In order to correctly construct and fit heart bar shoes, good quality radiographs will need to be taken so the heart bar shoe will be able to be applied with accuracy and increase the chances of success. These few simple preliminaries will make the difference between a radiograph that has some use for diagnostic and prognostic purposes and one which is not.
In order for the Farrier to obtain the most accurate measurements, radiographs should be taken within 48 hours of the Farriers shoeing visit.
A wooden block is needed about 2 1/2" to 3" high and wide enough for the horse to stand on. A cut off bicycle spoke or metal rod is embedded into the top of the wooden block to highlight the ground line. The horse’s feet should be brushed/cleaned out and the frog and sole should have any defoliation removed.
The frog does not show up well on lateral/medial radiographs. In order to show the frog in relation to P-3, a tack is used to highlight the frog. The tack is merely a reference point to determine proper placement of the frog plate on the heart bar shoe. The tack is pushed into the apex of the frog. The exact placement is not as important as long as its position on the frog is marked in some way. A heavy felt tip pen is ideal for marking the frog and sole. The marked sole makes is more accurate to know the exact placement after the tack is removed.
Due to the design of both CR and DR units, radiograph images are subject to a magnification mechanism of minor or larger magnitude. This means that all objects measured in a radiograph image will always appear larger on the image than in reality (Sectra, 2009). The magnification depends on both the distance between the focal point of the radiograph tube and the image plate as well as the distance between the imaged object and the image plate. If the imaged object is moved toward the focal point of the radiograph tube the magnification is increased and if the imaged object is moved toward the image plate the magnification is reduced. Since all radiograph units are different, they will all create different magnifications on radiograph images. A larger distance between the focal point of the radiograph tube and the image plate reduces the effect of such movements (Sectra, 2009).
When acquiring a conventional radiograph image on which measurements of any type should be made, a calibration marker should always be present in the image (Sectra, 2009).
To correct for magnification, a marker is used on the front of the hoof wall. A straight stiff wire of known length (30 mm is best) is used to highlight the front and top of the hoof wall. A piece of copper or steel wire works best. Do not use flexible or braided wire as this makes radiographic interpretation more difficult. The length of the wire must be known so the effects of radiographic magnification can be adjusted. The wire is taped to the hoof wall so the top of the wire is located where the wall changes from hard to soft (Sectra, 2009 Eustace, 1996 Buff, 1990)
Also, for prognostic purposes, the wire marker is used on the front of the hoof wall. This information will yield the founder distance, which is the most useful radiological prognostic indicator for acute founder and sinker cases. This measurement will also help you monitor the horse’s progress.
The horse should ideally stand with one foot on each block with the cannon bone vertical. BOTH feet need to be on equal radiograph blocks to diminish the effects of unequal weight bearing. The radiograph beam should be parallel to the top of the block and perpendicular to the axis of the limb so that an absolutely lateral/medial radiograph is produced.
Once the radiograph has been developed, the data can be collected by following the instructions on the Founder Data Collection and Analysis Form Instruction Sheet
©2003 Esco Buff, PhD, CF
The following data is to be collected from the radiographs in order to be able to correctly construct or modify and apply a heart bar shoe (Buff, 1990). The Founder Data Collection and Analysis Form© will aid in the collection of data.
The forms are clear and concise and include a laminated instruction sheet that enables the veterinarian and farrier to more accurately assess, determine prognosis and establish treatment for the foundered horse. The forms along with the Founder book will help the professional determine the chances that the horse will return to its previous soundness state. The forms teach consistent radiograph techniques, thus enabling the veterinarian and farrier to obtain more accurate information from the radiographs. They also help determine where to correctly place the frog plate of the heart bar shoe.
Actual Wire Length - The actual wire length is the actual length of the dorsal wall wire marker used.
Radiographic Wire Length - This is the measured length of the dorsal wall wire marker from the radiograph. With the known actual wire length and the measured length of the wire from the radiograph, the effects or radiographic magnification can be adjusted.
Magnification Correction - In order to get actual working measurements, calculations need to be made. The magnification formula is actual wire length divided by radiographic wire length. For example, if an 30 mm wire is used and the wire measures 35 mm on the radiograph, then the magnification correction is 0.86 (30 ÷ 35). For any measurement taken from the radiograph, it will need to be multiplied by the magnification correction in order to obtain the actual measurement. For example, if you take a measurement of 45 mm on the radiograph, then you need to multiply that number by the magnification correction, to get the actual length. In this example, 45 mm x 0.86 = 38.6 mm.
Wall Thickness - This is the distance from the wire marker on the dorsal hoof wall to the dorsal cortex of the distal phalanx. This is to be measured half way up dorsally from the tip of the distal phalanx to the base of the extensor process, and at a right angle to the dorsal cortex of the distal phalanx. Normal wall thickness, uncorrected for magnification, has been shown to be 13-15 mm for miniatures, 15-17 mm for horses, and 17-19 mm for drafts (Cripps and Eustace, 1999 Buff, 1990, 2005). Wall thickness will be use to determine the Shoe Toe placement of the toe of the heart bar shoe.
This point is very important and quite often overlooked by many veterinarians and farriers. In the early stages of founder, the hoof wall and the distal phalanx will draw apart and move downward, but remain parallel. Rotation of the distal phalanx occurs later. By recognizing these early signs, the veterinarian and farrier can provide immediate treatment that could help limit the amount of damage sustained.
Founder Distance - This is the vertical distance between the top of the dorsal hoof wall marker and the proximal limit of the extensor process of the distal phalanx. Founder distance is the most useful radiological prognostic indicator for acute founder and sinker cases. This measurement helps you monitor the horse’s progress and along with type of founder (Laminitis, Acute, Chronic Type I, Sinker and Chronic Type II), aids in helping estimate the prognosis and probability of return to soundness.
Palmar Cortex of the Distal Phalanx Length - This is the length of the palmar cortex of the distal phalanx from the tip of the distal phalanx to the articulation of the distal phalanx and the navicular bone. It has been shown that the wall thickness in the normal horse is approximately 25% of this measurement when corrected for magnification (Pollitt, 2001). For example, if you take a measurement of 65 mm on the radiograph, then you need to multiply that number by 25% (0.25) to get wall thickness. In this example, 65 mm x 0.25 = 16.25 mm. Remember, normal hoof wall thickness for horses is between 15 mm and 17 mm, uncorrected for magnification. In this case, the horse has a normal hoof wall thickness of 16.25. This measurement will later be used to establish the correct placement of the toe of the heart bar shoe.
Shoe Toe Placement Calculation - This is the distance between the tack (which is merely a reference point to determine the proper placement off the toe of the shoe), and a line drawn parallel to the dorsal aspect of the distal phalanx, at the normal hoof wall thickness that was calculated from the Palmar cortex of the distal phalanx length. In this case, 16.25 mm. The spot that this line interests the bottom of the hoof is the spot that the toe of the heart bar shoe will be placed at. This is the easiest and most accurate method to determine the toe placement of the heart bar shoe. After taking this measurement, correct for magnification and transfer this measurement to the foot. After the shoe is applied, the distorted hoof will then be removed, exposing the dead laminar wedge.
Frog Plate Placement Calculation - This is the distance between the tack (which is merely a reference point to determine the proper placement of the frog plate), and a line drawn perpendicular to the ground, immediately behind the extensor process and bisecting the coffin joint space. This is the easiest and most accurate way to calculate this measurement. This is the reason why correct radiographs need to be taken and utilized for the shoeing treatment of any laminitic horse that heart bar shoes will be applied to. After taking this measurement, correct for magnification and transfer this measurement to the foot. A second method for determining frog plate placement is to measure the length of the solar margin of the distal phalanx and then measure back 37% from the tip of the distal phalanx (Chapman and Platt, 1984 Chapman, 1998 Butler and Platt, 2001). This method doesn’t work well when the distal phalanx is degenerating.
Other data collected and documented on the Founder Data Collection and Analysis Form© are:
- Founder Type (Laminitis, Acute, Chronic Type I, Chronic Type II, Sinker)
- Dorsal Wall Angle
- Distal Phalanx Angle
- Phalanx Angle
- Solar Border Angle
- Angle of Hoof Capsule Rotation
- Angle of Distal Phalanx Rotation
- Sole Depth
- As well as......
- Owner's Name
- Veterinarian's Name
- Farrier's name
- Horse's Name
- Breed of Horse
- Gender of Horse
- Age of Horse
- Date Radiograph Taken
- Date Data Collected
- Which Limb is Radiograph of
- Treatment Notes
