Paw pad pain: A review of corns in dogs - Veterinary Medicine
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Paw pad pain: A review of corns in dogs
In this overview, experts make the case that these painful lesions are likely caused by repetitive mechanical trauma and recommend a treatment and prevention plan.


VETERINARY MEDICINE


A look at the theories

The scar tissue, scar tissue and foreign body, and viral papilloma theories are probably not the cause of most corns in greyhounds for a variety of reasons.

Recurrence. Surgically removing the corn generally results in alleviating signs of pain; some dogs may be cured, and most remain corn-free for more than six months.3 Recurrence could be because of poor surgical technique, but it is more likely caused by underlying mechanical factors that have not been corrected (e.g. chronic low-grade pressure on the pad).3 The same reasoning holds true for the foreign-body-and-scar-tissue theory. If the foreign body has been removed, reaction or recurrence should not occur but it often does.

Lack of evidence. An electron microscopic examination of corns that had been removed did not show the presence of the papilloma virus.9 Likewise, immunohistochemical staining and polymerase chain reaction assay testing did not find evidence of viral etiology in corns removed from 18 greyhounds.1

Anatomic differences. Several suggestive factors support the pressure theory as a major cause of corns. One factor is the anatomic differences in the greyhound paw. Greyhounds have long, narrow paws with little distance between pads, which results in greyhounds experiencing more ground reaction forces than dogs with wider paws.14 The average velocity of a medium-grade racing greyhound is 36 miles per hour (extrapolated from track data), and photographic evidence shows that during a gallop, the dog is airborne and lands initially on the extended paw of a thoracic limb on a firm sand surface. As a result, ground reaction force is high.3

Sparsity of tissue. It has also been theorized that since greyhounds have a sparsity of subcutaneous adipose tissue throughout their bodies, a sparsity of fibroadipose padding tissue may also exist in the paw pads. Thus, the distal interphalangeal articulation of the digit is in closer apposition to the dermis of the pad skin. And, thus, when the dog ambulates, pressure on the pad skin by this joint causes corn-type lesions to form.3,7,9,10

Anatomic abnormalities. The mechanical theory is supported by the presence of anatomical abnormalities, resulting in abnormal weight bearing on the pad. Deep digital flexor tendon rupture or stretching is a common finding. Also if the anatomic abnormality can be corrected then the corn will disappear.3

Weight-bearing digits primarily affected. Another factor that supports the pressure theory is that digits 3 and 4, the major weight-bearing digits, are primarily involved. In a study of 30 dogs with a total of 40 corns, 36 of the corns were on digits 3 and 4 of the thoracic limbs.3 In another study of 24 dogs—18 of which were greyhounds—24 of 26 corns were on digits 3 and 4.1

In a national epidemiologic survey of 484 greyhound owners, 275 male greyhounds and 209 female greyhounds were evaluated for corns (Wright JC, Borghese IF, Swaim SF, College of Veterinary Medicine, Auburn University, Ala: Unpublished data, 2003). The median weight of the dogs was 70 lb (31.8 kg) with a range of 44 to 104 lb (20 to 47.3 kg). One hundred seventy-five owners reported that their dogs had corn-type lesions, and 121 of the owners indicated the location of the corns on the digits. The survey asked the greyhound owners to report any racing injuries, if known. The responses indicated that no significant racing injuries were associated with the occurrence of corns.


Table 1: Distribution of corns on forelimb and hindlimb paws in 121 greyhounds*
The corn lesions were not associated with either the sex or the weight of the dogs, and there was no significant difference in location among paws (Wright JC, Borghese IF, Swaim SF, College of Veterinary Medicine, Auburn University, Ala: Unpublished data, 2003). However, digits 3 and 4 had a significantly higher occurrence of lesions (Table 1). Thus, from a wide geographic area and a large population of greyhounds, the same phenomenon was evident—predominance of corns on the primary weight-bearing digits.

There appears to be a predilection for corns to occur on the paws of the thoracic limbs. This tendency was noticed in the epidemiologic survey of greyhound owners (Table 1) and may be related to ground reaction forces.3 In dogs, the vertical forces placed on the thoracic limb paw pads during walking are about 1.1 times body weight; whereas, on the pelvic limb pads, this force is 0.8 times body weight.15


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Source: VETERINARY MEDICINE,
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