Overview

Problem Statement:

Dr. Mahesh Shenai has asked us to develop a medical device that will aid in pedicle screw placement during spinal fixation surgery. The device must be applicable to patients with varying bone densities. The surgeon using the device should be able to use it for any region of the spine. It should give appropriate real-time feedback to the surgeon if he or she is at risk of breaching the cortical wall of the pedicle or of the vertebral body. Current methods for guided pedicle screw placement often involve radiation. Dr. Shenai would like us to develop a guiding device that does not require radiation. Some current methods only give feedback in two dimensions so another goal of this device is to give feedback in 3 dimensions.

Our goal is to design a “gearshift” for pedicle screw placement by combining impedance feedback with A-Mode Ultrasound feedback.

Device Attributes:

Objectives tree1

 

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Functions and Requirements:

Function

Respective Requirement

Detect the difference between cortical and cancellous bone. Use ultrasound to detect differences in tissue structure and utilize electrical feedback to detect differences in impedance between cancellous and cortical bone.
Provide real time feedback during surgery. Use an imaging device that does not use radiation, extremely small A-mode ultrasound transducer.
Generate electrical current. Instrument will possess two electrodes at the tip to measure the difference in impedance.
Convert electrical and/or ultrasonic signals into audible feedback. Sound will be produced at a certain rate. As the tip of the instrument approximates the cortical bone wall of the pedicle, such rate will increase.
Convert electrical and/or ultrasonic signals into visual feedback. Use of LED lights that will flash at a certain frequency. As the tip of the instrument approximates the cortical bone wall of the pedicle, the lights should blink at a higher rate.
Able to go through cortical and cancellous bone. Instrument should be made of a resistant material and taper towards the tip for easier insertion.
Withstand considerable forces. Instrument should be made of a durable material, such as titanium.
Protect ultrasound transducer and electrodes. Protective material should possess an acoustic impedance that is between the acoustic impedance of the ultrasound transducer and bone.
Form ergonomically to surgeons grip. Handle should not be made of a slippery material.
Determine distance to cortical bone. Use the reflection of the ultrasonic signal to determine the distance between the transducer and cortical bone wall of the pedicle.

 

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