StenAIR aims to revolutionize back surgery

A new surgical instrument will reduce cost, time, and rehabilitation for patients and doctors

by Elizabeth Sheeley | Communications and Community Outreach Office

Severe back pain is often caused by a narrowing of the spinal canal, known as spinal stenosis, which can result from normal aging, severe trauma, or repeated spinal trauma. Stenosis is a prevalent problem among the general population and military personnel. The current treatment involves decompression of the spine by an invasive surgical procedure and often requires four to six days in the hospital followed by months of physical rehabilitation that generates significant surgical and rehabilitation costs.

Researchers at MIT Lincoln Laboratory and Massachusetts General Hospital (MGH) are developing a new tool to enable a minimally invasive approach to spinal decompression. "We want to help usher out the days of back surgery being a major life event," said Matthew Johnson, the lead researcher from Lincoln Laboratory who helped design and develop this surgical instrument, the StenAIR. The acronym in the name stands for access, identify, and remove—access the spinal canal safely and minimally invasively, identify the surgical area with high-fidelity video imagery, and remove the overgrown tissue that is compressing the spinal cord. It is expected that this new procedure will be performed as an outpatient operation, take about one or two hours without the need for physical rehabilitation, and lead to increased quality of life for the patient and reduced overall costs.

In 2006, 162,008 laminectomies, the current wide-use surgical method, were performed to alleviate spinal stenosis in patients with crippling back and extremity pain, numbness, weakness, or even paralysis in severe cases. A laminectomy involves making a large incision along the spine, removing bone to access the surgical site, and then extracting the overgrown ligamentum flavum (LF) whose overgrowth causes spinal stenosis and the resulting back pain. The removal of the overgrown LF that is compressing the spinal cord is known as decompression. A large amount of healthy tissue is removed in simply accessing the surgical site.

StenAIR deviceLeft, The laser fiber within the inner tube will destroy the overgrown tissue and decompress the spine. Right, This module that surgeons will use to control StenAIR within the body is made to sit comfortably within the hand and provide precise control over the placement of the laser fiber.


StenAIR, developed by Johnson, Westin Hill, and Tara Boettcher from Lincoln Laboratory, along with Patrick Codd from MGH at the time, can solve these issues associated with the current invasive surgical method. The instrument allows surgeons to perform spinal decompression without destruction of the surrounding bone and muscle that normally happens in an open-back surgery. The immediate application of the device is to treat spinal stenosis with an outpatient surgery, but it could also be used in the future for other surgeries that require the removal of material from within the spinal canal.

"[StenAIR] should be able to selectively identify and remove only the tissue that is compressing the spinal cord, thereby restoring function, and reducing or eliminating the pain associated with it," said Boettcher.

The StenAIR instrument, which has a diameter of about 3 mm, is introduced into the spinal canal through the sacral hiatus, a naturally existing hole at the base of the sacrum. The only necessary incision is 2 cm long and through the skin covering the sacral hiatus. Because of the device's native curvature, StenAIR tracks along the dorsal wall of the spinal canal while it moves up the spine, keeping it from getting caught on nerve roots. The StenAIR uses a complementary metal-oxide semiconductor sensor with advanced image processing to produce the high-quality video imagery necessary for the surgeon to identify the compressive tissue to be removed. To protect the spinal cord and nerves, and to provide a clear surgical field of view, the device is equipped with two laterally deployable petals on either side of the end of the device.

Once the compressive tissue has been identified, the surgeon deploys a set of two concentric nitinol tubes from the face of the device, steering the laser fiber contained within the inner tube near the compressive tissue. The outer tube is straight and stiff, which guides the slightly curved, inner concentric tube. By using a control handle mounted on the instrument, the surgeon can vary how much of the inner tube (carrying the laser fiber) is contained within the stiffer outer tube, thereby controlling the overall curvature and aim of the laser fiber. The type of laser was specifically selected to minimize damage of the surrounding tissue—once it is positioned correctly by the surgeon the laser ablates the overgrown tissue without causing undo harm. The StenAIR gives the surgeon unprecedented access, visualization, and precise instrument control within the spinal canal with minimal disruption to surrounding tissue.

The team envisions many benefits arising from StenAIR. "It could drastically reduce the morbidity associated with current spine surgery for lumbar stenosis and many other forms of spinal conditions resulting in the compression of these delicate nervous tissue," said Codd. "By reducing the operative times, length of hospital stays, need for postoperative narcotic pain control and physical rehabilitation, this approach could change this surgery from a dramatic life event to a quick outpatient visit."

However, Hill notes that, "It's a great feeling being able to turn an idea into a device, and we've come a long way. That said, we're not successful until that device makes its way into the operating room."

Posted November 2016

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