Python Teeth Device Doubles the Power of Rotator Cuff Repair

Summary:

Researchers at Columbia University have developed a python-inspired device that doubles the strength of rotator cuff repairs by effectively gripping soft tissue without tearing it.

Key conclusions:

The new device mimics the shape and action of python teeth, allowing tendons to be securely attached to bone, reducing the risk of re-tearing.
The device is made of biocompatible resin and can be adapted to the patient’s individual anatomy using 3D printing.
Scientists are working on a bioabsorbable version of the device and are preparing to seek FDA approval to bring it to market.

When most people think of pythons, they imagine a giant snake that strangles and swallows its prey whole. But did you know that pythons initially hold their prey with sharp, backward-curved teeth? Medical scientists have long known that these teeth are ideal for gripping soft tissue rather than cutting it, but no one has yet been able to apply the concept to surgery. For years, imitating these teeth for use in surgery has been a hot topic of discussion in the lab of Dr. Stavros Thomopoulos, a professor of orthopedics and biomedical engineering at Columbia University.

Biomimicry the key to new research

A leading researcher focused on the development and regeneration of the tendon-to-bone attachment, Thomopoulos is particularly interested in advancing tendon-to-bone repair, essential for rotator cuff repair and anterior cruciate ligament reconstruction. In a paper published by Science Advances, his team reports that they developed a python-tooth-inspired device to complement 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 decreased mobility,” says Thomopoulos, who holds joint appointments at Columbia Engineering and Columbia’s Vagelos College of Physicians and Surgeons as the Robert E. Carroll and Jane Chace Carroll Professor of Biomechanics (in Orthopaedic Surgery and Biomedical Engineering). “The best medical intervention is rotator cuff surgery, but a surprisingly high percentage of these repairs fail within just a few months. Our biomimetic approach, based on the python tooth design, helps reattach tendons to bone more securely. The device not only increases the strength of the repair, but it can also be customized to the patient. We’re really excited about the potential of our device to improve care for rotator cuff injuries.”

Rotator cuff injuries

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 the age of 65 experiences a rotator cuff tear.

Because rotator cuff tears usually occur at the site of the tendon’s insertion into the bone, rotator cuff repair aims to anatomically restore the tendon’s insertion. Surgical repair is the primary treatment for restoring shoulder function, with more than 600,000 procedures performed in the United States each year at a cost of $3 billion.

However, successful reattachment of the tendon to the bone remains a major clinical challenge. High failure rates occur after surgery, and rates increase 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 repairs is tearing of the sutures through the tendon at two or four points of attachment, where forces are concentrated.

Although there have been advances in rotator cuff repair techniques over the past 20 years, the basic approach of stitching two tissues together has remained largely unchanged, still relying on tension-transfer sutures at high-stress grip points. After surgery to reattach the tendon to the bone, the sutures can tear the tendons at these high-stress points, a phenomenon known as “suture pulling” or “cheesewiring,” leading to separation or rupture of the repair site.

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

Device

The team’s initial 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 the mechanics of grasping and cutting. Kurtalij produced a series of tooth designs, optimizing individual teeth, tooth arrangements, and finally a rotator cuff-specific tooth arrangement. The end result was a biomimetic device made of biocompatible resin—an arrangement of teeth on a curved base—that could grip rather than cut the tendon. The teeth are relatively small—3 mm tall for a human rotator cuff, about half the length of a standard staple—so they won’t cut through the tendon. The base can be customized with 3D printing to fit the patient’s specific curvature of the humeral head at the insertion of the supraspinatus tendon (the most commonly torn rotator cuff tendon).

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

Team

Kourtaliaj led the research as a graduate student under the supervision of Dr. Stavros Thomopoulos and Guy Genin, the Harold and Kathleen Faught Professor of Mechanical Engineering at Washington University in St. Louis, with input on clinical implementation from William Levine, MD, chairman of the Department of Orthopaedic Surgery at Columbia University’s College of Physicians and Surgeons.

“Because of our lab’s close collaboration with orthopedic surgeons, we were especially fortunate to have the support of Dr. Levine, as well as other surgeons at Columbia, throughout the device design process,” Thomopoulos says.

Next steps

The researchers are currently working to develop a bioabsorbable version of the device that would degrade as the rotator cuff heals back to the bone, which would further enhance its clinical utility. They are also preparing for a pre-submission meeting with the FDA to help bring the device to market.

Main image: Diagram showing how the python rotator cuff repair device compares to traditional sutures. Photo: Columbia University