Negative palmar angle syndrome in racing horses - DVM
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Negative palmar angle syndrome in racing horses
Early recognition and correcton can prevent this potentially career-ending pathology


DVM360 MAGAZINE


Possible mechanisms


Photo 3: In the Grade I form of NPAS, sufficient sole depth under the tip of the third phalanx is present, so trimming alone can restore a normal plantar angle and digital alignment.
As professionals, we have long recognized that this hoof shape and these radiographic changes are abnormal. What we perhaps have failed to fully appreciate is the range of consequences and the long-term impact of this abnormality. Weakening and collapse of the horn in the heel region allows P3 to displace (in short, for the wings to drop, and, thus, for the entire bone to tip up). In the process, it alters the loads on various structures within the hoof capsule, rendering them more vulnerable to overload even under conditions of normal use. Whether a horse is at rest or in motion, repetitive and cumulative damage occurs in these feet because the reserve capacity of this marvelous structure (the equine foot) is lost when the heels collapse.


Photo 4: In the Grade II form of NPAS, there is insufficient sole depth under the tip of the third phalanx to correct the problem with trimming alone.
In fact, many of the specific digital pathologies we can now identify with sophisticated imaging techniques (e.g., subtle abnormalities in the navicular bone and related structures, deep digital flexor tenopathies, distal interphalangeal synovitis or arthritis) may have their foundation in this rather ordinary phenomenon of heel collapse. For example, calcification of the navicular portion of the deep flexor tendon is common in horses with NPAS, as is remodeling of the navicular bone and P3.


Photos 5: In the Grade III form of NPAS as shown in this photograph and radiograph, the hoof is trimmed to create two planes on the solar surface. A plantar angle of zero is created in the forward portion of the foot, and the heels are "floated" behind the quarters.
As for what causes NPAS, it is likely a multifactorial problem. Research has shown that when Thoroughbreds start galloping (i.e., race training), their hoof angles decrease unrelated to farriery changes. It has also been observed that foals born and raised in sandy, humid soil conditions do not develop good heels. There may be a genetic component to this problem as well. And improper trimming and shoeing must be on the list of contributing factors. Furthermore, farriers who do not have a good understanding of NPAS and its management may have difficulty correcting these feet and may actually worsen the condition. For completeness, it's also worth noting that NPAS can be a consequence of deep flexor tenotomy, particularly if DA is not properly restored at the time of surgery.

Grading system


Photos 6: In the Grade III form of NPAS as shown in this photograph and radiograph, the hoof is trimmed to create two planes on the solar surface. A plantar angle of zero is created in the forward portion of the foot, and the heels are "floated" behind the quarters.
The diagnosis and treatment of NPAS is discussed at length in the November 2010 issue of The Journal of Equine Veterinary Science.1 That paper focuses on a simple four-tier grading system for categorizing and managing these feet, as the severity of the problem dictates the finer points of the treatment approach. Briefly, the grading system can be summarized as follows:
  • Grade I: mild. There is sufficient sole depth under the tip of P3 that trimming alone can restore a normal PA and DA (Photo 3).
  • Grade II: moderate. There is insufficient sole depth under the tip of P3 to correct the problem with trimming alone; the hoof is trimmed to achieve a PA of at least zero (and into the positive range, if possible), and then a full rocker shoe is used to correct the PA and DA (Photo 4).
  • Grade III: severe. The hoof is trimmed to create two planes on the solar surface. A PA of zero is created in the forward portion of the foot (from the quarters to the toe), and the heels are "floated" behind the quarters. The heels are lightly rasped to remove the defective horn and bring the bearing surface back to the widest part of the frog. A full rocker shoe is nailed to the forward portion of the hoof, and a soft composite material (e.g., Equi-Pak—Vettec) is used to fill the gap between shoe and heel while the heels regenerate (Photos 5 & 6).
  • Grade IV: contracted. These cases are complicated by flexor contracture, causing a "post-legged" appearance in which the pastern is more vertical than normal and the fetlock angle is reduced. These horses may even knuckle forward at the fetlock. Correction is involved and protracted but can be rewarding (Photo 7).


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Source: DVM360 MAGAZINE,
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