Page 209 - Canine Lameness

13.4 rFrral HrrFrecroesg o ronf ctrF rFrral geraroc tesf ontFgres 181

Other causes, including collateral ligament damage, fractures, and luxations of the carpal bones,
as well as injuries to muscles and tendons traveling over the carpus, may also lead to chronic pain,
decreased carpal function, and carpal hyperextension. Subluxation or luxation of carpal bones
other than hyperextension injuries is rare. Luxations of the carpal joint are also rare but generally
associated with severe trauma.

13.4.1 Signalment and History

Traumatic carpal hyperextension most often occurs in large-breed active dogs. However, small-
breed dogs can also be affected. Carpal hyperextension is most commonly associated with a fall,
jump, or motor vehicle accident (Denny and Barr 1991). Carpal injuries related to trauma can also
be seen in competitive agility dogs (Levy et al. 2009; Cullen et al. 2013). The angle of the A-frame
(a tall “contact” obstacle that agility dogs must overcome) has been hypothesized to be related to CARPAL REGION
carpal hyperextension injury in these dogs. However, a prospective study evaluating the landing
carpal extension angles refuted this hypothesis (Appelgrein et al. 2018). In that study, the antebra-
chiocarpal landing angle was approximately 240° for any given A-frame angle and it was concluded
that this angle likely represents the maximum physiological carpal extension angle when contact-
ing the A-frame.
Another cause for carpal injury could be from repetitive trauma as seen in Herding dogs (Jerram
et al. 2009). A similar etiology could be considered for long-distance sled dogs. Indeed, carpal
injury and an increased risk to be dropped from a team during marathon sled dog racing was found
to be associated with increased training miles (von Pfeil et al. 2015).
Carpal hyperextension and collateral ligament injuries have no specific predisposition for age,
weight, or breed. However, older working Collies have been suggested to potentially be predis-
posed to progressive degenerative hyperextension as a result of chronic, repetitive carpal injury
(Jerram et al. 2009).
Regardless of the specific underlying traumatic cause, acutely affected dogs are in pain and
exhibit varying degrees of lameness of the affected leg. Carpal swelling can be present, particularly
if the injury is acute. Once the condition is more chronic, there is typically less discomfort. The
main abnormality noted by owners is hyperextension and lameness of the affected thoracic limb.
Depending on the severity of the injury, the degree of hyperextension can be mild or severe. In
severe situations, patients may develop a palmigrade stance with the accessory carpal bone in con-
tact with the ground (Video 13.1).

Video 13.1:

Video of patients with carpal hyperextension (traumatic and due to immune-mediated polyarthritis).

13.4.2 Physical Examination

Lameness can vary in severity, depending on the amount and location of damage and chronicity.
The contralateral side is used to compare the carpal angle and the presence of swelling. Upon
palpation of the carpus, soft tissue swelling and discomfort can be noted in addition to carpal
hyperextension (Figure 13.7). The examiner should also evaluate the presence of crepitus and
resistance and assess for collateral ligament instability (Figure 13.8), requiring knowledge of
normal motion. Palpation of the dorsal surface of the carpus will help to detect minor swelling or