A new device inspired by python teeth may reduce the risk of rotator cuff re-tear

When most people think of pythons, they picture a huge snake slithering down and swallowing its victims whole. But did you know that pythons initially hold their prey with their sharp, backward-curved teeth?

Medical researchers have long recognized that these teeth are ideal for gripping soft tissue rather than cutting through it, but no one has yet been able to put this concept into surgical practice. Over the years, mimicking these teeth for use in surgery has been a frequent topic of discussion in the laboratory of Dr. Stavros Thomopoulos, professor of orthopedics and biomedical engineering at Columbia University.

Biomimicry key to new study

A leading researcher in the development and regeneration of tendon-to-bone attachment, Thomopoulos is particularly interested in the advancement of tendon-to-bone repair necessary for rotator cuff repair and anterior cruciate ligament reconstruction.

In an article published science advances his team reports that they developed a device inspired by python teeth as an adjunct to current rotator cuff suture repair and found that it nearly doubled the strength of the repair.

“As we age, more than half of us will experience a rotator cuff tear leading to shoulder pain and reduced mobility,” said Thomopoulos, who holds joint appointments at Columbia Engineering and Columbia’s Vagelos College of Physicians and Surgeons as Robert E. Carroll. and Jane Chace Carroll Professor of Biomechanics (in Orthopedic Surgery and Biomedical Engineering).

“The best medical intervention is rotator cuff surgery, but a remarkably high percentage of these repairs fail within just a few months. Our biomimetic approach, based on the design of python teeth, helps to more securely reattach tendons to bone. The device not only increases the strength of the repair, but it can also be customized to the patient. We are truly excited about the potential of our device to improve rotator cuff injury care.

Rotator cuff injury

Among the most common tendon injuries, rotator cuff tears affect more than 17 million people in the United States each year. The incidence of injury increases with age: more than 40% of the population over 65 years of age has experienced a rotator cuff tear.

Because rotator cuff tears usually occur at the point of insertion of the tendon to the bone, rotator cuff repair is focused on anatomical restoration of the tendon attachment. Surgical repair is the primary treatment for restoring shoulder function, with more than 600,000 procedures performed annually in the United States at a cost of $3 billion.

However, successful tendon-to-bone reattachment remains a significant clinical challenge. There is a high failure rate after surgery, with rates increasing with patient age and tear severity. These rates range from 20% in younger patients with small tears to a staggering 94% in older patients with massive tears. The most common failure of rotator cuff repair is tearing of the tendon sutures at two or four grip points where forces are concentrated.

While there have been advances in rotator cuff repair techniques over the past 20 years, the basic approach of suturing the two tissues together has remained largely unchanged and still relies on tension-transferring sutures at high-tension grip sites.

After surgery to reattach the tendon to the bone, sutures can tear through the tendons at these high stress points, a phenomenon known as “stitch stretching” or “cheesewire,” leading to gaps or tears at the repair site.

“We set out to see if we could develop a device that mimics the shape of python teeth to effectively grip soft tissue without tearing and help reduce the risk of tendon re-tear after rotator cuff repair,” said Iden Kurtaliaj, lead author of the study. lead author and former biomedical engineer Ph.D. student in Thomopoulos’ lab.

Device

The team’s original idea was to copy the shape of python teeth, but they went much further, using simulations, 3D printing and ex vivo experiments on cadavers to investigate the relationship between tooth shape and grasping vs. cutting mechanics.

Kurtaliaj produced a number of tooth designs, optimizing individual teeth, sets of teeth, and finally a set of teeth specific to the rotator cuff. The end result was a biomimetic device made of biocompatible resin—an array of teeth on a curved base—capable of gripping, not cutting, tendon.

The teeth are relatively small – 3mm high for a human rotator cuff, which is about half the length of a standard clip – so they won’t push through the tendon. The base can be 3D-printed to match the patient-specific curvature of the humeral head at the supraspinatus tendon attachment (the most commonly torn rotator cuff tendon).

“We designed it specifically so that surgeons don’t have to abandon their current approach — they can simply add a device and increase the strength of their repair,” Kurtaliaj noted.

Kurtaliaj conducted the research as a Ph.D. student under the guidance of Drs. Stavros Thomopoulos and Guy Genin, Harold and Kathleen Professor of Mechanical Engineering at Washington University in St. Louis, with input for clinical implementation from Drs. William Levine, Chair of the Department of Orthopedic Surgery at Columbia University’s College of Physicians and Surgeons.

“Given our laboratory’s close collaboration with orthopedic surgeons, we were especially fortunate to receive input from Dr. Levine, along with other surgeons at Columbia, throughout the device development process,” Thomopoulos said.

Researchers are now working to develop a bioabsorbable version of the device that would degrade as the rotator cuff heals back to bone, further increasing its clinical utility. They are also preparing for a pre-submission meeting with the FDA to facilitate the transition of their device to market.