Page 446 - The Veterinary Care of the Horse

The condition is caused by asymmetric growth of the physis or growth plate of the lower part

of the radius, tibia and cannon bones. For example, if the distal growth plate of the radius
VetBooks.ir grows more on its medial side, this results in carpal valgus. Faster growth on the lateral side
of the lower part of the cannon bone results in fetlock varus. The imbalance of the growth

rate on either side of the growth plate is usually due to one side being subjected to abnormal
pressure which retards or stops longitudinal growth of the bone at that site. This can be

caused by:
• laxity of the ligaments and soft tissues around the joint allowing excessive movement

• delayed or defective ossification of the small cuboidal bones of the knee and hock – this

is often associated with prematurity; the affected bones may not be able to withstand the
weight of the foal and become compressed or misshapen

• malpositioning of the growing foal in the mare’s uterus before birth

• overfeeding of young foals so they become ‘top heavy’
• over-exertion of young foals

• any injury leading to reduced weight bearing on one limb can lead to an angular

deformity in the sound limb as the foal adjusts its stance and action to compensate
• trauma to the growth plate.

Clinical signs

• The signs may be slight or immediately obvious as a valgus or varus conformational

deformity. Sometimes a combination of varus and valgus is seen (Figure 10.9). The
condition may occur with a toe-in or toe-out conformation.

• Localized heat and swelling may be present.
• The foal may show a degree of lameness.