Sonography of the soft tissue structures of the canine tarsus

Currently, there are no available anatomic descriptions of the soft tissue structures that are visible with ultrasound in the canine tarsus. Eight cadaver hindlimbs and 10 clinically normal dogs (15-37 kg) were examined with ultrasound to establish which structures could be visualized in normal dogs. The structures always identified included the long digital extensor tendon, the tibialis cranialis tendon, the joint space, and the three bellies of the extensor digitum brevis muscle on the cranial/dorsal aspect of the tarsus. The lateral digital extensor tendon and the peroneus longus tendon were identified as a single structure on the lateral aspect of the tarsus. The caudal/plantar approach allowed identification of the calcaneal tendon, the deep and superficial digital flexor tendons, the plantar ligament, and the lumbricales and interosseus muscles. The medial collateral ligament can be identified on the medial tarsus of larger dogs. This technique has proved useful in the diagnosis of soft tissue injuries of the canine tarsus, and clinical examples of tibialis cranialis tendinopathy, deep digital flexor tendinopathy, fibrosis surrounding the medial collateral ligament and extent of invasion of a tarsal hemangiosarcoma are described.