ARCHIVE - ARTICLES 2009

April 09 - A preliminary study of a geometric proportioned foot trim on the bearing surface of the equine front foot

April 09 - How to make a concave bar shoe

 

Archive - Forge Magazine - April 2009
A preliminary study of a geometric proportioned foot trim on the bearing surface of the equine front foot

By Jon Mather, DWCF; Mark N. Caldwell, FWCF and Professor John Reilly, BSc, PhD, MRCVS

Summary

The reason for performing the study was to try to quantify a foot trimming protocol that would meet static and dynamic foot balance criteria. The objective was to check the validity of the geometric proportions theory (Duckett 1990), and to investigate the relevance of the centre of rotation (COR) to centre of pressure (COP) measurements in relation to the other anatomical reference points on the basal ground bearing surface of the hoof, and their possible relationship with foot function and hoof mechanism.
The hooves of 25 cadaver lower limbs were photographed and measured using a computer software analysis system (Ontrack) in five states: pre-trim, post-trim (eight, post-shoe), digital x-ray and post-sagittal dissection.
Duckett’s theory proved to be valid, with the toe to centre of rotation measurement and the dorsal toe length having a 1:1 ratio, and the centre of pressure/centre of rotation measurement proved to be inversely linked to heel width. The research did not support the common belief that the centre of rotation equally bisects the ground bearing surface.
In conclusion, Duckett’s theories stand up to scientific scrutiny, and the centre of pressure/centre of rotation measurements relate to heel width and, as a result, are linked to foot function and hoof mechanism. The centre of rotation splits the trimmed ground bearing surface of the foot 60:40 dorso/palmar.

This study provides a solid foundation of basic data that facilitates progression towards a science-based trimming and shoeing protocol that achieves the optimum biomechanical function for any given conformation.

Introduction

The trim adopted is based on geometric proportions of the external structures of the hoof that correspond to the internal physiology and anatomy of the foot (Duckett 1990, Russell 1908, Ovnicek 1997 and Savoldi 2003). This work mainly concerns assessing the validity of Duckett’s theories that dorsal toe length equals the distance from toe to centre of rotation of the distal interphalangeal joint in the trimmed foot, and the relationship between the marked centre of rotation and the marked centre of pressure (Duckett’s dot) when compared to other external anatomical reference points of the solar aspect of the trimmed hoof.
Any relationships of geometry and anatomy found would be cross-referenced with the parallel studies of foot shape (D’Arcy 2008, unpublished data) and bone length of P1 and P2 (Conroy 2008, unpublished data) and sagittal dissection.

Materials and Methods

Twenty-five cadaver limbs were removed above the carpus (to preserve suspensory attachment).
The equipment used included clippers, a hoof trimming kit (standard farriers’ tools), digital cameras (Fuji Finepix and Kodak C875 zoom), a photographic box with calibration and a digital software analysis system (Ontrack) on a laptop computer.
The hairline the limbs was shaved to enable accurate measurements to be taken from the coronary hairline as a proximal reference point. The legs were scored for conformation and marked, for example, toe in/toe out, near fore/off fore, and so on. They were labelled A to Y, and photographed in dorsal view; palmar view; lateral view (medial/lateral) and solar view.
The photographs were taken in a specially made box, which incorporated a calibrated ruler to ensure consistent accuracy of the Ontrack digital analysis system. The feet were trimmed to a strict protocol as set by M. Caldwell.

Trimming protocol

The trimming protocol utilises a combination of uniform sole thickness (Savoldi 2006) and geometric hoof proportions (Duckett 1990, Ovnicek 1997 and Caldwell 2006).
Uniform sole thickness
The exfoliating sole is removed to live sole including the sole callus found at the toe area between 10 and 2 o’clock.
The white line is exfoliated to reveal the sole and horny wall interface.
The bars are removed to live bars. The frog is trimmed back to live frog and proportionate to the foot with ground pressure engaged when the foot is static.
The excess wall at the bearing border is removed to a horizontal plane to the live sole.
Duckett’s theory
Duckett’s theory is based on external reference points as a guide to identifying anatomical structures within the hoof. Duckett advocates trimming away the chalky sole and trimming the wall to live sole. This determines dorsal wall height. To determine how far back the dorsal wall should be dressed he uses an external reference point 10 mm back from the true apex of the frog in the average-sized riding horse. This is known as Duckett’s dot (this measurement is said to correspond to the point directly below the insertion points on P3 of the extensor tendon and deep digital flexor tendon). A measurement from the dot to the outer edge of the medial wall should correspond to the distance from the dot to dorsal hoof wall at the toe. Rasping the dorsal wall back to this distance will ensure the dorsal wall is parallel with the dorsal surface of P3. The toe length should then correspond to the distance from the toe (ground bearing surface) to the centre of rotation of the distal interphalangeal joint. This measurement should also correspond to the distance from the dot to the last weight-bearing point of the heel.

Foot trimming protocol

■ Exfoliate the area from the seat of corn to the true point of frog medially and laterally.
■ Trim the bars to normal proportions, removing damaged or weak horn.
■ Continue to remove sole to live sole depth, identifiable as waxy horn at the sole white line interface at the sole’s leading edge. Trim all damaged structures back to viable tissue cleaning any questionable areas.
■ Identify the sole’s leading edge with the white line interface by carefully removing the horn at the sole leading edge from quarter to quarter, with the knife in upright position.
■ Revealing the true position of the sole white line interface determines 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.
■ Carefully remove the rest of the solar horn to reveal the true solar plane.

Trimming the bearing border

■ Before trimming the bearing border, reassess the solar plane with the long axis of the limb. This is not always practical if there are angular limb or hoof capsule deformities. In this case the bearing border is trimmed with the solar plane taking wall flaring or hoof compression into account.
■ Excess hoof wall is removed parallel to the live sole from toe to heel; care is taken not to trim down too far and invade the live sole.
■ The heels are trimmed (approximately) to the widest part of the trimmed frog, or the back of the central sulci.
■ Before applying the final rasping, the long axis and the solar plane is assessed.
■ Rasp the hoof using even pressure over the rasp, being careful not to rasp down past the live sole, or lowering the bearing border below the sole.

Hoof wall shape and thickness

■ The hoof wall is shaped at the wall border to a medial/lateral balance.
■ The wall thickness is determined by the width of the wall and the inner border of the white line interface at the quarters.
■ The wall is backed up dorsally from quarter to quarter.
■ The hoof is brought forward and flare dressed, going no more than approximately 25 mm up the wall so as not to compromise hoof capsule strength.
■ Once trimmed, the feet were re-photographed. Eight of the feet were selected for shoeing and shod by co-workers with fullered concave fitted to a leisure horse style, as defined in the National Standards of Competence (FTA 2007). The feet were photographed again.
■ The digital photos were downloaded onto a laptop and measured using the a digital software analysis system. The measurements taken were from external anatomical reference points as follows;
Dorsal view
CBT Coronary band vertical height at toe, CBM Coronary band vertical height medial wall, CBL Coronary band vertical height lateral wall, HWLM Hoof wall length medial, HWLL Hoof wall length lateral, MWA Medial hoof wall angle, LWA Lateral hoof wall angle.
Palmar view
MBH Medial bulb height. LBH Lateral bulb height, HD Distance between heels at bearing surface, MHA Medial heel angle, LHA Lateral heel angle, CBM Coronary band height medial, CBL Coronary band height lateral
Lateral view
TL Toe length of dorsal wall, TA Toe angle, HL Heel length, HA Heel angle, HH Heel height.
Solar view, palmar dorsal
(All measurements are taken from the palmar ground-bearing surface of the heels)
H Datum, COR Centre of rotation, COP Centre of pressure, FRA Frog apex, BO Breakover, WL White line, T Toe,
Solar view, medial lateral
(Frog axis median plane = 0 Datum)
CORM Centre of rotation (medial), CORL Centre of rotation (lateral), COPM Centre of pressure (medial), COPL Centre of pressure (lateral), FRAM Frog apex (medial), FRAL Frog apex (lateral), MBO Medial Breakover, LBO Lateral Breakover, MH Medial heel, LH Lateral heel.
The pictures were measured digitally, the calibration being taken from the photographic box. Ontrack digital measuring is accurate to 1 pixel.
All the data were entered onto a Microsoft Excel spread sheet (Mather 2007) using individual tables for each photographic view taken. Unlike the other measurements taken the centre of rotation of distal interphalangeal joint, and the centre of pressure, were not physical external structures but external reference points relating to internal physiological structures. The centre of rotation was mapped onto the solar surface of the foot by marking two vertical parallel lines through the centre of each heel and forward through the toe quarters. A horizontal line was placed across the toe where the two vertical lines bisected the white line and a second horizontal line was placed across the heels at the widest part of the frog. Two diagonal lines were used to find the centre of the box created, a horizontal line drawn through the centre of the ‘x’ was deemed to correspond to the centre of rotation, and also the widest part of the ground bearing hoof.
Unlike the centre of rotation, the centre of pressure is not a fixed anatomical point and will move or change during landing, loading and breakover phases of the temporal stride pattern due to the changing position of the centre of mass. The centre of pressure was therefore marked in accordance with Duckett’s theory (Duckett 1990) of where this point would be at mid stance. In the average horse, this point is said to be 10 mm back from the true point of frog and should be directly below the attachment of the superficial extensor tendon and the insertion of the deep digital flexor tendon. For this study, the centre of pressure measurements were marked 10 mm back from the apex of the frog. The accuracy of this arbitrary measurement would be checked later when the feet would be radiographed (Conroy 2008, unpublished data) and then finally dissected. (Balchin and Mitchel 2008, unpublished data). The feet were initially categorised into five groups using visual examination of the bearing border outline shape. Subsequent data from a parallel radiographic study reduced this to four distinct foot shapes. From data gathered from the x-rays, the feet were placed into four sub-groups defined by the bone length ratio of the proximal and middle phalanges. In order to compare data collected with other studies the groups were colour coded, orange, purple, red, and grey. The feet could then be analysed as a group or compared as sub-groups. Data results for this study are recorded with these colour groups.

Results

Toe length (TL) versus toe to centre of rotation (T-COR).

COP/TL/T-COR as percentage of T averages
Group
Orange
59.99% ± 2.88% standard deviation
Purple
59.81% ± 3.01% standard deviation
Red
59.22% ± 6.75% standard deviation
Grey
59.94% ± 0.98% standard deviation

TL was greater than T-COR in 20 of the 2 feet studied (80 per cent) by an average ratio of 1.06:1 (see Fig 1).
The group averages were added together to give whole group percentage averages for each measurement.
Combined group average, centre of pressure percentage of toe measurement equals 57.66% ± 4.31% standard deviation
Combined group average toe length percentage of toe measurement equals 62.2% ± 2.3% standard deviation
Combined group average toe centre of rotation percentage of toe measurement 59.36% ± 0.9% standard deviation
A combined group centre of pressure, toe length, toe centre of rotation average was calculated 59.74%. ±2.45% standard deviation
Toe measurement (heel to toe) versus CORM plus CORL (hoof width)
Hoof width was greater in 22 of the 25 feet studied (88 %) by an average ratio 1.04:1
(see fig 3).
To remove the variable of hoof size the individual foot scatter graph was calculated as percentages. The COP COR was calculated as a percentage of width, whereas the heel width was calculated as a percentage of the heel to toe measurement due to the widely recognised morphological link between long toes and week under slung heels. The inverse relationship between heel width and COP COR can both be seen as a percentage of toe measurement in Fig 6

Frog apex and COR as a percentage of T

Percentage ratio of frog (FRA) of basal length (T) was as an average of the group averages 66.79 % this fits in with Ovnicek’s findings of the frog being two-thirds of the basal surface.
The COR was found to be on group average 40.64 per cent of the ground bearing surface T (basal length heel to toe) Fig 7.
This figure was consistent on all feet regardless of foot shape or size and does not agree with the commonly held belief of a 50:50 split, such as Williams Deacon (1999). The average group centre of rotation measurement was 40.64 per cent ± 0.96 per cent standard deviation. The standard deviation shows just how consistent this figure is.
The group averages of heel width and centre of pressure-centre of rotation were expressed as percentages of the groups’ average width and then added together; orange, 68.49 per cent; purple, 68.53 per cent; red, 69.09 per cent; grey, 65.45 per cent. This gave an overall group average of 67.89 per cent (standard deviation ± 2.44 %), which is approximately two-thirds of the width measurement. It is interesting to note how consistent this ratio is across the groups, given the different foot shapes.

Discussion

The feet were grouped by bone length ratio of P2 to P1 (Conroy 2008, unpublished data) and gave four distinct foot shapes (D’Arcy 2008, unpublished data). Across the groups there were consistent percentage findings on anatomical references, suggesting that although some feet appeared longer and narrower (grey group) and others wider and more upright (red group), they were trimmed correctly for their individual conformation and physiology.
Our research showed a trend for an inverse relationship between heel width and the centre of pressure/centre of rotation measurement, for example, the greater the heel width, the closer the centre of rotation was to the centre of pressure. This measurement may be viewed as a guide to foot function and hoof mechanism, and more research needs to be done to confirm this. As stated in the introduction, the centre of rotation is anatomically fixed by the pedal bone and the bony column above it.
Empirical evidence has shown that with neglect a healthy functional foot can become dysfunctional, and so one would assume that the centre of pressure-centre of rotation measurement would alter with changing hoof morphology. Take a hoof that has contracted, the centre of pressure/centre of rotation measurement should have increased if this theory is correct. As the centre of pressure was measured on all feet 10 mm back from the true apex of the frog it would appear that the anatomically fixed centre of rotation has moved? The author postulates there are three possible reasons for this:
1. The methodology for mapping the centre of rotation may not be as accurate on contracted feet as on normal feet, the dissection work being carried out by co-workers Balchin/Mitchel 2008, unpublished data) and radiographic study by Conroy (2008 unpublished data) should verify the accuracy of this.
2. The trimmed apex of the frog has migrated forward with the solar plate as the toe has become elongated?
3. The COR is anatomically fixed to its present or current hoof morphology. As the morphology of the hoof begins to alter from functional to dysfunctional, the orientation of P3 moves palmar distal. As the heels start to collapse, the extensor process of P3 tips back and the bone assumes a ground parallel position, the centre of articulation of the distal extremity of P2 will also correspondingly have to move caudally. This may explain the compressed palmar aspect of the foot. More research needs to be done to confirm or disprove the above theory as a mechanism of foot function/dysfunction.
Interestingly, each group’s average centre of pressure-centre of rotation and heel width measurement added up to two-thirds of the average width, further confirming a correlation between these measurements.
Surprisingly, the centre of rotation bisected the ground-bearing surface of all the feet in a near 60:40 split regardless of hoof shape or conformation. This is in marked contrast to claims made in many books and articles on farriery (Williams and Deacon, 1999), which states the centre of rotation of the coffin joint should bisect equally the ground-bearing surface of the foot. Our findings did, however, concur with a recent study (Craig and Craig 2005) in not supporting this 50:50 split. Their study found an average of 67.06 per cent of the ground bearing surface in front of the centre of rotation but had a higher standard deviation of 5.41 per cent (our study found 0.96 per cent). Although their study was based on radiographic evidence and not external reference points, they did not state what foot trimming protocol was used and so foot trimming may account for this variable. Duckett (1990) states the junction between the navicular and P3 as the centre of rotation of the distal interphalangeal joint, and refers to it as the ‘bridge’. Duckett cites the bridge as the balance point between the anterior and posterior halves of a well-shod foot. Although the base length Duckett refers to is from the dorsal toe to the bulbs of the heel, which is greater than the ground bearing surface toe to heel and where he believes the heels of the shoe should be fitted too. It is interesting to note that in all four groups the toe length/centre of pressure/toe to centre of rotation average was within less than 1 per cent of a 60:40 split.
Given the results of this preliminary study, the only way these feet would achieve a 50:50 split in the ground bearing surface would be with the application of a shoe, although the dynamics of the shod foot is different to the unshod foot. A live horse study by co-workers A. Shuttleworth and D. Beardmore should shed light on this. The only way a bare foot horse may naturally have a centre of rotation 50:50 split in ground bearing surface may be when it has a broken forwards hoof pastern axis, which is a conformational trait, clearly more research would be needed to see if this was the case.

Conclusion

Duckett’s theory stands up to scientific scrutiny with only the red group showing a larger than 5 per cent difference between centre of pressure and toe length and toe to centre of rotation but this group was statistically weak with only three feet included. The centre of pressure/centre of rotation measurement seems to be related to heel width and, as a result, could be linked to foot function and hoof mechanism, but a larger group study with feet showing pathology would be needed to confirm this. The centre of rotation of the distal interphalangeal joint bisects the ground-bearing surface of the correctly trimmed foot in a 60:40 dorso/palmar split. The trimming protocol produces the optimum physiological proportions for the hoof regardless of foot size, shape or conformation, without compromising structural integrity of any structure and this must benefit function.

References

CALDWELL, M. (2006)
CRAIG, J. J. & CRAIG, M. F. (2005) Hoof and Bone Morphology of the Equine Digit: American Farrier’s Journal.
DUCKETT. D (1990) The assessment of Hoof Symmetry and Applied Practical Shoeing by Use of an External Reference Point. International Farriery and Lameness Seminar. Newmarket, England. Second supplement,
p 1-11.
OVNICEK, G. D. (1997) New Hope for Soundness. EDSS Publishers.
RUSSELL, W. (1908) Scientific Horseshoeing. Robert Clark Company, Cincinnati Ohio.
SAVOLDI, M.T & ROSENBERG, G. F. (2003) www.americanfarriers.org
WILLIAMS DEACON (1999) In No Foot, No Horse, figure 3.1
P. Conroy (2008 submitted)
C. D’Arcy (2008 submitted)
P. Balchin & D. Mitchel (2008 submitted)
A. Shuttleworth & D. Beardmore (2008 submitted)
M. Oliver & M. Jones (2008 written up Foot Trimming Protocol submitted)

 

Toe length versus toe to centre of rotation

Centre of pressure (COP) versus toe to centre of rotation (T-COR) versus toe length (TL). The feet were organised into their colour groups and the heel to centre of pressure. Toe to centre of rotation (T-COR) and dorsal wall toe length (TL) were calculated as group averages, they were then calculated as a percentage measurement of their respective group average heel to toe measurements (T) thus removing the foot size variable (see Fig 2)

Centre of pressure versus toe length versus toe centre of rotation as a percentage of toe measurement.

Duckett theorised that in the properly trimmed foot, the above three measurements (COP, TL and T-COR) would be equal. The percentage measurements for each group COP, TL and T-COR were combined to calculate an average for the three measurements; the standard deviation figure would indicate how closely they were correlated.

Figure 1. Hoof width versus heel to toe measurement

The group hoof width versus heel to toe measurement (T) shows the red group to have the shortest basal length percentage ratio of 92.28% and the purple group the greatest at 98.62 % (see Fig 4)

Figure 2. Heel to toe as a percentage of width

The average COP-COR ratio of width was approximately one sixth at 6.08:1 the average COP-COR ratio of T was 5.84:1, see Fig 2. The average heel width was 63.40 mm and the average COP-COR 20.07 mm this gave a ratio of 3.15:1

Figure 3. COP-COR versus heel width scatter graph

Individual scatter graph showing trend line, demonstrating a correlation between a large COP COR and reduced heel width. The trend line in the group scatter accentuates this correlation, although the red and grey groups that cause this are statistically weak. This could be because the 25 feet chosen did not have any major pathologies.

Figure 4. Heel width/COP COR percentage of T

Trend lines above show inverse heel width COP-COR relationship.

Figures 5, 6 and 7

 

Archive - Forge Magazine - April 2009
How to make a concave bar shoe

World Champion Farrier Richard Ellis demonstrates how he makes a concave bar shoe at his forge in Tewkesbury

Forging is, of course, the primary process used for making horseshoes. Despite the fact that improvements in horseshoe design have reduced the amount of forging work required by farriers, the skill involved in making horseshoes has to be successfully mastered in order to gain the diploma of the Worshipful Company of Farriers. The skill of forging shoes is practised by all farriers, and is essential for those who wish to achieve higher examinations. Success in the Associateship allows farriers to take on more challenging cases that may require therapeutic shoes to be made on a regular basis.
Horseshoe-making competitions form a popular part of many agricultural shows up and down the country – popular for visitors and competitors alike – culminating in championship status for the very best. For some time now, readers have asked for picture-based articles showing how to forge horseshoes, and Forge is indebted to World Champion farrier, Richard Ellis, who demonstrates how he makes a concave bar shoe at his forge in Tewkesbury.

This technique requires a little practice. When mastered you can make good bar shoes with a large frogplate very efficiently. Good luck

1 - Take a suitable length of concave for the bar shoe allowing enough material for the shoe plus the bar. Practice the technique so you are familiar with how much material is used in the bar

Figs 2,3,4 - Heat the bar about 1 to 1.5 inches at one end and bump up slightly on the face of the anvil (fig 2), then finish bumping over the edge (figs 3 and 4)

Figs 5,6 - Turn the toe bend for the shoe

Take a short hot heat at the end of the bar and turn a sharp 90 degree bend being careful not to twist or squash the section (figs 7, 8 & 9). Note – ‘hockey sticking’ concave does not work very well as the section collapses when you knock it back on itself so try to get a good tight bend

Scarf the end of the bar (figs 10 & 11). With concave I usually roughen the scarf surface as I thin the ends to prevent the weld slipping open when I weld. Knock the tip of the scarf back (fig 12) so when you overlap the scarfes the tips don’t stick out either side.
Turn the branch of the shoe (fig 13)

Figs 14,15,16 - Turn the branch of the shoe (fig 13), then repeat the process for the other branch (figs 14 & 15) making sure the shoe is balanced and the scarfes overlap the same amount (fig 16)

Fig 17 - The scarfes ready for welding. Fig 18 - Flux scarfes if required.

Take a full welding heat and tack the eges of the scarfes taking care not to reduce the thickness of the section and not to make deep hammer marks on the surface (fig 19). Reduce the centre of the weld to form the frog plate (fig 20). Whenever you are forging the welded area always keep the temperatures high to avoid stressing the weld.
You can improve the look of the weld by fullering either across the bar or towards the centre of the frog plate (fig 21) and finishing off with a rasp (fig 22)
You now have a blank bar shoe you can either toe clip, side clip or roll the toe, whatever you wish (fig 23)