HOW TO MANAGE HOOF LAMENESS II


Fig. 7. A, Yearling with a Grade 2 club, 55° bone angle that was 5° larger than the opposite foot and a 15° capsule PA. This could be a good candidate for the check desmotomy but will always have a slightly steeper foot than its opposite due to bone angle. B, This foot has a 45° bone angle and a positive capsule PA but appears as a long toe underrun heel foot. C, This weanling had a 60° bone angle, 10° greater than the opposite foot. HL zone, 15/10 mm and a 5° PA. The opposite foot had a 50° bone angle and zero PA and 15/10 HL zone. This was a 20° difference in hoof angles. This appearance would lead one to believe a check desmotomy was highly indicated. Unfortunately, that would only result in a 5° advantage due to the low PA still leaving a 15° difference in toe angles, therefore surgery would not be very beneficial both functionally and cosmetically.


the coffin bone. The lateral image consistently re- veals an adequate sole along with a natural cup. The lateral image also reveals some degree of coffin joint luxation that supports inadequate tension of the DDFT as a possible contributing factor. These mechanical alterations are only discernible


with podiatry focused radiographs. A helpful tip is that the frog trimmed to its natu-


ral base also lies along a very similar plane as the palmar rim of the third phalanx. The linear area of the deepest part of the sulci along the frog is quite close to the same plane as the palmar rim. Paste defining this area (sulci) on a lateral view can be a helpful teaching aid as it can help guide the trim plane that oftentimes is strikingly different than that of a routine trim. An imaginary line that con- nects a dot of paste placed at the skin frog junction and another at the apex of the frog also will be in a very similar plane as the palmar rim. Using these landmarks helps the farrier develop an eye for a more precise trim when specific goals are indicated.


Bone Angle


The bone angle is the angle made by the dorsal and solar surfaces of the coffin bone. Why is it impor- tant to measure bone angle? The answer is that bone angles typically differ between right and left and front and hind feet. Farriers are most often expected to match toe angles as it is assumed that all feet should match and be symmetrical. The old saying, “assumptions and expectations are different than fact,” is an understatement. Feet seldom if ever match and certainly are not symmetrical inside or out. The bone angle is approximately 50° in the majority of feet however it can vary 10° to 12° less or greater than 50°. Exceptionally low bone angles are often the cause


for low toe angles in spite of adequate PA and sole mass. The mismatched syndrome is prevalent in most all breeds and it is common to find mismatched bone angles, especially in the front feet that vary as


394 2020  Vol. 66  AAEP PROCEEDINGS


much as 10° or 12°. When the bone angle is re- markably larger in one front foot than the other, trying to match toe angles with a rasp can be a futile attempt and go against the natural mechanical bal- ance of the foot. It is not uncommon to find various grades of club feet with 5° to 10° greater bone angle than the opposing foot. Therefore, the commonly termed “high/low” horse can have matching PAs yet have toe angles that are 10° different. Attempts to match them without this radiographic evidence can be futile as well as detrimental. One should also be aware of the bone angle relative to the capsule PA when considering an inferior check ligament desmo- tomy as a high bone angle (60°) and a low PA (5°) will not offer favorable results due to the low PA (Fig. 7, A and C). As a rule, the majority of light-boned breeds have


a bone angle of 50° give or take a couple degrees, although, much lower bone angles are also relatively common (Fig. 7B).


Horn-Lamellar Zone


The horn-lamellar zone (HL) is defined as the dis- tance between the dorsal surface of third phalanx and the outer surface of the dorsal hoof wall, mea- sured perpendicular to the dorsal face of the third phalanx. It is commonly measured just distal to the extensor process and near the distal tip of the third phalanx. It consists of horn wall and the opaque dermal/epidermal zone that borders the horn and the laminae. Ranges of normal vary de- pending on type and size of the horse and so this measurement is best used when comparing serial radiographs over time. It is also important to mea- sure both the horn (H) and lamellar (L) zone sepa- rately, as significant, life-threatening lamellar swelling can occur without rotation. One must also consider that the horn portion of the HL can be drastically altered by the farrier in an attempt to make the foot look normal and so measuring the HL


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