Gravity dependent pedicle screw tap hole guide and data processing device
A gravity dependent pedicle screw tap hole guide comprises a guide shaft maintainable parallel to a drill bit during the drilling of a pedicle screw tap hole; an accelerometer associated with a reference direction and responsive to gravity to determine an angular difference between an acting direction of gravity and the reference direction; and a mounting attaching the accelerometer to the shaft and establishing a positional relationship between the reference direction and the longitudinal axis. The accelerometer is preferably in communication with a data processing device or system, which data processing device is able to use signals from the accelerometer to perform one or more actions, such as, for example, displaying the angular difference.
1. A method of forming a hole in a pedicle, comprising:
determining a trajectory of a pedicle with reference to an acting direction of gravity;
positioning an elongated element in a desired trajectory for advancement into the pedicle by angulating the elongated element about a distal end of the elongated element until a sensor fixed in a positional relationship with said elongated element establishes that the elongated element is aligned with the determined trajectory of the pedicle; and
advancing the distal end of the elongated element into the pedicle.
2. The method of claim 1 , wherein the step of determining the trajectory of the pedicle comprises finding a first trajectory angle in a first reference plane and finding a second trajectory angle in a second reference plane.
3. The method of claim 2 , wherein said first reference plane is a cephalad-caudad plane defined by a vertebral body comprising the pedicle, and the second reference plane is a medial plane defined by said vertebral body.
4. The method of claim 2 , wherein the first reference plane is a cephalad-caudad plane defined by a vertebral body comprising the pedicle, and the second reference plane is a medial plane defined by the vertebral body.
5. The method of claim 4 , wherein the second trajectory angle is determined from at least one of a preoperative transaxial MRI and a preoperative transaxial CAT scan.
6. The method of claim 4 , wherein the first trajectory angle is determined from intraoperative radiography.
7. The method of claim 6 , wherein determining the first trajectory angle comprises:
generating a radiographic image of the vertebral body including a zero-axis indicator formed by vertically aligning a radiodense device with the acting direction of gravity; and
determining from the image an angular difference between the orientation of the pedicle and the orientation of the zero-axis indicator.
8. The method of claim 7 , wherein the radiodense device is a clamp.
9. The method of claim 1 , wherein establishing that the elongated element is aligned with the determined trajectory of the pedicle comprises determining the angular difference between a longitudinal axis of the elongated element and the acting direction of gravity.
10. The method of claim 9 , comprising the additional step of communicating the angular difference to a user.
11. The method of claim 10 , wherein communicating the angular difference comprises visual communication.
12. The method of claim 11 , further comprising displaying a first angular difference determined in a first reference plane and displaying a second angular difference determined in a second reference plane.
13. The method of claim 1 , wherein said sensor is an accelerometer.
14. The method of claim 1 , comprising the additional step of receiving signals from said sensor in a data processing device communicatively linked to said sensor.
15. The method of claim 14 , wherein said data processing device interprets the signals from said sensor, determines data from said signals, and at least one of presents the data and directs a second device using the data.
16. A method for directing the positioning of a surgical implant, comprising:
advancing a distal end of an alignment guide to a surgical target site;
angulating the alignment guide about said distal end;
determining the angular trajectory of said alignment guide using an accelerometer fixed in a positional relationship with said alignment guide; and
presenting said angular trajectory on an external display forming part of a data processor linked to said accelerometer.
17. The method of claim 16 , wherein the accelerometer is permanently fixed to said alignment guide.
18. The method of claim 16 , comprising the additional step of implanting a surgical implant according to the determined trajectory.
19. The method of claim 18 , wherein said surgical implant is a pedicle screw.