Spinal fixation rod made of titanium alloy
A spinal fixation titanium alloy rod fixes a plurality of spinal-fixing screws embedded and fixed in vertebrae of a human body. The rod is cylindrically shaped, has a sufficient length for coupling with the spinal-fixing screws, and has a diameter adjusted to 4 to 7 mm. In the titanium alloy constituting the rod, Nb content is 25 to 35 percent by weight, Ta content is such that the Nb content+0.8×Ta content ranges from 36 to 45 percent by weight, Zr content is 3 to 6 percent by weight, and the remainder is Ti and unavoidable impurities, excluding vanadium. The titanium alloy is manufactured by swaging processing at a cross-sectional reduction rate of at least 90%, and aging the swaged titanium alloy by heating at a temperature of 600 to 800K, preferably 700 to 800K, for 43.2 ks to 604.8 ks.
1. A spinal fixation rod made of titanium alloy for fixing a plurality of spinal fixation screws embedded and fixed in vertebrae of a human body,
the titanium alloy comprising:
Nb content of 25 to 35 percent by weight,
Ta content of such that the Nb content+0.8×Ta content ranges from 36 to 45 percent by weight,
Zr content of 3 to 6 percent by weight, and
the remainder is Ti and unavoidable impurities, excluding vanadium,
wherein the rod is cylindrically shaped,
wherein the rod has a diameter adjusted to 4 to 7 mm,
wherein the rod has a sufficient length for coupling with the spinal fixation screws, and
wherein the rod is produced by:
subjecting a cylindrical rod made of the titanium alloy to a swaging processing of cross-sectional reduction rate of at least 90%, and
aging the swaged rod by heating at a temperature of 600 to 800K for 43.2 ks to 604.8 ks.
2. The spinal fixation rod made of titanium alloy of claim 1 , wherein the aging treatment is performed by heating the swaged titanium alloy rod at a temperature of 700 to 800K for 43.2 ks to 604.8 ks.
3. The spinal fixation rod made of titanium alloy of claim 2 , wherein a crystal structure of the titanium alloy is such that mother phase of the titanium alloy is β phase; and wherein α phase portions are precipitated within the mother β phase in a shape of a plurality of fine needles.
4. The spinal fixation rod made of titanium alloy of claim 3 , wherein the titanium alloy rod having properties under JIS of:
a) tensile strength is greater than or equal to 1,150 MPa,
b) fatigue strength is greater than 900 MPa,
c) elastic modulus is less than 110 GPa,
d) 0.2% proof stress is greater than 1,000 MPa, and
e) percentage elongation after fracture is greater than or equal to 15%.
5. A spinal fixation titanium alloy rod for fixing a plurality of spinal fixation screws embedded and fixed in vertebrae of a human body,
the titanium alloy comprising:
Nb content of 25 to 35 percent by weight,
Ta content of such that the Nb content+0.8×Ta content ranges from 36 to 45 percent by weight,
Zr content of 3 to 6 percent by weight, and
the remainder is Ti and unavoidable impurities, excluding vanadium, the titanium alloy rod having properties under JIS of:
a) tensile strength is greater than or equal to 1,150 MPa,
b) fatigue strength is greater than 900 MPa,
c) elastic modulus is less than 110 GPa,
d) 0.2% proof stress is greater than 1,000 MPa, and
e) percentage elongation after fracture is greater than or equal to 15%.
6. The spinal fixation titanium alloy rod according to claim 5 , wherein the titanium alloy rod is produced by:
subjecting a cylindrical rod to a swaging processing of a cross-sectional reducing rate of at least 90%, and
aging the swaged titanium alloy rod by heating at a temperature of 700 to 800K for 43.2 ks to 604.8 ks.
7. A spinal fixation rod made of titanium alloy for fixing a plurality of spinal-fixing screws embedded and fixed in vertebrae of a human body, wherein the rod is produced by:
subjecting a cylindrical rod made of titanium alloy to a swaging processing of a cross-sectional reduction rate greater than or equal to 90%,
wherein the titanium alloy comprises:
Nb content of 25 to 35 percent by weight,
Ta content of such that the Nb content+0.8×Ta content ranges from 36 to 45 percent by weight,
Zr content of 3 to 6 percent by weight, and
the remainder is Ti and unavoidable impurities, excluding vanadium,
aging the swaged titanium alloy by heating at a temperature of 700 to 800K for 43.2 ks to 604.8 ks; and
machining the aged titanium alloy into a cylindrical shape having a diameter of 4 to 7 mm.
8. A spinal fixation system comprising:
a plurality of screws made of titanium alloy;
a spinal fixation rod manufactured by steps comprising:
subjecting a cylindrical rod made of titanium alloy to a swaging processing of a cross-sectional reduction rate greater than or equal to 90%,
wherein the titanium alloy rod comprises:
Nb content of 25 to 35 percent by weight,
Ta content of such that the Nb content+0.8×Ta content ranges from 36 to 45 percent by weight,
Zr content of 3 to 6 percent by weight, and
the remainder is Ti and unavoidable impurities, excluding vanadium; and
aging the swaged titanium alloy by heating at a temperature of 600 to 800K for 43.2 ks to 604.8 ks; and
a plurality of set screws for fixing the plurality of screws with the rod.
9. A spinal fixation system according to claim 8 , wherein the set screws are made of Ti-6Al-4V alloy.