Aims

1.  To describe previously uncharacterised soft tissue structures of the canine hock that are visualised with ultrasound.

2.  To develop an optimal technique for ultrasound examination of these structures.

3.  To present initial results in establishing reference ranges for some of these structures.

Materials and Methods

8 hindlimbs from 6 dogs euthanased for reasons other than hindlimb pathology were prepared for ultrasound examination. Structures identified by ultrasound were injected with methylene blue dye, and the specimens were dissected to confirm the identity of the structure. Cross sectional measurements of the plantar ligament, deep and superficial digital flexor tendons and the long digital extensor tendon were taken from three of the cadaver hindlimbs, which were sectioned to confirm the accuracy of the ultrasound measurement. In addition, 10 volunteer dogs free from orthopaedic disease were examined, and measurements taken.

Results

1.  Structures identified included: the long digital extensor tendon, the tendon of muscle tibialis cranialis, the joint space, and the three bellies of muscle extensor digitum brevis on the cranial/dorsal aspect of the hock. The lateral digital extensor tendon and the tendon of muscle peronus brevis were identified as a single structure on the lateral aspect of the hock. The caudal/plantar approach allows identification of the three portions of the common calcaneal tendon at their insertion on calcaneus, the deep digital flexor tendon passing over the sustentaculum tali, the plantar ligament, and the lumbricales and interosseus muscles plantar to the metatarsals. The medial collateral ligament can be identified in some dogs on the medial hock.

2.  A technique was developed to ultrasound each of the soft tissue structures of the hock on the cranial aspect of the hock, followed by the lateral, caudal, and medial aspects in a systematic manner.

3.  The long digital extensor tendon was 0.07 (±0.03)cm2, the deep digital flexor tendon was 0.12(±0.04), 0.17(±0.04) and 0.15(±0.05)cm2 at tibia, proximal tarsus and distal tarsal levels respectively. The plantar ligament showed most variation: 0.39(±0.14) and 0.33 (±0.14)cm2 at proximal and distal levels respectively.

Conclusions

Many of the soft tissue structures are identified with ultrasound. This technique has been applied to clinical cases of soft tissue trauma including deep digital flexor tendon trauma, tibialis cranialis tendonitis, and plantar ligament rupture.