Objects penetrating the palmar half of the frog (green dots in Photo 2) are capable of causing devastating injury, as the
deep flexor tendon, navicular bone and its bursa lie in this area. The ideal surgical procedure for this problem is commonly
called the street-nail procedure.
For wounds that penetrate to the depth of the deep flexor tendon, navicular bone or navicular bursa, aseptically prepare the
foot for surgery, perform an appropriate block and place a tourniquet at the level of the fetlock. General anesthesia is often
preferred to provide the best access and sterility.
Make a large rectangular incision (around the puncture wound) through the palmar frog. The incision should be large enough
to give good visualization of the surgical site. It's easiest to lift out the frog and surrounding tissue in layers. This
allows slow access to the site and continued step-by-step visualization of the foreign body tract.
Perform a culture and test sensitivity when first reaching the end of your surgical incision (i.e., the appearance of devitalized
tissue). When you've reached the deep flexor tendon level, remove any tendon that appears dark, soft and devitalized. Check
the surrounding tissue for damage or debris. If the navicular bone also appears devitalized, use a curette to scoop out all
necrotic portions of the bone until healthy white bone tissue is observed.
If you're unsure as to whether the navicular bursa or distal interphalangeal joint have been compromised by the penetrating
object, infuse the joint through the navicular bursa or through a traditional distal interphalangeal injection site with saline
solution and appropriate full-spectrum antibiotics. This will either yield a flow with pooling in your surgical site or will
appear patent and under pressure.
Once the wound is clean of all devitalized and necrotic tissue, perform a strong saline flush of the site, and then pack it
with antibiotic-impregnated polymethylmethacrylate beads (AI PMMA). Using pressure, fill the rest of the lesion with gauze
soaked with diluted povidone-iodine. The most commonly used antibiotic for AI PMMA is imipenem and cilastatin (Primaxin—Merck
Deep structures in the palmar half of the frog that have been penetrated will rapidly grow exuberant granulation tissue. The
necessity for pressure packing the surgical site cannot be stressed enough. Deep packing under pressure allows the structures
to regrow without producing granulation tissue. The packing should be changed daily, and the AI PMMA beads should be changed
every 10 days (Photo 4).
Photo 4: AI PMMA beads within a street-nail surgical incision that are ready for replacement with fresh beads.
It is important to apply a Patten shoe with a hospital plate (Photo 5). If the deep flexor tendon has been affected, apply
the Patten shoe before surgery and the 3-inch bar postoperatively.
Photo 5: A typical Patten shoe with removable 3-inch bar.
Lower the Patten shoe bar as the wound heals. The foot will require shoe removal and trimming four to six weeks postoperatively;
at that time, the Patten bar can be lowered to 23/4 or 21/2 inches. If the horse is lame after the bar height is reduced,
go back to the height you just removed. The reduction in bar height provides a step-down process for the deep flexor tendon
that allows it to accommodate small increments of increasing load during the healing process (Photo 6).