The wooden shoe as an option for treating chronic laminitis

Reprinted with permission from Equine Veterinary Education (EVE). Original published in Equine Veterinary Education Vol 21 Febuary 2009.

Summary

Various farriery methods have been described for treating chronic laminitis, yet no particular method has become the preferred choice. The wooden shoe may possess certain advantages such as redistributing load evenly over the palmar/plantar section of the foot due to its flat solid construction and the mechanics (bevelled perimeter, breakover and heel elevation) that can be incorporated directly into the fabrication of the shoe. It should be apparent that the advantages of this farriery option will also be limited unless strict attention is paid to the details involving radiology, foot preparation and alignment of the distal phalanx within the hoof capsule.

Introduction

Chronic laminitis is a frustrating and often disheartening disease for veterinarians, farriers and horse owners to manage. Our ability to rehabilitate horses with laminitis, despite the type of farriery employed, is related to the severity of damage to the lamellae (Hunt 1998). For this reason, treatment failures with any given methodology are commonplace. Chronic laminitis is defined by the presence of mechanical collapse of the lamellae and displacement of the distal phalanx within the hoof capsule (Hood 1999). The various forms of displacement of the distal phalanx recognised are: dorsal capsular rotation, distal displacement (sinking) medial or lateral displacement of the distal phalanx or any combination of the above (O'Grady et al. 2007a; Parks and O'Grady 2008). The most common type of displacement encountered is dorsal capsular rotation. If dorsal capsular rotation is severe, the instability of the distal phalanx combined with the weight of the horse often leads to prolapse of the sole or penetration of the distal phalanx through the sole. The wooden shoe has become another farriery option that has been found to be a consistently successful method to address dorsal capsular rotation (Fig 1) (Steward 2003; O'Grady et al. 2007a). The wooden shoe allows the distal phalanx to be realigned, has all the mechanical components of other farriery systems previously advocated for the treatment of chronic laminitis yet may possess many additional advantages over previous methods used. One major advantage may be its ability to distribute weightbearing evenly over a specified section of the foot due to its flat solid construction.

Other advantages are:

• Readily accessible materials
• Simplicity of construction
• Mechanics such as breakover and heel elevation can be fabricated into the shoe
• Nontraumatic application
• Bevelled perimeter of the shoe concentrates the load under the distal phalanx
• Solid base of shoe allows maximum recruitment of surface area in the palmar/plantar section of the foot to accept load
• Solid base combined with an appropriate Silastic material places even pressure and load across the palmar/plantar section of the foot
• Heel elevation, when necessary, can be applied in a uniform manner
• Easily altered according to the radiographic guidelines and structural requirements of individual foot conformation.

Fig 1: A wooden shoe attached to a hoof model. Note the mechanics incorporated in the shoe - bevelled perimeter of the shoe for lateral/medial breakover, extended dorsal to palmar breakover and heel elevation.

Fig 2: Radiograph of asymmetrical distal displacement of the distal phalanx on the medial side. Note that the red line drawn through the solar foramina is not parallel with the ground. Also note the disparity in the joint space from the lateral to the medial side (yellow arrow).

Fig 3: a) The basic wooden shoe where the proximal piece is cut vertical and the thicker piece is cut on a 45° angle. Note the wedge pad attached to the wooden shoe for heel elevation if necessary. b) An expanded view of the construction of the wooden shoe.

Fig 4: Ethyl vinyl acetate (EVA) glued to a 1⁄2 inch section of plywood and sanded into a dome shape. Note the leather pad on the foot surface of the wooden shoe, which is cut in the form of a 'W' to further unload the toe.

Fig 5: Wooden shoe fabricated from a single piece of plywood. Note the recess in the foot surface of the shoe created with a router used to remove pressure from the dorsal aspect of the foot.

Fig 6: A wooden shoe with the thinner section of plywood cut in the shape of a 'W' to distribute the weight under the palmar area of the foot and unload the dorsal toe. A wedge pad has also been cut in the shape of a 'W' and added to the shoe for heel elevation.

Fig 7: a) Schematic illustration of a radiograph with dorsal capsular rotation showing the lines drawn parallel to the solar surface of the distal phalanx and the line drawn parallel to the dorsal surface of the distal phalanx (Illustration courtesy of Andrew Parks, University of Georgia, USA). b) The illustration applied to a radiograph with dorsal capsular rotation. Black line represents the widest part of the foot.

Radiology

The lateral radiograph has always been considered the 'gold' standard for evaluating chronic laminitis but it does not allow identification of asymmetrical medial or lateral distal displacement (O'Grady et al. 2007a; Parks and O'Grady 2008). Therefore, the authors consider it crucial that a dorsopalmar (0° dorso palmar) radiographic projection must be included as part of the radiographic study for either acute or chronic laminitis. This allows the examiner to evaluate the distal phalanx in both a dorsalpalmar plane and a medial-lateral plane. High quality radiographs are required to visualise the osseous structures within the hoof capsule as well as the hoof capsule itself. Radiopaque markers can be used to determine the position of the distal phalanx in relation to surface landmarks.

The radiographic features of chronic laminitis are well documented (Redden 2003). The following observations from the lateral radiograph are important in assessing the severity, determining the prognosis and guiding treatment: the thickness of the dorsal hoof wall; the degree of dorsal capsular rotation; the angle of the solar surface of the distal phalanx relative to the ground; the distance between the dorsal limit of the solar margin of the distal phalanx and the ground; and the thickness of the sole.

The dorsopalmar radiograph is examined to determine the position of the distal phalanx in the frontal plane. Asymmetrical distal displacement of the distal phalanx on either the lateral or medial side is present if an imaginary line drawn across the articular surface of the distal interphalangeal joint or between the solar foramina of the distal phalanx is not parallel to the ground, the joint space is widened on the affected side and narrowed or compressed on the opposite side, and the width of the hoof wall appears thicker than normal on the affected side. If the position of the coronary band is visible on the radiograph, then the distance between the coronary band and the palmar processes of the distal phalanx will be greater on the affected than the unaffected side (Fig 2). The aetiology, diagnosis and management of asymmetrical distal displacement of the distal phalanx will be considered in a subsequent paper.

Goals of treatment for chronic laminitis

Trimming and shoeing has always been the 'mainstay' of treating chronic laminitis and is directed towards reducing/removing the adverse forces on the compromised lamellae. In considering hoof care in horses with chronic laminitis, there are 3 goals for therapy: to stabilise the distal phalanx within the hoof capsule; to control pain; and to encourage new hoof growth to assume the most normal relationship with the distal phalanx as possible. Realignment of the distal phalanx to create a better relationship of the solar surface of the distal phalanx with the ground is used as the basis for treating chronic laminitis (Redden 1997; Parks 2003; O'Grady 2006). Applying the wooden shoe following this procedure compliments the realignment of the distal phalanx and appears to decrease the forces on the lamellae due to the bevelled perimeter of the shoe. The same shoeing principles are applied to the wooden shoes that are applied to other shoeing methods used in treating chronic laminitis which are to recruit ground surface, reposition the breakover palmarly and to provide heel elevation as needed (Parks 2003; O'Grady 2006).

Construction of the shoe

The authors chose wood due to its accessibility, light weight, the ease with which it can be constructed and shaped (both before and after application) and its ability to dissipate energy at impact while remaining rigid (Reid 1994; Steward 2003; O'Grady et al. 2007a). The wooden shoe can be constructed in 2 ways. A wide web aluminium shoe with a broad toe that is available in sizes 00 to 5 is used as a template¹. The basic shoe can be made from 2 pieces of plywood. One piece of plywood is 0.64– 0.95 cm thick and the second piece is 1.91 cm thick. Using the aluminium shoe as a template, the thinner piece of plywood is cut out with a vertical border while the thicker piece is cut out with the border bevelled at a 45° angle using an angle saw². As a modification to the basic pattern, the palmar or heel section of the wooden shoe can be cut at a 15, 30 or 45° angle or left straight if desired. The 2 pieces of plywood are glued together with the thinner portion proximal and two 2.54 cm drywall screws or wood screws are used to secure the 2 pieces together. A wood rasp or belt sander is used to blend the cut angles into a uniform slope (Figs 3a,b). Alternatively, the shoe can also be fabricated from a single piece of 2.86 cm plywood (purchased as sub-flooring plywood) using the same technique as described above.

Recently, one author (M.L.S.) has occasionally substituted ethyl vinyl acetate (EVA) for the thicker 1.91 cm section of plywood and bevelled it in a similar manner. EVA is an extremely elastic material that can be sintered to form a porous material similar to rubber, yet with excellent toughness. The compressibility and wearability of this material allows 'selective' loading on the ground surface of the shoe which appears to further decrease the stresses on the lamellae and increase comfort (Fig 4). Additional layers of plywood, rubber or EVA can be added to increase the height of the wooden shoe when desired. Shoe height is dictated by the conformation of the hoof and the amount of displacement of the distal phalanx present; i.e. the greater the rotation of the distal phalanx, the more shoe height is necessary in order to achieve a more palmar placement of breakover. If the sole is prolapsed or the distal phalanx has penetrated the sole, a recess can be created in the dorsal surface of the shoe by cutting a half moon shape in the thinner piece of plywood using a router under the prolapsed tissue or a hand grinder can be used to create a trough in the shoe below the area of the sole or bone that has prolapsed (Fig 5).

The same end can be achieved by cutting the thinner piece of plywood or a leather pad in the shape of a 'W' and then attaching it to the thicker section of plywood as described above (Fig 6). If heel elevation is required, the heels can be raised accordingly by applying a wedge pad to the hoof surface of the wooden shoe. The angle of the wedge is usually 2–4° depending on the amount of heel horn removed. The wedge pad is attached to the shoe with 2.54 cm drywall screws or wood screws. An alternative method to raise the heels is to cut the ground surface of the wooden shoe itself at an angle to the hoof surface.

Application of the shoe

A generalised outline will be used to describe the preparation of the foot and application of the wooden shoe in horses with dorsal capsular rotation; bear in mind each case of chronic laminitis must be treated on an individual basis. The foot must be trimmed appropriately, and the shoe sized and positioned in relation to the underlying distal phalanx regardless of the conformation of the hoof. Therefore, measurements must be made from a lateral radiograph taken prior to shoeing as a guide. To use the radiograph for guidance, a vertical line is drawn from the center of rotation of the distal end of the second phalanx to the ground. This line should correspond to the widest part of the foot and can be used as a landmark on the foot to begin the trim. Next a line is drawn parallel to the solar border of the distal phalanx, starting 15 mm distal to the palmar process of the distal phalanx and continuing dorsally. The hoof wall to be removed in the heel area can be determined from the mass below this line. A second line is drawn 15 mm dorsal and parallel to the dorsal surface of the distal phalanx; this line is used to align the dorsal hoof wall with the parietal surface of the distal phalanx (Fig 7a,b) (Parks 2003; Parks and O'Grady 2003; O'Grady 2006).

The trim

The initial step is to trim the heels and quarters of the wall as well as the angle of the sole to coincide with the first line drawn on the radiograph. Any exfoliating horn is removed from the frog and the bars are trimmed on an angle to widen the sulci. If possible, the ideal end product is to have the hoof wall at the heels and the frog trimmed so that they are on the same plane. This alone increases the ground surface in the heel area and thus the ability to accept load. If the foot can be trimmed to coincide with the line drawn parallel to the solar surface of the distal phalanx, the palmar aspect of the ground surface of the foot will be on a different plane to the dorsal aspect of the ground surface, which will often unload the dorsal section of the foot. The dorsal hoof wall is trimmed to approximate the line drawn parallel to the parietal surface of the distal phalanx to create a more acceptable alignment between the dorsal hoof wall and the parietal surface of the distal phalanx.

Following the trim, the foot is placed on the ground and the horse is observed for any additional discomfort. Additionally, the horse is observed to see whether the heel of the foot is touching the ground at rest, and whether the horse lands markedly toe first as it moves in a straight line. If any of these signs are present, heel elevation will be necessary to compensate for the increase in tension in the deep digital flexor tendon caused by lowering the heels of the hoof capsule. Heel elevation is generally used if a flexural deformity involving the distal interphalangeal joint described as phalangeal rotation is noted radiographically (O'Grady et al. 2007b). (Capsular rotation describes the divergence of the dorsal hoof wall from the dorsal parietal surface of the distal phalanx independent of the relationship of the distal phalanx with the phalangeal axis whereas phalangeal rotation describes rotation of the dorsal surface of the distal phalanx palmarly/plantarly from its normal orientation and relationship with the first and second phalanges.) The trim should never violate normal farrier practices, such as invading sensitive tissue.

Fitting the shoe

A line is drawn across the widest part of the trimmed foot. Next, the foot surface of a wooden shoe is measured from dorsal to palmar and then a line is drawn across the middle of the shoe from lateral to medial. The correct size of the shoe is determined by superimposing the line drawn across the foot and the line drawn on the shoe on top of each other; the appropriate size shoe will extend from the line drawn across the foot to the end of the heel or 0–8 mm palmar to the heel. Using a 1.98 mm drill, a guide hole is drilled through the lateral and medial side of the hoof wall at the widest part of the foot and 3.75 cm drywall screws or wood screws are placed in each hole and screwed in until just visible on the ground surface. To recruit the sole, bars, frog and sulci for weightbearing, deformable impression material³ is applied to the palmar/plantar section of the foot of the foot.

Fig 8: Wooden shoe being further secured to the foot using screws as struts and 5 cm fibreglass casting tape.

The shoe is now set in place on the ground surface of the foot and attached using the 2 dry wall screws or wood screws. The foot is placed on the ground and allowed to bear weight in order for the impression material to conform between the palmar section of the foot and the shoe in the optimal form. Two or 3 more holes are drilled through both sides of the hoof wall and the shoe is secured in place using additional screws. These holes may be predrilled from the solar surface of the foot if desired to ensure accurate screw placement in the wall. If the mass of the hoof wall is insufficient or if the quality of the hoof wall is insufficient to hold the screws, screws can be placed in the wooden shoe against the outer surface of the hoof wall to act as struts and 5 cm casting tape⁴ is used to form an attachment between the hoof wall, screws and wooden shoe (Fig 8). With the foot on the ground, a vertical line is drawn from the dorsal aspect of the coronary band to the ground. The point where the line meets the ground is where the breakover point of the shoe should be positioned (Figs 9a,b,c). This point will usually be just dorsal to the dorsal limit of the solar margin of the distal phalanx. Setting the breakover to this point in the shoe is easily accomplished using a hoof rasp with the foot being held in the farrier position. Deep digital tenotomy has been the recommended treatment when penetration of the distal phalanx through the sole has occurred secondary to dorsal capsular rotation. One author (S.E.O.) has observed that the wooden shoe has provided an alternative and often better means to treat this condition without surgery.

Fig 9: a) Application of a wooden shoe with impression material. Black line is the widest part of the foot. Red line denotes the point of breakover on the ground surface of the shoe. b) A wooden shoe fabricated from a single piece of plywood with the same guidelines as shown in (a). c) Radiograph of foot following the application of a wooden shoe. Again, note that the black line is the widest part of the foot; the red line denotes the point of breakover on the ground surface of the shoe.

Prolapse of the sole or penetration of the distal phalanx

If the sole bulges distal to the level of the hoof wall or if the distal phalanx has penetrated the sole, the foot is trimmed to establish realignment, the wooden shoe is fitted to the trimmed foot and heel elevation is applied to the shoe to decrease the forces on the deep digital flexor tendon (Redden 1997). Before applying the shoe, the wooden shoe is placed against the solar surface of the foot and pressed against the sole or the exposed corium of the distal phalanx. The moisture of the tissue or a suitable dye applied to the corium will create an impression on the foot surface of the wooden shoe which can then be cut out using a router or a trough can be created with a grinder as illustrated in Figure 5. The shoe is now applied with screws and fibreglass tape, being sure that the impression material is concentrated palmar to the apex of the frog and not allowed to migrate dorsally. A window can be created in the fibreglass tape and the affected area can be packed with an appropriate antiseptic from the front of the shoe.

Conclusions

The authors have used the wooden shoe in their combined practices for the past 5 years and found this technique provides another very consistent farriery option when treating a horse with chronic laminitis. Removing the stress on the lamellae has always been difficult with traditional shoes used to treat chronic laminitis as the shoe is placed under the hoof wall concentrating the load on the compromised lamellae. The solid plane of the wooden shoe, combined with the impression material allows load sharing across the ground surface of the foot especially in the palmar section of the foot and appears to decrease the load borne by the hoof wall. This concept of load sharing is very helpful in horses with foot conformation that has limited hoof mass in the palmar section of the foot. Furthermore, cutting the perimeter of the wooden shoe at a 45° angle around the circumference of the foot is thought to decrease the lateral/medial torque on the lamellae especially when the horse turns (Steward 2003; O'Grady et al. 2007a). Therapeutic shoes used for treating chronic laminitis are often deficient in providing sufficient breakover and heel elevation due to the physical limits of the particular shoe whereas increasing the height of the wooden shoe allows the desired mechanics to be fabricated into the shoe. Shoe height enhances mechanical advantages as it allows dorsal breakover, lateral medial breakover and heel elevation to be incorporated into the shoe in a uniform manner. Creating a recess in the shoe under the distal phalanx in the toe area relieves the load on dorsal aspect of the foot while the weightbearing function is concentrated in the palmar section of the shoe. When displacement of the distal phalanx within the hoof capsule is severe, the wooden shoe seems to be an excellent method to act as a transient treatment to build sufficient hoof mass (wall and sole) to where a more conventional shoe can be applied or the horse can remain barefoot. It should be noted that the heel elevation provided by the wooden shoe should not be discontinued abruptly when this farriery method is changed but rather decrease the heel elevation gradually over the next few months.

Manufacturers' addresses

1. EDSS Inc, Penrose, Colorado, USA.
2. Sears, Roebuck and Co., Hoffman Estates, Illinois, USA.
3. Equilox International, Pine Island, Minnesota, USA.
4. 3M Animal Care Products, St Paul, Minnesota, USA.

References

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