Page 321 - Canine Lameness

18.4 Tarsal oint Luxations 293

damage to the short lateral collateral ligament can produce just a subtle rotational instability that
can only be detected with the dog under heavy sedation. Testing is done with the tarsus in 60–90°
of flexion; the tibia is stabilized, and the foot is rotated in both directions. When the short lateral
collateral ligaments are torn, a click may be felt on the lateral side as the pes is supinated (Sjöström
and Håkanson 1994).
Dogs walk with the tarsocrural joint in some degree of flexion throughout the weight-bearing
phase of the gait. Below the tarsocrural joint, the rest of the tarsus resists this bending tendency and
normally remains straight, but disruption of the plantar tarsal ligaments or their attachments allows
flexion (and often subluxation) here. With acute distal tarsal joint injuries, the affected limb may be
held up throughout the gait, but most patients return to a severe but weight-bearing lameness. In
animals with proximal intertarsal luxation due to disruption of the plantar ligaments, the tarsus can
be seen to flex distal to the tarsocrural joint (i.e. at two levels rather than just at the tarsocrural joint), TARSAL REGION
when the dog is bearing weight (Video 18.1). There is usually some firm swelling on the plantar
aspect of the tarsus, at or distal to the base of the calcaneus. To demonstrate this instability, the exam-
iner holds the calcaneus in position and applies pressure on the pes through the metatarsal pad as a
dog would do while walking (Figure 18.4). Normally the distal pes will remain aligned with the long
axis of the calcaneus, but in dogs with tarsal injuries the pes will angle cranially. In contrast, disrup-
tion of the dorsal ligaments does not cause these obvious instabilities, since weight-bearing does not
stress the dorsal ligaments. Instability may be visible during liftoff/swing phase or during palpation,
which is performed by reversing the palpation performed for plantar ligament pathology. These inju-
ries are encountered less frequently and cause less severe signs and pain. Depending on the plane of
instability, dogs with tarsometatarsal luxations may show similar exam findings to dogs with proxi-
mal intertarsal luxation. If severe displacement is present (Figure 18.6), obvious instability, pain, and
deviation of the bones will be palpable, but with less severe injuries exam findings can be subtle.

Video 18.1

Achilles tendinopathy gaits.

18.4.3 Diagnostics

Orthogonal radiographs are part of the database, but diagnosis of the specific condition is usually
made through stress radiography. Stress radiographs can be done in any direction and are per-
formed in the same fashion as palpation during the physical exam. For example, for detection of
collateral ligament disruption, dorsoplantar radiographs should be taken both with the tarsus in
neutral position and with varus and valgus stress applied using a radiolucent fulcrum such as a
wooden spoon placed slightly above the tarsocrural level to lever against; the tarsocrural joint will
open up on the side of the collateral disruption (Mauragis and Berry 2012). There is also almost
always marked soft tissue swelling evident at the tarsocrural joint at the side of the collateral liga-
ment that is affected. With shearing injuries, the medial malleolus may be ground flat. Malleolar
fractures may be apparent, or small bone fragments may suggest avulsion of the origin of the col-
lateral ligament. Oblique views may show other injuries accompanying the ligament tear.
For detection of plantar ligament instability, a lateral view is made with the stifle held in
moderate extension while upward pressure is placed on the metatarsal pad and plantar aspect