Quantitative Horse Hoof Trimming Protocol for Research Purposes.

M. N. Caldwell*¹. FWCF, J. D. Reilly, BSc (Hons), BVSc, PhD, MRCVS.

& M. Savoldi² CJF.

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

² 9350 Canyon Rd, Sheldon. 93175 CA. 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.3490

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

Summary

Many approaches to gathering data on the shape of the equine hoof make reference to a trimming protocol that has been used without specifying the full farriery details that have contributed to that protocol. In the past this may have sufficed for a veterinary-based approach to a particular subject, but a rigorous farriery appraisal requires detailed information about the techniques used in order to achieve a repeatable hoof trim for research standardisation and control purposes. The aim of this paper is to give detailed information about the important farriery reference points that can be used to give a defined and repeatable trim. This can then be used for research purposes as a means of controlling important variables which will then allow both reliable and farrier controlled quantitative data to be collected. It is from this base that both farriers and veterinary surgeons could accurately calculate interventions and gauge their effects on static proportions and dynamic variations of the current biomechanical model. The availability of a quantifiable morphometric assessment of hoof proportions and skeletal orientation and alignment may well enable accurate prescriptive farriery interventions such as heel or mediolateral elevations

INTRODUCTION

Farriery as a science has relied on the transfer of knowledge, custom and practice

from one generation to another.

Current farriery texts (Stashak. 2002; Butler. 2005) suggested that symmetrical

proportions of the hoof capsule at any two points around Lateromedial, dorsopalmar

axial coordinates and with the bearing border perpendicular to the longitudinal axis is

static “Foot Balance”, and the foundation of good farriery practice. This historical

interpretation of foot balance is largely based on the work of (Russell. 1897). More

Recent texts (Wilson et al; 1998; O’Grady & Poupard. 2003; Van Heel et al 2004)

however have focused on the need to achieve “Dynamic Balance” often defined as

uniform mediolateral impact and loading of the hoof suggesting a point of force

(POF) trajectory along the central axis through the stance phase.

The debate over the correct or desired proportions and angles that are associated

with a normal hoof capsule and what might constitute a balanced foot has teased

farriers and veterinary surgeons for generations. Turner (1992) proposed a series of

hoof measurements to assess static foot balance. These suggestions were made in

relationship to the proportions of a standardised model (Caldwell 2001). To this day

Russell’s (1897) model of symmetry within the equine foot remains the basis for

recommendations for corrective farriery intervention and manipulation of the hoof.

Turner and Stork (1988) attempted to define a number of hoof abnormalities,

including sheared and under-run heels, as deviations in height, angle or orientation

of specific areas of the hoof from the so called normal model. The authors failed to

describe any degree of biomechanical variance from the standard text model or

allude to a trimming technique from which abnormalities could be assessed more

objectively.

Debate amongst hoof-care professionals on what constitutes a normal balanced foot

rages to this day. Poor static and dynamic hoof balance is often cited as a major

causative factor in numerous foot and lower limb pathologies (Kane et al. 1998;

Eliashar et al 2004). Conventional farriery teaching is based on the principal that the

bearing border of the foot should be trimmed to the longitudinal axis in order to

centralise the point of force within the hoof capsule (Williams & Deacon 1999 &

Curtis 2002, 2006). The assertion is that a large portion of lameness seen today can

be treated with correct farriery intervention and all feet can and should be trimmed in

the same manner, including those exhibiting angular limb deformities (ALD). This

suggests that there is no link between the form and function of the hoof capsule and

skeletal orientation and implies that stability is not affected by variable loads

associated with different conformation types.

Van heel et al. (2004; 2006) suggested that the point of force is located medially to

the central axis of the frog, although the trimming method wasn’t specified in this

work. Eliashar et al. (2004) however, discovered that position of point of force could

be manipulated and moved towards the intervention applied. Unfortunately specific

details of neither the trim nor the intervention were given. Whilst neither author made

reference to a particular trimming protocol other than to quote hoof phalangeal

alignment as their basis for foot balance, they both suggested that these

manipulations of POF trajectory may be a significant factor in the pathogenesis of

major foot pathologies. This is in contradiction to suggestions made by Williams and

Deacon (1999) and Curtis (2002, 2006).

Whilst the trimming protocol given in this paper does not attempt to influence

conformational defects and ALD’s, it does result in the leading edge wall and sole

being weight sharing at the ground or shoe surface (Fig 4). It also gives a repeatable

standard by which loading over the foot during the duration of the stance phase can

be measured and the affect of interventions assessed more accurately.

There are numerous theories on the subject of trimming feet to balance.. Ovnicek

(1995) advocated the “Natural Balance” trim. Based on the interpretation of foot

condition in feral horses Ovnicek et al; (2003) suggested that the wall depth is

reduced to the level of non exfoliating sole, which they refer to as the live sole

margin and describes as a soft waxy type horn, through to the heel buttresses which

are trimmed to the ground bearing level of the frog at its widest point. The dorsodistal

margin of the toe is rounded to reduce leverage at enrolment with length of the frog

from palmar dorsally representing 2/3rd of the length of the bearing border heel

termination to the point of break over

Duckett (1990) suggested trimming the feet to a specific formula around the centre of

articulation of the distal interphalangeal joint (DIP) using external reference points

around the hoof capsule. Duckett theorised that the location of these external

reference points of the hoof give an indication as to the location of specific internal

anatomical and biomechanical land marks around which the foot should be trimmed

and or shod in order to achieve dynamic balance.

Duckett (1990) claimed his “Dot” located 3/8” palmar to the true apex of the frog is

representative of the location of the POF within the foot, proximal to the insertion of

the deep digital flexor tendon (DDFT) and distal to the insertion of the common

digital extensor tendon (CDET). Duckett’s “Bridge”, approximately 11/4” palmar of

the “Dot”, and visualised as the widest part of the bearing border is said to be

representative of the centre of rotation (COR) of the distal interphalangeal joint.

Duckett (1990) argued that COR the bearing border some 40% along its length

border from heel termination this is in sharp contrast to Colles (1983 & 1989) and

others (O’Grady and Poupard, 2003) who stated that a vertical line dropped from

COR should bisect the ground bearing border equally.

Savoldi (2006) utilised the uniformity of sole thickness (UST) as a term of reference

and links hoof form to the orientation and function of the internal structures. Savoldi

suggested that the form of the external hoof is directly related to the form and

function of the internal structures. UST has been used to quantify orientation of

internal structures in cadaver feet in saggital and frontal planes (Craig. 2005; &

Savoldi. 2006). Whilst UST may be a useful theoretical method in cadaver feet of

achieving a reference-based trim it may not be suitable on welfare grounds for use in

vivo research This is because of the difficulty in achieving a horizontal bearing

border hoof and sole plane in those feet exhibiting gross distortion, particularly where

the subsequent application of a level shoe may be required.

The conclusions of recent studies on the dynamic effects of foot trimming on the

stance phase (Balch et. al 1997, Van Heel et. al 2004, 2006) including point of force

loading and trajectory may have also been influenced by their trimming protocol and

biomechanical variation within their study group. However both Balch et al (1997)

and Van Heel et al (2004; 2006) cite the restoration of correct “Hoof – Pastern Axis”,

corresponding dorsal hoof wall and phalangeal angles, as their preferred method of

achieving dorsopalmar / plantar foot balance and make no reference to lateromedial

proportions.

Given the complexity of the biomechanical interactions of the foot and its internal

anatomical structures during impact and whilst under load it is difficult to see how

their results can be assimilated into every day farriery practice. Van Heel (2004)

suggested lateral first landing is common place contrary to Ovnicek & Page (2003)

who advocated heel first landing as the norm. Williams & Deacon (1999), Curtis

(2002) and Butler (2005) all suggested the attainment of level foot fall as the main

objective of farriery intervention. The authors also suggested dynamic efficiency is

achieved through equal mediolateral loading of the hoof capsule throughout the

stance phase all assume a centralised POF trajectory through the longitudinal axis of

the frog.

The Geometrical Proportions trimming protocol (GP) is aimed at restoring theoretical

static foot balance and is based on trimming the foot with reference to easily

recognisible external reference points along the bearing border of the hoof capsule.

which are thought to relate to internal anatomical or physiological structures at fixed

points within the foot (Duckett 1990). Elements of other previously described

trimming methodologies of Ovnicek (2003) and Savoldi (2006) are also utilised. The

aims of the protocol are to maintain a healthy hoof capsule that retains some degree

of weight sharing between the bearing border of the hoof wall, the leading edge of

the sole at its junction with the white line, bars and frog. Trimming in this manner is

thought to orientate the basal border of P3 parallel to the ground (Ovnicek. 2003;

Savoldi. 2006). Once the bearing border is trimmed in this manner the dorsal hoof

wall (DHW) thickness can be reduced without compromising its integral strength.

TRIMMING PROTOCOL.

Initial Assessment

The limb is assessed for conformational deviation and hoof capsule orientation using

lateromedial, dorsopalmar / plantar, solar and longitudinal axial projections (Fig.1).

Particular reference is made to hoof proportions at easily identifiable anatomical land

marks on individual projections of the hoof and their geometric relationship with each

other (Turner. 1988) in order to build a three dimensional mental image of the

finished proportions of the trimmed foot. The hoof wall phalangeal alignment, heel

toe height ratio as well as the height of wall from coronary band to ground bearing

border should be the same at any 2 opposite points (Hickman and Humphries 1987;

Stashak.1990; Butler 1988; 2005) form the basis against which initial assessment is

compared and from which post trim interventions and shoe modifications can be

calculated.

Frog, Sole and White Line

Since the trim relies heavily on the initial assessment and identification of anatomical

landmarks and proportions, it is essential that the co-lateral sulci are clearly visible to

their full depth and that the true apex of frog is identified, where the frog horn blends

into the solar horn. To achieve this The perioplic horn that envelops the heel

buttresses is removed to expose the collateral sulci to their full depth at the heel

termination. The collateral margins of the frog are trimmed along its entire length

forming an angle of about 55-60° with the bars (Fig. 2).

The exfoliating solar horn is removed, exposing confluent solar horn, identifiable by

the waxy horn at the sole white line interface at the soles leading edge (Ovnicek;

2003). This does not include the sole callus, the flat area of sole approximately 8mm

wide and found at the toe area between 10 and 2 o’clock (Ovnicek; 2003). The white

line is then exfoliated to reveal the sole and horny wall interface (Savoldi. 2006)

(fig. 2).

This is accomplished by:

1. Removing compacted and exfoliating sole from the seat of corn area between

the wall and the bar both medially and laterally

2. Removing exfoliating sole to live sole depth (Fig.2). This reveals not only the

true plane of the sole white line interface and restores the soles concavity

from the point of frog radially to soles leading edge but will reveal the amount

of excess dorsal hoof wall that can be safely removed from the solar surface

and the dorsal area by way of flare dressing (Fig.3).

3. Trimming all damaged structures back to viable tissue, cleaning any areas

suspect tissue likely harbour foreign debris or lead to infection.

4. Identifying the soles leading edge with the white line interface by carefully

removing the exfoliating horn at the sole leading edge from quarter to quarter,

with the knife in upright position The white line area is then exfoliated

exposing the true interface with the live sole (Fig. 2.).

5. Carefully removing the rest of the exfoliating solar horn; this reveals the true

solar plane (Fig.2).

The bars are trimmed to normal proportions, removing only damaged or weak horn,

to confluent bar tissue (Fig3). The ground bearing surface of the frog is trimmed

back, removing damaged and diseased tissue. The trimmed frog should be

proportionate to the foot with the caudal aspect of the bearing border level with the

horizontal plane of the wall and sole and able to allow ground contact during the

contact and loading periods of the stance phase (Fig.6).

Bearing Border

The excess wall at the bearing border is removed to the level of the sole producing a

horizontal plane (Fig.4) with the live sole. This determines the vertical height of the

DHW (Duckett. 1990).

Note: Before trimming the bearing border reassess the solar plane with the

long axis of the limb, it is not always practical to trim the bearing border

perpendicular to the longitudinal axis of the limb. In cases with even mild ALD

the bearing border is trimmed horizontal to the solar plane (Fig.4) taking into

account any wall flaring or hoof compression.

1. Excess hoof wall is removed parallel to the live sole from (the author prefers

to trim toe to heel others may trim commencing at the heel). Care is taken not

to trim down so far as to reduce the level of the previously trimmed sole (Fig.2

)

2. The heels are trimmed, reduced in height, to extend the bearing border to

approximately the widest part of the trimmed frog or the palmar / plantar

aspect of the exfoliated central sulci (Fig. 2 & 6).

Note: Before applying the final rasping the orientation of the bearing border to

both the longitudinal axis of the limb and the solar plane are visually re-

assessed for level.

3. Rasp the hoof with even pressure over the rasp, being careful not to rasp down past

the live sole, or to lower the bearing border below the sole.

Note: Trimming the bearing border and dorsal wall in this way is thought to

lead to an approximate heel to toe height ratio of 3:1 being maintained (Fig.

6).

Hoof Wall Shape and Thickness

Hoof Wall Thickness.

To determine the optimum thickness of the DHW we identify an external reference

point on the bearing border positioned 9.5 mm, in the average sized riding horse,

palmar to the true apex of the frog, often referred to as Duckett’s Dot. Duckett (1990)

and others (Chapman and Platt 1984) believe this to represent the theoretical

internal location of the centre of pressure (COP) at mid stance. The distance from

“Duckett’s Dot” to the outer edge of the medial wall should correspond to the

distance from “Duckett’s Dot” to the dorsal distal tip of the DHW (Fig.3). “Flare

dressing” the DHW back in line with this measurement determines P3 orientation

with the DHW without compromising the DHW’s structural integrity (Fig.8).

Note: Anatomically we visualize the COP as being located between the

insertion of the DDFT at the semi lunar crest and the insertion of the CDET at

its insertion around the extensor process of P3 (Arabian et al; 2001).

Hoof Wall Shape. Two imaginary lines are projected dorsally from the heel

buttresses parallel to longitudinal axis of the frog to intersect the white line sole

interface, the location of what has been referred to as the pillars (Duckett. 1990) (Fig.

5).

1. From the farrier position the toe is reduced in thickness and shaped at the

distal dorsal hoof wall symmetrically.

2. The medial and lateral hoof walls are reduced in thickness from toe pillar to

quarter, widest point of the foot, leaving an equal thickness of DHW from

quarter to quarter (Fig. 5).

Note: DHW thickness is determined by the width of the wall and the inner

border of the white line interface at the quarters.

3. The hoof is then brought forward and the DHW flare dressed, going no more

than approx. 25mm – 50mm dorsoproximal so as to not compromise the hoof

capsule’s integral strength (Fig. 6).

Note: The DHW is only flare dressed where there are deviations in symmetry

to correspond to the phalangeal axis. This leaves an equal amount of wall

from the white line / solar interface around the DHW circumference.

Dorsopalmar proportions were verified by comparison of physical toe length

measurements taken with engineers calliper / dividers to measurements from the

dorsodistal tip of the DHW to key external anatomical land marks along the bearing

border.

1. The linear length of the toe should then correspond to the distance from the

dorsodistal border of the toe to the widest point of the foot (Fig. 6). This is said

to represent the COR of the distal interphalangeal joint (Duckett. 1990;

Caldwell. 2001).

2. This measurement should also correspond to the distance from the position referred

to as Duckett’s dot or COP to the widest point of the frog at its juncture with the heel

bulbs (Fig. 6) (Duckett 1990).

The foot is said to be proportionate if all three distances are of a similar value± 6mm

(Mather et al; 2009).

Discussion

Science has yet to determine if the optimum trimming methodology is with the

bearing border perpendicular to the longitudinal axis of the limb or horizontally

planed with the sole. However with the bearing border trimmed to a horizontal plane

with the sole hoof wall proportions can be compared against easily identifiable

external anatomical landmarks and a series of measurements can be taken. It is

from this base that both farriers and veterinary surgeons could accurately calculate

interventions and gauge their effects on static proportions and dynamic variations of

the current biomechanical model.

We cannot state that the preceding technique of trimming the bearing border to the

solar plane constitutes what might be defined as correct static balance. It does

however appear to orientate the hoof capsule in line with skeletal deviations, and

may lead to a more accurate mediolateral and proximodistal orientation of the

skeletal structure with the bearing border of the hoof and placement of the hoof on

the ground at first strike. Accurate skeletal alignment and so called level foot fall are

thought to eliminate collateral motion, thought to be contributory factor in

degenerative joint disease (DJD) and desmitis (Dyson & Marks. 2003 and Chateaux

et al; 2005)

Given the long established link between general limb conformation and hoof capsule

morphology (Dollar and Wheatly 1897; Stashak. 2002) it would appear that dynamic

balance might only be achieved when the hoof is able to accommodate a range of

stresses. The ability of the foot to maintain optimum function throughout the stance

phase might more commonly be associated with a broader band of common hoof

capsule morphometric tolerances than the strict interpretation afforded by current

texts.

Savoldi (2006) described his UST trim as achieving uniform sole thickness around

the white line / solar interface. He also argued that the orientation of the solar plane

of P3 within the hoof can be related to specific pathologies. In addition to measurable

dorsopalmar proportions preliminary studies (Balchin. et al 2009; Mather. et al 2009)

suggested that when feet have been trimmed in this manner the external references

cited by Duckett (1990) would appear to be an accurate representation of the

location of the internal biomechanical positions of both COP and COR ± 4%.

It would seem reasonable to assume that the range of (SD) provisionally referred to

might be an acceptable basis on which further data can be collated. Further

radiographic, cadaver and in vivo studies are ongoing. Our initial results (Caldwell

and Reilly 2010 unpublished data) appear broadly comparable with a parallel study

on Australian Brumbies in New South Wales (Hampson and Pollitt 2010 personal

communication unpublished data).

The horizontal hoof plane element of this trimming technique allows for more

accurate evaluation of radiographic measurements in the treatment of lameness

(Vargas et al; 2004 & Kummer.et al 2006). The availability of a quantifiable

morphometric assessment of hoof proportions and skeletal orientation and alignment

may well enable accurate prescriptive farriery interventions such as heel or

mediolateral elevations (Chateaux. et al; 2006; Kummer et al 2006).

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Illustrations

Fig.1 After Stashak (2002) the assessment of limb conformation and hoof capsule

orientation prior to trimming. a) Axial limb / hoof deviations dorsal palmar projection.

b) Metacarpal hoof orientation Lateral medial projection. c) Heel and heel bulb

displacements plantar dorsal projection. d) Medial lateral hoof capsule deviation

Dorsopalmar projection. e) Phalangeal hoof orientation Lateral medial projection. f)

Bearing border orientation. The pink Lines are representative of common hoof

capsule relationship viewed in the so called “normal foot”

Fig. 2. After Savoldi (2006) foot mapping protocol. With frog trimmed and sole and

white line exfoliated in preparation for trim (Savoldi 2006).

a) The white line is then exfoliated to reveal the sole and horny wall interface.b) Removal of the remaining exfoliating solar horn reveals the true solar plane.c) The bars are trimmed to normal proportions, removing only damaged or weak horn.d) The frog is trim back to live frog and proportionate to the foot.e) The excess wall at the bearing border is removed (red arc) to a horizontal sole

plane (yellow arc). f) Excess hoof wall is removed parallel to the live sole (care is taken not to trim

down so far as to invade the live sole) (Fig 4a).g) The heels are trimmed approximately to the widest part of the trimmed frog or

the palmar / plantar aspect of the exfoliated central sulci (Fig. 4a).

Fig. 3 Exfoliating the white line solar junction requires care. With the knife held

between the white line and the sole at the angle of the wall (left) it is pushed through

the soft waxy white line horn by the supporting thumb until the solar interface is

revealed. This gives the practitioner an indication of both depth of sole and thickness

of wall prior to reducing the bearing border (right).

Fig. 4 Trimming protocol with the bearing border trimmed to a horizontal solar plain

(Savoldi 2006). The excess wall at the bearing border is removed to a horizontal

plane with the live sole; this helps determine the vertical height of the dorsal hoof

wall (Fig.6) (Duckett. 1990).

Fig. 5 Once the bearing border is trimmed the Dorsodistal wall thickness (red) is

reduced with a rasp to the same thickness from medial to lateral COR.

Note: perpendicular lines projected dorsally from the heel buttresses intersect the

toe in the region sometimes referred to as toe pillars (Duckett. 19990). Diagonal lines

projected from the heel buttresses to the toe pillar should intersect the COR along

the longitudinal axis of the frog.

Fig 6 After Duckett (1990) Verification of external measurements for the geometric

proportions trim. If all three distances are of a similar value± 6mm and the heel toe

height ratio is approximately 3:1 (Mather et al 2009) the foot is said to be

proportionate.