Development of a Diagnostic Method for Spinal Fusion, 10-9177

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Principal Investigators
Susan W. Zogbi
Larry D. Canady
Jerome A. Helffrich
Christopher B. Catterson

Inclusive Dates: 01/01/00 - 1/1/01 and 6/4/01 - 8/13/01

Background - The current practice of spinal fusion surgery is being impeded by the inability to determine objectively if the fusion surgery was successful. Current diagnostic methods for fusion assessment include 1) flexion-extension radiographs to measure relative motion and 2) computed tomography (CT) scans to measure bony ingrowth, both of which have proven to be unreliable and time consuming.

Approach - The objective of this project is to develop a noninvasive prototype that incorporates available sensor technology to diagnose spinal fusion, postoperatively, by measuring the changes in separation of the vertebrae involved in the fusion. The changes in the sensor response will be correlated to an assessment of motion between vertebrae and, in the future, success of the surgical fusion.

Accomplishments - The method incorporates implantable passive sensor technology and an external interrogator to diagnose spinal fusion, postoperatively, by measuring the changes in separation of the vertebrae. The changes in the response of the sensor(s) measured externally can be correlated to the relative motion of the vertebrae, enabling an assessment of the success of the surgical fusion. The system consists of sensors attached to each vertebrae involved in the spinal fusion. Implantation would occur at the time of surgery. During postoperative follow-up visits, the physician would be able to monitor successful fusion attainment without radiographic flexion/extension X-rays, CT scans, or unnecessary follow-up surgeries. This monitoring could be accomplished by measuring the sensor response with an external interrogator device at the physician's office. Information from this interrogator would then be processed to determine the relative distance between the sensors, and ultimately the vertebrae. With accurate fusion information, the physician can give a differential diagnosis to patients returning with pain or could prescribe a more aggressive rehabilitation program that provides a faster recovery time.

Bench tests of the sensor and interrogator demonstrated that the system could differentiate changes in separation of ±0.5 millimeter. In addition, it was illustrated that the distance between the interrogator and sensor does not affect the device response, thereby indicating that the interrogator position is not critical.

Click on picture for avi file

The implantable sensor is shown attached to the spinous process of a human
lumbar spine model. As the sensor is displaced, the frequency output
changes, as does the relative displacement.

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