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18

Tarsal Region

1
Kathleen Linn and Felix Michael Duerr 2
1 Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, TARSAL REGION
Saskatoon, Saskatchewan, Canada
2 Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University,
Fort Collins, CO, USA

18.1 Introduction and Common Differential Diagnoses

The tarsus is a joint with minimal soft tissue covering, making the bones and ligaments susceptible
to traumatic injuries such as fractures and ligament disruption. This lack of soft tissue covering is
a boon for diagnosis of lameness, because even subtle swellings, bone displacements, or instabili-
ties are readily palpable. Injuries to components of the common calcanean tendon (CCT) comprise
the other major cause of lameness attributable to the tarsal region. As dogs walk with a degree of
tarsal flexion through most of each stride, this extensor apparatus is critical in preventing collapse
when the limb is weight-bearing. Extensor tendon injuries are rare and seldom a cause of more
than transient lameness as they do not have to counteract the same magnitude of force.
Since there is no “tarsal dysplasia,” osteoarthritis (OA) of the tarsus is less often encountered
than, for example, hip or elbow OA. The only developmental disease of the region that is associated
with the development of OA is osteochondritis dissecans (OCD), which is rarely encountered.
Other causes for tarsal OA include traumatic injury and instability. Being a distal joint, immune-
mediated polyarthritis (IMPA; Chapter 13) also needs to be considered as a differential diagnosis.
Therefore, arthrocentesis and synovial fluid evaluation should be considered in cases where
inflammatory arthritis is possible.
The most commonly employed tests include radiographs and computed tomography (CT) for the
diagnosis of osseous disease and ultrasound for the diagnosis of pathology involving the CCT. Figure 18.1
and Table 18.1 outline common differential diagnoses and diagnostic steps for the tarsal region.

18.2 Normal Anatomy

The tarsus is a complex joint that works largely as a hinge, with 90% of its motion occurring at the
junction of the talus with the tibia and fibula (tarsocrural joint). A normal canine tarsus can move
from approximately 35° in full flexion to 155° in full extension, although the gastrocnemius apparatus

Canine Lameness, First Edition. Edited by Felix Michael Duerr.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/duerr/lameness