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The therapy depends from the time you get the call: If you are called when the nail is still in the foot it is generally recommended to keep the horse from moving until radiographs can be taken.
These initial films will be crucial in determining the depth and angle of penetration of the nail. The position of the nail will indicate if there is a possibility of navicular bursal damage, coffin bone or coffin joint involvement or, hopefully, only subsolar foot trauma.
If the horse is in an area that is without electricity or the animal needs to be moved for other reasons, then a pad or block should be taped to the foot. This pad should elevate the hoof and be positioned around and protecting the nail so that the horse can walk without putting more weight on the nail and possibly driving it further into the foot.
A minimum of two films (AP and lateral) are necessary, but more views should be taken if your initial evaluation suggests possible trauma to lateral margins of the coffin bone or other areas. Once quality films have been obtained you should remove the nail and pare open, clean and flush the tract as you would for any penetrating injury to the hoof.
First therapeutical option
The hoof should be packed with magnapaste, ichthammol, or other medicated poultice and wrapped. Tetanus vaccination history should be reviewed and appropriate vaccine given if needed. Antibiotics are the next step and it must be assumed that the puncture is contaminated by both gram-positive and gram-negative organisms commonly found on the animal`s skin and in the environment.
Previously it was felt that systemic antibiotics provided acceptable levels in the navicular bursa, digital flexor tendon sheath and in the coffin joint. Penicillin combined with an aminoglycoside (typically gentamicin or kanamycin) was the standard treatment approach. The bursa or coffin joint can be tapped for fluid analysis and lavage of these structures is sometimes warranted as well.
The typical fluid from a septic joint or bursa will be cloudy to turbid and yellow to serosanguinous. There should be increased volume, though probably not in the acute stage, and this fluid will have an elevated protein (4g/dl or greater) and an elevated WBC (30,000 or greater with the majority being neutrophils.) Horses with high WBCs in their bursal taps can still do well and seem to respond to antibiotics, but horses with high protein counts tend to be more problematic.
Culture of this fluid will help define which organisms are present but because a nail puncture is an emergency situation, antibiotics should be started as soon as possible and treating veterinarians should not wait on culture results.
`New thinking`
Dr. Andy Parks, a surgeon at the University of Georgia Veterinary Medical School has altered his approach to treating horses with a traumatic nail puncture to the foot and his comments reflect new thinking about this condition.
Parks attributes his current treatment program to two major factors.
The first is arterial perfusion. A tourniquet is placed above the area to be perfused.
A cannula or catheter is placed into an artery and antibiotics are injected. The stronger arterial pressure forces antibiotics into the area and the tourniquet slows the venous removal of those antibiotics. `Regional perfusion can also be done via the osseous method,` says Parks, `where a hole is drilled into the cannon bone of the affected leg, a tourniquet is placed above the hole, and a cannula is placed into the hole and antibiotics are infused.` Both methods of regional perfusion can deliver high levels of antibiotics to a local site of infection while not causing as great a systemic response to antibiotics.
Regional perfusion is also associated with decreased development of antibiotic resistance. The arterial cannula can be maintained for awhile but usually must be replaced during the treatment period. The hole in the cannon bone from the osseous approach typically stays open four to five days before granulation tissue closes it, so these horses can be easily retreated during that time. The drug of choice for perfusion is Amikacin. The typical dose is 50,000 IU.
Minimum active concentration
According to Parks, Bertone, a board-certified medicine specialist, was commenting on the importance of a culture and sensitivity of bacterial organisms introduced into the coffin joint or deep digital flexor sheath by a nail injury and he remarked that if you can achieve a concentration of 10 to 100 times minimum inhibitory concentration (MIC) that is the concentration of antibiotic needed to effectively kill a particular bacterial organism) then what difference does the organism make?
Essentially, what Bertone was suggesting was that if we could put enough antibiotics into a specific area then we would be able to kill just about all bacteria and regional perfusion allows us to do that.
Regional antibiotic perfusion is also enabling some cases to avoid surgical treatment of septic navicular bursitis.
Source: Kenneth L. Marcella (`004): Nailed. In: DVM Newsmagazine March 1, 2004. www.dvmnewsmagazine.com/dvm/
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