Researchers Find Way to Double Strength of Rotator Cuff Repairs

Fun fact: Though they generally are known for constricting and swallowing their prey whole, pythons initially hold on to their catch with sharp, backward-curving teeth.

Fun fact No. 2: Python teeth are an ideal mechanism for grasping soft tissue instead of cutting through it, but the concept has remained elusive to surgeons and medical practitioners. Until now. 

For years, Columbia University Orthopedics and Biomedical Engineering Professor Dr. Stavros Thomopoulos has grappled with ways to replicate python teeth for surgical use to improve tendon-to-bone repair, which is essential for fixing rotator cuff injuries and reconstructing damaged anterior cruciate ligaments. Thomopoulos’s past research has focused on the development and regeneration of the tendon-to-bone attachment.  

According to a paper published by Science Advances, Thomopoulos’s team has developed a python-tooth-inspired device as a supplement to current rotator cuff suture repair that nearly doubles repair strength. 
 
“As we grow older, more than half of us will experience a rotator cuff tear leading to shoulder pain and decreased mobility,” said Thomopoulos, who has 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 orthopedic surgery and biomedical engineering). “The best medical intervention is rotator cuff surgery, but a remarkably high percentage of these repairs will fail within just a couple of months. Our biomimetic approach following the design of python teeth helps to reattach tendons to bone more securely. The device not only augments the strength of the repair but can also be customized to the patient. We’re really excited about the potential of our device to improve the care of rotator cuff injuries.”
 
Rotator cuff tears are among the most common tendon injuries, affecting more than 17 million people annually in the United States. The incidence of injury increases with age: more than 40% of the population older than 65 experience a rotator cuff tear.
 
Since rotator cuff tears typically occur at the tendon-to-bone insertion site, repairs aim to anatomically restore 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, successfully reattaching tendon to bone is not so simple or easy. The surgery has a high failure rate depending on patient age and tear severity; failure rates range from 20% in younger patients with minor tears to 94% in elderly patients with massive tears. The most common rotator cuff repair failure is sutures tearing through the tendon at the two or four grasping points where forces concentrate.
 
While there have been advancements in rotator cuff repair techniques over the past 20 years, the fundamental approach of sewing two tissues together has remained largely unchanged, still relying on sutures transferring tension at high-stress grasping points. Following tendon-to-bone reattachment surgery, sutures can tear through tendons at these points of high stress, a phenomenon known as “suture pull-through” or “cheesewiring,” leading to repair-site gapping or rupturing.

“We decided to see if we could develop a device that mimics the shape of python teeth, that would effectively grasp soft tissues without tearing, and help reduce the risk of tendon re-tearing after rotator cuff repair,” said Iden Kurtaliaj, the study’s lead author and a former biomedical engineering PhD student in the Thomopoulos’ lab.
 
The Columbia University 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 explore the relationship between tooth shape and grasping vs. cutting mechanics. Kurtaliaj manufactured numerous tooth designs, optimized individual teeth, arrays of teeth, and finally a rotator cuff-specific teeth. The end result was a biomimetic device, made of a biocompatible resin—an array of teeth atop a curved base— capable of grasping, not cutting, tendon. The teeth are relatively small—3mm high for a human rotator cuff, about half the length of a standard staple—so they won’t poke through the tendon. The base can be customized through 3D printing to match the patient-specific curvature of the humeral head at the supraspinatus tendon attachment site (the most commonly torn rotator cuff tendon).
 
“We designed it specifically so surgeons won’t need to abandon their current approach. They can simply add the device and increase the strength of their repair,” Kurtaliaj noted.
 
Kurtaliaj led the research as a Ph.D. student under the mentorship of Thomopoulos and Dr. Guy Genin, the Harold and Kathleen Faught Professor of Mechanical Engineering at Washington University in St. Louis, with input for clinical implementation from Dr. William Levine, chair of the Department of Orthopedic Surgery at Columbia University’s College of Physicians and Surgeons.
 
“Due to our laboratory’s close collaboration with orthopedic surgeons, we were especially fortunate to get input from Dr. Levine, along with other surgeons at Columbia, throughout the device’s design development process,” Thomopoulos stated.
 
The researchers are now working to develop a bioabsorbable version of the device that would degrade as the rotator cuff heals back to bone, further enhancing its clinical applicability. They are also preparing for a pre-submission meeting with the U.S. Food and Drug Administration to market the device