Understanding the disease progression of abnormal hoof anatomy, Part 3

Grade IV cases are the bad boys of laminitis. These cases can involve edema and separation of the laminar structures that surround the dorsal face of the distal phalanx (P3), with seromas that rupture through the coronary band dorsally (Figure 1), medially or laterally or penetrate the sole (solar prolapse). The final sequela is often fatal sinker syndrome with hoof capsule loss. Complications that I have seen (as if the aforementioned were not bad enough) are rupture of the distal interphalangeal (DIP) capsule, fatal emboli, P3 fractures, ankylosis of the DIP joint, gangrene and unusual infections within the hoof capsule such as botulism.

Figure 1: A typical coronary band rupture. Note the use of a reverse wedge tenotomy trailer rail shoe.

Characteristics

For the sake of simplicity, I divide Grade IV cases into two categories—the rotators (cranial rotation cases) and the sinkers (fatal sinker syndrome, or FSS).

All horses with Grade IV laminitis are in extreme pain. They are recumbent and rarely stand unless asked to. I have seen these horses walk in on their hind legs, rather than place weight on their forefeet. I have also watched them walk out of their hoof capsules. Grade IV cases of the forefeet will always have a degree of laminitis in the hind feet as well, so be sure to radiograph all four feet when starting your work-up.

Cases of Grade IV laminitis of the hind feet (originating there first) are rarely bilateral and are often less complicated than forefoot cases, but they can also become euthanasia cases rapidly if not taken seriously—especially if the laminitis has a supporting limb etiology. (Remember to radiograph the forefeet as well.) Horses with a fractured hind leg or severe pain of any origin are candidates for supporting limb laminitis. I have also seen smooth wire fencing become a tourniquet when wrapped around the leg during a struggle in the fence line. When the wire is placed in such a way as to allow intermittent blood flow, laminitis can be a sequela (Figure 2 and Figure 3).

Figure 2: A venogram of an intermittent constriction of smooth wire around a limb that resulted in a Grade IV laminitic event. The venogram shows complete absence of the dorsal and circumflex circulation.

Grade IV laminitis has a series of pathologic events that avalanche to final cases that may be beyond salvage. The Grade IV case can present in 24 hours or five or six weeks. The usual course becomes more critical over a longer period as the structures within the hoof capsule collapse slowly. It is common to see a case "recur" five to six weeks after the acute phase, when in actuality this is simply the final stage of the original case.

Figure 3: A lateral radiograph of the limb in Figure 2 showing the separation of laminae in the dorsal and solar regions of the hoof capsule that was prognosticated by the venogram.

The rotators

The rotators, or cranial rotation cases, will have rotation of greater than 15 degrees palmar angle and often 20 to 30 degrees palmar angle. The horn lamellar zone (HLZ) will be 25 to 30 mm. The extensor process-coronary band (EP/CB) measurement will be increased as the extensor process of the P3 tips downward with the rotation. The sole depth at the tip of P3 (SDT) will be greatly decreased, with as little as 0 mm once the solar corium penetrates the mature sole. The sole depth at the wing of P3 (SDW) will be greatly increased.1 Soft tissue changes will include triangular lucencies or lamellar wedges in the dorsal structures that are composed of gas pockets and serum or purulent material.

Figure 4: A Grade IV laminitic event with reduced blood flow to the coronal cascade and the dorsal and circumflex circulation. No solar fimbria are present, and the twisting of the circumflex circulation is indicative of the distal margin of P3 falling below the circulation.

Venography views of the lateral hoof will show marked congestion or total absence of the coronal cascade circulation. The dorsal lamellar and circumflex circulation will be absent, congested or markedly twisted at the tip of P3 as the margin of the P3 slips out of the circulation (Figure 4). No fimbria will be present. The terminal arch is usually normal in appearance, as is the bulbar circulation.2

The sinkers

The sinkers, or horses with FSS, usually start as cranial rotation cases but continue to sink into the hoof capsule as all soft tissue loses its ability to support the bone column (Figure 5). Horses with FSS can have all the characteristics of a cranial rotation case (because they have already experienced that part of the disease process) and are so structurally unsound that the P3 then starts descending in the hoof capsule parallel to the ground.

Figure 5: A case of FSS in the healing phase. Note the cornified sensitive laminae and the twisted and stretched distal margin that would be evident on a venogram.

Quittor type lesions or rupture of the lateral cartilages and rupture of the bulbs of the heels are not an uncommon sequela to FSS. The sole becomes flat and very thin, and the entire hoof capsule may be freely twisted by hand.

Any horse with laminitis that has swelling within the pastern region that extends downward to the coronary band is an immediate medical emergency that requires venography to determine the extent of congestion within the area and the degree of loss of circulation distal to the swelling. Should all or almost all of the circulation be impeded distal to the pastern, a hoof wall ablation and casting with a fixation cast should be performed immediately.

Note: A depression at the coronary band or hair above the coronary band that sticks out or up is not a good prognostic indicator of FSS unless the depression runs around the entirety of the coronary band. Horses with depressions or changes in hair direction that run from quarter to quarter are usually just cases of high-grade palmar angle or cranial rotation.

The palmar angle of an FSS case can be 1 to 2 degrees or 0 degrees. The HLZ is usually greater than 30 mm at both measurements, which indicates that the P3 is sliding down and backward in the hoof capsule. The EP/CB will be greatly increased but must be interpreted in conjunction with the other measurements such as the increased HLZ and decreased SDT or SDW.1 There will be a marked lucency of the dorsal laminae, but unlike the more triangular pattern of a case of cranial rotation, the FSS case will have a lucency that runs the entirety of the hoof wall and may be more rectangular than triangular.

The venographic findings will show compression of the circumflex or total lack of the circumflex circulation. The dorsal and circumflex circulation will be greatly reduced or absent. The terminal arch will be markedly reduced or absent. The bulbar circulation, which in cranial rotation cases always appears full and healthy, will be markedly congested or absent.

Treatment

Treatment should be directed at the type of Grade IV laminitis—is it cranial rotation (abnormal increase of the palmar angle), or is it FSS?

In my experience, it is almost always impossible to recover the Grade IV increased palmar angle foot without a deep digital flexor tendon (DDFT) tenotomy. Why? The entire and only reason for performing a DDFT tenotomy is to increase the dorsal palmar mobility, thus allowing you maximum extension of the hoof capsule in order to gain a "0" palmar angle after the surgery. Do not attempt to treat a Grade IV (or any grade of laminitis) by simply cutting the deep flexor tendon and walking away. The DDFT tenotomy is 1 percent of the procedure, and the digital realignment is 99 percent of the procedure. I can't stress this enough.

Please obtain radiographs of the foot before tenotomy, after tenotomy but before digital realignment and after the realignment. You will notice that your interim radiograph shows some relaxation of the P3 within the soft tissue of the hoof capsule following surgery. We consider the post-tenotomy radiograph a necessary feature for proper alignment of the digital structures.

I will not go in-depth here into the entire deep flexor tenotomy procedure since it has been well-described by many authors. But here are a few useful hints:

• I perform all tenotomies with the horse standing or in a sling under light sedation.

• I ring block below the carpus.

• I maintain a good sterile environment at all times.

• I use special tenotomy blades.3

• I make my incision mid-cannon.

• I get in and get out (the more you muck around in there, the more scar tissue you will have).

Figure 6: A subluxation of the DIP joint after a DDFT tenotomy. One more good reason to radiograph the foot after the tenotomy procedure. The use of the tenotomy trailer rail will correct this problem and allow it to heal.

After surgery, we take an interim radiograph and then decide whether we can gain a "0" palmar angle by a simple trim of the hoof wall from the quarters back to the heels or if we need to apply a reverse wedge and tenotomy trailer rail. High level rotation cases will usually subluxate the DIP joint (Figure 6) as all of the supportive structures have been stretched (all DIP lateral collaterals and extensors and possibly other supportive structures of which I am not aware) and will require a tenotomy rail.

Figure 7: A radiograph of the use of a tenotomy trailer rail.

Figures 7 and 8 show two different horses—one shod with a reverse wedge and tenotomy trailer rail and one that was able to be realigned through remodeling of the hoof capsule. Notice that both feet were realigned beyond the normal range of dorsal palmar motion thanks to the tenotomy procedure. Also notice that when a "0" palmar angle is achieved, the originally loaded toe is now floating above the ground surface.

Figure 8: A foot with sufficient hoof mass and sole that allowed the foot to be realigned to a "0" palmar angle without the use of a tenotomy trailer rail. Note that the original loading surface of the toe is now no longer contacting the ground.

Complications

One complication of deep flexor tenotomies is further contracture of the P3. Should this happen, dropping down to the level of the pastern for a second tenotomy is an option and often curative. I prefer my first attempt to be mid-cannon because, should contracture happen and I have done a mid-pastern tenotomy, I have no further options for surgical correction.

Cutting the volar nerve or the major blood vessels of the limb are other possible complications that can be avoided with careful dissection of the area around the tendon with long, curved Metzenbaum scissors—inserting closed blades and then opening the blades as you withdraw from your skin incision.

Some breeds of horses are more prone to contracture. Halter Quarter horses and some warm blood breeds will have further flexor contracture. Paso Finos, Thoroughbreds and some working Quarter horses breeds will often have a tendency to go the other direction, resulting in a negative palmar angle. These cases, regardless of the shoeing type used for realignment, will be set with a 2- to 3-degree palmar angle to avoid this problem.

Correction of a horse with FSS laminitis requires hoof wall ablation and transcortical pinning of the cannon bone (MC3 or MT3) and casting so the foot is nonweightbearing.4

Monitoring

All cases should be radiographed weekly to assess the continuing proper alignment and to assess growth. Horses with coronary band separation should be resected and treated daily with aseptic bandaging and topical antibiotics. Horses with solar prolapse should be treated with antibiotics and gauze packing weekly.

The work necessary to recover a Grade IV case is intensive and requires monitoring on a daily basis. All of our cases are treated in hospital as critical patients and are monitored with the use of stall video cameras. I have been rewarded more times that I can count with complete recovery and return to performance. I have also known defeat with the continual contractual cases and those sad sinking cases that get to us too late. But if we do not try, we do not learn, and if we do not learn, we cannot help.

Andrea E. Floyd, DVM, has specialized in equine podiatry for more than 25 years. She is the owner of Serenity Equine, Evington, Va., and the author of Equine Podiatry. Dr. Floyd is a member of the American Veterinary Medical Association, American Association of Equine Practitioners and the American Farriers Association.

References

1. Floyd AE, Mansmann RA. Table 16.2. In: Equine podiatry. St. Louis, Mo: Saunders Elsevier, 2007;323.

2. Floyd AE, Mansmann RA. Table 16.3. In: Equine podiatry. St. Louis, Mo: Saunders Elsevier, 2007;323.

3. Floyd AE, Mansmann RA. Figure 18-13. Equine podiatry. St. Louis, Mo: Saunders Elsevier, St. Louis, MO, 63146, 2007;352.

4. Floyd AE, Mansmann RA. Figures 16-19, 16-20. In: Equine podiatry. St. Louis, Mo: Saunders Elsevier, 2007;327.