VOLUME 1 | ISSUE 7 | June 2018 
A-Frame-Induced Carpal Injuries
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Studies of injuries in agility dogs have suggested that the A-frame might contribute to agility-related injuries (1,2). A just-released study examined the angle of the carpus (wrist joint) when dogs were ascending the A-frame (3). The goal of the study was to determine whether lowering the height of the A-frame , thus reducing the angle at which the A-frame meets the ground, would reduce the amount of carpal extension that dogs experience when ascending the obstacle.
This figure from the publication shows how the angle of each dog’s carpus as it ascended the A-frame was measured. Superimposed lines have been added for clarity.
Carpal angles of dogs ascending A-frames that were set at angles of 30º, 35º and 40º to the ground were measured. The diagram to the left shows the angle for the AKC large dog A-frame and lists the angles for the AKC small dog A-frame and the A-frames used in other agility venues.
The results showed that regardless of whether the A-frame was positioned at angles of 30º, 35º and 40º to the ground, the dogs’ carpi always extended to about 62º . The authors compared this angle to studies showing that maximal carpal angles in dogs walking on flat surfaces were 26º, and in dogs traversing a jump were 44º. They concluded that the carpal angles they measured in dogs ascending the A-frame represented maximal carpal extension. They suggested, as others have, that repetitive maximal carpal extension could damage soft tissue structures that support the carpus.

This was very well-designed study using a large number of dogs
(n = 40) of a wide variety of breeds, and it asks a very important question about repetitive injuries . Their data are very solid. However, my conclusions are slightly different than the authors’.

I think that while the dogs in the study were likely experiencing maximal carpal extension, that nonetheless, that degree of carpal extension is not out of the ordinary for dogs . Instead of comparing the carpal extension angles of dog ascending the A-frame to those of dogs walking or even jumping, it might be more relevant to compare the carpal angles of dogs ascending the A-frame to dogs using the same gait and speed on the ground.
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The dogs in the study were running at an average of 6.7 m/s, indicating that they were cantering or galloping . An examination of the literature of more rapidly moving dogs revealed a study of trotting Beagles demonstrating maximal carpal angles of 49.2º(4), of Rottweilers 61.5º (5) and of Labradors 71.8º (5). 

A search of the internet did not turn up studies of carpal angles of dogs cantering or galloping. However, slow motion, high resolution videos of dogs galloping permitted measurement of maximal carpal angles. Dogs galloping on grass demonstrated carpal extension angles of about 64º   (see figure below), slightly greater than those measured in the agility dogs in the study.
Thus the dogs ascending the A-frame were experiencing carpal extension that is normal for galloping dogs and even within the range of normal for some breeds of dogs when trotting. This suggests that carpal extension during the ascent of the A-frame is an unlikely cause of carpal injuries in agility dogs.

In any case, kudos to the authors of this study for addressing questions that are important to the health of our active dogs!
References:
 1. Levy M, Hall C, Trentacosta N, Percival M. A preliminary retrospective survey of injuries occurring in dogs participating in canine agility. Vet Comp Orthop Traumatol 2009;22(04):321–324.
2. Cullen KL, Dickey JP, Bent LR, Thomason JJ, Moëns NM. Internetbased survey of the nature and perceived causes of injury to dogs participating in agility training and competition events. J Am Vet Med Assoc 2013;243(07):1010–1018.
3. Appelgrein C, Glyde MR, Hosgood G, Dempsey AR, Wickham S. reuction of the A-frame angle of incline does not change the maximum carpal joint extension angle in agility dogs entering the A-frame. Vet Comp Orthop Traumatol 2018;31:77-82.
4. Lorke M, Willen M, Lucas K, Beyerbach M, Wefstaedt P, Murua Escobar H, Nolte I. Comparative kinematic gait analysis in young and old Beagle dogs. J Vet Sci 2017;18(4):521-530.
5. Agostinho FS, Rahal SC, Miqueleto ML, Vergugo MR, Inamassu LR, El-Warrak AO. Kinematic analysis of Labrador Retrievers and Rottweilers trotting on a treadmill. Vet Comp Orthop Traumatol 2011;24:185-191.
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