Rice University mechanical engineers and Baylor College of Medicine neurosurgeons have identified simple changes to surgical tools that could reduce strain on the esophagus and potentially lower the risk of swallowing difficulties after neck surgery.
The study, published in the Journal of the Mechanical Behavior of Biomedical Materials , focuses on anterior cervical discectomy and fusion, or ACDF, a common procedure used to treat damaged or degenerating discs in the neck.
To reach the spine from the front of the neck, surgeons temporarily move the esophagus and nearby tissue aside using rigid metal retractors. Although the procedure can relieve pain and pressure on nerves, difficulty swallowing, known as dysphagia, is a frequently reported complication. The researchers found that changing the width and surface of a retractor blade can significantly affect how pressure is distributed across the esophageal wall.
"During these procedures, the surgeon needs a clear and stable path to the spine, but the mechanical effects of holding the esophagus aside have been difficult to quantify," said Raudel Avila , assistant professor of mechanical engineering at Rice and the study's corresponding author. "Our work connects the mechanical design of the surgical tool directly to the forces experienced by the tissue for a simulated ACDF."
Surgeons typically rely on sight and manual feedback to assess tissue retraction, but these methods cannot show exactly how the esophagus is deforming or where potentially harmful stress may be concentrated. To study those forces, the researchers combined computer simulations with experiments using a soft, anatomically inspired model of the esophagus and surrounding neck tissue. They created a hollow silicone esophagus, embedded it in a larger block representing surrounding neck tissue and added thin pressure sensors. A surgical retractor was then inserted through a simulated incision and opened in controlled increments. The measured pressure closely matched the computer simulations at clinically relevant levels of retraction, suggesting the models could help predict how surgical tools load the tissue.
"We wanted to move beyond treating retraction as a simple displacement," said Chihtong "Lily" Lee , a mechanical engineering graduate student in Avila's lab at Rice and the study's lead author. "The esophagus bends, stretches and bulges around the blade, producing highly localized forces that may not be apparent from what a surgeon can see."
The researchers tested retractor blades ranging from 20 to 50 millimeters wide and found that wider blades reduced stress beneath the center of the blade by as much as 82% by spreading the force over a larger area. However, wider blades also shifted some of the highest stress toward their edges, where tissue bends around the instrument, suggesting that both blade width and edge shape should be considered. The team also tested a soft polymer sleeve placed over the metal blade. The softer layer reduced the mismatch between the rigid instrument and the surrounding tissue, lowering peak stress in the simulations by up to 20%.
"These are mechanically simple modifications," said Alexander Ropper, professor and director of spinal neurosurgery at Baylor College of Medicine and one of the authors of the study. "A softer interface or a more carefully optimized blade geometry could redistribute tissue loading without fundamentally changing the surgical workflow."
While measured forces were below levels associated with immediate tissue failure, the researchers said sustained or concentrated pressure could still contribute to swelling, inflammation or temporary dysfunction, especially during longer procedures. They noted that this study does not establish a direct link between a particular stress level and postoperative swallowing difficulties, as patient anatomy, inflammation, surgery length and other factors can also affect recovery. Instead, they said, the work provides a way to compare surgical tool designs before clinical testing.
"Our goal is to give surgeons and device designers measurable criteria they can use to make informed decisions," Avila said. "By understanding where stress develops and how it can be redistributed, we may be able to reduce an important complication of an otherwise highly effective procedure."
"This work highlights the incredibly important relationship between engineers and physicians to advance clinical technologies, and it underscores the partnership between Rice and Baylor College of Medicine," added Alex Flores, a neurological surgery resident at Baylor College of Medicine and one of the authors of the study. "This work, in particular, represents the groundwork science behind what could be a field-changing technology, namely within spine surgery. We are excited to move this technology to the next stages of testing and risk mitigation in hopes to eventually directly impact patient care for the better."
This research was supported by Rice's Educational and Research Initiatives for Collaborative Health (ENRICH) Office, the Haythornthwaite Foundation of the American Society of Mechanical Engineers' Applied Mechanics Division and the Rice Engineering Alumni Student Project Grant Program.
