How to Construct and Apply the Wooden Shoe for Treating Three Manifestations of Chronic Laminitis
Reprinted with permission from the American Association of Equine Practitioners.
|Fig. 1. Radiograph of asymmetrical downward displacement of the distal phalanx on the medial side. Note that the line drawn through the solar foramens is not parallel with the ground. Also note the disparity in the joint space from the lateral to the medial side.|
|Fig. 2. 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.|
The dorsopalmar radiograph is examined to determinethe position of the distal phalanx in the frontalplane. Asymmetrical distal displacement of thedistal phalanx on either the lateral or medial side ispresent if an imaginary line drawn across the articularsurface of the distal interphalangeal joint orbetween the solar foramens of the distal phalanx isnot parallel to the ground, if the joint space is widenedon the affected side and narrowed on the oppositeside, or if the width of the hoof wall appearsthicker than normal on the affected side. If theposition of the coronary band is visible on the radiograph,then the distance between the coronary bandand the palmar processes of the distal phalanx willbe greater on the affected than the unaffected side(Fig. 1).
3. Materials and Methods
Construction of the Shoe
The authors chose wood because its light weight, theease with which it can be shaped (both before andafter application), and its ability to dissipate energyat impact while remaining rigid.4 The basic shoe ismade from two pieces of plywood. An aluminumshoe with a broad toe that is available in sizes 00-5is used as a template.a One piece of plywood is0.250-0.375 in thick, and the second piece is 0.75 inthick. Using the aluminum shoe as a template, thethinner piece of plywood is cut out with a verticalborder, and the thicker piece is cut out with a borderbeveled at a 45° angle using an angle saw.b As amodification to the basic pattern, the palmar or heelsection of the wooden shoe can be cut at a 15°, 30°, or45° angle or left straight, if desired. The pieces ofplywood are glued together; the thinner portion isproximal, and two 1-in drywall screws are used tosecure the two pieces together. A wood rasp is usedto blend the cut angles into a uniform slope (Fig. 2).
|Fig. 3. Wooden shoe fabricated from a single piece of plywood. |
Note the recess in the foot surface of the shoe created with a router.
|Fig. 4. Proximal section of plywood cut in the shape of a "W." Note the 3° wedge to elevate the heels.|
The shoe can also be fabricated from a single pieceof 1.125-in plywood (purchased as subflooring plywood).If the sole or distal phalanx is prolapsed, arecess can be created in the proximal surface of theshoe by cutting a half-moon shape dorsal to a linethat is one-third the length of the shoe in the thinnerpiece of plywood with a router. A hand grinder canbe also used to create a trough in the shoe below thearea of the sole or bone that has prolapsed (Fig. 3).
The same end can be achieved by cutting the thinnerpiece in the shape of a "W" and then attaching itto the thicker section of plywood as described above(Fig. 4).
Goals of Treatment for Chronic Laminitis
Trimming and shoeing has always been the "mainstay"of treating chronic laminitis, and it is directedat reducing/removing the adverse forces on the compromisedlamellae. In considering hoof care inhorses with chronic laminitis, there are three goalsfor therapy: to stabilize the distal phalanx withinthe hoof capsule, to control pain, and to encouragenew hoof growth to assume the most normal relationshipto the distal phalanx possible. Realignmentof the third phalanx to create a betterrelationship of the solar surface of the distal phalanxwith the ground is used as the basis for treatingchronic laminitis.5-7 Applying the wooden shoe afterthis procedure compliments the realignment ofthe distal phalanx and further decreases the forceson the lamellae. The same shoeing principles forother methods are applied to the wooden shoes thatare used to treat chronic laminitis. They are torecruit ground surface, to reposition the breakoverpalmarly, and to provide heel elevation as needed.5
|Fig. 5. Lateral radiograph showing dorsal capsular rotation. |
Note the lack of hoof-wall growth at the coronet at the toe. The red arrow denotes the center of articulation. The black line shows the amount of heel to be removed.
Dorsal Capsular Rotation
Dorsal capsular rotation describes the divergence ofthe dorsal hoof wall from the dorsal parietal surfaceof the distal phalanx independent of the relationshipof the distal phalanx with the phalangeal axis.8A generalized outline will be used to describe thepreparation of the foot and application of the woodenshoe for this type of displacement; it must be notedthat each case of chronic laminitis must be treatedon an individual basis. The foot must be trimmed,and the shoe must be sized and positioned in relationto the underlying distal phalanx, regardless ofthe conformation of the hoof. Therefore, measurementsmust be made from radiographs taken beforeshoeing. Using the radiograph for guidance, a verticalline is drawn from the center of the distal endof the second phalanx to the ground. This lineshould correspond to the widest part of the foot.A line is then drawn parallel to the solar border ofthe distal phalanx starting 15 mm below the palmarprocess of the distal phalanx and continuing dorsally.The hoof wall to be removed in the heel areacan be determined from the mass below this line(Fig. 5).5-7
A line is drawn across the widest part of the footand the hoof wall; the area palmar to this line istrimmed according to the lines drawn on the radiograph.If, as is frequently the case, the wall andsole dorsal to the line drawn across the sole is <15mm, trimming in this manner will create two differentplanes on the ground surface of the foot. A lineis also drawn across the center of the wooden shoe(Fig. 6).
|Fig. 6. Using the widest part of the foot as a guideline (red line), the heels are trimmed in a palmar direction. The red line drawn in the middle of the wooden shoe is used to determine the proper size wooden shoe to use.|
The correct size of the shoe is determined by placingthe lines on the foot and the shoe on top of eachother; the appropriate size shoe will extend from theline drawn across the foot to the end of the heel or 6-8mm palmar to the heel. To compensate for theincrease in tension in the deep digital flexor tendonthat is caused by lowering the heels of the hoofcapsule, the heels can be raised by applying a wedge pad to the hoof surface of the wooden shoe. Theangle of the wedge is usually 2-4°, depending on theamount of heel horn removed. The wedge pad isattached to the shoe with 1-in drywall screws.Using a 0.078-in drill, a guide hole is drilled throughthe lateral and medial side of the hoof wall at thewidest part of the foot, and a 1.5-in drywall screw isplaced in each hole and screwed in until just visibleon the ground surface of the foot. To better increaseweight bearing by the sole, bars, frog, andsulci, a deformable impression materialc is appliedto the solar surface of the foot. The shoe is nowplaced on the ground surface of the foot and attachedusing 2-in drywall screws. The foot is placed on theground and allowed to bear weight; this allows theimpression material to set between the foot and theshoe in the optimal form. Two to three more holes are drilled through both sides of the hoof wall, andthe shoe is secured in place using additional screws.If the mass of the hoof wall is insufficient or if thequality of the hoof wall is insufficient to hold thescrews, screws can be placed in the wooden shoeagainst the available hoof wall to act as struts, andan acrylic composited is used to form a bond betweenthe hoof wall, screws, and wooden shoe. With thefoot on the ground, a vertical line is drawn from thedorsal coronet to the ground. The point where theline meets the ground is where the breakover pointof the shoe should be positioned (Fig. 7).
|Fig. 7. (A) A wooden shoe with impression material and a wedge pad to provide heel elevation. The black arrow is the widest part of the foot. The 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 A.|
This point will usually be just dorsal to the marginof the distal phalanx. Setting the breakover to thispoint in the shoe is easily accomplished using a hoofrasp with the foot being held in the farrier position.Deep digital tenotomy has been the recommended treatment when prolapse of the distal phalanx hasoccurred secondary to dorsal capsular rotation.One author (SEO) has observed that the woodenshoe has provided an alternative and often bettermeans to treat this condition without surgery.
|Fig. 8. Left forelimb with distal phalanx offset toward the medial side.|
|Fig. 9. Diagrammatic illustration of the method used to move the forces toward the unaffected side.|
Medial or Lateral Asymmetrical Displacement of the Distal Phalanx
In displacing asymmetrically, the distal phalanx rotatesin the frontal plane within the hoof capsuleand moves away from the hoof wall on the affectedside. The reason that some horses displace asymmetricallyis not completely understood. Clinicalobservations by two of the authors (SEO and AHP)suggest that asymmetrical displacement is usuallytoward the medial side, and the distal phalanxwithin the hoof capsule is usually offset toward theaffected side (Fig. 8).
Occasionally, these two authors have observeddistal displacement laterally in instances where thehorse developed laminitis in one foot after prolongedweight bearing subsequent to severe lameness in thecontralateral limb. Aside from general trimming ofthe foot, removal of hoof wall at the heels may not benecessary. The sizing of the shoe and the applicationof impression material will be the same as describedfor dorsal capsular rotation. The crucialdifference between treating medial or lateral asymmetrical displacement compared with dorsal capsulardisplacement is the mediolateral positioning ofthe shoe. Based on the apparent asymmetry of thedistal phalanx within the hoof capsule visible onradiographs, a clinician's first response might intuitivelybe to try and restore the asymmetry of thedistal interphalangeal joint and the position of thedistal phalanx in relation to the ground. Thiswould most readily be accomplished by raising theside of the hoof on which the distal phalanx is displaced.However, this will increase the weightbearing on the affected side and cause the distalphalanx to displace further in relation to the hoofcapsule, which will increase the pain. Therefore,the appropriate technique is to decrease weightbearing by the affected wall, which is accomplishedby sharing weight bearing with the sole and frog andincreasing weight bearing with the unaffected wall.This can be achieved by placing an extension on theunaffected side (Fig. 9).
Because of its flat solid surface, the wooden shoecombined with impression material seems to loadthose structures away from the affected side. Thewidth of the hoof wall on the affected side is reducedusing a rasp on the outer surface. The wooden shoeis then fitted so that the edge of the shoe is even withor just under the hoof wall on the affected side, andthe shoe forms an extension of ~0.25-in beyond thehoof wall on the unaffected side (Fig. 10).
If insufficient hoof wall is present on the affectedside to accommodate screws, screws can be placedinto the wooden shoe on an angle so that they lieagainst the hoof wall. They should be bonded withan acrylic composite.
|Fig. 10. (A) Wooden shoe fitted with an extension on the lateral side. Note the screws that are inserted as struts to attach the shoe to the hoof wall with acrylic. (B) Wooden shoe with extension being attached to foot with screws.|
Prolapse of the Sole or Distal Phalanx
For prolapse of the distal phalanx, the foot istrimmed to establish realignment, and heel elevationis applied to the shoe to decrease the forces onthe deep digital flexor tendon. Before applying theshoe, the wooden shoe is placed against the groundsurface of the foot and pressed against the exposedcorium of the distal phalanx. The moisture of thetissue or a suitable dye applied to the corium willcreate an impression on the foot surface of thewooden shoe. A router can be used to cut out theimpression, or a trough can be created with agrinder. The shoe is now applied, making sure thatthe impression material is concentrated palmar tothe apex of the frog. The affected area can bepacked with an appropriate antiseptic from the frontof the shoe.
Success of any given treatment for chronic laminitisis hard to evaluate because of the individual diversitybetween each case. In reviewing the records onhorses with the three types of displacement describedin this paper, the authors established basicguidelines to evaluate the response after applicationof the wooden shoe. All evaluations were for a periodof 8 wk post-application of the wooden shoe.All three types of displacement were evaluated for adecrease in the level of pain. To better evaluate thewooden shoe for dorsal capsular rotation, the authorschose cases that had been treated previouslywith other methods of farriery with minimal response.Increased hoof-wall growth at the coronetat the toe and an increase in sole depth were used onhorses where the wooden shoe was applied for dorsalcapsular rotation. Increased hoof-wall growth atthe coronet on the affected side of the foot was usedfor horses with unilateral displacement. Finally,cornification of the exposed corium of the distal phalanxas well as hoof-wall growth was used on thosecases where the distal phalanx had penetratedthrough the sole.
|Type of Displacement||Number of Cases||Favorable Response||%|
|Dorsal capsular rotation||21||17||81|
|Penetration of distal phalanx through the sole||9||7||77|
There were 21 cases of dorsal capsular rotation,and 17 (81%) had a favorable response to woodenshoes. There were 11 cases of asymmetrical displacement,and 8 (65%) had a favorable response towooden shoes. There were 9 cases of penetrationof distal phalanx through the sole, and 7 (77%) hada favorable response to wooden shoes.
The wooden shoe provides another very consistentfarriery option when treating a horse with chroniclaminitis. Removing the stresses on the lamellaehas always been difficult when using traditionalshoes to treat chronic laminitis. Traditional shoesare placed under the hoof wall, which concentratesthe load on the compromised lamellae. The planeof the wooden shoe combined with the impressionmaterial allows the foot to become load sharing,because the load is shared by the hoof wall and thesoft-tissue structures of the foot. Furthermore, cuttingthe perimeter of the wooden shoe at a 45° anglearound the circumference of the foot is thought todecrease the torque on the lamellae.6 Creating arecess in the shoe under the distal phalanx in the toearea relieves the load on the bone, and then, theweight-bearing function is concentrated in the palmarsection of the shoe. When displacement of thedistal phalanx within the hoof capsule is severe, thewooden shoe can be used as a transient treatment tobuild sufficient hoof mass for the application of amore conventional shoe.
References and Footnotes