Shoeing the Laminitic Horse

Stephen E. O'Grady, DVM, MRCVS

Many advances have been made over the last few years in shoeing the laminitic horse. We have seen much success in treating these cases but we still see far too many failures. A couple of farriers have made significant strides with their shoes - Burney Chapman with the heart-bar shoe1 and Gene Oveneck with his digital support system2. Both of these shoeing procedures require attention to detail, a skilled farrier and both procedures rely on posterior support using the frog and related structures. Numerous other methods of foot care have been recommended for treating laminitis with varied success; the ideal has yet to be found. We must remember that the outcome of these cases is directly proportional to the extent of the lamella damage suffered during the original insult. For the purpose of this discussion, we will focus on the chronic laminitic horse. We are still unclear in the veterinary profession as to when a horse becomes chronic. Is it when radiographic changes first take place within the hoof capsule or is it when rotation and/or displacement stop? When should a laminitic horse first be shod? This is a difficult question with no clear-cut guidelines. Hopefully our medical treatment and foot support in the acute stage was effective in halting the disease process rendering the horse comfortable, on minimal medication and having gone a reasonable length of time with no further radiographic changes. It is at this stage that shoeing should be considered. There are many horses that have such severe lamella damage that they will not respond to any method of therapeutic shoeing. Every laminitic case must be approached on an individual basis and not every shoeing method will work for every horse.

PURPOSE OF SHOEING:

The veterinary literature abounds with reports of corrective shoeing for laminitis and distal phalanx rotation and/or displacement. The primary purpose of shoeing a laminitic horse is to protect the foot, minimize breakover, relieve dorsal hoof wall pressure, prevent sole pressure and provide posterior support by using the frog and heels of the foot3. If the above five points cannot be accomplished then, in many cases, the animal may be better left unshod. To minimize breakover, the shoe should be placed just in front of the apex of the distal phalanx (P3). Shoeing methods that increase weight bearing through the hoof wall, especially in the toe area, will increase pressure on the compromised lamina. This may worsen or prolong the problem.

TYPES OF SHOES:

There are countless types of shoes used to treat laminitic horses. Among the most popular are:
  1. the heart-bar shoe
  2. the egg-bar/heart-bar shoe (full support shoe)
  3. an egg-bar shoe with a square, rolled or rockered toe
  4. a reverse shoe which leaves the toe open, often used with a frog support pad
  5. an open shoe with extended heels, using a heel insert such as a frog support pad or rubber polysiloxanea
  6. Elite wedge shoes
  7. the digital support system shoe
  8. various types of glue-on shoes and modifications thereof

All of the above shoes allow us to address, to some degree, the primary purpose of shoeing the laminitic horse. The above list also allows the farrier to take into consideration his or her individual skill level and particular interest in therapeutic shoeing.

GOALS OF SHOEING

There are three main biomechanical forces imposed on the foot of a horse with laminitis. Firstly, there is the vertical load of the horse's weight placed on the hoof with compromised laminae. An attempt to counteract this force is made through various means of support. The second biomechanical force placed on the foot is the proximal-palmar pull of the deep digital flexor tendon (DDFT). Lengthening the shoe and manipulating the hoof angle may effectively reduce it. The last biomechanical force is the bending force or lever arm placed on the compromised laminae by the dorsal hoof wall. This force can be effectively managed by moving the breakover point closer to the perimeter of the third phalanx. THEREFORE, THE GOALS OF SHOEING THE LAMINITIC HORSE SHOULD BE FIRST, TO EASE BREAKOVER; SECOND, TO DECREASE THE DISTRACTIVE FORCE OF THE DEEP DIGITAL FLEXOR TENDON AND THIRD, TO SUPPORT THE PALMER/PLANTAR PART OF THE HOOF. To ease breakover effectively, radiographic guidance is used to place the shoe just in front of the third phalanx. Breakover is further enhanced by a square-toe shoe, a rolled or rocker-toe shoe or the use of an open-toe shoe. This effectively decreases the lever arm associated with the hoof wall (sometimes-excess) present in front of the third phalanx.

To decrease the distractive pull of the deep digital flexor tendon (DDFT), the heels of the shoe can be extended beyond the heel of the foot. In addition to decreasing the force exerted by the DDFT. The increased length of the shoe moves the weight bearing function palmar/plantar and this appears to further unload the toe. The assumption that less load is placed on the toe is based on the fact that in subsequent radiographs, there is a rapid increase in sole depth. Wedges in the form of heel inserts (bar wedges) can be placed under the heel if additional relaxation of the DDFT is necessary. Palmar/plantar support can be accomplished through the use of heart bar shoes. The heart bar shoe has the ability to transfer much of the weight bearing function from the hoof wall to the frog. Weight transfer can also be accomplished through the use of wide-web steel or aluminum shoes, various bar shoes, frog support pads and polysiloxane impression material. (elastomere putty.) These methods utilize the posterior portion of the foot, i.e. heels, bars and frog.

Addressing these three goals results in rapid growth of sole which is necessary to protect the third phalanx and is essential for long-term soundness.

RADIOGRAPHS

Emphasis must be placed on the necessity for current readable lateral radiographs. From the radiographs, the clinicians (veterinarian and farrier) can access the amount of rotation and/or distal displacement of the third phalanx that has occurred, the current position of the third phalanx and the amount of sole depth that is present. Laminar separation or abscessation can also be assessed. The radiographs are also used as a baseline to follow the progression of the case at periodic intervals. Of equal importance, the radiographs can be used as a guide when trimming and shoeing the foot. When taking the radiograph, a wire should be placed on the dorsal surface of the hoof wall and another wire should be placed in the top of the radiographic block. The horse should also have a block of identical height placed under the opposite fore or hind foot so weight bearing is evenly distributed. This allows more accurate measurements to be drawn. Measurements can also be made from the radiographs to determine the most accurate point of breakover when fitting the shoe. This can be accomplished by placing a radio-opaque marker near the apex of the frog prior to taking the radiograph, and then measuring the distance from this marker to the perimeter or tip of the third phalanx. Alternatively, this distance can be measured from the wire on the dorsal hoof wall. The amount of heel that must be removed to realign the third phalanx within the hoof capsule and the point on the ground surface of the foot where the trimming should begin can also be accurately measured. The degree of flexion in the coffin joint should be measured. It has been our observation that chronic laminitic horses with significant rotation and a high heel accompanied by marked flexion of the coffin joint when weight bearing, require some degree of heel elevation following trimming in order to become comfortable. This can easily be accomplished with various degrees of wedge heel inserts or, in severe cases, by an inferior check ligament desmotomy or deep digital flexor tenotomy. It is our feeling that chronic laminitis with significant rotation results in a rapid shortening of the musculo-tendonous unit of the deep digital flexor tendon.

SHOEING

Shoeing the laminitic horse should always be a combined effort between a veterinarian and a farrier. Input from both parties is necessary for a successful outcome. Over the last few years, this author has been using a method of shoeing chronic laminitic horses that encompasses the goals mentioned earlier (minimize breakover, decrease the pull of the DDFT and support the digit). The shoe has a wide margin of safety and is relatively simple to construct. The foot is trimmed according to the radiographs; the point where we want our breakover is measured from the radiographs and marked on the sole of the foot with a magic marker. The size and length of the shoe is then determined. Our shoe of choice has been the plain or wedge, Elite® aluminum shoe. These shoes have the properties of being lightweight and easy to work with. The shoes have a wide web, the nail holes are punched nicely and the fuller extends back to the heels so it is easy to drill small holes for additional nails, if desired. If the foot is bigger than the available sizes of this shoe we usually employ a handmade wide web steel shoe. The toe is squared on all shoes and a grinder is used to roll the toe up to the inside of the swedge. A grinder is also used to concave the solar surface of the shoe. The inside edge of the shoe is placed so it corresponds to the mark placed on the sole for breakover. This mark is at or just in front of the third phalanx.

The length of the shoe should extend beyond the heels of the foot to a perpendicular line drawn from the hairline at the bulbs of the heels to the ground. The shoe can be lengthened or shortened if necessary, depending on the conformation of the foot. This not only decreases the distractive force of the DDFT; it also shifts the weight bearing function to this area. As a routine, we have placed at least a 2o wedge heel insert under the shoe. The amount of heel elevation can also be determined from the radiographs. This counteracts any shortening of the musculo-tendonous unit of the DDFT. If there is significant rotation or distal displacement, this is accompanied by some degree of contracture of the DDFT. It may be possible to remove these wedges gradually over time.

The last point to consider is palmar/plantar support. This can be accomplished very effectively and safely through the use of rubber-polysiloxane. This is a dental impression material consisting of a putty base and a catalyst. When the two are mixed together they cure to form a firm resilient material that molds to the heel area of the foot. In this manner, we are able to utilize all of the structures in the heel area, which are capable of providing additional support, not just the frog. After the shoe is fitted, plastic gutter guard is placed between the shoe and the heel insert. The bar wedge is attached to the shoe with copper rivets. The gutter guard can cover the entire solar surface or an area on the bottom of the foot from the point of the frog back. By placing the material over just the frog, the sole can be monitored for discoloration, seepage of serum or prolapse. The two components of the polysiloxane are mixed thoroughly and pushed through the gutter guard until the material is observed underneath the heel insert. Additional material is added until the elastomere putty is level with the ground surface of the shoe, creating a platform-like structure. The foot is held off the ground until the material sets (approximately one minute, but varies slightly with temperature. Allowing the impression material to cure with the weight off the foot assures that the material forms a mirror image of the contour of the palmar/plantar portion of the foot and to not be pushed out from weight bearing. It therefore provides uniform support when weight is borne on the foot. If there is adequate sole thickness noted on the radiographs and the sole is intact, the entire solar surface can be filled with the impression material. If the shoe is of adequate length and the load has been concentrated in the heel area, then the additional support to the sole dorsal to the frog provided by this resilient material may be beneficial. If the sole surface is compromised and requires treatment, an aluminum treatment plate can be easily attached to the shoe. The treatment plate can be fitted to the inside of the swedge on the toe of the shoe so one doesn't lose the function of the rolled toe. One-quarter inch Allen head screws are used to attach the treatment plate. The screws are countersunk in the treatment plate. This type of screw head will facilitate breakover when compared to bolts or studs. Forshams hoof packing can be placed in the screw heads in between removal of the plate to prevent material from accumulating there.

CONCLUSIONS

Success with this method is based on clinical impressions and numerous cases which became comfortable post-shoeing. Gross and radiographic improvement of the affected feet was also noted on subsequent resets. Shoeing the chronic laminitic horse is seldom curative and treatment usually entails long-term maintenance. Regardless of the type of shoe used, it is important for the veterinarian and farrier to consider the biomechanical forces exerted on the foot and the use of radiographs as a guide to trimming the foot for a consistent successful outcome.

REFERENCES:

1) Chapman B, Pratt G. Laminitis. Proc Am Assoc Equine Pract 1984; 30:129.

2) Ovnicek G, et. al. Wild horse patterns offer a formula for preventing and treating lameness. Proc Am Assoc Equine Pract 1995; 41:260.

3) White N A, Leesburg, VA, Personal Communication, 993.

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