Maggots Improve Chronic Hoof Puncture Wound Healing

You might have heard about the value of using medical maggots to clean infected, nonhealing wounds in horses and humans, but did you know they can also help clean up infection in structures deep within the hoof?

At the 2009 American Association of Equine Practitioners Convention, held Dec. 5-9 in Las Vegas, Nev., one presenter described improved success with treating certain difficult deep hoof puncture wounds using maggots. Specifically, Raul Bras, DVM, of the Rood & Riddle Equine Hospital in Lexington, Ky., reported increased success with using maggots to treat punctures of the navicular bursa compared to previous studies.

The navicular bursa is a small, fluid-filled sac between the navicular bone (behind the coffin bone) and the deep digital flexor tendon that runs over it. Puncture wounds that compromise the navicular bursa can be especially problematic because the navicular bursa is a deep structure that's hard to evaluate, clean, and medicate. Bras advised that puncture wounds affecting this structure often go unnoticed until the horse becomes severely lame within hours or a few days. Complications such as osteomyelitis (bone infection) and damage to the deep digital flexor tendon sheath and/or coffin bone are not unusual if the infection can't be eradicated quickly.

Some procedures commonly used to clean and treat these wounds might help resolve the infection, but they can damage nearby tissues to gain access to the bursa (such as the "street nail" procedure used for cases with complications, which cuts away significant amounts of tissue to leave a window for treatment).

In contrast, medical maggots (disinfected greenbottle fly larvae) can debride (remove) dead, nonhealing tissue without causing trauma to healthy tissues. Bras explained that they work in four ways:

1) Debride wounds by dissolving the necrotic, infected tissue (using enzymes);

2) Disinfect the wound by killing bacteria (maggot-derived proteins appear to be responsible);

3) Stimulate wound healing (also a property of maggot-derived proteins); and

4) Break down and inhibit the formation of biofilm (masses of bacteria stuck together).

"The aim in treating septic bursitis is eradication of bacterial load, removal of any foreign material, debridement of necrotic tissue, elimination of inflammatory mediators and free radicals, pain relief, and restoration of the normal synovial (joint fluid) environment to promote tissue healing," explained Bras.

He described 20 navicular bursa puncture cases treated at Rood & Riddle with maggots, among other procedures that included lavage (cleaning by irrigating or flushing out), debridement (light surgical removal of superficial dead tissue), endoscopic lavage (done using an endoscope to visualize the bursa), Penrose drain placement, and/or street nail procedure. All wounds were at least three days old before presentation. Bras noted that antibiotics can be given systemically or via regional limb perfusion along with the maggot therapy, as the antibiotics do not damage the larvae.

Maggots were placed on gauze covering the wound and covered with a treatment plate for protection. Bras reported that they cleaned the wound for five to seven days before slowing down, at which time a second batch of maggots was placed if needed. The clinicians used elevated-heel shoes such as wedge shoes, rail shoes, or adjustable-height (Patten) shoes to reduce the deep digital flexor tendon's pressure on the bursa.

Navicular bursa infection resolved in 18 of 20 cases for a 90% success rate (70% of the cases returned to their previous jobs). This stacks up favorably against previous studies, which found at best a 75% infection resolution rate without maggot treatment (sometimes even with "fresher" wounds that were less than three days old, compared to this study where wounds were three to 31 days old).

The maggot option isn't inexpensive; Bras estimated the cost of this treatment at around $2,500 including three to five days in the hospital, diagnostic procedures, surgical debridement, lavage, maggots, bandaging, local and regional antibiotics, anti-inflammatory medications, and therapeutic shoes. The maggots themselves cost approximately $100-$200 per case.

"The use of maggot debridement treatment is effective as adjunctive treatment for navicular bursa puncture wounds," he concluded. "The ability of horses in this series to return to work was better than previously reported."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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