Abstract
Titanium alloy currently used in medicine contains 6% of aluminium and 4% of vanadium. It has long been used as titanium plates or pedicle screws. While it is considered to be safe as a material, its durability, especially when used as aneurysm clips, is not clear.
Sugita type titanium aneurysm clips are made in shapes similar to cobalt alloy (Elgiloy) clips except for spring diameter, which was enlarged by 10%. Their neuroradiological and mechanical characteristics are compared with Sugita cobalt clips. CT was taken at 120 KV, 300 mA by hanging a clip on a thread in a plastic bottle filled with saline. Cobalt clips caused strong high density artifacts around the clip with a low density linear shadow along its long axis. The shapes of titanium clips could be seen since they were surrounded by only faint artifacts. T1 weighted (TR: 500ms, TE: 20ms) and T2 weighted (TR: 4100ms, TE: 80ms) MRI images were taken by hanging a clip on a thread in a plastic bottle filled with baby-oil (Johnson & Johnson). The cobalt clip caused on both T1 and T2 weighted images a candle-flame-shaped high-signal-intensity artifact by longitudinal image and triangular high-signal-intensity artifact separated into three blocks on the axial image. Artifacts by titanium clips were about 1/3 that of cobalt clips but the difference was not as big as CT images.
The closing force of titanium clips was measured at 2mm from the tip of the blades, which were opened by 1.5mm. After manually repeating full opening and closing of the clips by clip appliers 500 times, the reduction of closing force remained less than 3%. The closing force of a #2 titanium clip measured at 1mm step from the tip toward the spring base showed an increase in a hyperbolic curve, from 120 to 240g, which was similar to that a #2 cobalt clip. The closing force of a # 2 titanium clip measured at 1.5 mm from the tip when the blades were opened by 0.5mm step from 0.5 to 3.5 mm increased in a straight line from 120 to 160g, which was similar to that of a #2 cobalt clip.
These results show that Sugita titanium clips are durable within tested conditions and they have similar characteristics of closing force to cobalt clips. They seem to be quite useful especially for postoperative radiological follow-up. However, accidental scissoring of titanium clips that are commercially available in Japan has been reported. This may be due to weakness of titanium alloy in both tensile and compression strength, which is only one half that of cobalt alloys. Thus, titanium clips do not seem to be able to totally replace cobalt clips but, with care, they can be used in easily clippable and uncomplicated aneurysms.
