Titanium alloy hip prosthesis

Details Titanium alloy hip prosthesis Titanium alloy hip prosthesis

1995-02-27

2001-10-23

Yu, Mickey (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

C623S018110

Reexamination Certificate

active

06306175

ABSTRACT:

The present invention relates to artificial hip joints consisting of a femoral component consisting of a spherical head attached at an appropriate angle to a shank by means of which it can be attached to the upper end of a femur belonging to a patient who is to receive the hip joint, and a bearing cup, called the acetabular cup which is attached to the associated end of the pelvis of the patient.
In total hip replacements, a preferred material for the femoral component is a titanium alloy because of its high corrosion resistance, good tensile strength and fatigue resistance. The acetabular cup preferably is made of a plastics material, ultra high molecular weight polyethylene being a particularly suitable material.
However, wear debris from these components can cause inflammation of local tissue and a susceptibility to infection which may, in turn, lead to attack of the bones and the loosening of the prosthesis, particularly the femoral component. Also, abrasive wear of the femoral component can take place to such an extent that it commences to gouge the acetabular cup, creating massive particles of polymeric debris.
According to the present invention there is provided a femoral component as herein before described for an artificial hip joint made out of an alloy containing titanium, wherein at least a major load bearing portion of which has been subjected to bombardment by a beam of nitrogen or other light ions having energies in the range of 10 Kev to 200 Kev until a surface fluence of between 1 and 8×10
17
ions/cm
2
has been implanted. Light ions are considered to be at least nitrogen, carbon, boron, or neon as is set out in the abstract of our U.S. Pat. No. 4,465,524, granted on Aug. 14, 1984, the teachings being incorporated herein by reference.
Preferably the ion implantation is carried out in such a way that the surface fluence over the said load-bearing portion of the femoral compound varies in the same way as the expected load when the femoral component is in use.
Also according to the invention there is provided an apparatus for carrying out the process of implantation of the nitrogen ions or other light ions, comprising a chamber, means for evacuating the chamber, a carriage adapted to carry a plurality of femoral components as hereinbefore described of an artificial hip joint one behind the other with the direction of offset of the heads of the femoral components parallel to the direction of movement of the carriage, a plurality of ion sources so positioned that the region of the heads of the femoral components which in use will bear the maximum load receive a maximum surface fluence of ions, and the region of minimum load receives a minimum surface fluence of ions, and means for moving the carriage past the ion sources.
Preferably, the temperature of the heads of the femoral components during the implantation of the nitrogen ions is some 300° C. This may be achieved as a result of the implantation process, or the femoral components can be heated to the required temperature. Furthermore, preferably there is provided in the chamber trace amounts of a carbon-containing gas or vapour. At the temperature indicated above, carbon impinging on the surfaces of the heads of the femoral components will be able to penetrate the metal where it augments the hardening action of the implanted nitrogen. An advantageous concentration of carbon is half that of the implanted nitrogen. A suitable way of providing the carbon is to use as the means for evacuating the chamber a vacuum pump utilising a hydrocarbon oil. A residual pressure of about 5×10
−5
torr will then provide the required carbon concentration.


REFERENCES:
patent: 3583361 (1971-06-01), Laudel, Jr.
patent: 3953619 (1976-04-01), Matsubara
patent: 4346123 (1982-08-01), Kaufmann
patent: 4365359 (1982-12-01), Raab
patent: 4401719 (1983-08-01), Kobayashi et al.
patent: 4465524 (1984-08-01), Dearnaley et al.
patent: 4466991 (1984-08-01), Andreev et al.
Oliver et al., “The Wear Behavior of Nitrogen Implanted Metals”, Met. Trans., vol. 15A, p. 2221-2229, Dec., 1984.

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