This procedure allows veterinarians to see blood flow in the foot.

Although it's still not widely used, the venogram (a procedure for visualizing blood flow within the foot) has been acclaimed by many as an essential tool for treating lame horses, especially laminitic ones. In her presentation "Aspects of Normal Digital Venogram, Anatomy, Parameters, and Variations" at the 16th annual Bluegrass Laminitis Symposium on Jan. 16, Amy Rucker, DVM, of the University of Missouri, discussed this procedure with illustrations, venogram images, and video to provide what one attendee described as "exactly what we need in order to understand this better."

"The venogram is a very simple procedure that doesn't require any special equipment (that a veterinarian doesn't already have)," she began. "And it allows you to assess a horse, develop a tailored treatment program, and assess the horse's progress."

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Sketch showing the major blood vessels in the horse's hoof. Sketch showing two other major blood vessels in the horse's hoof.

This drawing shows the vasculature (blood supply) of the equine foot, with major vessels labeled.

Images courtesy Amy Rucker, DVM

This drawing shows two other major vessels--the bulbar and coronary arteries. Note that the bulbar artery originates in the pastern and supplies the heel. Even with significant rotation, many laminitic horses will still have vascular supply to the heel and frog.

Beginning with a detailed description of normal hoof anatomy and vasculature (blood vessel network), she explained how various areas of the foot are supplied with blood. "The importance of all this is to understand that each area of the foot is perfused by more than one source, that blood vessels anastomose or join together rather than perfusing an area and terminating, and that bone and soft tissue depend on the vascular supply to survive," she said.

 "For the compromised foot to repair, you have to treat it acutely," she stated. "You can't treat it conservatively for months, hoping it will get better, and then get aggressive. You need a blood supply." She cautioned that for any treatment to work in regenerating tissue growth, the vascular dermis can't be damaged beyond repair.

She used several case studies to illustrate the initial presentation, venogram appearance, and follow-up venograms' value in assessing the healing process.

Venogram Tips

"With a venogram, you have five areas of focus," Rucker explained. "You're looking at the terminal arch of the palmar digital vessels, the coronary band plexus, the laminar vessels, circumflex vessels under the coffin bone, and the heel area."

She presented a video clip of a venogram procedure, explaining what she was doing and feeling on the leg as the procedure progressed. Her narration included what could have been improved as well as what had been done well, thus reflecting a real-life situation rather than a textbook example. She discussed several tips for taking and interpreting a venogram as follows:

  • Stand the horse comfortably. If he toes out, don't make him stand straight. You want to assess the horse's usual stance and alignment.
  • Wires inserted in the blocks under the horse's feet help give you an idea of any oblique angle to the X ray.
  • Never guess distance from X ray machine to the foot. Always measure it, then you can directly compare different venograms later.
  • Hoof capsule angle can be very misleading if there is any dish to the hoof wall. It isn't a necessary measurement.
  • Measure the horn-laminar zone (H-L zone, the distance between the dorsal, or front, face of the coffin bone and the outer edge of the hoof wall) just below the extensor process of the coffin bone (the prominence where the extensor tendon attaches) and at the distal aspect of the coffin bone.
  • Measure sole depth beneath the apex of the coffin bone, and include any cup to the sole.
  • Mark the entire toe with radio-opaque paste (to show any wall deformities) for a lateral view, and remember to wipe it off for the dorsopalmar (front) view.
  • The entire H-L zone swells with a sinker (one where the entire bony column is descending deeper into the hoof).
  • You can often see a dark area about seven millimeters from the dorsal aspect of the coffin bone--this is the white line. Widened areas of the dermis indicate problems such as laminitis, while widening of the tissue outside the opaque line suggests white line disease.
  • If you're trying to compare a bad front foot with a normal foot on that horse, and the other front foot is also problematic, you can radiograph a back foot for a comparison.
  • The terminal arch (blood vessel) goes through the coffin bone about halfway down from the top of the bone, and it can usually be seen on a venogram.
  • The lateral and front views give a podiatrist the most information about that foot.
  • It is essential to hone your venogram technique on normal horses to learn the procedure and the normal appearance before using it on lame horses.
  • Always take a final X ray so you can see that you accomplished your goals with the shoes.
  • It's much easier and safer for the practitioner to catheterize the lateral vein than the medial one.
  • If you end up with perivascular (just outside the vein, also known as blowing veins if the vein is punctured through and through) injection, apply a pressure wrap for about 30 minutes for treatment. The pastern will swell with fluid following removal of the wrap, but this will shortly dissipate.
  • If you blow a vein, wait 24 hours before catheterizing a different vein on that foot to allow blood flow to re-establish.

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Diagram of radiograph (X ray) setup and internal hoof measurements.

This is the proper angle for the X ray machine in order to evaulate the foot. This drawing shows the bone and soft tissue parameters that an equine podiatrist looks for when evaluating a problem foot.

• Horn-laminar zone (H-L zone)--the distance between the outside of the hoof wall and the front face of the coffin bone (P3). This helps determine if rotation has occurred, among other things.

• Coronary band-extensor process (CE)--the distance between the coronary band and the top of the extensor process on P3 (where the extensor tendon attaches). This can help detect sinking of the bony column if it increases over time.

• Sole depth--the distance between the bottom face of the coffin bone and the ground. Any cup to the sole should be accounted for as shown.

• Palmar angle (or plantar for a hind hoof)--the angle the coffin bone makes with the ground. Knowing and manipulating this angle is essential for corrective shoeing.

• P3 (coffin bone) angle--normal P3 angle is about 50°. It might be greater with a club foot.

• Breakover--the distance between the toe of the hoof and the apex of the coffin bone. Decreasing breakover is often helpful for sore horses.

Venogram Safety

Some people have voiced concern about the safety of injecting the concentrated radio-opaque solution into the foot of a horse that might already have circulatory problems. Rucker discussed several informal safety studies that she had done at the University of Missouri to assess the safety.

One study she described included performing venograms on one limb each of 10 horses which were soon to be euthanized for various reasons. Following euthanasia (minutes to six weeks later), pathologists compared feet with and without the contrast media, and could not find any difference at the tissue level. "Thus, we don't feel that we've caused any damage to the feet with these venograms," she said.

Another study involved making a small mark at a consistent spot on the hoof wall of eight horses in order to later evaluate wall growth. Six horses had a venogram in the left front, one had bilaterally blown veins from venograms, and one had had no venogram. Six to eight weeks later, there was no significant difference in growth between the hooves that had had venograms and the control hooves. "Some of the feet with venograms grew more than the opposite feet, and some were the other way around," she commented. "The important thing to recognize is that these were all normal horses. Dr. Redden believes that in some pathologic feet, the venogram accelerates hoof growth."

She also described clinical examination findings that blowing veins on a normal horse during a venogram procedure caused no apparent problem at 24 hours after the procedure.

"Our goal is to understand the relationship of the bone, soft tissue, and blood supply," she said. "Then we can discuss the wide variations of normal."

Normal lateral venogram

Normal venogram, 5-year-old Arabian mare. This lateral (from the side) venogram (radiograph of foot with contrast media injected into the blood vessels) shows the information that an equine podiatrist can gain from this procedure.

Fairly normal venogram, front or dorsopalmar view

This dorsopalmar (front) view of the same healthy foot shows some compression of the blood vessels of the coronary band on the left side of the venogram (the horse's inside quarter). This is likely due to pinching in that area from a mediolateral imbalance that leaves that side of the foot slightly longer than the other.

Toe closeup of normal venogram

Closeup of normal tip of P3. Note:

• Dorsal vasculature (blood supply in the forward, or toe, aspect of the foot) is 3 mm from dorsal P3;

• Papillae (small downward projections) that perfuse the sole (supply it with blood) are evident. Vasculature of the sole is 10 mm distal to (below) P3.

Toe closeup of normal venogram

7-year-old Appaloosa mare, acute laminitis. We see that the apex of this horse's coffin bone has rotated down past the circumflex vessels (which normally run beneath the coffin bone).

Fairly normal venogram, front or dorsopalmar view

7-year-old Appaloosa mare, 16 months after initial onset of laminitis. Here we see that something odd is going on at the toe--note the dip in what should be a smooth progression of blood vessels down the face of the coffin bone and around the tip. The coffin bone has remodeled slightly due to the laminitis. The blood vessels have also remodeled, and have resumed the blood supply to the tip of P3 and the hoof.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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