Page 1082 - Adams and Stashak's Lameness in Horses, 7th Edition

1048 Chapter 10

ANGULAR LIMB DEFORMITIES (ALDS)

VetBooks.ir AND CUBOIDAL BONE MALFORMATIONS

nicolas s. ernsT, Troy n. TruMble, anD Gary M. baxTer

ANGULAR LIMB DEFORMITIES (ALDS) seen in foals, followed by fetlock varus, carpal varus, and
tarsal valgus. 4,5,15,18,19,22 Tarsal varus is rare, as are devia­
Angular limb deformities (ALDs) are defined as con­ tions of other parts of the limbs. 4,13,20 Foals with ALDs
formational deviations in the frontal plane. These are due to asynchronous physeal growth typically are not
axial deviations that are based on the relationship of the lame and have few physical examination abnormalities
limb distal to a particular joint. Valgus and varus are the other than crooked legs. If lameness is present, physeal
terms used to describe ALDs in foals. Valgus indicates an trauma, fracture, collapse, or sepsis of the cuboidal bones
outward shift of the limb distal to the joint of origin, should be suspected as the cause of the limb deformity
while varus indicates an inward shift of the distal limb. (Figure 10.17). 6
For instance, carpal valgus refers to a deformity in which
the carpus is the site of the lesion and the limb distal to
this joint (third metacarpal bone) is deviated away from
the midline of the body (Figure 10.16). ETIOLOGY
A large number of foals examined during the first Foals can be born with ALDs or can develop them over
month of life can present with limb deviations, which will time. Proposed causes in foals born with ALDs include
decrease on prevalence and severity with increasing age malpositioning in utero, in utero chemical insults such as
and exercise. Carpal valgus is the most common ALD locoweed, and hormonal or nutritional imbalances. 6,21,24,32
However, most ALDs occur over time with 73.2% of
acquired deviations appearing between 3 months of age
and weaning age, irrespective of the joint. Acquired
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causes of ALDs in foals include laxity of periarticular sup­
porting tissues, incomplete ossification of the tarsal or
carpal cuboidal bones, direct trauma to the physis as with
concussion or fractures, traumatic luxation or fracture of
the carpal bones (Figure 10.17), and asynchronous longi­
tudinal growth of the metaphysis and epiphysis
(Figures 10.10 and 10.16). 4,6,22,32 By far the most common
reason for ALDs in foals is asynchronous metaphyseal
growth. For often unexplained reasons, one side of the
growth plate grows faster than the other, resulting in a
deviation of the normal limb axis. Trauma across the
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growth plate is believed to be one of the main underlying
causes of asynchronous growth. Trauma may retard cal­
18
cification of the matured and dying chondrocytes, result­
ing in thickening of the physeal plate with an increasing
6
number of chondrocytes at the hypertrophied cell layer.
If compression is excessive, chondrocytes may undergo
necrosis and the physis may prematurely close or growth
is slowed. Any factor that causes asymmetric loading
across a growth plate can lead to this sequence of events,
resulting in an ALD. 6,15 Such factors include joint laxity,
hypoplasia of the cuboidal bones, poor foot trimming,
heavy muscling, excessively active foals, or lameness in
the opposite limb (i.e. foals develop support limb ALDs
instead of laminitis). 4,6,18

CLINICAL SIGNS
Laxity of Periarticular Support Tissues
Foals with ligamentous laxity are often termed wind­
swept because their limbs are very flaccid and tend to
deviate in the same direction. The carpus or tarsus is usu­
Figure 10.16. Young filly with bilateral carpal valgus. ally affected, and one limb has a valgus deviation and the