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With A Flick of the Wrist

In the hundreds of agility trials I have attended over the years, only rarely have I seen a dog suffer an acute, serious injury. An exception happened in early May this year. I was relaxing at ringside, enjoying one of the rare rain free moments this spring offered, watching a bi-black Sheltie named ‘Shadow’ negotiate the Open Jumpers course with smooth abandon. Suddenly the dog took a misstep, completely misjudged where he should take off, and crashed into the jump. As he fell, his front legs landed on the fallen jump bars, and he immediately let out an agonized scream. He was still crying as he was carried out of the ring. I ran over to help and examined the dog in a shady area some distance from the ring.

Shadow’s left front leg was extremely painful and he held it stiffly away from his body. In a few minutes he had relaxed enough for me to determine that there were no major bone breaks. In fact, the main problem appeared to be a severe sprain of the carpus (wrist). Later X-rays not only confirmed my finding, but interestingly showed that the dog had preexisting arthritic changes in the carpal joints of both front legs. Thus, although this dog did have an acute agility injury, he had chronic problems, too. In fact, it is possible that the arthritis contributed to his lack of coordination in approaching the jump.

Once Shadow was on the mend, his human teammate had many questions for me. How common is carpal arthritis in performance dogs? How painful is carpal arthritis and what can be done to relieve the pain? Will Shadow still be able to play agility, obedience and other fun doggie games? Since carpal arthritis is quite common, I thought I would share the answers in this column.

In the last several years, while doing sports-medicine consultations for performance dogs across Canada and the United States, I have seen many canine athletes with carpal arthritis. Interestingly, this condition is much more common in dogs that have had their front dewclaws removed. To understand why, it is helpful to understand the structure of the carpus. This joint consists of seven bones that fit together like fieldstones that are used to build the walls of a house

The carpus joins to the radia and ulnar bones (equivalent to our lower arm), and to the metacarpal bones (equivalent to our hand). Each bone of the carpus has a convex or concave side that matches a curve on the adjacent bone. Unlike the bones of the elbow, for example.

The elbow bones have ridges that slide into interlocking grooves the bones of the carpus do not have ridges that slide into interlocking grooves on the adjacent bone. The relatively loose fit of the carpal bones is supported by ligaments that join each of the carpal bones to the adjacent bones.

With so many carpal bones that don’t tightly interlock with the adjacent bones, the ligaments of this joint can be easily stretched and even torn when torque (twisting) is applied to the leg. The dewclaws have the important function of reducing the torque that is applied to the front legs, especially when dogs are turning at a canter (the main gait used in agility).

In the canter, there is a moment during each stride when the dog’s accessory carpal pad (on the back of the carpus) of the lead front leg touches the ground and the rear legs and other front leg swing forward to prepare for the next stride. At this point, the dewclaw is in contact with the ground and if the dog turns, the dewclaw can dig in for extra traction to prevent unnecessary torque on the front leg. Without the gripping action of the dog’s ‘thumbs’ there is more stress on the ligaments of the carpus. This may cause the ligaments to stretch and tear over time, resulting in joint laxity and ultimately, arthritis.*by Chris Zink, DVM, PhD

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