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The Dewclaw

Full Title: The Dewclaw

Author: Christina Lemnotis

Date of Publication: October 9, 2012

PDF: http://petmassage.com/wp-content/uploads/The-Dewclaw-by-Christina-Lemnotis-2012-10-09.pdf

Research Paper Text:

The dewclaw is the rudimentary first digit of dogs and cats, found on the inner side of the front legs, above the weight-bearing digits. It is defined as an accessory appendage of the integumentary system (Colville et al. 2008, 147). They are also considered to be an accessory claw of the ruminant foot, analogous to a false hoof of a deer, hog, goat etc. In dogs, the dewclaw is the first digit, but actual bones are only found in the dewclaws of the forelimbs. Pigs, cattle, and sheep also have dewclaws but only in pigs are bones present. Both the metacarpal and phalangeal bones are present in the dewclaws of pigs, just as they are in weight-bearing digits (Colville et al. 2008, 178). There are no dewclaws present in aquatic mammals due to its definition of “a claw not touching the ground.”

In the dog, the dewclaw contains two bones; a proximal phalanx and a distal phalanx. This is a similar structure to the human thumb, which also only contains two phalanges as well. There are no sesamoid bones in the dewclaw of a dog. Each distal phalanx contains a pointed ungual process, which is surrounded by the claw (Colville et al. 2008, 489). An ungual process is the process on the distal end of the distal phalanx of dogs that is surrounded by the claw in the living animal (Colville et al. 2008, 147). Blood does reach the dewclaw of a dog and therefore, if torn, the dewclaw can become infected. Branches of the radial, median, and ulnar nerves transmit sensations from the digits to the brain. These nerves can be blocked with local anesthetic above the site of the dewclaw prior to surgery. This helps control pain in the immediate postoperative period.

The dewclaw is commonly removed from puppies at an early age due to the susceptibility to injury and infection throughout life. There are some breeds, which must have the dewclaw present in order to be recognized as the breed standard. These dogs include the Great Pyrenees dog and Briard. The Briard must have double rear dewclaws present (Zink). However, the removal of the dewclaw is debated amongst veterinarians and owners.

It is believed by some that it should be removed due to the possibility of injury in life. Other veterinarians say that such injuries are actually not very common at all and it is far better to deal with an injury than to cut the dewclaws off all dogs as a precaution (Zink). In canine athletes it is believed that the dewclaw still does have a function and is not just the remains of a digit that has regressed in the course of evolution (Zink). According to the Miller’s Guide to the Anatomy of Dogs, there are five tendons attached to the dewclaw, which would atrophy if the dewclaw were removed. The muscles attached to the dewclaw indicated that the dewclaws actually do have a function, which is to prevent torque on the leg (Zink). When the dog is cantering or galloping the dewclaw comes in contact with the ground. If the dog needs to turn, the dewclaw digs into the ground to provide support to the lower leg and prevent torque. It is thought if the dewclaws were absent, the dog’s leg would twist each time. After a lifetime of twisting, it could cause carpal arthritis, or injury to other joints such as the elbow, shoulder and toes (Zink).

References

  • Colville, Thomas, and Joanna M. Bassert. Clinical Anatomy and Physiology. St. Louis: Mosby Elsevier, 2008. (accessed May 27, 2012).
  • Zink, M. Christine. “Do the Dew(claws)?.” Canine Sports Productions. http://www.caninesports.com/DewClawExplanation.pdf (accessed May 25, 2012).

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