Page 714 - Adams and Stashak's Lameness in Horses, 7th Edition

680 Chapter 5

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A B
Figure 5.81. Malformation of the distal tarsal bones can occur third tarsal bone may be a predisposing factor to formation of
in dysmature/immature foals but more often occurs in premature degenerative changes within the distal tarsal joints (B).
foals (A). Developmental abnormalities such as wedging of the

The disorder is often bilateral. 2,23 Once the cartilage do occur are usually associated with a significant exter-
model/immature bones are crushed, the malformation nal force or impact, such as a kick from another horse.
becomes permanent. The cuboidal bones continue to Twisting and torqueing of the tarsus while the lower
ossify around the malformed cartilage model. Continued limb is fixed is felt to contribute to disruption of col-
loading on these immature bones may result in valgus lateral and periarticular ligaments and subsequently
deformities and/or pathological fracture or collapse of lead to fractures. These animals are almost always
the tarsal bones. The reader is referred to Chapter 10 for non‐weight‐bearing lame, and the tarsus is diffusely
more information about this condition. swollen. Fractures of the talus can range from simple
fragmentation of the trochlear ridges to comminuted
fractures of the entire body of the talus. The degree of
Angular Deformities of the Tarsus comminution usually determines the severity of the
Angular limb deformity refers to an axial deviation of lameness and the extent of associated swelling. The
a limb in the frontal plane. The nomenclature to describe degree of lameness associated with fractures of the tar-
an angular deformity is derived by combining the name sus can be mild to moderate in the case of chronic cen-
of the involved joint (i.e. with cuboidal bone abnormali- tral tarsal bone fractures to severe and non‐weight‐bearing
ties) or the joint immediately distal to the affected growth such as in comminuted fractures of the talus or calca-
plate and the type of deviation. A lateral deviation of the neus. External trauma can fracture specific areas of
distal limb is termed valgus, while a medial deviation is exposed bone such as the tibial malleoli, trochlear
termed varus. Tarsal angular deformities often originate ridges, tuber calcaneus, and fourth tarsal bone. Injuries
from within the physis of the distal tibia but can also that involve the TC joint are frequently more apparent
occur from the cuboidal bones of the tarsus (see above). due to swelling of the dorsomedial and dorsolateral
Tarsal valgus deformities are more common than tarsal synovial pouches. Fractures of bones within the TMT
varus deformities. Perinatal factors are usually involved and DIT joints are less noticeable due to the dense liga-
when a foal is born with an angular limb deformity. In mentous coverage and tight joint capsules that limit
neonatal foals angular deformity can be a consequence of swelling and effusion. Luxations of the tarsus are
laxity of the supporting soft tissues of the tarsus or related uncommon and often involve significant trauma that
to hypoplasia and/or incomplete ossification of the tarsal disrupts many of the support structures around the
bones. A large number of foals are noticed to have some tarsus.
type of angular deformity at birth. The cause of angular
limb deformities is complex and probably multifactorial Traumatic Luxations of the Tarsus
and is discussed in more detail in Chapter 10.
Traumatic luxations that involve the tarsus are usu-
ally created from kicks from other horses, trauma from
FRACTURES AND LUXATIONS OF THE TARSUS moving objects, or by having the limb entrapped in fixed
objects such as a fence or cattle guards. The soft tissue
Fractures and luxations of the tarsus are rare prob- injuries and fractures that accompany TC luxation are
ably due to the dense supporting structures that cover often so significant and incapacitating that salvage of
the bones in this area. 29,52,75,97,104,105 Fractures when they the horse is frequently not possible. Lameness is usually