How To Treat High Scale Laminitis With Wall Ablation And Transcortical Cast

2003 - 16th Annual Bluegrass Laminitis Symposium Notes

Written and presented January 2003 by R.F. (Ric) Redden, DVM

Laminitis remains one of the horse industry’s biggest killers. Insurance companies recognize colic just ahead of laminitis, therefore it is a very important subject. Unfortunately there are no consistent guidelines to help clinicians and farriers successfully deal with laminitis. In my book, Understanding Laminitis, I have a very simple scale that helps group the cases according to degrees of damage to the vascular supply, soft tissue and bone. The scale in reality is quite complex requiring in-depth knowledge of the subject and good clinical experience. Most veterinarians and farriers see less than six cases a year and may never see a high-scale case. The low to low mid-scale cases fortunately make up the majority of cases across the board. These cases are responsive to a multitude of mechanical devices that include shoes, trim techniques and often professional neglect (simply doing nothing). Mother Nature often smiles on these cases and most recover with little or no life threatening damage. The lower scale cases offer a false sense of security to those responsible for treatment and when no effort is made to clearly define the degree of damage, disaster strikes when the higher scale cases are treated in the same manner.

Let's take a quick look at a high scale case. A typical history of the cases I see during foaling season; mare foals, very difficult dystocia. The foal is usually very large, has to be pulled or possibly requires fetatomy to deliver. Heavily stressed, the mare has acute laminitis within hours of delivery. Most cases very painful, grade 5/5, glued to the ground in front and treading water with the hind feet which spells big trouble with this history. Placing her in Modified Ultimates or in Styrofoam doesn't alter her clinical picture as one normally finds with the lower scale cases. The mare continues to fall apart as the day proceeds, heavy breathing, very anxious eye, unwilling to move, eat or drink. Coronary bands are changing rapidly; a very distinct ledge can be felt around the entire coronary crown. Taking radiographs can be a task due to the pain response, blocking the feet just for the sake of taking film is not recommended as more damage quickly ensues when the feet are blocked. Without prior base lines the first set of film may be difficult to accurately interpret. Large Thoroughbred broodmares with some age will often have 20-22mm HL (horn - lamellar) zones and frequently are found with chronic capsular rotation, especially those with poor quality feet. Flat or dropped soles, full thickness toe cracks, typical dish are common findings on some of the world’'s best mares. Nevertheless the radiographic damage may be seen only as lamellar swelling which can be up to 25mm or not demonstrable at this stage. I have seen a handful of cases that went through the massive lamellar slough so quickly that little or no swelling was seen radiographically, they are rare cases. Most cases will show very distinct thickening of the laminae within hours of a significant bout of laminitis. Very disciplined, methodical, repeatable, soft tissue films are necessary to see these early changes. Rotation remains a popular radiographic sign but be keenly attuned to what is happening at the HL (horn - lamellar) zone as it is by far the most useful information. Films made only a few hours later can clearly show an increase in horn - lamellar zone, decrease in sole depth and an increase in C.E. (coronary band - extensor process). Palmar angles may be unchanged. All these subtle but measurable signs indicate massive lamellar dysfunction has occurred and the boney column is descending. Heavy, strong hoof capsules with 25mm of sole certainly have a better reserve than the previously described case, but this case can be very deceptive as rotation may not be seen at all.

A venogram is the only way that I can accurately assess the degree of damage at this or any other stage for that matter. The procedure is quite easy, requires very little equipment, but is a timely exercise that must flow along quickly in order to produce quality film. All film must be made within 45 seconds following injection of the dye. I strongly advise everyone to practice the technique on normal horses before attempting a severe laminitic case. Film interpretation must be relative to what is normal. A large range of normal exists as well as a large range of pathology. Making life or death decisions based on little or no experience is high risk and often spells disaster. I cannot stress enough the importance of technique and interpretation. The venogram on most of the mares above will have stark loss of contrast along the anterior face of PIII, stark loss along the circumflex zone and often little or no contrast in the terminal arch. The coronary plexus will appear as a crown well above the hoof, the heel area is most often well perfused. Caution: Tourniquet failure is one of the biggest problems I see with many of the venograms I read. The typical under perfused pattern may appear as described above, but the vessels in the heel region appear as an upside down tree, the vessels taper to finer points much like tree limbs. Avoid misinterpreting the artifacts found with poor technique as it may decide the fate of your patient. When the venogram describes a foot that is basically depleted of the vital blood supply, the primary emergency goal is to restore adequate blood supply to the digit before irreversible damage has occurred.

I have used my partial decompression technique to include lower wall resection, upper wall resection and internal decompression technique (deep flexor tenotomy) followed by realigning the palmar surface of PIII, all with a reasonable degree of success. Looking back over literally hundreds of cases, some that pulled through, many that made it but were left crippled and others that simply slipped away from me regardless of my efforts has been humbling. I have often asked myself, what were the determining factors that seperated these cases? Venograms during all stages of the syndrome on a large number of cases has convinced me it was the degree of vascular damage,the speed that it occurred and the time lapse or chronicity of the comressive forces. Full Wall Ablation: The fall of 2000 I removed the entire hoof capsule from a nice filly that was draining sersosanguineous fluid from the top of the right front coronary band. I placed her in a transcortical cast to protect the healing digit offering her immediate clinical relief and bought her enough time to cornify the laminae and grow 10-15mm of sole before the pins were removed. She grew a very nice horn capsule, sole and frog and was very happy for several months, but unfortunately the coffin bone had large areas of irreversible vascular damage and the new horn was formed around the partially dead bone with a pseudo laminae attachment. The persistent decaying effect on the bone and less than favorable horn attachment finally resulted in the decision to euthanize this very nice prospective broodmare. Seeing this opportunity to help others I realized the technique had promise but I had to move much quicker in order to minimize permanent damage to the coffin bone. Since this case I have removed the entire hoof capsule on 13 feet, 8 horses;

• 1 case euthanized due to lack of a favorable response.

• 1 case responded well and appeared to be on the mend. It developed a septic coffin joint and was euthanized.

• 1 case responded well and cornified the laminae in spite of off-the-scale vascular damage. It developed renal failure and was euthanized.

• The other cases continue to show steady, but slow, improvement.

Technique: The transcortical cast can be applied under general anesthesia or standing using a sling and a local anesthesia. I have performed the procedure using both techniques, the downside of general anesthesia is removing the hoof capsule as it is very difficult to peel off when there is no weight on the limb to stabalize the foot. Drilling and tapping the cannon bone and placement of the pins is much easier though on the recumbent horse. Recovery can be tough on the bone around the pins as well as the digit. The standing horse bypasses this risk. The surgical time can also be very short with the standing case, typically 30 to 45 minutes per leg, requires one person on the head and one assistant. I don't advocate the standing approach for anyone that is not comfortable with sudden outbursts of horses that are not broken to the sling. It can be quite harmful for your health as well as others in the immediate vicinity.

Standing Technique: I use a high ring block just beneath the knee and allow 30 minutes to totally desensitize the limb. I put a snug Vetrap snuggly over the blocked area to prevent unwarranted edema while waiting for the block to take effect. The lower limb is clipped and prepped once the animal is well sedated and standing quietly in the sling with just slight sling lift placed on the abdomen. Using a Dewalt, 12 volt drill with sterile sleeve and 6.2mm bit, I place two holes through the cannon bone approximately 1-1.5 inches apart. The best location for the holes is where the cannon bone flares outwardly at the fetlock and the other just above. Using a 1/4 inch tap (Imex) and the drill running very slowly I tap both holes. The positive threaded pin is also run in with the drill very slowly. Use a large amount of saline on all drilling and taping tools as thermal bone damage is a big concern. Cut the Pin off with one inch exposed on either side, a good pair of bolt cutters is needed. A sterile bandage is placed over the pins during hoof removal. Raise the horse slightly in the sling, hind feet remain on the floor. Using your nippers remove the sole wall junction all the way around, being careful not to injure the laminae or bone. A pair of half round nippers is then used to get a firm grip on the wall at the heel. Slowly peel the wall, the goal is to peel it in one piece, go slow and allow time for the papilla at the coronary groove to turn loose. Often I will put on a loose fitting tourniquet for this step for those casess that have small areas of perfusion. Most will have quite dark laminae and do not bleed as you would suspect. Once the wall is removed I gently massage the dark laminae until it feels warm and fresh hemorrhage can be seen throughout the entire area. Place a piece of Betadine soaked 1/2 inch felt over the laminae (the shape should mimic the wall you removed). Tape it in place with firm pressure. Place two pieces of Betadine soaked felt on the bottom, apply two rolls of Gortex cast padding over the foot and limb. A piece of 1/2 inch felt at the top of the cast prevents pressure and rub sores. I position the foot in a normal loaded position and apply a cast using five rolls of five inch Dynacast. Often I will use the sling to help control the stance of the animal and position of the limb during casting. When necessary you can lift the horse completely off the ground for a few minutes of pure sling tranquilization, be careful though they blow after five to ten minutes -don't push your luck. Placing a cup shaped piece of aluminum on the bottomreduces twisting pressure on the pins when the horse turns.

All cases have show immediate clinical relief, all cases have cornified the laminae within the first three weeks. Pins are normally pulled three to seven weeks once micro fractures appear radiographically. Another cast is applied for three to four weeks. They are not as happy with the pins out and are expected to be down more over the next two to three weeks, therefore bed very heavily. After six to eight weeks I may decide to cut the deep flexor tendon depending on the palmar angles; most have a tenotomy at this stage. Most cases have already had a tenotomy at this stage.

Results: Five to six months is required for the majority of the primary horn tubules to grow from coronary band to the sole surface. The sole and frog regenerate very quickly, all have had some degree of bone damage but all those surving continue to show a steady response, they have good body condition and attitude. It is far too early to know how the long range future looks for these cases but it is very obvious that timely decompression of high scale cases is a viable option, especially when all cases were facing euthanasia as the only other option. Call me, I will help you evaluate and move into this exciting treatment option for those with seemingly impossible odds.