Page 1093 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness in the Young Horse 1059

FLEXURAL DEFORMITIES

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

Flexural deformities, or contracted tendons, of limbs tarsus occur, but much less frequently. 10,23 Tarsal flexural
of young horses are classified as congenital (apparent at deformities are rarely seen because the deformity often
or near the time of birth) or acquired (develop during the causes a dystocia, leading to stillbirth, but, when present,
growth period). 2,23 Limb deformities secondary to trauma are often combined with multiple other congenital
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also may be considered as acquired flexural deformities. deformities (Figure 10.31).
The term contracted tendons is often used synonymously Rupture of the common digital extensor (CDE) tendon
with flexural deformities, but the potential for contrac­ may occur concurrently with carpal or fetlock flexural
tion of dense tendinous tissue is limited and the primary deformities (Figure 10.32). 23,38 Occasionally, flexural
defect is usually not in the tendon itself. For this reason, deformities may not be noted despite evidence of a rup­
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as well as the fact that other structures such as the suspen­ tured extensor tendon. The extensor tendon rupture may
sory ligaments, distal sesamoidean ligaments, joint cap­ occur secondary to flexor tendon contracture, or it may
sule, and fascia can be involved, the contracted tendon predispose to the flexural deformity. Affected foals may
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terminology should be obsolete. The mechanism for have other associated birth defects including progna­
development is not well understood, but in many thism, underdeveloped pectoral muscles, and incomplete
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instances the result is an effective functional length of the ossification of the carpal/tarsal bones. 23
musculotendinous unit(s) that is less than what is neces­
sary for normal limb alignment. These abnormalities are
most accurately discussed relative to the joint(s) around Diagnosis
which the deformity is centered rather than the probable The diagnosis is usually based on the history of being
affected tendons and ligaments because more than one born with the problem and physical examination of the
structure may be involved. foal. Affected limb(s) cannot be straightened manually, and
the foal may have difficulty standing. It is important to try
to get the foal to stand, if possible, as the deformity is usu­
CONGENITAL FLEXURAL DEFORMITIES ally not as bad as it seems when trying to straighten the limb
while they are recumbent (Figure 10.33). In more mild cases
Etiology it may be possible to palpate which tissues tighten while
trying to extend the limb, but this becomes increasingly dif­
Several factors have been incriminated as causes of ficult in more severe cases and those with contracture of the
congenital flexural deformities in neonates. This condi­ carpal fascia and/or palmar ligaments. This contributes to
tion primarily has been attributed to uterine malposi­ an arthrogryposis‐like position of the carpus with minimal
tioning or overcrowding, but more complex influences flexion or extension capabilities (Figure 10.29A).
have been implicated, such as genetic factors, equine Radiographs or ultrasound can be performed but are usu­
goiter, and teratogenic insults from toxic and infectious ally not necessary for the diagnosis. Radiographs can be
agents during the embryonic stage of pregnancy or from useful though for identifying any underlying abnormality of
malnutrition of the mare. 10,12,23,25 Arthrogryposis, as a the cuboidal bones when the carpus is affected.
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cause of congenital flexural deformities, has been well Radiographs should be considered more often in the distal
documented in calves but is less well defined in horses. 23 limb since fetlock flexural deformities can lead to subluxa­
tion of the DIP joint (Figure 10.30B). In addition, rare pas­
tern flexural deformities are hard to diagnose early in life
Clinical Signs without the benefit of radiographs.
Generally, congenital flexural deformities may affect Concurrent extensor tendon rupture is characterized
one or more limbs with the superficial and deep digital by the presence of unilateral or bilateral swelling over
flexor musculotendinous units being most commonly the dorsolateral aspect of the carpus (Figures 5.8 and
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affected. Therefore, the carpus and/or fetlock cannot be 10.32). It may or may not be possible to palpate the
completely straightened. The carpus is most commonly enlarged ends of the ruptured tendon. Commonly, the
affected. The fetlock can also be affected with the carpus ruptured CDE tendon is not recognized, and the problem
or on its own (Figure 10.29). With fetlock flexural is diagnosed as a carpal flexural deformity.
deformities the foals may be able to stand but knuckle
over at the fetlock. In newborns, the fetlock flexural
deformity may be combined with laxity at the level of Treatment
the distal interphalangeal (DIP) joint (Figure 10.30); if Medical treatment usually consists of NSAIDs and IV
the flexural deformity of the fetlock is not corrected, oxytetracycline and is often combined with bandaging
subluxation of the DIP can occur. In severe instances, and splinting. Treatment of congenital flexural deformities
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the foals walk on the dorsal surface of the fetlock. should be initiated soon after recognition of the problem,
Involvement of the deep digital flexor tendon (DDFT) with the severity of the deformity dictating how quickly
alone may manifest as a flexural deformity of the DIP and aggressively treatment should proceed. 10, 31 Foals with
joint. Congenital flexural deformities of the pastern and minor congenital flexural deformities ( particularly of the