Clinical Application of the Digital Venogram

2007 - 18th Annual Bluegrass Laminitis Symposium Notes Written and presented January 2007 by Amy Rucker, DVM

(Watch the Digital Venogram video performed by Amy Rucker, DVM.)

Objectives Briefly stated, laminitis is the failure of attachment between the distal phalanx and the hoof wall. The classic layman's idea of a "foundered" horse is one that got into the grain in the past and now lives with extreme pain, standing in a saw-horse stance as it attempts to shift weight off the front feet, with distorted hooves growing in an "elf-shoe" curl. The reality of laminitis is that it is a complex disease that we still do not fully understand. Furthermore it manifests itself in many forms and clinical presentations. The purpose of this presentation is to explain some ideas of how laminitis develops, classify the various presentations of the disease, and discuss treatment options that I use in my practice.

Anatomy

The palmar digital vessels enter the palmar surface of P3 and join to form the terminal arch (A) within P3. The terminal arch gives off several branches which course through P3: they supply the dorsal lamellar vessels (B) which join proximally with the coronary plexus (C) and distally the circumflex vessels (D) of the sole. The circumflex vessels (D) are located a few millimeters peripheral to the rim of P3 and perfuse the sole corium via dermal papilla. The blood vessels anastomose, or join with one another; they do not perfuse an area and then terminate.

The dermis is the soft tissue containing connective tissue, vessels, and nerves. The dermal lamellae are oriented on the "face" of the distal phalanx, projecting outward towards the hoof wall. There are 550-600 primary lamellae within the foot, and each of those has 150-200 secondary lamellae projecting from its axis. These dermal lamellae interdigitate with the avascular epidermal lamellae of the hoof wall and bars, separated only by the basement membrane: a structure that unites the epidermal basal cells and the dermal connective tissue attachments to the distal phalanx.

Although it can withstand great stresses associated with galloping and jumping, the hoof anatomy is complex and even delicate. During the acute phase of laminitis, the hoof capsule epidermal laminae separate from the dermal laminae and P3 as the basement membrane is broken down. The loss of structural integrity renders the distal phalanx unstable within the hoof capsul. As the distal phalanx displaces, the dermal architecture is altered as tissue is stretched or torn. Vessels in the dorsal lamellae are compromised and may hemorrhage into the submural dermal space or be completely disrupted. There is abnormal loading of sole by the distal phalanx, initially reducing the perfusion within the sole papillae and progressing to eliminate the solar vasculature including the circumflex vessels. Coronary perfusion may be eliminated by tissue shearing or mechanical compression. Continued loading of the diseased foot by the weight-bearing limb perpetuates the mechanical damage. The sole may prolapse or bulge downward due to displacement of the distal phalanx. With "rotational" displacement of P3 away from the dorsal wall, the apex of P3 may penetrate the sole; if complete breakdown of the laminae occurs, the entire P3 will "sink" onto the sole.

Phases of Laminitis Laminitis can be initiated by multiple diseases, each causing an alteration in the normal mechanisms of an organ system. One theory is that during the developmental phase of laminitis, diseases somehow activate a laminitis trigger factor which arrives in the feet via the circulation. This factor activates enzymes which destroy the basement membrane and break down the attachments of the basal cells of the epidermis, beginning the destruction of the hoof architecture. (see Chris Pollitt's website.) The developmental phase lasts 24 to 30 hours and although pathology is occurring, these changes might not be evident to an owner.

The acute phase begins when the feet change clinically. Elevated digital pulses, foot pain and lameness may be noted. If the horse is lucky, it enters a sub-acute phase, with milder signs and minimal damage to the hoof architecture. The foot may remain stable, and the horse fully recovers.

Unfortunately most horses have changes within the hoof capsule, and enter the chronic phase. The chronic phase lasts an indefinite time period, and has many manifestations. During the early chronic phase, some horses are able to recover and become compensated with the amount of damage to their foot. The distal phalanx may be stable, the wall and sole are able to grow appropriately and the horse becomes sound. Other horses are not able to compensate, have a persistent level of pain associated with bone disease or continued loss of integrity of the dermal and epidermal structures. Many factors determine the course of the chronic phase of laminitis.

Key Points for Horse Owners: When your horse shows clinical signs of laminitis, damage to the hoof architecture has already occurred. How you respond to these signs will help determine the course of the disease. 1. Limit the movement of the horse!!! Ignore old thoughts of walking the horse to "increase the circulation." Movement will further damage the architecture of the hoof. (Pollitt) 2. Research suggests that standing a horse in an ice water bath up to its knees and hocks will reduce blood flow to the feet, and perhaps prevent the trigger factors from reaching the feet. Standing a horse in an ice bath PRIOR to the development of lameness may PREVENT laminitis from occurring. (See Pollitt's website.) Standing a horse in icy water AFTER the development of lameness reduces blood flow to tissues which need to repair and may be contraindicated. 3. Support the foot! Styrofoam insulation cut to fit the foot will help support the sole surface until help arrives. (See Ovnicek's website.) 4. Call your veterinarian and farrier. The successful outcome of a laminitis case requires a team effort be made by three individuals: the veterinarian, farrier and horse owner. If any one of the members of this team is not willing to give a 100% effort, success will be compromised.

Initial Medical Treatment Laminitis is a medical emergency, and should be treated as such. "Waiting to see" how the horse does over time only decreases you chances of having a functional horse. Aggressive, immediate treatment should be aimed at reducing inflammation and pain via anti-inflamatories such as Phenylbutazone, Flunixin Meglumine (Banamine), or DMSO. Depending on the case, vasodilators and other drugs may be used in an attempt to increase blood flow to the feet. Most importantly, an effort is made to identify and treat the initiating cause of the laminitis.

Part 2: Assessing the Laminitic Horse

Physical Exam A physical exam should begin with assessment of the demeanor of the horse. A level of comfort or pain should be established. Note the stance of the horse, degree of lameness, comparison of lameness between limbs, and conformation of body, legs and feet. Finally, the owner can provide vital information concerning the use, environment, feed, and care regime of the horse.

The digital pulses may be increased if the horse is painful or the foot inflamed. Increases in wall temperature may be noted. Distortion of the coronary band, hoof wall, frog, bars and sole is noted. If the sole appears thick, some may GENTLY place hoof testers on the sole to ascertain areas of sensitivity. Alternatively, the sole may be flat or prolapsed due to displacement. Separations or draining tracts may be evident. With chronic laminitis the white line may be widened at the toe due to long term changes within the laminae. Growth rings of the wall may be close together at the dorsal hoof wall, but diverge at the heels as the rate of heel growth exceeds toe growth.

Compare all the feet on the horse. Laminitic horses typically have one foot that is most painful on a given day. Be considerate of the horse. Don't attempt hoof testers if the animal is obviously painful. Don't expect the horse to stand with a foot up for long periods of time. QUICKLY perform your examination, diagnostics and therapeutics!

Radiographs It is essential that you perform quality radiographs, and consistently use the same techniques so that you may compare films!!! If proper techniques are not used, information obtained from radiographs (x-rays) may be distorted, leading to incorrect conclusions. Again, information gained from radiographs allows assessment of the location of the distal phalanx within the hoof capsul, and precise measurements allow a "blueprint" to be developed regarding treatment strategies to support the foot. Limitations of radiographs include a poor correlation between the amount of displacement of the distal phalanx and the eventual outcome of the case. For example, a horse may have only subtle or no rotation, yet the blood supply to the laminae and circumflex vessels is completely occluded.

Another limitation of single radiographs is the inability to assess changes in paramet ers of the foot with chronic laminitis. As the hoof tries to repair by epidermal proliferation within the dorsal laminae, the CE and HL zone numbers increase. It is sometimes difficult to distinguish between acute distal displacement of the phalanx (sinking) and a chronic "healing" by tissue proliferation/remodeling.

The Digital Venogram

One method of better assessing the internal changes and load within the foot is the digital venogram. The venogram is a radiograph that is taken with contrast dye in the blood vessels. The amount and patterns of displacement of the contrast suggests where the foot is heavily loaded, where architecture has collapsed, or areas of vascular impairment. Patterns are also identified as typical of acute or chronic changes, which helps determine the state of disease. Also, serial venograms allow assessment of progress within a case, or the lack thereof.

To perform the venogram, gather the following equipment: X-Ray machine, foot blocks, five cassettes, grid with at least 6:1 ratio, detomidine, mepivicaine, contrast medium (Hypaque76 or Reno60) (20 to 24 ml for a 5" wide foot), 21 gauge X 3/4" butterfly catheter with 12" tubing, +/- catheter injection cap, 12 ml luer lock syringes, 36" long X 1" wide car inner-tube, 4" and 2" elastikon tape, mosquito hemostats, scissors, 4x4" guaze, one horse holder, an assistant and a vet. The foot is meticulously cleaned, blocked with mepivicaine at the level of the proximal sesamoids, and the pastern is clipped and scrubbed. The horse is sedated with detomidine and stood on the radiograph blocks with the xray machine positioned for a lateral view. The assistant is caudal to the xray machine and has the xray cassettes, contrast medium in syringes, and hemostats within reach. The veterinarian is dorsal to the xray machine, and he applies the 4" elastikon at the level of the fetlock, tapes the tourniquet under the tag end, tightens the tourniquet at the level of the sesamoid bones, and tapes the tourniquet in place with 2" elastikon. Get the tourniquet tight!!! The vet's inside shoulder is in contact with the horse's knee as he reaches his inside arm medially around the leg and uses his lateral hand to catheterize the lateral palmar digital vein. Blood should flow freely from the tubing, and the assistant may attach an injection cap. The vet injects one syringe of contrast, the assistant changes to a second syringe which is also injected. (Do not use a 20 cc syringe-you are not able to appreciate injection resistance and wont realize when you're blowing a vein.) As the second syringe is injected the leg is gently flexed to cause laxity in the deep digital flexor tendon. When the second syringe is empty the assistant clamps the tubing and tapes the hemostat under the tag end of elastikon. The veterinarian changes settings on the xray machine as the assistant exchanges cassettes; a lateral, lateral with grid, DP with grid, DP, and late lateral views are taken WITHIN 45 SECONDS of clamping the tubing. The tourniquet is released, the medial and lateral palmar digital vessels are padded with gauze 4x4's and taped into a pressure bandage which is removed 15 minutes later.

Part 3: Principles of Treatment

The basis of treatment of the laminitis horse relies on correcting the initiating disease process, medically managing the pain of the horse, and mechanically altering the "mechanics" of the hoof to place it in a healing mode. The displacement of the distal phalanx primarily involves damage in the dorsal or front half of the foot. Loading the palmar portion of the foot and unloading the diseased areas will encourage the return of blood supply to the tissues, allowing healing and growth of the foot capsule.

Five principles of treatment: 1. Move break over back. Reduce the lever-arm of the toe, which pulls the laminae apart as the foot moves forward. 2. Unload the Deep Digital Flexor Tendon. Increasing the palmar angle(PA) will decrease the tension of the DDFT. 3. Derotate the foot. The palmar surface of the coffin bone will be parallel to the load bearing solar surface of the foot. 4. Load the relatively healthy portion of the foot. Provide support for the sole, especially in the heels, bars, and frog. Do not place pressure on the sole beneath the apex of the coffin bone. 5. Do not stress the foot-be fast with treatments and keep the PA elevated. NEVER take an unstable foot out of a therapeutic device (such as a modified-ultimate shoe) and leave the horse standing flat footed or walk the horse.

There are many ways to accomplish those goals, and each farrier and veterinarian will make recommendations based on individual cases as well as techniques that have worked well for them in the past. There is no "cook-book" formula for treating laminitis; instead you must ascertain the horse's stage of laminitis, degree of damage, and owner capabilities and long-term goals to develop a plan.

If you suspect that the horse is in the developmental phase of laminitis, attempt to prevent structural changes within the foot by applying solar support, making certain the toe is not excessively long, and stall resting the horse. If appropriate, place the legs and feet in an ice bath (see Pollitt website and Andrew Van Eps paper on Cryotherapy.) Venograms taken during the developmental phase should be normal. Pay particular attention to the solar papillae which should be long and oriented in the same plane as the dorsal surface of P3. If there is leakage of contrast from the vessels or if the papillae are beginning to fold or are compressed and not visible, then lamellar separation has begun.

To support the sole during the developmental phase, horses may be trimmed then placed on the EDSS Custom Support Foam or on cut-outs of 2" Styrofoam home insulation. (See Gene Ovnicek website.) The Styrofoam is wedged beneath the heel to reduce the strain of the DDFT, and multiple layers increase the amount of cushion. This system is very economical, but may be difficult to maintain on the foot. Another device is the Redden Modified Ultimate shoes with a sole packing. (See Nanric website.) Ultimates are a plastic shoe with two wedge pads that elevate the palmar angle 20 degrees, loading the heel and reducing the tension of the DDFT. The toe and sides of the shoe are beveled to enhance break over. To apply the shoes the foot is radiographed and derotated (heels are trimmed until the palmar angle of the coffin bone is zero degrees.) When applied the DB = 0; you may need to dress the dorsal wall back or rocker the bottom of the shoe to achieve this. Support putty is placed within the sole, and the shoes are glued to the foot or bandaged onto the leg. A baseline xray of the foot in the modified ultimate is taken. The horse may be maintained in these shoes indefinitely.

If the horse enters the subacute category, the venograms at that time would remain normal, consistent with those taken during the developmental phase. Two weeks after the inciting disease and medical treatment the sub-acute horse is sound without phenylbutazone, digital pulses are normal, and there is no radiographic change within the foot except increase in sole depth. Four weeks after the initial insult one of the heel wedges may be removed. If the horse remains clinically and radiographically normal at six weeks, shoes may be applied and the horse returned to light work.

I prefer putting acute horses with milder degrees of damage in the Modified Ultimate shoes. By "mild" I mean leak into the soft tissue but not pooling; minimal folding of the circumflex vessel at the apex but not rotation of the apex of P3 distal to the anastomosis of the circumflex vessel/dorsal lamellar vessels; distortion or elimination of the solar papillae. These horses are reevaluated in two to ten days with follow-up radiographs and venograms. If I feel that when I do the initial workup the horse is still experiencing damage at the cellular level, I repeat the venogram in two to three days. If I feel comfortable with a case then I wait 10 to 14 days and repeat venograms (should have improved perfusion) and radiographs (the sole depth should have increased by 3mm. If sole depth isn't increasing, then our treatment has not allowed perfusion of the damaged areas, and the treatment plan is reevaluated.) If the sole is growing, then the Modified Ultimate shoes are continued for four more weeks when more radiographs (with or without venograms) are used to either replace the modified ultimates or to shoe the horse. Acute laminitis horses placed in the Modified Ultimate shoes that have radiographic displacement of the coffin bone, or aren't completely sound and cannot be taken off phenylbutazone, or maintain a bounding digital pulse, require more long term treatment. The heel wedges or shoes are not removed. These horses have pathologic changes on the venograms; utilize that information to anticipate future events (such as seromas breaking out the coronary band).

Once the chronic laminitic foot is stable enough to allow nailing, I use radiographs and apply an Aluminum Four Point Rail shoe (Nanric website). The shoe has "elevated" railed heels and break over is reduced by the beveled toe and sides. I "rocker" the entire shoe, placing it in a banana shape. Break over is placed under the center of the coffin joint. The palmar angle is placed around 20 degrees so the strain of the DDFT is reduced. The horse is able to adjust its weight bearing without having to move forward or pick up the foot. When the horse does move, the resistance to moving is decreased because of the roller motion. These shoes may not make the horse immediately sound, but should allow vascularization to improve and the hoof should grow. Our goal is to double the sole depth in six weeks. If the horse is not growing foot, then reevaluation and more aggressive therapy is indicated. Venograms may indicate compromised circulation in spite of our therapeutic shoe.

The rocker-rail shoe has been very beneficial to our practice; however it does require precise placing on the foot to ensure success. If the balance point of the shoe is place too close to the toe, the horse rocks back and increases the strain on the DDFT. If the rocker is placed too close to the heel, the horse rocks forward and locks onto the toe.

Radiographs are required to properly place this shoe, and farriers must be comfortable hot-shaping the aluminum shoe. ( If these factors are a problem, then I suggest using the Equine Digit Support System shoe with the high rails. (Ovnicek website.)) Furthermore a strict shoeing schedule must be followed; after 4 to 6 weeks some horses have their heel grow forward which moves the belly forward and disturbs the balance-point of the foot.

Aggressive treatment is indicated for both a horse that presents with acute significant reduction in perfusion on the venogram, and a chronic uncompensated horse that is not improving on venograms or growing sole with the rocker rail shoe. These horses may benefit from a deep digital flexor tenotomy. Venogram indications for a tenotomy include elimination of perfusion at the coronary plexus, pooling of contrast in the lamellar area, no perfusion in the lamellar area, and displacement of the apex of P3 distal to the circumflex vessels with lack of perfusion to the sole. Cutting the DDFT will eliminate any pull of the distal phalanx away from the dorsal laminae, and reduce loading of the sole corium beneath the apex of the coffin bone. After doing a venogram to assess perfusion, shoe the foot with the Aluminum Four Point Rail shoe with a heel extension, and do a deep digital flexor tenotomy. The shoe is set so that the palmar surface of the coffin bone is parallel with the foot surface of the shoe, and the breakover point of the shoe is directly below the apex of P3 (PA=5, DB=0.) The horse is bandaged and stall rested for three months, then gradual hand-walking and turnout into a small paddock begins.

If an acute horse has high-scale damage to the foot, the most aggressive treatment or euthanasia is indicated. Most of these horses are lame on presentation, and venograms reveal no blood supply to the foot distal to the coronet. The coronary band may be separated and leaking serum and blood. The coffin bone may protrude from the sole. On these horses the foot is actually suffering more of a compartmentalization injury. The wall acts as a tourniquet, and pressures elevate within the foot from the edematous damaged tissue and vascular stasis. If the owner elects treatment, the hoof wall is removed. Pins are placed through the cannon bone and a cast is applied to the leg; the weight of the horse is suspended on the pins, and the foot is completely unloaded, allowing healing of the tissue. If damage to the tissue is not overwhelming, the foot capsul will re-grow and bone damage is minimal. These horses are at best pasture sound upon recovery, and they require life-long treatment and monitoring by the veterinarian and farrier.

If a horse has chronic compensated laminitis, is stable and relatively sound, I will trim the foot by rockering the toe to reduce break over, and attempt to strengthen and load the heels by trimming them from the widest point of the foot back towards the heel bulbs. DO NOT remove any sole unless Sole Depth is greater than 20mm. I use what is called a "Four Point Trim" (see Redden or Ovnicek web sites.) This technique may also be effective on mild cases of laminitis where little or no mechanical damage has occurred. Those feet will have a Digital Breakover of zero and a Palmar Angle of 5 to 10 degrees after trimming. If trimming alone does not give me those mechanics, I'll put that horse in a shoe that will. If the horse is still not comfortable in that shoe or is not able to maintain an adequate sole depth (15 to 20mm) then I will maintain that horse in a rocker rail shoe with a PA at 10 to 15 degrees and DB -5 to -10 depending on the foot and the mechanics it needs.. Some chronic compensated laminitic horses are maintained in a rocker shoe for the rest of their life.

Long term treatment depends on the case. Low-scale damaged feet will grow out over six to eight months, and then the horse may return to use. High-scale damaged feet may return to work or only achieve pasture soundness. It is important to have a realistic goal in mind before you begin treating the laminitic horse. Use the diagnostics that we have discussed to assess the scale of damage within the foot and develop a short and long-range treatment plan. Be realistic when assessing your financial limitations, physical or environmental capabilities of caring for the horse, and the horse's ability to overcome the initiating cause of laminitis.

Part 4: Prevention

It is estimated that laminitis is one of the leading killers of horses, second only to colic. A USDA survey regarding laminitis listed causes such as lush pasture (46%), feed problems, complications of injury, obesity, old age or pregnancy. Other causes included grain overload (7%), colic or diarrhea (3%), and retained placenta (2%). The majority of cases of laminitis could be prevented! Routine hoof care by a competent farrier, yearly physical examinations by your veterinarian, exercise, and dietary management are all necessary tools to prevent laminitis in your horse. This may include dry-lotting or using a grazing muzzle on an overweight horse, monitoring sugar content of pasture or hay, and strict dietary control. If your horse is at high risk for developing laminitis, make lateral foot radiographs part of your yearly preventative health program. These radiographs will become a record to assess changes within the feet and will be the standard for comparison if your horse does develop laminitis.

Recommended websites: www.ivis.org(website that allows you to read proceedings from AAEP meetings, including How-To Perform the Digital Venogram at the 2006 San Antonio convention) www.uq.edu.au/~apcpolli/ Dr. Chris Pollitt's website at the University of Queensland, Equine Laminitis Research Unit. www.safergrass.org (compares sugar levels in dry versus soaked hay.) www.nanric.com (Dr. Redden's website. Review the "monthly tips and archives".) www.hopeforsoundness.com (Gene Ovnicek's website) www.myhorsematters.com (American Association of Equine Pracitioners) www.bestfriendequine.com (Grazing Muzzle)