The Equine Foot, Biomechanical and Anatomical Form Function. Hoof Balance and Symmetry, a Review of Current Theory.

M. N. Caldwell FWCF¹* & D. Duckett FWCF²

¹The School of Veterinary Nursing & Farriery Science, Myerscough College, Myerscough Hall, Bilsborrow, Preston, Lancashire, PR3 0RY

². 709 Tennis Avenue, Ambler. PA. 19002. U.S.A.

*¹ Tel: 01995 642000 ext; 2057 Mob: 07792374551 emails; markncaldwell@btinternet.com or mcaldwell@myerscouch.ac.uk

Word count does not include figures and references.3758

Key words: Farriery, anatomy, biomechanical, conformation, hoof trimming, foot balance, hoof capsule, pathology.

SummaryFarriery attempts to maintain equilibrium within the foot by trimming to achieve an ill-defined and subjective empirical interpretation of “Static Foot Balance” (Hickman & Humphrey 1987; Stashak 2002). This interpretation of foot balance is mostly derived from historical texts (Dollar & Wheatley 1898; Russell 1897; & Lungwitz 1891; 1897).

In nature shape and form of a structure relate directly to function. The hoof capsule is such an example of this concept. The primary functions of the hoof capsule and its associated structures are to absorb impact shock during locomotion, assist in the transfer of weight from the skeletal column and protect the underlying structures whilst providing grip during locomotion (Butler 2005).

This paper reviews the anatomical and biomechanical considerations of the current foot balance model. It explores the relationship between the anatomical structures and the mechanical function within the foot and reviews the farriery considerations of our understanding of both static and dynamic foot balance models.

It appears that the physics of load distribution casts doubt on the validity of theoretical foot balance model given the range of biomechanical variations within the population. Further investigation needs to be undertaken into the common morphometrics that might constitute a range of normal.

1

IntroductionA fundamental principle of farriery is to achieve equilibrium of static and dynamic

forces acting on internal structures within the foot and lower limb. External

influences should be neutralised by internal forces with the form of the foot

maintained so as not to inhibit its natural function. Farriery attempts to maintain

equilibrium within the foot by trimming to achieve an ill-defined and subjective

empirical interpretation of “Static Foot Balance” (Hickman & Humphrey 1987;

Stashak 2002). This interpretation of foot balance is mostly derived from historical

texts (Dollar & Wheatley 1898; Russell 1897; & Lungwitz 1891). Today’s modern

domesticated horse is far from the forces of nature that historically shaped and

controlled their development. Horses are more reliant than ever on the knowledge

and skill of the hoof care professional with an understanding of the anatomy,

physiology and function of the lower limb, foot and all its component parts . The

composition, position and functional relationship of the component parts of the foot

are so densely compacted that within the hoof capsule there is little room for

manoeuvre.

In nature shape and form of a structure relate directly to function. The hoof capsule

is such an example of this concept. A horse’s natural protection against predators is

“fright and flight” the hind quarters of the horse are a compact mass of large loco

motor muscles which are designed primarily to propel the horse quickly forward. The

front limbs are designed to primarily support the horse through impact, deceleration

and loading during locomotion (Back & Clayton 2001). Movement is effected via

neurological impulses causing the limbs to retract or protract. To minimise the

energy required for this movement the limbs are as light weight as practical and are

manoeuvred via a series of levers and pulleys. The pulleys are the joints, which are

2

held together with a complex array of ligaments. The levers are the tendons which,

together with the ligaments, act like a coil spring releasing stored energy when

movement is necessitated. In simple terms every time the limb is loaded the

elasticated collagen fibres that make up the tendons and ligaments store energy

which is released when the limb needs to be lifted and propelled forward.

Anatomical Considerations

The gross anatomy of the foot and limb is well documented. In farriery the foot of the

horse is referred to as the keratinized hoof capsule and its contents. The hoof

capsule is a continuation of modified epidermal tissue which forms a firm yet flexible

protective layer surrounding the skeletal components at the distal extremity of the

limb (Kempson. 1987). The primary functions of the hoof capsule and its associated

structures are to absorb impact shock during locomotion, assist in the transfer of

weight from the skeletal column and protect the underlying structures whilst

providing grip during locomotion (Butler 2005).

Each epidermal structure has a different density and hardness dependent upon its

primary function and is produced by its own corresponding dermal layer and gains

its strength and flexibility from its chemical composition and moisture content. The

outer layer of hoof wall is rich in disulphides giving additional strength. The sole and

frog are rich in sulfhydryl a group which gives these structures greater elasticity

(Pollitt 1988) which gives flexibility. The average growth rate of 6-8mm per month

(Stashak 2002) is said to be equal to the wear of the foot at the bearing border

ground interface (Back and Clayton. 2001).

The horn itself is composed of densely packed, longitudinally aligned, horn tubules

which are generated from tiny projections of the dermis known as papillae (Fig 3).

3

These tubules are cemented together by intertubular horn cells which proliferate

from germinative cells of the dermis between the papillae. The intertubular horn is

formed at right angles to the tubular horn and gives the hoof wall a mechanically

stable, multidirectional, fibre-reinforced composite (Bertram and Gosline, 1987).

Interestingly hoof wall is stiffer and stronger at right angles to the direction of the

tubules. This contradicts the usual assumption that the ground reaction force is

transmitted proximally up the hoof wall parallel to the tubules. The hoof wall appears

to be reinforced by the tubules but it is the intertubular material that accounts for

most of its mechanical strength stiffness and fracture toughness. The tubules are

three times more likely to fracture than intertubular horn (Leach, 1980; Bertram and

Gosline 1986).

Contrary to common misconception these tubules are not aligned randomly but

appear to be arranged in 4 distinct zones and differing in “tubule density” from the

inner most layers to the outer layer (Reilly et al. 1996). The highest tubular density is

at the outermost layer (fig 4). Since the ground reaction force is transmitted

proximally up the wall (Thomason et al 1992) the construction of the epidermal

structures appears to be part of the mechanism that allows the transfer of impact

load across the hoof wall from the rigid, high tubule density, outer wall to the more

plastic, low tubule density, inner wall. The material properties of hoof are said to

have plastic elastic characteristics (Reilly et al; 1996). These characteristics allow

for deformation under stress and then return to original form following a limited

period of strain. Maximum stress for prolonged periods of strain reduces the

elastomeric property and the structures ability to return to its original form.

4

Projecting from the inner wall are some 600-900 primary laminae each with 100-200

secondary epidermal laminae (Pollitt. 1988). The primary epidermal laminae are

produced by the dermis of the coronary corium. The secondary epidermal laminae

are produced by a germinative layer of the epidermis of the laminar corium. The

primary and secondary epidermal laminae interdigitate, dovetail, with the

corresponding dermal lamellae. The dermal lamellae originate from the laminar

corium surrounding the parietal surface of P3 and the lower border of the ungual

cartilages. This relationship of interdigitation of laminae is thought to allow for the

partial suspension of P3 within the hoof capsule and the transference of tensile

forces radially from P3 (Reilly 2006) (Fig 5).

As hoof wall continues to grow distally the primary epidermal laminae are allowed to

slide past the secondary epidermal laminae. The process involves the remodelling

of the epidermis around the proliferation of new cells. The basement membrane

which surrounds the secondary dermal laminae is thought to release itself via tissue

inhibiting desmosomes and demisomes (Pollitt.1998).

At the solar border the sole and wall are separated by the white line. The white line is

produced by epidermal primary lamellae and the terminal papillae at the distal fringe

of P3. The white line is a flexible junction between both horny structures allowing for

movement between the two structures during load bearing.

The soles concavity combined with the shape of the frog are implicated not only as

an anti-slip device (Butler 2005; Stashak 2002) but are said to play a major role in

the anti-concussive mechanism. It is generally accepted that the horses mass is

distributed through the limbs with 60% being supported by the fore limbs and 40%

through the hind limbs (Butler, 2005:, Back & Clayton, 2001; Williams & Deacon

5

1999). Both hind and front limbs play a role in support and propulsion however the

primary role of each differs. Front feet are generally larger and rounder with less concavity

to the soles to provide a greater surface to dissipate impact shock. Hind feet have a less

acute dorsal hoof wall angle and a more concave sole. This configuration is best suited for

grip and rapid propulsion, pushing as they dig into the ground.

The frog is a wedged shaped mass of elasticated horn. Located at the basal surface

of the solar margin it is occupies the space between the sole and bars uniting either

side its longitudinal axis to form the collateral sulci. It extends palmadorsal from the

heel bulbs approximately 2/3rd the length of the bearing surface (Ovnicek 1995). The

so called true point of frog, where solar horn and frog horn merge, lies distal to the

internal insertion of the deep digital flexor tendon (DDFT). Given its close

relationship to the bars, and the composition and topography of the internal frog

stay, it is more likely to act as an expansion mechanism for the heels during impact

(Emery et al. 1977) whilst serving to protect the DDFT, digital cushion, distal

sesamoidean bone and its associated bursae.

Occupying the space between the large flexible ungual cartilages, which are attached

to the palmar processes of P3 and distal to the DDFT, lies the digital cushion and

venous plexus (Fig 2). The digital cushion is a large mass of highly elastic fibro fatty

cartilage forming the heel bulbs. It is said that venous blood is flow is assisted by

compression of the cartilages through the interactive mechanism of the frog and

digital cushion during the impact and loading phases of the stride (Hickman &

Humphreys 1987, Pollitt, 1988 and Butler, 2005). Bowker (1988) referred to this

hydraulic compression of the vascular bundles as hemodynamic flow. Ratzlaff et al;

(1985) and Bowker (1988) suggested that this action assists in the absorption of

6

impact shock. Bowker argued that there is a complex inter-relationship between the

ungual cartilages and the digital cushion. The medial projection on each ungual

cartilage is thrust upward by the bars on contact causing being transferred through

the venous plexus dissipates high frequency energy waves reducing impact shock on

the bone and ligaments of the foot. Bowker noted that horses with good foot

conformation had more blood vessels in caudal aspect their feet than those with a

history of foot problems. Bowker (1988) also noted that the digital cushion was made

of fat and an elasticated fibro cartilaginous material. Fibro cartilage is made up, in

part, by a protein called collagen. Collagen makes up the fibres found within tendons

and ligaments and whose mechanical properties allow for the storage of energy.

Physiological Considerations

The relationship between the anatomical and mechanical function of the structures

within the foot is integral to our understanding of static and dynamic foot balance.

The biomechanical function of the individual anatomical structures within the foot

are dependent on the ability of all of them to work in harmony for the good of the

whole. This relationship is called a “mechanism”. The mechanisms within the foot

enable the horse to travel at great speed over long distances and across varied

terrain. As the foot makes contact with the ground up to 90% of the external shock

is dissipated before it reaches P1 (Douglas et al 1998). A pluralistic approach to

understanding the anti-concussive mechanism of the hoof recognises more than

one ultimate principle.

The foot’s internal and external structures combined exhibit three functional

characteristics that allow for the dissipation of forces during operation of the foot

mechanism described. (Barrey, 1990)

7

1. The absorption of impact and rapid deceleration forces through

friction, resistance, and the elastic properties of structures that deform under

load.

2. The dissipation of ground reaction force via pressure resistance to

force and stress resistance through the material properties of the wall

3. Plastic structural characteristics that allow for the return to original

form following deformation.

During the stance phase the horse’s weight is transferred through the limb to the

distal interphalangeal articulation. Because of the distal phalanx’s (P3) unique

attachment to the hoof capsule via the laminar interdigitation, this weight is

transferred to the wall radially as tensile forces (Reilly 2006). The dermal epidermal

laminar interface acts partially as a suspensory apparatus for P3. The tensile forces

are transferred distally along the hoof wall (Fig 5) and converted into pressure at the

ground bearing border by ground reaction force vectors (GRFV). Both the sole and

frog have a supporting role following initial contact and impact phases of the stride.

At the first point of impact, this is usually heel first or flat the hoof is rapidly

decelerated by the vertical landing forces. Heel first landing is accentuated at faster

gaits (Back, et al, 1995). Horizontal movement is rapidly reduced to zero within

milliseconds of impact. The shape and geometry of the foot changes as it comes

under load. Following initial impact Bowker (1988) suggested a hemo-dynamic flow

theory. He argued that there is a complex inter-relationship between the ungual

cartilages and the digital cushion. At the point of impact the collateral cartilages are

thrust upward by the heel buttresses and bars, causing negative pressure in the

digital cushion draining blood from the front to the back of the foot, creating

8

hydrostatic cushioning. Simultaneously tendons and ligaments under load store

excess energy from the vertical loading and fetlock extension. During the loading

phases the proximal dorsal wall flattens and moves palmar distal, the heels expand

(Fig 6) whilst the sole and frog flatten under load following the outward movement of

the quarters (Douglas. et al. 1998, Lungwitz 1891). The relatively flexible laminar

attachment at the heels compared with the toe allows greater expansion caudally.

The frog descends with the sole until it contacts the ground. Known as the pressure

theory (Hickman & Humphrey 1987; Butler 2005) this movement simultaneously

compresses the digital cushion. Colles (1989) noted that in some horses with

reduced frog pressure, such as those recently shod, the heel actually contracted

under load. The Depression theory suggests that under the influence of weight

during impact and loading that P3 is rotated palmardistally. This is more likely to be

linked to hyperextension of the distal interphalangeal joint (DIPJ) caused by GRF

vectors following heel first landing (Rooney 1969). This rapid deceleration of the foot

by vertical landing forces and horizontal braking forces immediately post impact

have been associated with the pathology of disease (Raddin, et al; 1972; Viitanen,

et al; 2003). As the fetlock reaches the maximum extension required for the force

applied the stored energy is used to accelerate retraction of the fetlock through to

mid stance. Foot geometry and bearing borders are returned to their original

position (Back & Clayton 2001).

Theoretical Considerations in Static Foot Balance

The English dictionary defines Balance: as ‘the harmony of design and proportion”

or “stability produced by even distribution of weight on each side of the vertical axis”.

Both definitions could easily be applied to the equine foot. Trimming and shoeing

9

are said to have marked effects on the performance and soundness of the equine

athlete. Ideally, trimming optimizes the interaction between the hoof and ground

during locomotion (Balch, et al 1998).

Since the hoof is a three-dimensional structure, it should be balanced in both the (X)

mediolateral and (Y) dorsopalmar planes whilst maintaining proportions through the

proximodistal axis (Z) with its centre of mass (COM) remaining in equilibrium (Fig 8).

For the purposes of biomechanical study the COM for the foot has been calculated

from previous studies of cadavers (Springs & Leach; 1986). Body segments were

weighed and calculated as a proportion of the overall body weight and then

suspended at a point of balance. These points were then referenced to anatomical

landmarks identifiable on the live horse for analysis purposes (Back & Clayton,

2001).

Static foot balance refers to the alignment and spatial orientation of the foot and limb

in the static mid stance position as a three dimensional object. All three dimensional

objects have three axes and six co-ordinates. The dimensions of the foot are

measured along these axes to the point where the X and Y axis intersect each other

at along the longitudinal Z axis. This is an important concept in retaining static

balance as it assumes equal weight / force at both coordinates of the axis.

Dorsopalmar (lateral projection)

The phalangeal axis of the adult horse is a natural conformation that can only be

altered either by injury or surgery. However, the hoof axis in relation to the pastern

axis can and often is, altered either by neglect on the part of the owner, or worse

10

still, by inadequate farriery practice. Textbooks tend to be misleading, all too often

quoting the ideal front foot angle as being between 45º and 50º (Hickman &

Humphrey 1987). (Turner 1988; 1992; Stashak 2002; and Butler 2005). stated that

the heels should be parallel to the toe angle. More importantly both should present

parallel to the internal dynamic structures the mid-line of the phalanges. A

perpendicular line dropped from the centre of rotation of the DIPJ should bisect the

ground bearing border equally (Colles 1983; 1989; Balch et al, 1997; O’ Grady &

Poupard 2003).

Dorsopalmar (Solar View)

When viewed at its solar margin the following should be noted: The hoof wall is

thickest and is most dense around the toe region, thinning as it wraps around the

quarters arriving at the buttress to become the last weight bearing point of the foot.

This is roughly adjacent to the widest point of the frog, before inverting on itself to

form the bars which then terminate at the approximate centre of rotation of the coffin

joint (Colles 1983; 1989; Balch et al, 1991; 1997; O’ Grady & Poupard 2003). The

centre of weight distribution through the hoof capsule is said to be approximately

1cm palmar of the trimmed point of frog (Ovnicek 2003). A perpendicular line drawn

from the buttress to the toe will intersect the medial and lateral optimum points of

break-over (Duckett 1990; Caldwell 2001).

Mediolateral

The height of wall from coronary band to ground bearing border should be the same

at any 2 opposite points (Russell 1897; Stashak 2002 and Butler 2005) with both the

bearing border and coronary borders perpendicular to the longitudinal axis of the

limb.

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Discussion

Farriery is an empirical craft with much of its knowledge and tradition handed down

from one generation to the next. Much of what is quoted in standard farriery text

regarding the hoof represent the mean approximation and should at best be

regarded as “guidelines” to work within.

It has long been accepted practice in farriery to relate the morphology of the hoof

and its bearing border (BB) shape to an ideal form which is symmetrical around its

longitudinal axis (Stashak, 2002; Butler, 2005). The reality of biological systems is

that small-to-moderate asymmetries are present in the majority of structures. The

BB shape is no exception. It has been well documented that external influences

(Thomason 1998) can have an effect on the hoof’s shape. Leach and Zoerb (1983)

noted that the percentage of total body weight acting through the forelimbs of adult

horses is approximately 60% and as a result front feet are reportedly larger and

rounder with less concavity to the soles to provide a greater surface to dissipate

weight.

According to Wolfe’s Law (1986) biologic systems such as hard and soft tissues

become distorted in direct correlation to the amount of stress imposed upon them.

Horn is said to posses both “elastic” and “plastic” deformation characteristics. The

compressive forces (C) and the tensile components (T) in reaction with ground

reaction force vectors (GRF) stress the horn over time until it reaches its yield

strength (Hall 1953; 2003). At this point plastic deformation begins, for example

collapsed heels. Once the process has begun, plastic deformation is not generally

reversible. Hoof wall is thickest at the toe, the region of greatest friction, and thins

gradually towards the heels with the medial quarter thinner than lateral (Pollitt,

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1998). The wall is oblique to the direction of the GRF. The centre of pressure (COP)

location and point of force (POF) trajectory (Wilson et al; 1988) are said to be

influenced by external factors, such as conformation. By extending the moment arm

the stress time line will influence the magnitude of force on the axial coordinates is

likely to be a significant factor in both structural orientation and integrity and lead to

permanent plastic deformation.

The resultant increase in torque application from an increase in moment induces

stress by moving the pressure towards the limbs longitudinal axis (Hall 1953). The

resulting stress from pressure being applied externally to the cross section of the

limb would seem to cause distortion of those soft tissue structures within the foot

compromising both their integrity and biomechanical function. The physics of weight

distribution and support suggest that each hoof capsule would take not only a

different form around the bearing border but throughout its structure dependant on

the forces applied to it. It would further indicate that pressure applied outside the

hoof’s ability to absorb might restrict the dermal structures responsible for

regeneration.

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Conclusion

It appears that the physics of load distribution cast doubt on the validity of

theoretical foot balance model given the range of biomechanical variations within

the population. Further investigation needs to be undertaken into the common

morphometrics that might constitute a range of normal. The affects of farriery

protocols on the structure, function, loading and movement of the equine foot are

not fully understood. If we are to fully understand farriery’s role in lameness

resolution clearly a more appropriate definition of the term foot balance needs to be

recorded.

 

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References

Back, W., Schamhardt, H.C., Hartman, W. and Barneveld, A. (1995a) Kinematic differences between the distal portions of the forelimb and hindlimbs of horses at trot. Am. J. vet. Res. 56, 1522-1528.

Balch, O.K., Ratzlaff, M., Hyde, M., Grant, B. and White, K. (1988) Correlation of equine forelimb hoof impact patterns to changes in the medio-lateral balance of the hoof. Anat. Histol. Embryol. 17, 361-362.

Balch, O., White, K. and Butler, D. (1991) Factors involved in the balancing of Equine Hooves. J. AM. Vet. Med. Ass 198, 1980-1989

Balch, O.K., Butler, D. and Collier, A. (1997) Balancing the normal foot: hoof preparation, shoe fit and shoe modification in the performance horse. Equine Vet. Educ. 9, 143-154.

Barrey, E. (1990) Investigation of the vertical force distribution in the equine forelimb with an instrumented horseboot. Equine vet. J., Suppl. 9, 35-38.

Bertram, J.E.A. and Gosline, J.M. (1986). Fracture toughness design in horse hoof keratin. J. exp. Biol. 125, 29-47.

Bertram, J.E.A. and Gosline, J.M. (1987). Functional design of horse hoof keratin: the modulation of mechanical properties through hydration effects. J. exp. Biol. 130,121-136.

Butler K.D. (2005) The Principles of Horseshoeing 3. Butler Publishing. Maryville, Missouri

Bowker, R. M., Van Wulfen, K. K., Springer, S. E., & Linder, K. E. (1998), Functional anatomy of the cartilage of the distal phalanx and digital cushion in the equine foot and a hemodynamic flow hypothesis of energy dissipation, Am.J.Vet.Res., vol. 59, no. 8, pp. 961-968.

Caldwell. M. N. (2001) The Horses Foot: Function and Symmetry, Proceedings1st UK farriers Convention, Equine Vet. Jour. Publishing, 28-33

Colles, C. M. (1983), Interpreting radiographs 1: the foot, Equine Vet. J., vol. 15, no. 4, pp. 297-303.

Colles, C. M. (1989). The relationship of frog pressure to heel expansion, Equine Vet. J., vol. 21, no. 1, pp. 13-16.

Clayton H. M. (2004) The Dynamic Horses. Sport Horse Publications. Mason

Dollar, J. A. W. (1898): A handbook of horseshoeing. Neill and Co, Edinburgh, Britain

Douglas, J.E., Biddick, T.L., Thomasson, J. J. And Jofriet, J.C. (1998) Stress / strain behaviour of the equine laminar junction. J. Exp Biol. 201: 2287 - 2297

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Emery, L. (1977) Horseshoeing Theory and Hoof Care, Lea & Febiger, Philadelphia, pp 65-68, 74-76.

Hall, S. (1953, 2003) Basic Biomechanics. McGraw-Hill. New York. pp 70-74

Hickman J. and Humphrey M (1987) Hickman’s Farriery. J.A. Allen & Co. London

Kempson. S.A. (1987). Scanning Electron Microscope Observations of Hoof Horn. Vet. Rec. 120. 568-570

Leach, D.H. and Zoerb, G.C. (1983) Mechanical properties of the Equine Hoof Wall Tissue. Am. J. of Vet. Res. 44, 2190-2194

Lungwitz, A. (1891). The changes in the form of the horse’s hoof under the action of the body-weight. J. comp. Path. Ther. 4, 191–211

O'Grady, S. E. & Poupard, D. A. (2003), Proper physiologic horseshoeing, Vet.Clin.North Am.Equine Pract., vol. 19, no. 2, pp. 333-351.

Ovnicek G, Erfle JB, Peters DF. (1995). Wild horse hoof patterns offer a formula for preventing and treating lameness, in Proceedings. 41st Annu ConvAmAssoc Equine Practnr 1995; 258–263.

Ovnicek, G. D., Page, B. T., & Trotter, G. W. 2003, Natural balance trimming and shoeing: its theory and application, Vet.Clin.North Am.Equine Pract., vol. 19, no. 2, pp. 353-77, vi.

Pollitt. C. C. (1998). The Anatomy and Physiology of the Hoof Wall. Equine Vet. Educ. Manual 4, 3-10

Radin. E.L., Paul. I.L. and Rose. R.M (1972). The Role of Mechanical Factors in the Pathogenesis of Primary Osteoarthritis. Lancet. 519-522

Ratzlaff,M.H., Shindrel, R.M. and Debowes, R.M. (1985) Changes in Digital Venous Pressures of Horses Moving at Walk and Trot. Am. J. vet. Res. 46: 1545-1549

Reilly, J.D., Cottrell, D.F., Martin, R.J. and Cuddeford, D. (1996) Tubule Density in Equine Hoof Horn. Biomechanics 4, 23-36

Reilly, J. D. 2006. The Hoof Capsule in Curtis. S. A. Corrective Farriery; A Text Book of Remedial Farriery Volume 2 Newmarket Farriery Consultancy. pp. 343 – 376

Rooney J.R., (1969) Lameness of the forelimb, in: Mechanics of lameness in horses, The Williams and Wilkins Company, Baltimore, , pp. 114-196.

Russell, W. (1897) Scientific Horseshoeing. Roberet Clark Co., Cincinnati, Ohio. P93-99

Stashak, T.S. (Ed.) (2002) Trimming and shoeing for balance and soundness. In: Adam’s Lameness in Horses, 5th edn. Lippincott Williams & Wilkins, Philadelphia. pp 1110-1113.

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Thomason, J.J., Biewener, A.A. and Bertram, J.E.A. (1992) Surface strain on the equine hoof wall in vivo: implications for the material design and functional morphology of the wall. J. Exper. Biol. 166,145-165.

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Illustrations

Figure 1 to Figure 8

FIG.1. Sagittal section of the foot illustrating some of the important anatomical structures contained within the hoof capsule. The red dotted line is the frontal plane at section 1 (Denoix. 2000).

P2

P3

CORONARY CORIUM

DERMAL LAMELLA

WHITE LINE

SOLE

FROGWALL

DS

CSLDIGITAL CUSHION

CDETDDFT

SOLAR CORIUM

CORIUM OF FROG EPIDERMAL

LAMELLA

FIG. 2

P1

PROXIMAL PHALANX

MIDDLE PHALANX

DISTAL PHALANX

SDFT

FRONTAL PLANE at section1 (Denoix. 2000),

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FIG.2 Transverse section through heel bulbs illustrates some of the important anatomical structures contained within the hoof capsule. In this plane the collateral cartilages, coronary plexus, coronary corium, digital cushion, frog stay and solar corium are all visible within the hoof capsule whilst externally the wall, frog, bars and collateral sulci are visible.

Bars

Frog

Frog stay

Coronary Coria

P2

Coronary venous plexus

Collateral cartilages

Digital Cushion

PLANTER PALMER DISTAL OBLIQUE VIEW

19

.

Fig 3 Each dermal papillae fits a corresponding hole within the coronary groove and

produces individual horn tubules.

20

Fig 4 A transverse section through the hoof and internal structures. The section is

taken from the region of mid toe. Illustrated are P3, the laminar corium (LC) attached to the parietal surface of P3 the primary dermal (DL) and epidermal (EL) lamellar interdigitation, (secondary lamellar are not visible at this magnification) the

stratum internum and medium demonstrating the 4 zones of density (1, 2, 3 & 4).

P3

LC

DL

EL

ZONE 4

ZONE 3

ZONE 2

ZONE 1

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Fig 5 Weight of P3 (W) is transferred to the wall as tensile forces via the dermal

epidermal laminar interface (LI). The LI acts as a suspensory apparatus for the distal

phalanx (P3). The tensile forces are transferred distally along the hoof wall (Green

Arrow) and converted into pressure (P) at the ground bearing border or the bearing

border shoe interface

(Budras et al. 1998)

BEARING BORDER

LI

TENSILE FORCES W

P

22

Fig 7 Lateral Venogram of a normal foot illustrates the complexity and magnitude of

the venous return system of the equine foot. Clearly visible are the coronary, solar and

laminar venous plexus. (www.thehorse.com)

Coronary Plexus

Laminar Plexus

Solar Plexus

Coronary Plexus

Lateral Digital Vein

23

z

x yxy

z

Fig 8 Diagrammatic representation of 3 dimensional static foot balance.

X axis represents mediolateral coordinates viewed dorsopalmar / plantar and

Y axis dorsopalmar viewed mediolateral whilst Z represents the proximodistal

(longitudinal) axis of the foot. Movements around the dorsopalmar axis Y are

referred to as “Roll” (indicated by the blue arrow). Movements around the

mediolateral axis X are referred to as “Pitch” (indicated by the red arrows).

Movements around the longitudinal axis Z are referred to as “Yaw” (indicated

by the green arrow).

YAW

PITCH

ROLL

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