Written for the International Equine Veterinarian March/April 2013 Issue by R.F. (Ric) Redden, DVM
Radiographs are an essential part of most physical exams of the lower limb and foot, whether the focus is a pre-purchase, exam or soundness issue. Veterinarians are responsible, licensed and required by state law to take and interpret radiographs, make a diagnosis and formulate a treatment plan, which is a straightforward process that does not require the input of other professions until the exam is focused on the foot.
Farriers share a significant responsibility for the overall health of the foot in spite of having limited or no formal education in farrier services or veterinary medicine, and are expected to maintain strong, healthy feet, prevent imbalance and its ill effects and treat and correct many commonly occurring problems that can threaten the career or even life of the horse. Veterinarians, even though licensed to treat the foot, as a rule have very limited or no farrier experience or skill however are expected to have as much working knowledge of the foot as the farrier and vice versa. Caring for the equine foot is an overlapping, duel responsibility that requires a totally different mindset, level of knowledge and skill that encompasses the basic principles of each profession.
Veterinarians and farriers who accept the responsibility of treating career and life threatening foot problems need to take this responsibility very seriously and constantly strive to strengthen the weak areas of their respective knowledge branch and experience. Radiographic information is the missing link that can help bring farriers and veterinarians to the same page. By taking the standard recommended radiographic views a step further and educating farriers to read and understand radiographic information, we develop a "platinum" standard of care that can increase the accuracy and degree of information a vet/farrier team can use to improve their ability to care for the foot.
Bridging the gap with platinum standard radiographs
The farrier with years of extensive experience trimming, shoeing and forging develops an eye for detail that can only be gained through hands on day in and day out. However the most valuable information is most often not available and many have not had the opportunity to work with veterinarians willing and eager to teach basic radiographic interpretation. Therefore they are limited at best when attempting to sort out an internal problem by altering the shape and balance of the capsule.
Developing my exclusively equine podiatry practice and clinic three decades ago led me on a pursuit for knowledge and success with a multitude of career and life threatening foot syndromes. Every case demanded more and more information, better interpretive skills, improved planning and better execution of the plan. I had to develop a more meaningful approach to gathering radiographic information that would give me answers to questions raised by routine radiographic views. This search opened my eyes to the mechanical formula that is the direct link from film to rasp, and how important it is to understand the effect internal structures of the foot have on the outside.
The next step is teaching this information to other veterinarians and farriers. Putting everyone on the same page allows us to develop common goals and an efficient way to achieve them. Simply put, veterinarians and farriers who study together can greatly enhance their knowledge and perception of the radiographic information they need to make it happen. What follows is confidence and understanding: the hallmarks of success.
Designing and utilizing the platinum standard
Standard, recognized radiographic views are informative but limited relative to the information required to understand the mechanical requirements of a foot. Beam orientation and other factors affect specific areas of interest. Therefore we must modify our protocol in order to get the most accurate film with the best information to base our interpretation and decision making from. I refer to this consistent, dedicated protocol as the 'platinum' standard of hoof care.
The farrier friendly lateral view:
Beam orientation is crucial for accurate measurement of soft tissue parameters that are of the greatest concern. The primary beam should strike the hoof in a horizontal plane between the palmar rim and ground surface and perpendicular to the sagittal plane. Lining up the heel bulbs works well when they are relatively symmetrical. Proper beam orientation will reveal one branch of the shoe, as the primary beam superimposes one over the other.
Zero film/subject distance minimizes magnification.
Opaque wall marker (paste preferred) from the hairline of the coronary crest to the toe is required for traditional as well as digital film to assure accurate horn-lamellar (HL) zone and coronary/extensor process (CE) measurements.
Both feet should be placed on blocks in their natural stance regardless of conformation.
Figure 1: Low beam projection ensures only one branch of the shoe will be visible on the lateral radiograph. This beam orientation makes it possible to accurately and comparatively measure certain key soft tissue parameters such as sole depth and HL zone (provided radiopaque paste is present from the hairline to the toe).
Low beam orientation just like the lateral.
Two block technique.Head held straight and forward; as the head moves so do the digits and articular surface.
No wall marker.
Figure 2: A low beam projection DP view allows accurate assessment of medial/lateral balance and sole depth under each wing of PIII.
There are several parameters that are important for the farrier to know, as each is altered with every trim and shoeing procedure. When pathology and imbalance requires specific mechanical benefits, it is vital that the farrier know what they have to work with and what, if any, limitations need to be addressed before they start. Those parameters are:
Sole depth (SD): Measure the vertical distance between the apex of the coffin bone and ground or shoe surface, to include the cup of foot if present.
Palmar angle (PA): Measure the angle made between the palmar rim and the ground. When the apex is eroded or altered by load and/or pathology, measure along the straightest part of the wings.
Digital breakover (DB): Measure by dropping a vertical line from the apex to the ground surface, then measure the distance from this line to where the toe or shoe leaves the ground.
Bone angle (BA): Farriers as well as veterinarians and horsemen need to be well aware of a foot's bone angle. Many think all feet are alike inside and should therefore look alike and match outside, but this is a misconception at best. Bone angle can vary from 35° up to 65° and often varies 5-10° between feet on the same horse. The farrier need to know this when asked to match feet that are grossly different.
Farriers worldwide are eager to do a better job and know more about the foot they are working with, and most realize that specific radiographic information would help them make better decisions concerning trim, shoe fabrication and application.
Other parameters of paramount importance for a veterinarian's interpretation of the overall health, balance and ill effects of various pathological syndromes include:
Horn/lamellar (HL) zone: Measured from the face of the coffin bone (just below the extensor process) to the face of the wall, which is marked with radiopaque paste from heel to toe. Paste clearly delineates the surface of the wall along with all growth rings. A lucent area will always exist between the paste and the visual hoof wall, even with digital film. Therefore accurate measurements cannot be taken without paste. The HL zone is measured in two places, at the apex and just below the extensor process, and can only be accurately evaluated with zero film/subject distance and a wall conforming opaque wall marker.
Dermal/epidermal (DE) line: This is the opaque linear zone lies between the face of the wall and the face of the coffin bone. It is apparently formed by the increased density of epidermal lamellar leaves along the face of the wall. This zone can be an efficient tool for monitoring lamellar health, e.g. acute laminitis; bone remodeling, e.g. club feet; and load induced syndromes.
Coronary band/extensor process (CE): CE is measured by drawing a horizontal line across the most proximal paste marker and another across the peak of the extensor process. Then measure the vertical distance between the two lines. This parameter can only accurately be used as a comparative zone as it varies from only a few millimeters up to 35mm in sound horses, with the large majority being 10-15mm. It is not indicative of sinking unless this zone increases during the active stage of digital displacement due to laminitis.
Tendon surface angle (TSA): This angle is measured along the distal half to third of the tendon surface of the navicular bone and varies considerably between feet on the same horse. It can be used as part of the mechanical design requirements for various foot problems.
Figure 3: Routinely measuring these parameters greatly enhances the eye for subtle changes that occur due to growth discrepancies, effects of trimming and shoeing and pathology. The information we gain from these parameters helps us better understand the mechanical formula and how we can use it to maximize foot health.
Foot focused veterinarians and farriers who routinely measure these parameters on all lateral and DP views, especially before and after shoeing, soon become very proficient in correlating external landmarks with internal parameters and vice versa. This is the only way I know to learn how to read the foot, and it requires time and repetition. Once the parameters are better understood and ingrained in the minds of the team, the mechanical formula becomes very obvious and tissue response to various mechanical applications are easily fitted, measured and monitored along with the positive or ill effects reflected in the capsule (wall, sole, bars, heel tubules), digital cushion and frog mass.
The bottom line is that farriers dealing with problem feet are working with one arm tied behind their back them if they are asked to make career or life threatening decisions with a rasp without any clue as to what they have to work with and what is required to make it happen. Veterinarians and farriers who work together and routinely use the valuable information obtained from the platinum standard soon learn the potency of mechanics and the limitless options that can enhance the healing environment, ultimately solving many problems that once seemed insurmountable.