A localised swelling in the hind limbs, slightly above the hock in front of the achilles tendon, visible on the medial and the lateral aspect of the limb. It represents a distension of the tarsal sheath, the tendon sheath surrounding the deep digital flexor tendon at the level of the hock. Only in exceptional cases is it responsible for a lameness; most cases are due to an asymptomatic low grade tenosynovitis (inflammtion of the membrane lining the tendon sheath).