Fig 01

“What you can measure doesn’t need to be estimated” Thornsten Eggert

1. Introduction

Farriery has an illustrious historical tradition and is at the origin of Equine Veterinary Science. [1 ]

Currently there is a large divide – with the farrier being considered as a manual professional or at best an artisan – while the equine veterinarian works on the premise of “science based medicine”.

In the (rediscovered) field of equine podiatry the two professions meet, each with its own “cultural luggage”, hopefully to the benefit of the horse.

In reality of course the picture is mudded, the expanding study programs of veterinary medicine schools leave less and less space for equine podiatry as course material, while the tradition based teaching methods of many farriery training programs (when they exist) often are anything but science based . [ 2 ] This doesn’t mean that tradition is wrong, but that it is often “ lost in translation” when communicating with the veterinary profession. Like each branch of applied medical science, equine podiatry needs empirical based science applied to it to progress. The sequence being: observation / intuition, development of a hypothesis, design of a study model, application of the right analytical instruments to measure variables and results enabling to draw reasoned conclusions, preferably applicable to everyday podiatry concerns.

The following chapter is a review of the measurement tools and techniques, useful in both studies and everyday treatment, available to the equine podiatrist, both vet and farrier.

2. Basic measuring tools, their use and relevance.

2.1. Hoof protractors, goniometers:

Perhaps one of the most wide spread tools, these measure the angle of the dorsal hoof wall with the bottom of the foot. In short Dorsal Hoof wall angle (DHWA) A study by Van Weeren et all [3 ] showed that different protractors and different users with the same protractor give different results of DHWA.

It should also be noted that DHWA can be influenced by:
- The trim of the distal part of the wall (the more heel is left, the higher the angle).
- The trim of the dorsal wall; if the wall is thinned with the rasp in its distal part the DHWA will increase.

There are angle measurers with a digital display available, these and some of the simple “normal” protractors can also measure the angle of the heels relative to the bottom of the foot (Heel Wall Angle, HWA).

It is usually easier to get accuracy on a bare foot than on a shod hoof, as the shoe and nail heads may interfere with the bottom of the tool being placed even with the bottom of the foot.

Shod feet and some bare feet are best measured when freshly trimmed. Most horses will lose a few degrees of DHWA in the period between shoeings, as the heels keep wearing on the upper surface of the shoe. [ 4 ]

Normal dorsal hoof walls are straight from the coronary band down, concave dorsal hoof walls indicate faster growth at the heels, convex dorsal hoof walls indicate faster growth in the toe area. Both conditions make accurate measurement of DHWA more difficult; in the first case the DHW should be trimmed straight before measuring (removal of the dorsal flare); in the second case the dorsal arm of the protractor should be tangential to the “belly” of the DHW.

A steep DHWA correlates with a tight deep digital flexor tendon (DDFT), a low DHW correlates with a lax DDFT. This can be shown with an extension test (see further on).

Many horses show different DHWA on paired feet, especially front feet. This may be due to the developmental conditions as a foal [5 ].

2.2 Measuring tapes, measuring sticks, compass, calipers:

Preferably metric, these tools obviously measure length; length of DHW, length of heel, width of the hoof, toe to heel length of the bottom of the foot, etc.

It is often practical to use an indirect measurement by applying a compass to the segment being measured and then measuring the opening between the ends of the compass, or comparing different segments with the compass.

For fine measurements calipers may be used, for example: white line width, hoof growth during a certain, know, time interval, free ungular cartilage length above the coronary band, shoe width and thickness etc.

Standard bred trainers often take note of both DHW angle and length of each hoof and correlate it with performance of the individual horse.

Some show and breed organizations have regulations on admitted DHW length and/or shoe width and thickness (Icelandic’s horses e.g.)

Hoof wall growth can be measured more reliably in the toe area and may help in establishing appropriate shoeing intervals.

2.3 Plumb lines, normal or laser aided:

Plumb lines can be used to observe conformation traits, like angular and flexural deformities. It is not always easy to place horses “square”. When axial rotations of the limb are present, it is very important to take these into account and to place the laser source in the sagittal plane of the limb (segment) being observed. Laser lines are better seen in dimly lit environments.

2.4 Large digital angle measurers:

These building tools, whether supplied with a digital readout or not, are extremely use full when measuring angular deviations. The long arms can easily be aligned with the long bones, taking eventual axial rotations into account and angular deviations (A.D.) can be accurately measured.

Progress in treatment of A.D.s in foals can be monitored objectively over time, without having to resort to special x rays.

2.5 Axial Hoof rotation measurer:

This tool with a weighted needle on circular scale, allows for the measurement of the degree of axial rotation of the hoof relative to the cannon bone especially on front limbs.

The cannon bone is held horizontal, the horse’s digit is allowed to hang free (front limbs), the long axis of the tool is aligned over the central sulcus of the trimmed frog and the weighted needle will indicate the degree of rotation and also the point or area of natural break over. This area is displaced laterally from the toe of the hoof in the case of medial rotation of the horse’s digit and medially in the case of lateral rotation. This tool also allows to measure the degrees of axial rotation (collatero motion) which can be applied manually to the hoof in each direction.

2.6 Digital extension device:

This device, developed by the author, is nothing more than the old board test with a spirit level protractor showing the maximum tolerated angle of dorsal extension, lateral or medial elevation and caudal elevation of a particular limb in the standing horse.

Normal values of front limbs on sound horses have been established in the dorsal, lateral and medial directions, so there is a baseline with which to compare the horse / limb being measured .[ 6 ]

The values obtained with this test are very use full in clinical settings, when establishing rational remedial shoeing prescriptions.

2.7 Kitchen weight scale:

Weight at the bottom of the foot affects performance including top speed, angles of maximal limb flexion and extension and (deviations of) flight path of the distal limb.

Measuring the weight of different shoes of similar sizes is therefore use full.

2.8 Hoof testers with digital pressure read out:

Every practitioner uses Hoof testers differently.

Hoof testers, which accurately measure the pressure being applied to the different parts of the hoof, allow for exact and standardized comparisons between sound and lame feet and between different areas of the same hoof. In the authors experience it is use full to do “a first round” of the hoof at a medium setting and follow up with a “second round” at a higher pressure setting, beginning with the sound hoof before going on to the sore one

2.9 Laser thermograph:

Laser guided thermographs are easily available and, when used properly, are more accurate in detecting heat in the foot than manual palpation.

In the case of solar abscesses the bulb on the side of the abscess usually shows a 2,5-3° centigrade heat increase at the hair line relative to the controlateral bulb. Thermographs measure only the surface temperature; the hoof capsule itself is extremely insulated, therefore the hairline is the best spot to focus on. The test should be done in the shade. In winter, with cold ambient temperatures, different hooves may naturally have different temperatures at any given time. [7]

2.10 Body circumference measuring tape:

By measuring the horse’s body circumference behind the withers regularly, owners can be made objectively aware of changes in body condition score.

The interest for equine podiatry lays in the prevention and management of the devastating condition of laminitis and founder, second cause of premature death in horses. [8]

3. X ray measurements:

X rays are two dimensional images of mostly hard tissues. When measures like sole depth, palmar / plantar angle of distal phalanx, dorsal wall thickness, digital axis, joint space congruity, etc., are taken, it is extremely important to use correct positioning protocols, accurate film – X ray source distances and scaling of the distances measured to the “original”. In the authors experience the proportion of correct foot X rays delivered by veterinarians to farriers for shoeing and trimming prescriptions is way too low.

The proprietary software of most digital X ray systems allows for linear and angular measurements. These will only be accurate if truly scaled 1:1 in the case of linear measurements, and in general only if the right positioning protocol is used. [ 9]

Dorso palmar / plantar takes of the digit, for measurements of joint congruity, need to be carefully aligned with the sagittal axis of the hoof and with the weight bearing limb placed on a freely rotating podoblock. [10 ]

4. Information technology mediated tools. (ITMT)

Specific ITMTs are available for photo, X ray and video analysis of the standing and moving horse.

The array of objective data obtainable from videos with these tools is amazing and extremely use full.

Although horse care givers have been able to measure DHWA for ages, accurately establishing how many degrees a fetlock extends at a given speed, with a given shoe and on a given surface is a “new tool in the box”.

These proprietary programs need adequate (reed powerful) hardware, a learning period and again depend on correctly taken pictures, X rays and videos to be meaning full. On the other hand they can facilitate long distance consulting and “before and after” analysis to objectively judge results.

5. Conclusion:

To measure means not having to estimate. It can also lead to interesting discoveries: many farriery textbooks for example, have described the DHW to be parallel to the inclination of the heels on normal feet, a recent study showed this to be the exception. [ 11]

Moreover measurements facilitate keeping records and communication between professionals.

Measurements have to be interpreted to have practical meaning, without them however, farriery remains more art than science and the effects of different trimming and shoeing techniques hard to prove and predict.

References :

[1] Causati Vanni, M.A.. In: Giordano Brusso nelle scuderie di Federico II imperatore ovvero ,l’arte di curare il cavallo. Velettri: Editrice Vela; 2000. pp. LVI-LIX.

[2] Falisse, D.,Editorial in “European Farriers Journal”, Vol. 154, pp 4-5; 02/2012.

[3]Moleman,M., et all., ”Accuracy of hoof angle measurement devices in comparison with digitally analyzed radiographs.”, Equine veterinary education, vol. 17, (6),pp. 319-322- dec. 2005

[4] Castelijns, H.H.,” Talloni bassi e sfuggenti, cause, conseguenze e rimedi.”, atti II° Convegno Internazionale di Mascalcia e Podologia - Desenzano del Garda, 28,29 Marzo 1998.

[5]Van Heel,A.,M., et all. “Uneven feet in a foal may develop as a consequence of lateral grazing behavior induced by conformation traits”. Equine vet. J (2006) 38 (7) pp.646-651

[6] Castelijns,H.H.,” How to Use a Digital Extension Device in Lameness Examinations”, proceedings 54th AAEP Convention San diego, California December 6-10 2008, pp 228-231

[7] Pollitt, C.C. and van Eps, A.W. (2004) Prolonged, continuous distal limb cryotherapy

in the horse. Equine vet. J. 36, 216-220.

[8] AAEP data (2007)

[9] Castelijns, H.H.,”La radiologia del casco del infosado”, actos, I Congreso internacional de podologia equina para herradores y veterinarios. Valencia 24-26 Abril 2008

[10] Caudron I., Meisen M., Grulke S., Vanschepdael P., Serteyn D., (1997a) Clinical and radiological assessment of the corrective trimming in lame horses. J. Equine Vet Sc. 17: 375-379

[11] Craig,J.J., Craig,M., "Hoof and Bone Morphology of the Equine Digit: Challenges to Some Common Beliefs" European Farrier's Journal (issue #114, 2005), American Farrier's Journal (Jun/Jul 2005 issue).

Hans Castelijns
D.V.M - Certified Farrier