Stereotactic frame-based error in magnetic-resonance-guided stereotactic procedures: a method for measurement of error and standardization of technique.

When using the stereotactic Leksell G frame for magnetic-resonance-based functional stereotactic lesions, the authors occasionally encountered a situation in which it was not possible to apply the anterior plate of the coordinate box successfully because it came into contact with the anterior posts of the frame; it was noted that the posts as well as the base ring became distorted by the force required to insert the cranial fixation pins. To examine this issue, measurements were taken of the amount of distortion relative to the torque on the screws, It was also found that backward movement of the posterior segment of the base ring indirectly narrowed the anterior spaces for plate insertion. A determination was made that torque over 6 inch pounds caused undesirable contact between the posts and the coordinate box.