Amorphous Silicate Dressing Reduces Proud Flesh in Lower Limb Wounds in Horses
New research shows that a wound dressing based on a silicon derivative might help prevent proud flesh development on horses’ lower limbs.
In a case review of 11 horses treated with amorphous silicate, researchers have shown that exuberant granulation tissue—also known as proud flesh—was so reduced in lower leg wounds that none of the horses in the study needed surgical debridement, said Jacqueline Chevalier, DVM, MSc, BSc, of Cornell University’s College of Veterinary Medicine in Ithaca, New York.
“This can be exceptionally important in horses that are difficult to handle or that have wounds on hind limbs (due to kicking risks to handlers), wounds that are unable to be bandaged, and/or wounds that are unable to be closed primarily (with sutures),” she said.
Proud Flesh Problems in Horses
Proud flesh frequently forms as horses’ lower leg wounds heal due to reduced oxygen in the tissues, tension on the skin, and a general microenvironment that’s not conducive to healing, among other reasons, said Garett Pearson, DVM, a resident at Cornell in large animal surgery.
This can prolong inflammation and interfere with full healing, he added.
Typically, pink and rough or bumpy, proud flesh contains many blood vessels but no nerve endings. Often veterinarians must surgically debride lingering or proliferating proud flesh repeatedly to allow the wound to close properly, Chevalier said.
Orthosilic Acid: An Anti-Proud Flesh Agent?
A promising agent for preventing proud flesh development could be a derivative of silicon known as orthosilic acid, said Chevalier. Similar derivatives are already known to fight inflammation by decreasing the production of certain pro-inflammatory interleukins, as well as inhibiting the growth factor that primarily drives the development of proud flesh, known as TGF-β.
“Orthosilicic acid helps regulate the wound environment via growth-factors and inflammatory mediators, to promote healing and decrease the formation of exuberant granulation tissue or proud flesh,” Chevalier told The Horse.
Amorphous silicate is a topical wound dressing composed of nanoparticles that deliver orthosilic acid into the skin using a slow-release mechanism that helps maintain its presence in the wound environment, said Chevalier. It was designed for human medicine to help treat poorly healing wounds in diabetic patients.
The dressing also includes two versions of polyethylene glycol, which “work as an antibacterial osmotic compound, maintaining a moist healing environment,” Chevalier said. “This helps to prevent scar formation and to enhance repair of damaged skin.”
Real-World Experiences with Amorphous Silicate Wound Dressing in Horses
Because of the reportedly good success rate in humans, practitioners developed an amorphous silicate dressing product for equine patients in Ireland, Chevalier said. (The authors wrote in the study that Zarasyl Equine is a patented barrier cream listed with the FDA as an unapproved drug with marketing approval to sell as labeled.) Some veterinarians in the U.S. also decided to try amorphous silicate on cases in which horses had sustained difficult-to-heal accidental wounds below the knee or hock, she said.
Hoping for a broader view of the dressing’s effects on equine wounds—especially regarding proud flesh development—Chevalier and Pearson gathered veterinary records on 11 horses treated by their own veterinarians in the U.S. with amorphous silicate. The horses included four Quarter Horses, two Thoroughbreds, one Paint Horse, one Tennessee Walking Horse, one Warmblood, one Welsh cross, and one Mustang. They ranged in age from 1 to 26 years.
Wound size varied from 2 to 8 inches (5 to 20 cm) in length and from ¾ to 6 inches (2 to 15 cm) in width, they said. All the wounds were either chronic—meaning their healing was particularly delayed—or could not be closed with sutures and had to be left to heal slowly over time due to excessive tension, contamination, or patient behavior.
At the start of the trial, the wounds were one to 90 days old and had been previously treated with manuka honey, systemic antimicrobial therapy, systemic non-steroidal anti-inflammatories, local antibiotics, silicone gel dressing, and/or wet-to-dry bandages. Before treatment with amorphous silicate dressing, veterinarians cleaned, clipped, and—if necessary—debrided proud flesh.
Once caretakers commenced amorphous silicate treatment, they applied a thin layer of the dressing once every one to three days. They bandaged some wounds but left others open depending on the veterinarians’ assessments.
Unexpectedly Positive Results Against Proud Flesh
While the researchers thought the treatment would reduce exuberant granulation tissue development, they didn’t expect such positive results. In fact, they didn’t need to debride any of the wounds again, Chevalier said.
Furthermore, none of the horses developed any complications related to the treatment, “including, but not limited to, cutaneous (skin) reactions, infection, or other adverse reactions,” Chevalier said.
On average, wounds took 49 days to resolve, but healing times ranged broadly from 14 to 126 days, she said. Both the owners and their veterinarians reported they were satisfied with the treatment outcome in all 11 cases.
“This study evaluated the results of the product under real-world circumstances—including wound variability,” said Chevalier.
“Distal limb wounds in horses pose a significant clinical challenge for veterinarians and horse owners. As a horse owner myself, I’ve lived the frustrations of proud flesh. I’d love to see this product help horses, owners, and their veterinarians with wound healing and reduce proud flesh.”
The study, “Amorphous silicate technology produces good results in equine distal limb wound healing” appeared in the Journal of the American Veterinary Medical Association in June 2023.
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