Innovative Rotator Cuff Repair Device Modeled After… Python Teeth?

Scientists say they may find a better way to repair torn rotator cuffs by looking inside a python’s mouth.

While these animals are known for squeezing their prey to death, they also rely on oddly shaped teeth to stop prey from escaping before the snakes have completely wrapped themselves around them. Now, a group led by Dr. Stavros Thomopoulos of Columbia University in New York has developed 3D printed devices modeled after python teeth to strengthen the tendon-to-bone connection beyond what is possible with conventional techniques.

Their invention has passed a series of laboratory tests, including tests on human cadavers, as Thomopoulos and his colleagues reported in The progress of science.

“Overall, our research not only introduces a device that significantly improves mechanical strength, but also – in future iterations of the design – aims to facilitate the delivery of biologics using bioabsorbable materials with a porous structure to improve tendon-to-bone healing,” they wrote. .

Torn rotator cuffs are, of course, one of the most common orthopedic injuries. An estimated 40% of Americans over the age of 65 are affected, and about 600,000 repair surgeries are performed in the U.S. each year.

Currently, researchers explained, rotator cuff repair involves sewing the tendons to the shoulder bones with sutures. However, over time, regardless of the technique used, the sutures tend to cut the tendon where the stress is greatest.

This “cheesewiring effect” is at least partly responsible for the high failure rates that surgeons are all too familiar with. “These rates range from 20% in younger patients with small tears to a staggering 94% in older patients with large tears,” Thomopoulos and colleagues wrote. They also noted that while biologic additives can speed healing, they do not add any mechanical reinforcement or protection against cheesewiring.

The researchers decided they needed something that would gently grip the tendon. It turns out that nature has developed solutions to this problem, and they usually look like hooks. This is the case with the python’s teeth, which bend inward so that when the snake bites its prey, the latter, trying to free itself, only digs its teeth deeper, but without tearing the flesh. (Something similar can be observed on the burrs of hitchhiker plants, rose thorns and asparagus leaf spines, researchers observed.)

To turn this idea into a practical medical device, Thomopoulos and colleagues used a 3-D printer to create small biocompatible plastic rectangles studded with curved teeth. Experiments showed that a “curvature factor” of 2.5—the deflection of the tooth’s tip divided by the width of its base—was best for gripping pieces of beef tendon without cutting. The group also tested different tooth arrangements and spacing to come up with the optimal design. A key advantage of 3-D printing is that it allows for the creation of devices designed specifically for individual patients, with the underside shaped to fit snugly over the humeral head.

Thomopoulos and colleagues envisioned using sutures to hold the device in place to attach tendons to the head of the humerus. They tested their best design on five paired shoulder joints from human cadavers. For each joint, the researchers simulated a rotator cuff tear by cutting the supraspinatus tendon with a scalpel. Each arm was then randomly assigned to undergo a conventional double-row suture repair or one that used the same technique to secure the python-tooth device. The devices measured 15.5-17.5 mm by 6-8 mm, each having 13 teeth approximately 3 mm high. The repaired joints were then placed under load until they failed.

“Pairwise comparisons showed that device-assisted repairs demonstrated an average increase in peak force (i.e., strength) of 83% compared with matched nondevice controls,” the researchers reported. They argued that this near doubling of repair force “could significantly impact postoperative outcomes by reducing the currently observed high rate of re-rupture.”

The researchers emphasized that they plan to explore further modifications to the design. “Future versions should incorporate a porous base that could better support tendon-to-bone healing and also serve as a depot for local drug delivery,” they wrote. “We will also evaluate long-term outcomes using studies in large animal models, examining both the mechanical integrity of repair and healing.”