Do Horses Stand with Phalanges Aligned? by EponaMind

Volume 5 Number 5 | September 2021

FORGE Monique Craig BSCE, APF

John Craig PhD

Monique Craig has spent many years researching, trimming and shoeing the hoof. Her research has been presented at veterinary and farrier conferences and in various publications. Together, she and her husband developed the Metron Imaging system; Monique also invented the EponaShoe.

John Craig has a PhD in engineering and is the author of ‘Introduction to Robotics: Mechanics & Control’. He has researched the hoof and shoeing systems for 20 years, and is the lead software developer for the Metron Imaging system used for digital radiography and other veterinary imaging modalities.

Tracy Turner DVM, MS, DiplACVS, DiplACVSMR Tracy Turner began his professional career as a farrier and used those skills to help finance his education. He received his DVM degree from Colorado State University in 1978, completed an internship at the University of Georgia and a surgical residency at Purdue University. At the University of Minnesota, he was Head of Large Animal Surgery and attained the rank of full Professor before leaving academia. In 2016, he started his own practice dedicated to sports medicine and surgery. His primary research efforts have focused on equine lameness with particular interest in equine podiatry, back issues in horses, rehabilitation and thermography.

Derek Poupard CJF, DipWCF Derek Poupard is the owner and inventor of 3D HoofCare and HoofCast. His farriery career began in South Africa and he has since been given the opportunity to work in the USA, Dubai and the UK on the highest-profile horses in the world. Having spent most of his career ambitiously trying to improve the quality of horses’ hooves, he has recently begun to use 3D printing to create his HoofCare product, and has developed it alongside his HoofCast product, with the goal of emulating the horse’s hoof in its natural state of being barefoot.

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CONTENTS

Phalangeal alignment assessed

3D printing a bespoke shoe

Research article

Technical article

41 Do horses stand with phalanges aligned?

44 3D technology in a vet-farrier joint venture

By Monique Craig BSCE, APF, Tracy Turner DVM and John Craig PhD

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RESEARCH ARTICLE

Do horses stand with phalanges aligned? It is commonly believed that the ideally conformed horse should stand with the phalanges of its lower leg aligned – but there appears to have been little research into whether horses do typically stand in such a way. Here, Monique Craig, Tracy Turner and John Craig study an extensive collection of radiographs to explore the alignment of the phalanges in a general population of horses. There is a common perception, supported by the literature, that the phalanges of the lower leg of the horse should be ‘aligned’ in an ideally-conformed horse (Back & Clayton 2013, Parks 2010). Many hoof care practitioners promote the use of trimming techniques and/or wedge pads as needed to bring the phalanges into alignment. However, we ask the question: do horses typically stand with phalanges aligned? If they don’t, should they be made to for therapeutic or performance reasons? The extent to which the phalanges are aligned can be measured on a well-taken lateral-medial radiograph of the hoof and lower leg. In many lay articles, lines are drawn on radiographs to shown alignment (or lack thereof) – but often it appears that no careful methodology was used to position these lines. We have previously documented and published a rigorous method to measure the rotations of the coffin joint and pastern joint and to assign a ‘zero’ location for these angles (Craig et al 2001). The methodology is strongly related to engineering methods used to quantify machines with rotating parts, such as industrial robots (Craig 2016). This measurement methodology is included in the commercial software package Metron-DVM (EponaMind 2020) and we have used that system for the measurements reported in this article. To answer the central question posed in the title of this article, we wanted to measure as many horses as possible. We believe that the best way to measure alignment is with the use of radiographs, and hence the population of horses we needed to assess was those that had been radiographed. We collected radiographs from veterinary clinics in the USA, Europe, South Africa and Australia. We believe our sample is representative of horses that are being radiographed in veterinary clinics. We do not have data on the reason the radiographs were taken. Presumably, many of the horses had some lameness issue for which they were radiographed, but others might be from prepurchase exams or reasons not associated with lameness. Given a large enough sample, however, we are able to make valid statistical claims about how horses stand, at least within the population of horses that have been radiographed.

The data Population #1

From a total of 16,922 lateral hoof radiographs from over 40 clinics around the world, we extracted only those that were taken on a calibrated hoof block (Craig & Craig 2019a), which reduced our pool of radiographs to 7577 images. Next,

we selected only front feet, and we removed any multiple images of the same hoof, resulting in 2604 images of which 1284 were of the right fore and 1320 were of the left fore. Some were metal shod, some plastic shod and many were barefoot. Some of the hooves had wedge pads and other shoeing systems that would alter the angular measurements that we wanted make (for example, we measured ‘palmar angle’ relative to the top of the block, so a wedge pad would increase this value). This group of 2604 images formed population #1 – the population of front feet that had been radiographed at clinics around the world.

Monique Craig BSCE, APF

Tracy Turner DVM

Population #2

In a study of this sort, there is a strong urge to remove obvious founder cases and images containing large wedge pads or other stance-altering artificial John J Craig PhD systems. To form the subset we called population #2, we removed 216 images (8.25%) with the most obvious founders and wedge pad systems. We also removed images from yearlings and miniature horses. Our resulting population #2 comprised 2388 images and contained only feet that were barefoot or flat-shod, so that artificial alteration of stancerelated measures was minimised.

Comparing palmar angles

Studying the palmar angles in the 2604 radiographs of population #1, indicated a median angle of 5.12 degrees and an average angle of 5.69 degrees (standard deviation [SD] 4.28 degrees). Due to our sample size, it is possible to say with 99% confidence that the average palmar angle of population #1 is within the bounds 5.47–5.91 degrees. In population #2, a study of the palmar angle results in the 2388 radiographs showed a median angle of 4.89 degrees and an average angle of 5.16 degrees (SD 3.63 degrees). Due to our sample size, we can say with 99% confidence that the average palmar angle of population #2 is within the bounds 4.97–5.35 degrees. Not unexpectedly, by removing hooves shod with wedges, and removing obvious founder cases, the average palmar angle

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RESEARCH ARTICLE

Fig 1: A straight line passes through the centres of rotation of the fetlock joint, the pastern joint and the coffin joint. This line is aligned with the cranial surface of the P3 bone, and (generally) with the dorsal wall of the hoof capsule. In this study, this positioning was taken as the ‘zero position’ – that is, ‘phalanges aligned’ – for the pastern joint and coffin joint. A ‘positive’ sense for each joint was deemed to be the direction that tended to make the bone become more upright

declines. But we removed only about 8% of the original image pool, and the change in palmar angle statistics is not huge. In the remainder of this article, we will report on population #2.

Joint angles and stance

Following the methodology described in Craig et al (2001), we measured the stance angles for the 2388 images representing population #2. For the purposes of this study, it is important to review the ‘zero position’ of joints according to that methodology. Fig 1 shows the lower leg with ‘phalanges aligned’ – meaning that both the coffin joint and the pastern joint are located at their respective zero positions. Our methodology adopts this same definition of the zero position of the pastern and coffin joints – so phalanges aligned is the same as saying that both joints are rotated to their zero position. In Fig 2 we show an example of a lateral radiograph with our measurement system applied. The palmar angle is 1.18 degrees, the coffin joint angle is 16.95 degrees, and the pastern joint angle is 4.89 degrees. We often do not show the fetlock joint angle as many radiographs are cropped so that the fetlock is not fully visible.

Fig 3: Histogram of the coffin joint angle for 2388 hooves: median = 10.1 degrees, average = 10.0 degrees, SD 8.19 degrees, 99% CI 9.57, 10.43 degrees. The vertical red line indicates the ‘phalanges aligned’ position – most horses stand to the ‘upright side’ of aligned

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Fig 2: Measurement example: the palmar angle is 1.18 degrees, the coffin joint angle is 16.95 degrees and the pastern joint angle is 4.89 degrees. The measuring methodology is described in detail in Craig et al 2001

Horses have a choice of how to stand: even while keeping the cannon bone vertical, there infinite choices for the coffin joint angle and pastern joint angle that the horse may adopt. The choice is made based on required muscular activity, comfort and habit.

Results The average coffin joint angle in population #2 was 10.0 degrees and the average pastern joint angle was 4.8 degrees. Figs 3 and 4 give more detail. We also find it convenient to talk about the sum of the coffin joint angle and the pastern joint angle, which we will call ‘uprightness’. The histogram of ‘uprightness’ for our 2388 hooves is shown in Fig 5. Our data show that the average horse does not stand with phalanges aligned. On average, the coffin joint is ‘broken back’ by 10.0 degrees and the pastern joint is ‘broken back’ by 4.8 degrees. The average ‘uprightness’ of the standing horse in population #2 is 14.8 degrees (99% confidence interval [CI] 14.3, 15.3 degrees).

How does stance vary with the size of the horse?

Studies on leg posture in animals (Biewener 1989) have shown

Fig 4: Histogram of the pastern joint angle for 2388 hooves: median = 4.9 degrees, average = 4.8 degrees, SD 4.35 degrees, 99% CI 4.57, 5.03 degrees. The vertical red line indicates the ‘phalanges aligned’ position – most horses stand to the ‘upright side’ of aligned

RESEARCH ARTICLE

Fig 5: The ‘uprightness’ of 2388 lower legs: median = 14.8 degrees, average = 14.8 degrees, SD = 8.64, 99% CI 14.3, 15.3. The vertical red line indicates the ‘phalanges aligned’ position – most horses stand to the ‘upright side’ of aligned

that larger and heavier animals tend to stand with a more upright leg posture than smaller, lighter animals. Presumably, this is because the muscular effort needed to stand is reduced with a more upright posture. Smaller, lighter animals choose to stand more crouched because it gives an advantage should it become necessary to flee. The major bend in the standing horse’s leg is at the fetlock. Our measure of ‘uprightness’ affects the size of the angular bend at the fetlock. Assuming an approximately vertical cannon bone, the size of the angular bend at the fetlock is reduced as the lower leg’s uprightness increases. Hence, an increased uprightness in the lower leg should reduce the muscular activity required by the bent fetlock. So, we ask the question: as the horse becomes larger and heavier, is there (on average) a larger bend at the fetlock (due to weight pushing down) or does the larger horse choose to stand more upright to reduce the angular bend at the fetlock? One measurement made on our images is called ‘P2 length’ – it gives a measure of the apparent length of the P2 bone in the lateral radiograph. The interesting thing about our P2 length measurement is that it is independent of the horse’s stance, and it is independent of the trimming and shoeing of the hoof. The longer the P2 length, the larger (and heavier) the horse. So, we use the P2 length as a proxy for the size of the horse and in Fig 6 we plot ‘uprightness’ of the lower leg versus the size of the horse, as specified by the P2 length.

Discussion Our sample size of 2388 measured radiographs allows us to state with 99% confidence that the average uprightness of

horses in population #2 is 14.8 degrees ± 0.5 degrees: 14.8 degrees is significantly different from 0.0 degrees and hence it can be said that horses do not, on average, stand with phalanges aligned. The only remaining question can be: was our sample set of images representative of the population? Population #2 was quite broad: it consisted of horses that had been radiographed in clinics around the world minus the obvious founder cases, hooves with non-flat shoeing systems and miniature and yearling horses. The images came from the USA, Europe, South Africa and Australia and so we believe our sample to be representative of horses that are being radiographed in veterinary clinics. The measurement of the images in this study was automated by recently developed techniques based on deep learning (Craig & Craig 2019b). The specifics of placing measurement points, placing lines and measuring angles was all done automatically without human intervention. This fact may help us argue that these measures were done without human bias. After the automatic measurement, the results of each image were reviewed by a human expert and in some cases slight corrections were made. Individual horses may show a large variation in how they stand, and farrier and veterinary manipulations might sometimes be warranted to ‘correct’ the horse’s stance. But if a given practitioner is routinely using techniques that on average move the stance away from the normal uprightness of 14.8 degrees, then it would be reasonable to expect that practitioner to give a rationale for what they are doing. In particular, the practice of adding wedge pads to a shoeing system to force the phalanges into alignment is a practice that perhaps should be reconsidered. We argue that a ‘slightly broken back’ stance (as specified by an uprightness of about 15 degrees) is normal and needs no correction. At a further level of detail, the stance that is ‘normal’ for a given horse would seem to depend on the size (weight) of the horse (Fig 6), which would seem to further invalidate the notion that all horses should stand with phalanges aligned. Indeed, the ‘correct’ stance for a horse probably depends on its weight. In our opinion, when expert recommendation differs dramatically from what is observed as normal in the population, the onus is on the expert to justify their recommendation. Despite the many references to phalanges aligned being correct, we have not seen any convincing biomechanical argument why that should be considered so. We do still believe some horses are too broken-back and others are too broken-forward and should be altered. With this study we have just addressed where the normal centre point is in between the extremes.

References

Fig 6: The dotted trend line shows that larger horses tend to stand with phalanges more upright than small horses – by a significant difference of about 10 degrees. The horizontal solid red line indicates the phalanges aligned position – most horses stand to the ‘upright side’ of aligned, and even more so as the horses become larger and heavier

BACK, W. & CLAYTON, H. (2013) In: Equine Locomotion, 2nd edn. Elsevier, p 154 BIEWENER, A. (1989) Scaling body support in mammals: limb posture and muscle mechanics. Science 245, 45–48. CRAIG, J. (2016) Introduction to Robotics: Mechanics and Control, 4th edn. Pearson CRAIG, J. & CRAIG, M. (2019a) Measuring the equine hoof in radiographs – a focus on calibration. https://medium. com/eponamind/measuring-the-equine-hoof-inradiographs-7db141bd28f2 CRAIG, J. & CRAIG, M. (2019b) Measuring the hoof: how deep learning is helping to measure the hoof and creating ‘big data’ for us to analyze. Presentation, EponaMind Educational Event, Paso Robles, California CRAIG, J., CRAIG, M. & WELTNER, T. (2001) Quantifying conformation of the equine digit from lateromedial radiographs. Presentation, 21st Association for Equine Sports Medicine meeting, Sacramento, California EPONAMIND (2020) www.EponaMind.com PARKS, A. (2010) Examination of the equine foot. Proceedings, 2010 American Association of Equine Practitioners Convention

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TECHNICAL ARTICLE

3D technology in a vet–farrier joint venture

By Derek Poupard CJF, DipWCF

Farrier Derek Poupard is often asked to use his expertise in 3D printing to create bespoke therapeutic solutions for individual horses. The case below describes how a simple diagram supplied by a vet was turned into a printed shoe to be used following fracture repair surgery with the aim of reducing the torque experienced by the healing limb. While in Dubai during the Dubai Racing Carnival I was approached by Dr Tom Yarbrough, chief surgeon at the Dubai Equine Hospital. He had an idea for a post-surgery low-resistant domed shoe for use on horses that had suffered fractures. The

aim was to minimise the torque experienced by the repaired area and so enable earlier removal of a leg cast. The domed shoe, which had to offer little resistance to the ground surface, would be applied using the non-traumatic HoofCast system. This is a typical screw and wire fracture repair process on a severe fracture that needs stability to heal. A cast is applied following surgery and using the lowresistant domed shoe restricts the torque that is applied to this area.

(top) Tom gave me a diagram to use to start designing… and (above) this is the CAD (computer-aided design) for the HoofCast-applied shoe. As you can see, the surface area that will be on the ground is very small, which will allow the foot to swivel easily.

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TECHNICAL ARTICLE

Measuring for a 3D print application is done by taking the widest point of the foot and from toe to heel. These measurements are used in the software that creates the 3D print file.

(top) The completed 3D printed pad showing the barbs for the HoofCast to grab and (above) the domed, low-resistant surface.

The shoe applied with HoofCast showing the purpose of the low-resistant dome.

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TECHNICAL ARTICLE

Summary The potential of 3D design and printing technology is proving to be invaluable in the veterinary and farriery professions as you are limited only by your imagination. If you can think it and sketch it, there is now the ability to design it and print it for application. Recently, a farrier in the USA asked

if was possible to apply an 8 degree HoofCast wedge for a navicular ulcer. Below is the design and successful application. If you have an idea for an application please don’t hesitate to contact me by email at dpoupard@ymail.com. To keep up to date with all the latest 3D applications, you can follow 3D HoofCare on Facebook.

Write for us Forge Knowledge is aimed at farriers. If you have an idea for an article, contact the editor by email with a short summary of your article. Your idea will be presented to the editorial panel for discussion. We offer an honorarium of up to £250 for suitable articles. Further guidance for authors can be obtained from the editor, Gill Harris, email: forge.bfba@gmail.com, telephone 07773 790257.

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