Pitt engineer applies structural monitoring technology to the human spine

Amir H. Alavi, PhD, assistant professor of civil and environmental engineering at the University of Pittsburgh's Swanson School of Engineering, has spent much of his career developing sensors to monitor the health of large, complex structures like bridges and roads. Now, he has applied those skills to a smaller and even more complex structure--the human spine. Alavi received $393,670 in funding from the National Institutes of Health to design and test a miniature, implantable, and battery-free sensor to monitor spinal fusion progress after surgery.

Spinal fusion is performed to treat a wide variety of spinal disorders. During the spinal fusion surgery, a special type of bone screw and symmetrical titanium or stainless-steel rods are implanted to stabilize vertebrae movement, which allow bone grafts to incorporate into the adjacent vertebra. Of the over 400,000 lumbar spinal fusion surgeries performed each year, approximately 30 percent of cases experience post-operative complications.

A clear understanding of the spinal fusion rate is essential for better surgical outcomes. Currently, spinal fusion progress is assessed using radiographic images, such as X-ray and CT scans, which are costly, expose the patients to significant radiation, and, more importantly, do not provide a continuous history of the spinal fusion process. To avoid relying on radiographic imaging, Alavi's team is developing wireless sensors that will be attached to the spine fixation device to monitor the spinal fusion process and will completely rely on the energy harvested from the spine's natural micromovements for operation.

This implantable sensor has a major advantage over other existing spinal implants in that it does not rely on batteries, which are not really suitable for biomedical implants due to their limited lifetime, large size, and chemical risks. If there is spine movement, the sensor will self-power itself and track the progress of spinal fusion. Also, the data from the sensor can be wirelessly interrogated using a diagnostic ultrasound scanner, rather than the commonly-used RFID technology, which faces severe limitations inside the tissue."

Amir H. Alavi, PhD, assistant professor of civil and environmental engineering, University of Pittsburgh's Swanson School of Engineering

Clinicians can read the generated time-evolution curves using the ultrasound scanner to properly assess the bone fusion period, and for more accurate implant removal scheduling.

"Surgeons will be able to monitor the fusion process consistently over time simply with a portable scanner," continues Alavi. "While CT scans and X-rays present only a 'snapshot' at the time where the measurements are taken, our sensor will give a clearer picture of the entire course of fusion."

In addition to avoiding the costly imaging appointments, the sensor itself is expected to be inexpensive to produce--less than $5 in raw materials each.