The development of a device to record spinal cord blood flow during surgery

In a normal spine, the spinal cord is suspended and centered within the spinal canal. Anatomically the cord consists of two main tracks: anterior which are the motor tracts and posterior, which are the sensory. The motor tracts are perfused by the single Anterior Spinal Artery (ASA) and the posterior by a plexus of radicular arteries. If a patient develops curvature of the spine, such as scoliosis, the spinal cord will follow the shortest path within the canal. This means that the cord is no longer centered but cuts the angle across the apex of the curve. This can often result in irritation to the cord, reduced bloodflow in the ASA, and the development of various clinical symptoms, including myelopathy, etc. If the patient undergoes surgery to correct the spinal curvature straightening the spinal column can result in stretching the spinal cord. The spinal cord does not like to be stretched, which can result in decreased blood flow to the ASA which, if uncorrected, will result in a postoperative motor deficit (i.e., paralysis).

To ensure that the functional integrity of the spinal cord is not compromised during spinal correction, intraoperative monitoring is performed. The goal of the monitoring is to detect the onset of spinal cord irritation, warn the surgeon, which will allow appropriate intervention to be initiated and thereby avoid postoperative neurological deficits. Comparatively the surgeon is more concerned about a postoperative motor deficit than a sensory deficit. Currently, the tests that we use to monitor spinal cord function (both sensory and motor tracts) record data that indicate how well the tracts are functioning, but do not directly test for causation of any changes in tract function. Consequently, if the ASA is compromised it will take approximately 11 minutes before the motor tract test demonstrates any changes. This means that 11 minutes have elapsed since the onset of insult, which will significantly affect the efficacy of intervention.

Our goal is to directly measure blood flow within the ASA at multiple levels of the spinal cord, but primarily below, at, and above the apex of the spinal curve. We would like to develop a small, but very flexible probe that the surgeon can slip into the spinal canal on the posterior surface of the dura and measure blood flow within the ASA. The ASA runs midline in the canal, approximately 7 mm below the posterior surface of the spinal cord. The sensor would then use near infrared spectroscopy (NIRS) to continuously record blood flow. The sensor would consist of an photoc-flash light source and a single photodiode. The light source can be a LED or a coherent fiber optic bundle. The photodiode would record the reflected energy. On the non-sensor end of the cable would be a small power supply, a Bluetooth transmitter, and a control board for the operation of the sensor.
The requirements would consist of:
1. A light source
2. A photodiode
3. a cable or fiber optic bundle that would bring the light source to the spinal cord and also record reflected energy.
4. A control box that contained a power supply, appropriate hardware and firmware to control the LED/sensor, and a Bluetooth transmitter.

The entire assembly must be very small in diameter, probably less than 5mm in diameter, very flexible, sterilizable, and disposable.

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