Page 59 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

34 CHAPTER 1

VetBooks.ir 1.2 The foal and developing animal

CONGENITAL MUSCULOSKELETAL ABNORMALITIES

Congenital defects are those abnormalities present and fetlock (typically varus) joints. Valgus is a devia-
at birth, either structural and/or functional, which tion in alignment of the limb which is lateral to its
result from abnormalities in embryogenesis or intra- long axis from the point of deviation and varus is a
uterine factors. Theoretically, these abnormalities deviation in alignment which is medial to its long
may be genetic or environmental in origin, but often axis; both are present at birth (Fig. 1.60). The fore-
no definitive cause is identified. limbs are more commonly affected and sometimes
there may be a degree of limb rotation. It is important
CONGENITAL ANGULAR that a primarily rotational deformity is identified, as
LIMB ABNORMALITIES attempted correction of this is ineffective. However,
in many cases rotational deformities seem to resolve
(See p. 49 for Acquired angular limb deformities.) as the foal grows in size and its chest and pelvis
become broader. ALDs are usually seen in larger,
Definition/overview faster growing breeds such as Thoroughbreds, and
Congenital angular limb deformities (ALDs) are may be uni- or bilateral.
common, especially at the carpus (typically valgus)
Aetiology/pathophysiology
The aetiology is multifactorial and not clearly under-
1.60 stood, but possible cited factors include intrauterine
malpositioning, overnutrition of the mare in the last
third of pregnancy, joint laxity and incomplete ossi-
fication of the cuboidal bones, with other hereditary
(poor conformation), nutritional and possibly hor-
monal influences also contributing.
Joint laxity is common at birth and will often
appear as an angular or hyperextension deformity.
Such cases almost always resolve spontaneously
within a few days following gentle exercise, which
encourages increased strengthening of muscles,
ligaments, tendons and periarticular structures.
Defective or incomplete ossification of the cuboidal
bones of the carpus or tarsus can also lead to con-
genital ALDs (see below).

Clinical presentation
All four limbs should be examined for deformity
in all planes, but particularly perpendicular to the
frontal plane through the limb. Examination and
manipulation of the affected limbs will reveal gross
instability in cases of joint laxity, but not in other
Fig. 1.60 Bilateral congenital carpal valgus angular cases. Sometimes, several limbs may be involved and
limb deformity in a neonatal foal. lameness is not usually a feature (Figs. 1.61, 1.62).