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Bio mechanics For Farriers Part 2

by | May 16, 2022 | 0 comments

Angular kinetics
Angular kinetics investigates the causes of angular motion, or rotation. The turning effect of a force applied to a body is called torque. Torque is produced when a force is applied to a body at some distance from an axis of rotation (figure 8).

To describe movement, bio mechanists use a spatial reference system. All three dimensional structures, such as a horses foot, have three axis each of which has two coordinates. The three axes intersect at right angles to each other at the body or body segments centre of mass or balance point (CoP).The origin is at the intersection of the horizontal, mediolateral and vertical axes and is designated as zero (0) (figure?).

Looking for the Hypotenuse
Some basic principles from geometry such as Pythagoras’s theory are very important in biomechanics. The right-angle triangle) is a useful figure when working problems in biomechanics, because the relationships among the lengths of the sides of the right triangle. This relates to how farriers provide a toolbox for not only working with vectors such as the optimum length of shoe. The side across from the 90-degree angle in a right triangle is called the hypotenuse. The hypotenuse is always the longest side of the triangle. In all triangles, the sum of the three angles is 180 degrees. Because one angle in a right triangle is 90 degrees, the sum of the other two angles is obviously 90 degrees. Each of these two other angles is less than 90 degrees; angles less than 90 degrees are called acute angles (figure 8).

Figure 8. in a right angled triangle one of the acute angles is set as the reference angle; it’s indicated with θ (the Greek letter theta). The reference angle is used to give names to the other two sides of the right triangle. The side across from θ is called the opposite (O) side. The side meeting with the hypotenuse to create θ is called the adjacent (A) side — it’s adjacent to the reference angle (θ).

Using Trigonometry
Trigonometry is the field of mathematics describing the relationship between the sides and angles of triangles. Just as Pythagoras’s theory allows you to calculate the optimum length of a shoe for example, the trigonometric functions allow you to calculate the length, and any necessary elevations required, of the sides of a right triangle if the length of one side and the measure of one acute angle are known. One of example of this is in calculating the size of elevation and the length of the hypotenuse (shoe) to achieve an effective right angled triangle for feet exhibiting collapsed weak heels.

The trig functions specify the ratios between two sides of the right triangle. A ratio is the relationship between two measurable quantities. Many farriers might be familiar with the so called “Golden Ratio” (1.618), which is often cited in articles on the subject of foot balance, made famous by Leonardo da Vinci’s “Vitruvian Man” in 1490. An example of the use of maths in understanding farriery theory was demonstrated in a recent study on foot geometry by Balchin (2012). The study suggested that geometric proportions may be present within the sample of feet in the tested. 19 off 25 feet examined revealed the right angle triangle had edge lengths in the geometric progression known to form “Kepler’s Triangle”, which has its roots based in the theorem of Pythagoras and the Golden Ratio, it was interesting to note that the centre of the triangle was located at the point where the Deep Digital Flexor Tendon inserts into the semi lunar crest on the solar surface of the Distal Phalanx, and equally as interesting is the fact that once the triangle and ratio are in position then another Golden ratio and Kepler’s Triangle are formed. The smaller triangle and ratio are clearly visible in figure? And It would appear that the centre of this triangle represents the centre of mass within the foot segment (figure 9).

Figure 9 below Shows the Tangent of the right angle triangle is from the hairline of the coronary band and the Sine is at the bearing border of the toe. This means that the Cosine will be situated at or within millimetres of the last weight bearing point of the heel. The Hypotenuse is then formed by the bearing border of the foot with the Opposite being formed by the Dorsal wall whilst the Adjacent was formed by the line from the Tangent to the Cosine or the hairline at the Coronary band to the last weight bearing point of the heel.

Figur 9. Balchin (2012) suggested that geometric proportions may be present within the sample of feet in the tested. 19 off 25 feet examined revealed the right angle triangle had edge lengths in the geometric progression known to form “Kepler’s Triangle”, which has its roots based in the theorem of Pythagoras and the Golden Ratio, it was interesting to note that the centre of the triangle was located at the point where the Deep Digital Flexor Tendon inserts into the semi lunar crest on the solar surface of the Distal Phalanx, and equally as interesting is the fact that once the triangle and ratio are in position then another Golden ratio and Kepler’s Triangle are formed. The smaller triangle and ratio are clearly visible in the figure And It would appear that the centre of this triangle represents the centre of mass within the foot segment.

Vector Quantities
In biomechanics, two types of quantities are important:

Scalars: A scalar is any quantity that can be fully described by its magnitude, size, or amount for example time, mass, distance, and speed (figure 10). A scalar quantity is fully described the specific number of units used to measure it — for example, time = 8 seconds (or s), mass = 75 kg, distance = 2 m, or speed = 20 m/s.

Vectors: A vector is described not just by its magnitude but also by a direction associated with the quantity (figure 11). Vector quantities include force, displacement, velocity, and acceleration and are only fully described if both magnitude and direction are specified — for example, force = 20 Newtons (N) to the right. For example; displacement = 5 m at an angle of 40 degrees to the horizontal, velocity = 5 m/s at an angle of 20 degrees to the horizontal, or acceleration = 10 m/s/s downward. A vector quantity is graphically represented by an arrow called, simply, a vector. A vector is drawn so the magnitude of the quantity is represented by the length of the arrow, and the direction of the quantity is represented by the tip, or arrowhead.

Vector resolution: Vectors can be resolved into components, typically a horizontal component and a vertical component (often called the x and y components) acting at 90 degrees to each other. This process applies the trigonometric functions, described earlier, of the sine, cosine, and tangent. Vector composition allows for the combination of two separate vectors into a single resultant vector. A resultant represents the combined effect of the two vectors (figure 11).

figure 10 A scalar quantity is fully described the specific number of units used to measure it
Figure 11 illustrates the 3-dimensional ground reaction force (GRFv) vector which is often resolved into 3 mutually perpendicular components acting in the vertical (GRF vertical), longitudinal (GRF horizontal or long), and transverse (GRF transverse) directions.
  1. Kinematics: the Science of Movement.

Kinematics isn’t concerned with the forces that cause the movement but is the branch of mechanics that describes motion including any change in position of a body over a period of time. Kinematics describes the spatial (movement through space) and temporal (timing) aspects of movement; it. The kinematic description of movement is the details of what is seen studying performance. The basic spatial measures in kinematics include where, how far, how fast, and whether the body is speeding up or slowing down. The timing measures include when, how long, and the sequencing of the component parts of the movement, including the sequential joint actions.

All movement can be classified as either linear or angular:

Linear motion: Linear motion occurs when all parts of a body or segment experience the same change in position during the same period of time. There are two types of linear motion.
I. Rectilinear motion is motion in a straight line. All points on the body move exactly the same, and the orientation of the body does not change.
II. Curvilinear motion is motion along a curved path. The body is moving simultaneously in two (or three) different planes. For example, when the foot is in the swing phase of the stride it follows a curvilinear path through the air. It moves up and then down at the same time that it moves away from you. This simultaneous movement in two different directions creates what is termed a parabolic path. The foot and limb can also be moving sideways along with the up–down and a forward path through the air but it still follows a parabolic path.

 Angular motion: Angular motion is the formal name for rotation — twists, spins, and turns. Rotation occurs when all points on the body go through the same angle. A point farther from the axis of rotation travels through the same angle as a point closer to the axis of rotation, but the curvilinear path travelled by a point farther from the axis of rotation is longer than the curvilinear path travelled by a point closer to the axis of rotation. The whole body can rotate, and the individual segments of the body rotate at the joints.

  •  General motion — a combination of angular motion and linear motion and is the most common form of motion. The linear motion of a point on a segment can only undergo linear motion because of a coordinated combination of angular motion at two or more joints. Synchronizing the angular motion of joints is a critical factor for successful performance,
figure 12. The parabolic curve when the foot is in the swing phase of the stride it follows a curvilinear path through the air. It moves up and then down at the same time that it moves away from you. This simultaneous movement in two different directions creates what is termed a parabolic path. The foot and limb can also be moving sideways along with the up–down and a forward path through the air but it still follows a parabolic path.

Describing how far: Distance and displacement

The terms distance and displacement are often used interchangeably in everyday conversation. Both terms describe how far a body moves. However, they have specific, and different, definitions in mechanics. Distance and displacement are measured in both linear and angular kinematics.

Distance
Distance is a scaler that simply describes how far the body moved during a time interval. Distance includes all the movement of the body from the start to the end of the motion, regardless of whether the body changes direction while traveling. Linear distance is defined as the length of the total travelled by a body, and it is measured in meters (m). How far the body moves and how long it takes to move affect the calculation of how fast. How fast a body moves depends on whether how far is measured as a distance or as a displacement.
Angular distance is equal to the entire length of the angle travelled between the first and the final angular positions and is measured in degrees (°). Angles are sometimes measured in radian (1 radian = 57.3 degrees).

Speed simply describes how fast the body moved when it travelled the measured distance. You calculate speed by dividing the length of the path travelled by the length of time. In other words, speed = distance/time .

Figure 13. Velocity
Velocity is a vector and describes how fast a body moved when it underwent a specific displacement. Velocity is calculated by dividing displacement by the length of time (figure?). Linear velocity is calculated as linear displacement divided by time and angular velocity is calculated as angular displacement divided by time. In describing either linear velocity or angular velocity, the direction of the body’s motion is also specified.

Pushing and Pulling into Kinetics

Kinetics is the branch of mechanics focused on the forces acting on a body. A force is a push or a pull created by the interaction of two bodies. Force is a vector quantity, and it’s described by the characteristics of magnitude (the size of the force) and the direction of the force. Two other important characteristics of a force are its point of application (where on the body the force is applied) and its line of action (an imaginary extension of the force vector in both directions, used to determine the torque, or turning effect, of the force). A familiar concept is seen in the shoe making process (figure 14) where both the magnitude of and the direction of the force are essential components of the process. Two other important characteristics of a force are its point of application (where on the material the force is applied) and its line of action (an imaginary extension of the force vector in both directions, used to determine the torque, or turning effect, of the force).

figure 14 A familiar concept is seen in the shoe making process where both the magnitude of and the direction of the force are essential components of the process

Inertia refers to a body’s resistance to changing its motion. Essentially, inertia means that when a body is at rest, it wants to stay at rest, and when a body is moving, it wants to continue to move at the same speed and in the same direction (the body tends to maintain its velocity). A good way to think of this is that when a limb is bearing a loading force another unopposed force, say muscular tension, must be acting on it. Inertia comes from the body’s mass is measured and reported as a single value of weight without considering each individual element within it.

The pushes and pulls on a body — the forces — are classified as either internal or external:
 Internal force: A force produced within the body. An internal force doesn’t affect the motion of the body — an internal force does not cause an acceleration of the whole body. An internal force pushes or pulls on the parts within the body, causing a deformation of the material called strain, depending on the magnitude of the stress produced. (Stress is a measure of how the applied force is distributed over the internal structure of the body). When looking at the body as a whole, the pulling force of stay apparatus is an internal force (figure 15).
 External force: A force applied to a body by something outside the body. External force acting on a body wants to change the motion of the body, to cause it to speed up or slow down (in other words, an external force wants to accelerate the body). We move around the environment because of the external forces that act on our bodies. We use our muscles to pull on our segments to produce external forces on our bodies.

External forces fall into two categories:

Non-contact force: A non-contact force occurs when the two bodies are not in contact with each other. The most common external force in biomechanics is weight. The weight of a body is caused by the pulling force of gravity. The weight of a body is calculated as the mass of the body multiplied by the acceleration of gravity, or W = mg, where
W is weight, m is the mass of the body (in kilograms), and g is the gravitational acceleration of –9.81 m/s/s. It’s important to remember that weight is a downward force. Because gravity pulls down on the body, weight always acts downward in the vertical direction. If the limb is moving in an upward direction the downward force of gravity acts to slow it down. When the limb is moving downward, weight acts to speed it up.

Contact force: A contact force occurs when two bodies touch. The force is created by the interaction of the two bodies. Sometimes the effect of the force is obvious, as when the foot impacts with the ground during movement. A contact force is present between the foot and the ground even when the horse is standing upright and not moving. Friction is a contact force present for example when the foot slides on the surface during deceleration; in this case friction always opposes the direction of the sliding. The factors affecting friction include the force squeezing the bodies together (called the normal force) and the materials in contact with each other where the sliding can occur (represented what is termed the coefficient of friction).

Figure 15. The equine stay apparatus is a good example of opposing push / pull Kinetic forces

To be Continued in Part 3.

This paper describes a method of treating cases of unilateral palmar/plantar laminitis using the Steward Clog ®(aka Wooden Shoe). This method varies significantly from a previously advocated technique using the Wooden Shoe. In this paper we report on the use of a different/modified technique to load the unaffected wall in horses with marked unilateral displacement (including sheared heel) of the distal phalanx. Additionally, the EVA/Wood Clog used- represents further development of the shoe as originally described (Steward Clog 2.0®).
Introduction:

The variety of benefits the Steward Clog® (Wooden Shoe) offers the laminitic horse is evident by the widespread usage throughout the horse industry. Ease of application and design modifications allow the shoe to be utilized effectively by practitioner and/or farrier without an expertise in therapeutic shoeing. The application process allows a non-traumatic procedure that relies heavily on the input of the horse in maximizing the horse’s comfort. Lateral and dorsopalmar (DP) radiographs are vital information to aid the proper trim in the therapeutic shoeing procedure.

Unilateral distal displacement can be accompanied by dorsal capsular displacement, in complicated laminitic cases. The damaged lamellae allow overload injury to portions of the wall / bone interface and this can manifest itself in variable displacement of the distal phalanx within the hoof capsule. The mechanical pull of the deep digital flexor tendon, combined with the weight forces produce the most common manifestation of laminitis- dorsal capsular displacement/phalangeal displacement. The pattern of displacement varies with the distribution of damage and load, the exact pathophysiology of which has yet to be determined. Displacement of a particular portion of the third phalanx is usually due to the area of displacement being overloaded and the damaged Suspensory Lamellar Apparatus’ (SLA) inability to support the load. The classic manifestations of laminitis are usually manifested as overload injury of a particular area of the distal phalanx. Depending on the extent of lamellar damage and the particular amount of load to P3, the variable displacement of the third phalanx is indicative of amount of damage and amount of load causing shear forces to the SLA.

Unilateral displacement is usually medial in the front limbs and lateral (author’s opinion) in the hind limbs (see Fig.1) -in typical cases. Conformational imbalanced (valgus) overloading of the medial wall’s damaged lamellae (in the fore limbs- with non-ambulatory perfusion deficits) is thought to be the usual cause of fore limb’s medial displacement (see Fig. 2). The hind limb is (typically) imbalanced overloaded on the lateral aspect of the hoof (because of the single leg resting stance) and this can often be manifested as lateral displacement (if the lamellae have been sufficiently damaged and overloaded). The diagnosis is based on the physical appearance of the foot, asymmetrical pain distribution and radiographs. Dorsopalmar (DP) radiographs are very helpful in revealing the condition. Abscesses and other pathologies causing particular areas of vascular discrepancies can alter the common areas of manifestations of this pathology. Current dynamic Positron Emission Tomography (Florodeoxyglucose) scans (Andrew VanEps, DVM) have shown extensive areas of (ie,-medial) wall that have deficits in vascular perfusion when non-ambulatory- in clinically normal feet. These deficits resolve upon ambulation. This may account for the medial UPD when dorsal phalangeal laminitis occurs, for example. The non-ambulatory lesions become pathological when the patient suffers lamellae damage and the painful condition further diminishes the compromised SLA wall perfusion.

In cases of dorsal phalangeal rotation of the third phalanx, the anterior ½ of the coffin bone distal displaces around the second phalanx’s distal condyles. The caudal ½ of the coffin bone displaces upward (unless a sinker). The lamellae in the heel area are stretched and are receptive to weight load, which would apply forces to aid in realigning the lamellae as the weight forces the bony column (P3) distally and the ground reaction forces (GRF) produce an upward vector force on the frog area of the hoof. When the lamellae are sufficiently damaged and overloaded, shearing of the lamellae occurs and the weight forces (WF) cause the distal migration of the affected portion of P3 (ie. – medial wing). Heel hoof growth can be considered to be enhanced because of the wide growth rings, but most of the enlarged ring is due to lamellar stretching and the pull on the newly formed hoof wall tubules in an unencumbered growing environment just below the dorsally displaced coronet. The horn tubules may be formed at the same rate around the coronet, but the stretching/compression and traffic jam/ fast-lane areas of tubular maturation and development just below the coronet account for wall formation/growth and growth ring conformation / thickness. The dorsoaxially displacing wall helps to shear the SLA as the third phalanx displaces distally. This is a tectonic plate-like biomechanical problem- comparable to an earthquake.

Once the displacement has occurred, a dip (recess) can be palpated in the integument immediately proximal to the wall on the affected side. The ungual cartilage/ wall relationship is displaced. Additionally, the toe and unaffected heel of the hoof capsule displaces dorsoaxially and rotates towards (yaw effect) the separated side (the plastic deformation usually occurs over time). This displacement (distal pitch of P3) and rotation (yaw of the hoof capsule) increase with time as the wall on the affected side shows little or no growth (due to disrupted blood supply in the damaged SLA) and the opposite side shows normal or increased growth. As the third phalanx rotates distally (pitch), the affected hoof wall is plastically displaced dorsoaxially (medial/roll (inversion roll), pitch-distally). This displacement is similar in pathophysiology to cases of “sheared heels” (traumatic/subclinical unilateral palmar laminitis (stretching) with dorsoaxial wall displacement), but the amount of overload shear trauma (and SLA damage) to produce heel (P3 &/or heel wall) displacement in the two cases- is substantially different. Both cases occur as a result of overload (shear or stretching) to the (damaged) lamellar apparatus of the particular area of the hoof. Laminitis cases have an enzymatic damage/weakening of the lamellae that lends itself to failure- if the lamellar damage is sufficient and overload exceeds this overload failure point. Unloading the affected wall is essential to the success of therapeutic intervention in both conditions. In severe cases of unilateral palmar/plantar displacement (UPD), extreme measures usually have to be implemented to have a chance of success. This involves unloading the affected wall by floating (cutting short/unloading) the affected heel, load redistribution, moment arm force reduction- to the affected lamellae, unloading pained areas, and stabilizing P3. The upward displacement of the hoof wall and distal displacing third phalanx create complicated biomechanics for resolution, as the wing of P3 is forced upward (biomechanically) as the coronet and affected wall needs to be displaced distally via plastically deforming biomechanics. The new growth attachments must be plastically deformed or artificially moved back into a more normal relationship- for functional healing to occur.

Previous descriptions¹ of the use of the Clog (wooden shoe) in the treatment of unilateral distal displacement have focused on extending the shoe towards the unaffected side to shift the center of pressure away from the most damaged lamellae, but the author finds this somewhat useful in some chronic, stable pathology, but not relevant in cases of acute laminitis. (See drawing-A.Parks)

The full roller motion design feature, particularly the mediolateral breakover (roll) portion of the Wooden Clog, and the subsequent use of an ethylene vinyl acetate (EVA) pad (similarly designed)- allowed the patients to (immediately) formulate a consistent, comfortable therapeutic formulation that enhanced soundness. This palliative effect, combined with other procedures (ie.- coronary grooving/wall resection) produced the most consistent success rate (curative effect).

Materials and Methods:

Plywood (1.125 inch) is cut and shaped to form the basic Wooden Shoe design. Mediolateral sloping can be increased to allow the patient to easily manipulate foot loading. The longer the slope (D/P) is extended toward the centerline of the shoe, the easier mediolateral (roll) breakover is achieved (see Fig. 3) and the hoof can shift weight to the less painful heel by slightly rolling the shoe- inversion roll for medial UPD and eversion roll for lateral UPD.. The sloping can be extended past the centerline to form a wedge effect to the shoe with the widest portion of the wedge under the affected heel (see Fig. 4).
The addition of EVA (ethylene vinyl acetate) to a layer of plywood (with the perimeter of the EVA cut in the same shape as the basic Wooden Shoe- Steward Clog 2.0®) allows the patient to self-adjust (plastically deform) the EVA and adds the same biomechanics to the shoe (see Fig. 5). Additional concussion absorption is a very beneficial feature- as well as the selective stabilization the elastic, plastic properties the EVA possesses.

Results:

Five horses (Four QH, 1 Arabian, ages 3 – 20 years) with bilateral medial displacement (front feet), 9 cases (8 QH, 1 Paint, ages (2-22 years) with unilateral displacement (seven front and 2 hind feet) have been treated using this technique. Increased comfort and a better radiographic DIP joint alignment were noted when modifications were made.
Successful outcome depended on the amount of lamellar damage and the amount of vascular damage as evidenced by bone loss and permanent bony displacement. Four horses (4) with minimal bilateral displacement- returned to pasture sound, six (6) patients with minimal unilateral displacement in a single foot are (occasionally) ridden at a walk. Four (4) of the horses are maintained in restricted environments with limited soundness.
Six feet required partial wall resection after displaying wall detachment (greater than 1 inch of detachment). The (dead / nutritionally compromised) wall below the attachment appears to shrink (dehydrate) toward the distal phalanx and the growth from the coronet prolapses over the distal wall if it is not removed. The wall detachment is often mis-diagnosed as a “gravel abscess” as it presents itself at the coronary band.

Discussion:

This shoe allows the patient to selectively load and self adjust breakover (pitching) and wedging (roll). The Steward Clog (aka Wooden Shoe) requires the practitioner have a knowledge of the breakover needs of the particular case: whereby, mediolateral point of breakover (roll) is appropriately applied to a nondeformable shoe material (wood, steel, aluminum, rubber, etc.). The addition of EVA to the shoe’s solar surface allows the patient to apply the point of breakover- and subsequent wedging effects to the shoe. Both shoe designs enable the horse to re-adjust the mediolateral breakover as the hoof growth’s mediolateral plastic asymmetries occur between shoeings.

The sloping of the mediolateral surface to the (EVA/Wood, Wood) Clog allows the patient to “roll” the shoe to realign the DIP joint and to load the hoof according to the comfort of the patient. The use of the EVA material on the bottom of a layer of plywood allows the patient to easily, immediately conform the shoe to the biomechanical / comfort needs of the patient (Steward Clog 2.0®). The plastic properties of the particular EVA allow the basilar surface (usually toe in typical laminitis, but medial or lateral heel in cases of UPD-both deformations may be needed in a particular case) to maintain the plastically compressed areas. All the while, the EVA maintains elastic properties to absorb concussion and further conform as the hoof grows and horse heals- or pathology worsens. These cases- immediately- loaded the shoe to the unaffected side, wedging (mediolaterally) the shoe such that the DIP joint was realigned (see Fig. 1,3,5 ) when the EVA foam was present. This is analogous to how a person would walk if the suffered a cut to the medial heel of their foot. One would roll up (dorsodistally pitch) off the heel (inversion), load the lateral portion of the foot (heel) and place the foot towards the midline (axially) to walk (redistribute load). The base slopes of the shoe can be altered to redistribute load. The affected side’s basal shoe heel/wall/ toe solar edge can be beveled at a 35 degree and the unaffected (lateral shoe branch) side can have a lesser slope to the ground connected surface (0 to 15 degrees). This will transfer more load (GRF/WF) to the lateral wall.
The basal (ground) surface of the Wood Clog (or urethane Clog) can be modified by solar grinding or addition of a wedged pad to produce an inversion roll (wedge sloped laterally). This will painfully overload the medial wall; therefore, wall floating measures should be implemented and load redistributed to offload the affected wall’s/solar load share. The dorsal surface of the “wooden shoe” should be ground down starting at the second nail hole and gradually slope the wall and solar area caudally to the affected heel. The triangular shaped area is from the wall to the medial sulcus of the frog. The surface of the shoe will be removed at a continual deepening slope to unload the floating wall. The wall can be trimmed in a sloping fashion (opposite the sole recess) to insure wall contact is avoided. The dorsoaxially displaced wall/coronet will usually migrate distally- to return to a more normal position – if adequately unloaded. Another option is to construct a W shaped caudal pad to redistribute the load off the medial wall (see Fig.7). Leather or wood can be used to construct the W pad. It is extended dorsally to the quarters. The pad(s) are under the shoe, and extend to the caudal region to provide wall and frog support. The affected side can be reduced by grinding the shoe surface of the pad in the above described fashion from the 2nd nail hole to the heel. The recessed area will extend under the bars and extend to the medial sulci of the frog. The recess should extend forward to unload the area of the sole that would be occupied by the distally projected shadow of the wing of the P3. The central leg of the W is to support the frog. The pad can be expanded in the frog area to accept more load by adding a layer of SIM to the central and lateral sulci of the frog. A configured pad (thickened frog) can be used to make sure the frog is actively loaded to overload the frog and make sure the medial wall and sole are protected (unloaded). Wetting a leather pad insures proper fit once the pad is applied and allows easier plastic deformation- via hammering. The pad can be conformed (hammered) on an anvil – (much the same as steel) to thin the medial wall/solar area- from the second hole, to the medial sulci of the frog and caudally to the heels ( wall to frog sulci / quarter to heel recess). This orthotic package (purchase) can be shod with a normal shoe that has the medial branch unloaded as described above. This is useful for a sheared heel that must continue working. A (Z bar) shoe can be used to transfer load to the lateral wall in some cases. The manipulative mixing, curing of the sole impression material can offload the affected heel and overload the unaffected heel. For example, the Shore value of SIM can be softened by 50% by using ½ the white portion of the 2 part SIM in the mix. This will reduce the Shore value by 50% and soften the SIM, effectively unloading pained areas. Curing/ manipulative adjustments can be used to overload normal areas of the frog/unaffected heel. Loading the hoof just prior to the SIM setting up, and not fully loading the leg will allow the unaffected area to be (actively) overloaded- increasing the area’s share of WF.

Excessive damage to the affected wall can result in an (comparatively) increase in hoof growth on the unaffected side as compared to the affected side. This causes increased wedging (pitch-d/p- and roll m/l) to the hoof capsule between trims (see Fig. 5). The affected wall (or portion) has lost a large portion (or all) of the nutritional and physical support of the SLA. This can cause a rotational hoof capsular deformity (yaw effect), over time, as the affected heel dehydrates and shrinks. Deleterious wall compression and detachment needs to be aggressively dealt with. Coronary grooving and other wall sculpting, floating methods (resections) must be done to allow the displaced wall and prolapsed coronet to return to a more normal form to re-establish a more normal function. These wall growth distortions cause a force on the elastic/plastic hoof capsule that results in the plastic yaw motion/deformity to be toward the affected side,. The faster growing un(less)affected side adds substantial mass to the lateral wall (in cases of medial sinkers) and further adds to the medial yaw effect. The dorsal capsular rotation of P3, especially if severe (incrementally -degreed), confounds the yaw effect. The rapid growing (net vector effect) heel causes a medial yaw and the slow growing toe region produces an initial, distally- orientated plane of growth (just distal to coronet) as it seeks the distal extensor process (SLA) of P3. The dorsoaxially displaced proximal wall and coronet compromises (via stretching or compression) the coronary vascular and needs to be encouraged to plastically return to a more normal architecture to return a more normally functioning wall. This encourages the mitotic area to restore the new portion (section) of connecting tubules as they encounter the previously produced, immature, (coronary band- terminal papillae produced/ very pliable) wall tubules, thus, distortions of growth rings occur. These distortions are a function of the amount of rotation that P3 has suffered. Their growth is retarded by coronary band vascular compression/stretching- because of P3’s displacement,’ thus denying them of the normal nutrition of the unaffected heel lamellar circulation. As the unkeratinized (uncemented, pliable, connected) terminal tubules (continuously) exit from their coronary papillar finger-like factories, they normally are attached (easily) to the SLA (suspensory lamellae apparatus).

The normal wall tubule is displaced distally as it is seeks to be attached to the SLA- in a complex manner- as to allow a ratcheting growth pattern of the continuous tubule/lamellae complex. The tubules are responsible for the observed growth rings of the hoof. In their pliable state, as they exit the coronet (papillae factory), they are easily deformed. The wall tubules are similar to hair shafts and the collective intercemented- collection of tubules- is the hoof capsule. They are interconnected to each other to form the continuous, complex wall -with a (normally) very tough hoof wall cementing system, -after their detoured route caused by P3 displacement. They can encounter previous (slow) growth which causes a “traffic jam” and results in very compacted, small growth rings, or the tubule can be folded resembling an accordion or “pleats”(displacement dependent). In severe P3 rotation (greater than 25 degrees), the large pleated sheets of (horizontally connected) tubules can appear as “folded layers” as they form unstable, distorted hoof wall. The interconnected (horizontally) tubules are connected to the (individual) continuous (coronet to ground) hoof capsular tubules as the individual tubules follow their previously produced segments to the ground. The keratinazation and “cementation” occur (only) within the perimeters of their close proximity to the lamellar corium (SLA). It is damaged by the displacement of P3, and often does not return to an acceptable / functional state, thus distorting normal wall formation and growth.

Unilateral palmar displacement is a very difficult, devastating overload injury / manifestation to cases of complicated dorsal capsular/ phylangeal displacement laminitis. The amount of damage to the entire lamellar interface¹ combined with the amount of load to a particular area of the lamellar interface accounts for the various manifestations of laminitis. Reducing load to the lamellae- prior to devastating overload injury- is possible in some cases, but unfortunately, some cases experience devastating lamellar damage and overload injury / consequences- such that therapeutic biomechanical manipulation aimed at lessening / redistributing the load is of no benefit in re-establishing acceptable long-term soundness.

The aggressive use of coronary grooving / affected wall resection and unloading the affected wall- by trimming to allow the coronet to unload and return to a normal position -is highly recommended by the author. Any laminitic episode in the palmar (plantar) area complicates healing due to the blood supply (hemodynamics) and load bearing features generally required by the heels.

Fig. 1. a,- Illustrated radiograph showing the radiographic changes on the DP in UPD, This hind limb suffered lateral (left) displacement of the distal phalanx as evident in this dorsopalmar radiograph (b.). The increased distance in the DIP lateral joint space (white line), increased thickness of the lateral hoof wall, and differential lines of the nutrient foramen of P3 compared to the distal aspects of P2- all suggest unilateral diplacement (a., b.).

Dr. Andy Parks’ sketch of the laterally placed shoe on this depiction of a medial sinker that was described the AAEP 2007 paper- How to treat 3 Manifestations of Lamimitis using the Wooden Shoe (O’Grady, Steward, & Parks).

Fig. 2. This acute laminitis case was suffering pre-existing mediolateral imbalance that was possibly creating increased loading to the medial lamellar interface. Both front feet of this bilateral valgus deviated horse were shod similarly to the above radiograph. Wooden shoes were applied and this hoof required medial hoof wall resection 45 days later (see Fig. 5) due to severe wall disruption. Note the abnormal radiolucent area (lamellar interface area) on the medial aspect (arrow).

Fig. 3. The hoof in Fig. 1 was shod using the wooden shoe. No trimming was done to the hoof between shoeing. The shoe has been outlined in white lines. The arrow shows the medial slope (red line) that was extended to past the shoe’s midline after extending the shoe medially. (The slope of the red line is exaggerated for illustration purposes.) Note how the joint space has realigned in a more normal manner. This is accomplished by allowing the horse to increase load to the medial heel in this lateral displacement. Hoof placement will be abaxially in lateral displacers, axially in medial displacers.

Fig. 4. Following separation of the medial wall at the coronet, the separated hoof capsule was resected. The growth rings proximally illustrate the disparity in hoof growth between the medial and lateral wall before resection; the lateral wall markedly outgrew the compressed medial wall. Prior to application of the shoe, the coronary band was tilted down towards the medial side. The foot is twisted (medial jaw inversion roll) to the medial side (red line) due to disparity in heel wall growth and mediolateral shoe positioning. Following application of the shoe, the EVA compressed such that the medial coronet is now proximal to the lateral coronet (inversion roll).

Fig. 5. This EVA / Wooden shoe has self-adjusted to meet the biomechanical and comfort needs of this medial sinker. The lateral heel has grown more than the medial heel and the shoe can readjust for this difference. Soundness improved in the 30 days this particular shoe was worn due to hoof stabilization and wall resection. The resected wall allows the upward displaced coronet to plastically return to a more normal architectural arrangement with P3.

Fig. 6. This drawing illustrates the loading and compression of the EVA material in this unilateral displacement drawing. The mediolateral wedging effect realigns the joint space and aids in comfort of the patient. The radiograph displays the joint and shoe angles. The sole was trimmed with no mediolateral imbalance 30 days prior. Note the upward displacement of the affected coronary band.

Fig.7. This leather “W pad” is used to redistribute weight to the palmar/plantar hoof. The affected side of the UPD case can be unloaded by thinning the leather pad on the affected side by “hammering the wet leather pad on the anvil” prior to application. Other methods- such as recessing the shoe or cutting (floating) the affected wall- can be used to offloaded the pained region of the hoof. The unilateral wing of the displaced third phalanx is usually very painful and warrants offloading with less sole impression material, or a softer durometer SIM in the pained areas. Usually a combinations of offloading are done to allow the new wall to regain a normal SLA attachment. Photo B. The affected side can be ground down to offload the sore solear area- the entire area from the quarter to the heel if needed.

Fig. 8 (a. b. c.) These pictures are of a healed medial UPD case that must be trimmed to offset the displaced medial wall (with chronic growth disparity). The upward shift of the medial wall and the distal displacement of the medial wing of P3 create trimming complexities and are distorted between trims due to wall growth disparities.

Fig. 9. (a. b. c.) These pictures show the proper trim and shoeing prescription provided by using an EVA Clog placed on the hoof. The conforming Clog plastically deforms to the special needs of these cases. Note the level coronet in picture a. (verses the same foot in Fig. 9a.) provided by the lateral compression of the Clog. The growth of the lateral wall promotes a medial jaw as the hoof grows. Shoeing allows the hoof to alter the hoof’s inversion roll as the lateral wall grows faster than the medial wall. The dorsal capsular displacement (pitch) is complicated by the medial unilateral palmar displacement (inversion roll) and will require special trims and shoeings for the life of the horse.

Acknowledgments:

i. Declaration of ethics- No ethics of the AVMA, AAEP, or AFA were violated in applications of these methods or writing this paper

ii. Conflicts of interests- The authors received compensation for the application and sale of the orthotics in treatment of these pathologies. The Steward Clog has been used extensively since 1986.

iii, Funding/Materials/Technical Support- No funding was provided by entities/businesses or material/technical support

References:

O’Grady, S.E., Steward, M., Parks, A.H. (2007a) How to Construct and Apply the Wooden Shoe for treating Three Manifestations of Chronic Laminitis. in Proceedings. Amer. Assoc of Equine Practnrs. 53, 423-429.

Steward, ML. How to construct and apply atraumatic therapeutic shoes to treat acute or chronic laminitis in the horse. American Association of Equine Practitioners 49th Annual Convention 2003;337-346.

Parks AH. Chronic Laminitis. In: Current Therapy in Equine Medicine. 2003 pp. 520-528. Saunders, Philadelphia.

Parks AH. O’Grady, SE, Chronic laminitis: Current treatment strategies, Vet. Clinics of N. America; 19: 393-416.

Steward, M.L. The Use of the Wooden Shoe (Steward Clog) in Treating Laminitis, Veterinary Veterinary Clinics of North America: Equine Practice- Laminitis, Vol. 26, Issue 1, April 2010, pages 207-214.

Hood DM. The mechanisms and consequences of structural failure of the foot
Vet. Clin. N Am 1999; 15: 437-461.

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