Mar 01, 2004

It has probably happened in your practice. You get a panicked call from a client who found their horse out in the pasture unwilling to walk and with a nail sticking into the foot.

The horse is a grade 3 of 5 or worse lame, the client is worried and upset about the nail, and these are the lucky ones.

The abscess in this horse's foot has been opened with a curette and is draining. This horse was severely lame but no nail or penetrating foreign body was noted at the time of examination. This horse should be treated as a suspected simple solar abscess, but if lameness continues or increases over the next 24 hours, then a septic condition should be assumed and more aggressive treatment (regional antibiotic perfusion and navicular bursal scoping or digital tenotomy) should be started.
At least they have found the horse when the nail is still present. More difficult to deal with are those horses that step on nails or other foreign objects in the pasture and are found after the object has pulled back out of the foot. These horses are still profoundly lame but the practitioner is without important information as to the depth and angle of penetration of the object.

Additionally, many of these horses are not severely lame initially and owners may not seek veterinary attention for 24 to 48 hours because they have no idea about what happened to their horse's foot. Many are suspecting a simple abscess or bruise. Treatment for a nail puncture becomes more difficult and ultimately less effective when crucial early response time is lost. Still, knowing how to handle this emergency situation and knowing some of the new ideas for treatment of this relatively common problem can make a difference.

Mission impossibleIt is impossible to make all pastures totally safe. Debris and buried nails are always coming to the surface because of erosion and other weather influences.

Clients should try to monitor their pastures as much as possible, though, and special care should be taken when construction projects such as sheds and fencing might introduce nails into the environment.

Areas around sheet metal and tin roofs should be monitored after heavy winds as the force of the gusts can loosen nails in these types of roofs. Old and poorly maintained structures within a pasture are other sources of stray nails and should be routinely checked. Still, despite all diligence, it will still happen occasionally. Horses will still step on nails.

Initial time crucialIf 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.

Image 1: A horse with a nail in its foot. No definitive information can be taken from one view alone and the lateral view is needed to determine the seriousness of this puncture.
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.

After filmsOnce 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.

Image 2: The lateral film of the horse in Image 1 shows this nail has penetrated the sole and has reached the navicular bursa. The nail is very close to the surface of the navicular bone and this horse was very lame on presentation. The foot is elevated because a protective pad was put on the horse prior to taking the radiographs. This horse was treated with systemic antibiotic perfusion and recovered fully.
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 thinkingDr. 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.

Image 3: Another nail-induced lameness.
"We had a resident here at Georgia from Saskatchewan who convinced me of the ease and ultimate usefulness of regional perfusion," says Parks. There are two types of regional perfusion in use in the horse.

Arterial perfusionThe 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 concentrationThe second fact that has changed the way Parks deals with these cases is based on a lecture that Dr. Joe Bertone made.

Image 4: The lateral view of the horse Image 3 confirms a less serious path for the nail and allows the practitioner to treat the horse as a severe heel abscess rather than as a potential septic navicular bursitis case.
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.

'Street nail operation'The previously accepted surgical treatment for horses that stepped on a nail is a procedure called a street nail operation whose name harkens back to an earlier time in equine veterinary history.

Correctly called a deep digital tenectomy, the procedure required that a hole be made in the bottom of the hoof. The deep digital flexor tendon is then approached and any damaged tissue is removed and the area is flushed, cleaned and infused with an antibiotic solution.