205 °C and 400°C respectively.
  • the wall thickness profile indicates the thickness range over the simulation model, Figure 11(a), 12(a), 13(a) and 14(a).
  • the fill time result shows the position of the flow front at regular intervals as the cavity fills.
  • the shading represents the parts of the mold, which were being filled at the same time.
  • the temperature at flow front is a mid-stream nodal result generated from a flow analysis, and shows the temperature of the polymer when the flow front reached a specified node, Figure 11(c), 12(c), 13(c), 14(c).
  • the pressure at V/P switchover is generated from a flow analysis, and shows the pressure distribution through the flow path inside the mold at the switchover point from velocity to pressure control, Figure 11(d), 12(d), 13(d) and 14(d).
  • tapered core given that it incorporates a reasonable wall section profile allowing the melt to flow the full length of the molding within a reasonable pressure of around 60 MPa.
  • An area of concern is the ability of the tubular core to withstand injection molding pressures within the cavity in the region of 60 MPa (8700 Psi). Core shift is also a concern as well as potential for the tube to collapse under the extreme pressure applied during molding.
  • shutoff design, gating, venting, and texture are key considerations when designing tooling for overmolded parts.
  • the design of the shutoff between the substrate and overmold is critical to the success of the resulting adhesion between the two components.
  • Injection molding potential offers the following advantages:
  • the volume of the tapered cannulated metal core (OD 8.9 mm / ID 4.8 mm - proximal section) and (OD 7.6 mm / ID 4.8 mm - distal section) is 6.2 cm A 3.
  • the combination of an over-mold and a reduced metal content will reduce the risk of metal ion toxicology in a patient through reduced incidence of wear at the bone-implant interface.
  • the over-mold component produces a radiolucent layer at the bone-implant interface making diagnosis of fracture healing easier for the surgeon.
  • the hybrid device only offers partial radiolucency compared to fully tape wound composite structures.
  • a still further method of securing the metal portion to the composite portion is by a shrink fit joint exemplified below with a spinal rod, Figure 15.
  • the shrink fit joint takes advantage of the orientation of the polymer chains during the production process of the shrink fit tubing. By heating above the glass transition point in the tubing, the orientated chains relax allowing the polymer to shrink onto the core component. The components are assembled at room temperature, and then the assembly is heated above 343°C to allow shrinkage to occur for at least 5 minutes. There is clearance between the metal portion and the composite device used; the dimensional characteristics of the metal portion and the composite portion will change relative to one another, causing a dimensional interference to secure the portions together. Consistent shrink ratios of up to 1.2 to 1.0 and above, and 10-20% longitudinal shrinkage
  • the core component would be made from a high strength polymer composite core, which would then be coated with a high strength nanocrystalline coating, e.g. cobalt chromium or nickel alloy using techniques such as electro-deposition.
  • a high strength nanocrystalline coating e.g. cobalt chromium or nickel alloy using techniques such as electro-deposition.
  • This coating technique would increase the mechanical properties of the polymer e.g. strength and stiffness.
  • the coating could be expected to suffer fatigue and flake off over time.
  • This process involves heating the core and forcing molten polymer either within the cavity or a separate vessel into the tool cavity.
  • the core is pre-heated to help receive the over-mold component.
  • the polymer is extruded from the profile die covering the metal core. Subsequently, the polymer melt flows through a channel of a die producing the final over-molded extruded part.
  • the melt temperature for PEEK is in excess of 380°C.
  • the over-molding component is produced separately, and secured to the core using methods described above.
  • the material of choice for the bone plate remains a metallic alloy, e.g. stainless steel.
  • the use of use of stainless steel plates for internal fixation has disadvantages such as stress shielding wherein the stresses are exerted primarily on the plate rather than bone in the region of the fracture causing a weakening of the cortical bone (at about 15 GPa) under the plate.
  • This stress shielding has been found to be the cause of significant bone resorption and consequent reduction of strength of the bone in the region of the healed fracture.
  • the use of a bone plate has not satisfactorily solved the problem of stress shielding, because the initial strength and rigidity of steel plates is desirable is desirable for most fractures.
  • an internal metal core in the bone plate to provide optimal strength, load-bearing ability and the ability to be shaped by either bending or twisting operations conducted by the surgeon intra-operatively, Figure 16.
  • the non-metallic over-mold component attached to the metal core allows the forming of complex shapes and thin sections to best adapt to and support the bone whilst minimizing damage to the periosteum and soft tissue.
  • the over-mold component also may cover the screw holes in the metal core providing additional stability for self-tapping screws.
  • the surface of metal endoskeleton can be roughened by either spraying of molten metal droplets, mechanical methods, chemical or electrochemical methods, or by direct casting, by direct forging.
  • the overmold component described in this IDR for trauma applications is non-resorbable to avoid direct coupling between the surface of the bone and the spacer unit via bone-ingrowth.
  • a resorbable spacer or overmold unit is absorbed as in prior art inventions, the gap between the bone and the plate can permit excessive motion of the plate relative to the screws, which can promote corrosion of the stainless steel plate. Given that the bone plate over-mold retains its structural integrity due to the non-absorbable nature of the material, this excessive motion does not occur.
  • the goal is to develop a nailing system with an optimum bending and torsional stiffness, which offers the potential for accelerated healing through improved stability of the bone fragments and the resultant quality of the regenerated bone compared to standard IM nails.
  • the nail behaves as a load sharing device. Initially, the majority of the load must be supported by the nail, but as the fracture heals and gains a greater mechanical stability, the load will be shared by the bone. It has been shown that on fracture healing, there is a reduction of up to 60% in loading of the interlocking nail. This shows that the nail still contributes significantly to the load-carrying ability of the construct when the fracture is fully healed. This residual load, transferred to the bone after nail removal, might lead to refracture unless patient activity was limited for a period.
  • Step 1 Patient images are captured from digital X-rays/CT imaging providing information relating to (but not limited to) the pattern of fracture, canal dimensions to ascertain the bend an bow in the nail and attachment points for the screws, bone density, cortical wall thickness, second moment of area, kinematics and anthropometric data. Other important variables which need considering include patient's age, ambulatory status, condition of the soft tissue envelope, and associated injuries.
  • Step 2 The patient images are converted into CAD files, e.g. stl files.
  • Step 3 FEA simulation is carried out to verify the number and placement of screw holes, wall thickness, material properties, e.g. Ti-6A1-4V; elastic modulus 110 GPa, Ti-24Nb-4Zr-7.9Sn; elastic modulus 33 GPa, and cross-sectional geometry for the custom implant (closed vs. open sections). It is also used to determine the stiffness range and degree of micromotion required for optimum healing.
  • Step 4 A CAD library of patient-specific implants designs is built up, which can be uploaded on the SLS rapid prototyping machine "Creation of device custom record.”
  • Step 5 The exported STL- file of the custom implant is sent to the AM- machine and prepared for manufacturing in a preparation software package and STL editor.
  • the part is oriented for building and a support structure is made for the downfacing surfaces of the part.
  • Nb Support structures are not required for an intramedullary nail.
  • cross-sections of a given thickness known as 'slices', are generated virtually from 3D CAD descriptions of the part and support structures.
  • Step 6 Additive fabrication is performed directly from a 3D CAD file in which a geometrical model of part is stored, Figure 2.
  • Step 7 Finally, the parts are post processed to meet the demands of the specific implant.
  • Bioactive overmolded metal core for patient at risk of infection or with compromised bone healing.
  • antibiotic- impregnated over-molded biodegradable layer where the antibiotic coating would be released over a period of time to help in the prevention and treatment of any infection that might occur.
  • Eccentrically cannulated nails produced by additive manufacturing i.e. a nail cannulation that tapers from large to small at large (proximal to distal).
  • the ideal bending and torsional stiffness may be significantly less than that achieved with current products.
  • Optimal micro-motion at the fracture site may results in an abundant amount of fracture callus distributed away from the neutral axis of the bone gives a large second and polar second moment of area and hence increased stiffness. This results in reduced stress shielding If the implant stiffness is closer to the bone.
  • the implant stiffness needs to be at its maximum during the early phases of fracture healing and then taper off as the fracture heals and consolidates minimizes the risk of stress shielding issues after the bone has healed.
  • the stiffness requirements between these two phases are unknown, however, the graph outlined in Figure 2 is representative of an idealized healing curve.*
  • the low-rigidity nail needs to be strong enough to maintain alignment of the fracture without delayed union and neutralizing shear forces at the fracture.

Abstract

L'invention concerne un procédé de fabrication d'un clou médullaire. Le procédé comprend : la fourniture d'un moule ayant une section proximale, une section distale et une section de courbure entre la section proximale et la section distale ; l'introduction d'au moins un noyau dans le moule ; la fusion à chaud entre 205 degrés et 400 degrés Celsius ; et l'injection de la fonte chauffée dans au moins deux emplacements de grille adjacents à la section de courbure. Dans le mode de réalisation préféré, la fonte est faite de matériau PEEK.
PCT/US2013/051281 2012-07-19 2013-07-19 Implants orthopédiques hybrides, composites, métalliques WO2014015262A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US201261673643P 2012-07-19 2012-07-19
US61/673,643 2012-07-19
US201261674092P 2012-07-20 2012-07-20
US61/674,092 2012-07-20

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WO2014015262A1 true WO2014015262A1 (fr) 2014-01-23

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015144131A1 (fr) * 2014-03-24 2015-10-01 Christian Lutz Procédé de fabrication d'un implant pour l'ostéosynthèse et clou orthopédique
US10610270B2 (en) 2018-01-15 2020-04-07 Glw, Inc. Hybrid intramedullary rods

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060247638A1 (en) * 2005-04-29 2006-11-02 Sdgi Holdings, Inc. Composite spinal fixation systems
US20100114097A1 (en) * 2007-04-27 2010-05-06 Synthes Usa, Llc Implant Devices Constructed with Metallic and Polymeric Components
US20100241120A1 (en) * 2004-10-04 2010-09-23 Saint Louis University Intramedullary nail device and method for repairing long bone
US20110208189A1 (en) * 2005-02-22 2011-08-25 Tecres S.P.A. Disposable device for treatment of infections of human limbs
WO2012065068A1 (fr) * 2010-11-11 2012-05-18 Zimmer, Inc. Implant orthopédique présentant une surface polymérique poreuse de contact osseux

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100241120A1 (en) * 2004-10-04 2010-09-23 Saint Louis University Intramedullary nail device and method for repairing long bone
US20110208189A1 (en) * 2005-02-22 2011-08-25 Tecres S.P.A. Disposable device for treatment of infections of human limbs
US20060247638A1 (en) * 2005-04-29 2006-11-02 Sdgi Holdings, Inc. Composite spinal fixation systems
US20100114097A1 (en) * 2007-04-27 2010-05-06 Synthes Usa, Llc Implant Devices Constructed with Metallic and Polymeric Components
WO2012065068A1 (fr) * 2010-11-11 2012-05-18 Zimmer, Inc. Implant orthopédique présentant une surface polymérique poreuse de contact osseux

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015144131A1 (fr) * 2014-03-24 2015-10-01 Christian Lutz Procédé de fabrication d'un implant pour l'ostéosynthèse et clou orthopédique
CN106170258A (zh) * 2014-03-24 2016-11-30 克里斯蒂安·鲁兹 用于生产骨接合术用植入物的方法以及骨钉
US20170105776A1 (en) * 2014-03-24 2017-04-20 Christian Lutz Method for Producing an Osteosynthetic Implant, and Bone Nail
JP2017512617A (ja) * 2014-03-24 2017-05-25 ルッツ，クリスティアン 骨接合用インプラントを作製する方法及び骨釘
US10610270B2 (en) 2018-01-15 2020-04-07 Glw, Inc. Hybrid intramedullary rods
US11826083B2 (en) 2018-01-15 2023-11-28 Glw, Inc. Hybrid intramedullary rods

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