Scissoring of cerebral aneurysm clips: mechanical endurance of clip twisting

Although the cerebral aneurysm clip "scissoring" phenomenon is known to occur due to twisting of the aneurysm clip blades during surgery, there have been few previous studies of scissoring. In the present study, we examined the in vitro endurance of clip twisting to assess clip scissoring. To evaluate the clip-scissoring effect, we measured torque at the rotating aneurysm clip head (Sugita and Yasargil clips) using our own manufactured product. A silicon sheet 1 mm thick was clipped at several depths (3, 6, and 9 mm), and the clip head was mechanically rotated. Straight and fenestrated clips of titanium alloy were used in the present study. Cobalt alloy straight clips were also examined. Preliminary experiments indicated that torque values during clip head rotation dropped when the blades crossed. In addition, torque values before blade crossing showed resistance to slippage of the blades. Torque values of both Sugita and Yasargil clips were directly proportional to the blade depth. There were no differences between straight and fenestrated Sugita clips. Although the torque was greater in cobalt alloy than titanium alloy Sugita clips, the torque values of Yasargil cobalt and titanium clips were identical. We found some differences in torque values during clip head rotation between Sugita and Yasargil clips. Based on the results of twisting experiments, scissoring is likely to occur when occluding the neck of the aneurysm only with the tips of long clip blades.