Venogram Technique, Indication and Interpretation
Dr Redden's Equine Podiatry Series In-Depth Laminitis
Venogram Technique, Indication and Interpretation
Written and presented November 2005 by R.F. (Ric) Redden, DVM
(Watch the Digital Venogram video performed by Amy Rucker, DVM.)
Introduction
I developed this clinical protocol out of the need to better understand the degree of vascular damage during different stages of the syndrome. Working with Dr. Chris Pollitt at my clinic, we used his in vitro study to perform the first in-vivo venogram procedure in 1992. It was conducted on a standardbred filly that was owned by the International Equine Podiatry Center. Since that time, I have modified the procedure to meet the requirements of specific breeds, as well as a variety of foot problems that involve the circulatory system.
Basic Steps
Sedate the horse.Block the feet just above the fetlock. Use only 4-6cc of blocking agent to prevent transient edema.Place the horses feet on approved positioning blocks. This will insure a pure lateral projection.Set the x-ray machine in place, and have all the necessary cassettes and grids within arms reach.Take a scout film with soft-tissue detail, using a barium paste marker on the face of the hoof wall.Wrap 4 Elastikon around the fetlock. This will provide an anchor point for the tourniquet and will prevent twisting the skin while applying the tourniquet.Place a tourniquet over the fetlock. Avoid a mid-cannon tourniquet.Catheterize the palmar vein using a 5/8, 21-gauge butterfly catheter. Be careful not to thread the needle too far into the vein. You risk making a second hole in the vein.Inject 20cc of Reno-60. I recommend using two 12cc syringes instead of one 20cc syringe. A 20cc syringe builds too much back pressure and complicates injection. Injection needs to be completed in less than one minute, as the contrast will leak from the vessels quickly and skew your interpretation.Pull the knee forward slightly while injecting the second syringe. The heel should remain flat on the block. This rocking assures lamellar perfusion and unloads the deep digital flexor tendon (DDF).Clamp a hemostat on the catheter, or apply a stopcock. Quickly tape the hemostat to the leg so it will not be in your way.Take your series of film. This series of film should be completed within 45 seconds.Lateral, soft exposureLateral, hard exposure with gridDP, hard exposure with gridDP, soft exposureLateral, soft exposureSoft exposures are needed when there are significantly compromised vessels. Hard exposures offer a diagnostic image of the terminal arch and deeper vessels. The last DP view offers a look at vascular leakage that may not be apparent in the first couple film. Acute and chronic cases will exhibit similar patterns, yet there are distinct differences in the two.Remove the tourniquet and place cotton or gauze over the vessels. Tape in place for 5-10 minutes.Indications
A venogram is a discovery experience, as it offers a means to track the disease syndrome as it alters the vascular supply. Therefore, it offers unlimited options concerning the medical, surgical and therapeutic regimes necessary to revive the compromised areas. Venograms can be used diagnostically for:
LaminitisWhite Line DiseaseKeratomasPuncture Wounds
Having performed a few thousand venograms over the years, I have discovered a pattern that appears to be repeatable as laminitis progresses from a mild onset to high-scale cases; whether it is acute or chronic.
Likewise, the venogram offers a reliable means of monitoring the progress of reperfusion in compromised areas. They also help explain why some cases fail to progress in a favorable fashion. Being able to correlate the altered vascular pattern with the clinical picture, growth pattern and tissue response greatly enhances your insight for the planning and treatment stage.
Before this unique discovery experience can be used to reveal how badly areas are compromised, we must first learn the range of norm for specific breeds and age groups. The lateral and DP views are the most valuable views when dealing with laminitis. The 65º, DP reveals another perspective when looking at the circumflex vessel and fimbriae, but this view is not vital for assessing the damage caused by displacement.
Lateral View Points of Interest
The normal foot will have a dense, uniform contrast pattern over the extensor process. I refer to this as the waterfall. These vessels continue down the face of PIII in a relatively parallel plane to the bone. Approximately 8-10mm proximal to the apex of PIII, these vessels meet and join the branches of the circumflex network. This network supplies blood to the palmar surface and the rim of the bone. The normal, healthy foot has 10mm of vascular corium ventral to the palmar surface of PIII. The fimbriae are clearly seen penetrating the sole proper. The fimbriae are of great interest, as they are the first vessels to be compressed or crushed as PIII descends, whether it occurs from rotation or sinking.
Sport horses that become foot sore, have thin soles and poor quality horn walls. They often have no more than 6-10mm of soft-tissue space between the palmar rim and the foot side of the shoe. In this case, the fimbriae are not visible on a soft-detail venogram, and the major vessels are compressed tightly between the bone and hoof wall. This may be one explanation why short feet stop growing at a normal rate.
Therefore, I conclude that a healthy sole requires a minimum depth of 15mm; 10mm for the vascular network and a minimum of 5 mm for the non-sensitive, protective sole. This information should be of particular interest to farriers who strive to maintain a healthy, sound foot.
When a foot is trimmed short, small red dots appear along the freshly trimmed sole. These dots are the ends of the individual fimbria. A healthy sole (20mm) will have longer fimbriae than a sole that is only 15mm in depth. This may explain why a long foot will bleed much easier than a short foot that is trimmed to within 15mm of the palmar rim.