SURGICAL ORIENTATION DEVICE AND METHOD
A device for detecting and measuring a change in angular position with respect to a reference plane is useful in surgical procedures for orienting various instruments, prosthesis, and implants with respect to anatomical landmarks. One embodiment of the device uses three orthogonal rate sensors, along with integrators and averagers, to determine angular position changes using rate of change information. A display provides position changes from a reference position. Various alignment guides are useful with surgical instruments to obtain a reference plane.
1 . A method of determining angular position change comprising:
a. sensing the presence or absence of motion of a rate sensor;
b. sensing a rate of change of angular position with respect to a reference using the rate sensor to provide an output that is a rate signal proportional to the rate of change of angular position of the rate sensor;
c. averaging the output of the rate sensor in the absence of motion of the rate sensor to provide an average signal representative of the output of the rate sensor in the absence of motion of the rate sensor;
d. integrating the rate signal when motion is sensed to provide an integral signal indicative of a relative angular position experienced by the rate sensor; and
e. presenting the difference between the integral signal and the average signal as indicative of the change of position of the rate sensor.
2 . The method of claim 1 wherein the integral signal is zeroed before step d.
3 . The method of claim 2 wherein the difference is presented as an absolute position change occurring after zeroing the integral signal.
4 . The method of claim 1 wherein step e. further comprises presenting the difference in a visually perceptible format.
5 . The method of claim 1 wherein step e. further comprises presenting the difference in an electronic format.
6 . The method of claim 1 further comprising an additional step:
a0. automatically zeroing the integral signal upon initial startup.
7 . The method of claim 1 further comprising an additional step:
f. continuing to integrate the rate signal for a predetermined period of time after motion stops.
8 . The method of claim 1 further comprising an additional step:
b1. detecting the presence of motion by determining when there is more than a predetermined difference between the output of the rate sensor and the average signal.
9 . The method of claim 8 wherein step b1 further comprises detecting the absence of motion by determining when there is less than the predetermined difference between the output of the rate sensor and the average signal.
10 . The method of claim 1 further comprising the additional step of:
g. detecting an error condition when the integral signal exceeds a predetermined maximum value.
11 . The method of claim 1 wherein step a. includes providing an indication of the direction of motion detected.
12 . The method of claim 1 wherein step d. includes providing an indication of the direction of motion detected.
13 . The method of claim 1 wherein each of the steps are performed for each of three mutually orthogonal dimensions.