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