Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B1/00—Processes of grinding or polishing; Use of auxiliary equipment in connection with such processes
  • B24B1/04—Processes of grinding or polishing; Use of auxiliary equipment in connection with such processes subjecting the grinding or polishing tools, the abrading or polishing medium or work to vibration, e.g. grinding with ultrasonic frequency
• • 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
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
  • B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
• • 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
  • A61F2002/30922—Hardened surfaces
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/47—Burnishing
  • Y10T29/479—Burnishing by shot peening or blasting

Definitions

• the present invention relates to a method for improving the strength characteristics of orthopedic prostheses, such as cotyloid elements, femur necks, femoral stems, systems of the spinal column and the like.
• orthopedic prostheses such as femur necks, femoral stems, cotyloid elements and systems of the spinal column, as well as other prostheses, are currently made of metal, for example titanium, so as to be very light and tough.
• Such prostheses are provided by using machine tools that use cutting tools for machining and such cutting tools leave micro-scoring on the surface of the prosthesis which is apparently not visible to the naked eye but constitutes initiation points of fatigue failure cracks.
• micro-scoring that is present on the surface of such prostheses constitutes weak points that produce cracks that ultimately lead to failure of the prosthesis, which may occur at any time in an apparently inexplicable manner.
• the peening treatment although effective in itself, may entail an increase in roughness due to the protrusions and hollows that it generates. Moreover, the peening treatment causes a variation of a few microns in the geometric dimensions of the treated part.
• the peening itself might create cracks if the parameters of the process are not calculated well as a function of the material used.
• titanium the material usually used for prostheses, is subject to crack forming.
• the aim of the present invention is to provide a method for improving the strength characteristics of prostheses and the like, substantially eliminating the likelihood that the micro-scoring caused by machining with machine tools might generate cracks that lead to the failure of the prosthesis.
• an object of the present invention is to provide a method for improving the strength of prostheses and the like that can be used after the standard production step of the prosthesis, thus without changing substantially its production cycle.
• Another object of the present invention is to provide a method for improving the strength characteristics of prostheses and the like that is highly reliable, relatively simple to provide and has competitive costs.
• the method according to the invention provides, starting from an orthopedic prosthesis, such as a femur neck, a femoral stem, a cotyloid element, a system of the spinal column or a similar prosthesis, for the application of a treatment adapted to eliminate substantially the micro- scoring that is present on the surface of the prosthesis due to machining performed with machine tools.
• an orthopedic prosthesis such as a femur neck, a femoral stem, a cotyloid element, a system of the spinal column or a similar prosthesis.
• This treatment is thus aimed at eliminating the micro- scoring that might give rise to cracks that lead to failure of the prosthesis and at increasing the surface hardness of the metal.
• the method provides for subjecting the prosthesis to a peening treatment, i.e., to a method by means of which the metallic surface of the prosthesis is struck (hammered), with a specific intensity, in order to harden the surface layer and at the same time eliminate the traces of the machining of cutting tools.
• the peening treatment entails the use of shot that can be made of metal, ceramics, glass or other material.
• the size of the shot varies and in general its diameter is a fraction of a millimeter.
• the intensity that defines the force with which the shot "hammers" the surface to be treated is also variable and is defined according to the curvature of specimens of known thicknesses.
• the diameters of the shot are comprised between 0.21 mm and 0.30 mm.
• the treatment is performed for example with a 200% coverage of the surface to be treated.
• the intensity of the treatment is comprised for example between 4 and 6 Almen.
• the peening treatment to which orthopedic prostheses are subjected allows hardening of the metallic surface of the prosthesis and at the same time elimination of the micro-scoring that is the cause of cracks and thus failures of the prosthesis.
• the peening treatment besides eliminating the machining traces of the tool and increasing the surface hardness of the prosthesis, allows the creation of a prestressed surface layer that makes it possible to reduce part of the traction stresses, the highest values of which are, as is known, concentrated at the surface. By reducing surface traction stresses one reduces the likelihood of initiation of fracture cracks and thus the likelihood of failure of the prosthesis.
• the peening treatment may be performed both on titanium prostheses and on prostheses made of other materials.
• the prosthesis After the peening treatment, the prosthesis is subjected to a surface finishing treatment provided by vibration finishing.
• the treatment cited above provides for causing the collision, at different speeds, of the prostheses being worked with an abrasive body (generally defined as "medium") and for repeating this type of collision for a sufficient number of times, so that the result obtained locally by the single collision event can become a general characteristic of the entire surface of the prosthesis.
• the vibration finishing treatment is performed in appropriate tanks in which the prostheses to be treated and a necessary quantity of medium are placed.
• the quantities of medium are selected so as to optimize the number of collisions that will define the surface of the finished prosthesis.
• the prostheses are arranged in a circular vibration machine with conical and double wedge-shaped polyester media that contain suitable abrasive fillers.
• the machining has the goal of eliminating material from the surface of the prosthesis in order to reach the desired and necessary roughness value.
• Surface finishing thus makes it possible to buff the prosthesis previously subjected to peening, eliminating all the remaining roughnesses and indentations and at the same time also the residues of the craters generated by peening.
• the surface finishing work is performed by a wet method, with a continuous input of water and of a suitable detergent.
• the duration of the process is about 16/19 hours.
• the prostheses are subjected to a polishing treatment, by means of a circular vibration machine with porcelain media (nonabrasive) of spherical shape and having a diameter of for example 4 mm.
• the purpose of the polishing step is to modify the roughness parameters of the surface of the prosthesis.
• This step is performed by a wet method with the addition of a polishing product.
• the duration of this last step is about 2/3 hours.
• the method according to the present invention fully achieves the intended aim and objects, since it allows improving the strength characteristics of prostheses of the known type with a treatment that is simple, economic and effective and at the same time it allows obtaining a prosthesis surface with optimum finishing.

Landscapes

• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Heart & Thoracic Surgery (AREA)
• Vascular Medicine (AREA)
• Cardiology (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Transplantation (AREA)
• Biomedical Technology (AREA)
• Veterinary Medicine (AREA)
• Orthopedic Medicine & Surgery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Prostheses (AREA)

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• 2010
  • 2010-09-28 IT ITMI2010A001762A patent/IT1401975B1/it active
• 2011
  • 2011-08-02 US US13/876,379 patent/US20130189905A1/en not_active Abandoned
  • 2011-08-02 EP EP11741190.0A patent/EP2621674A1/de not_active Withdrawn
  • 2011-08-02 WO PCT/EP2011/063280 patent/WO2012041571A1/en active Application Filing

Patent Citations (1)

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