Page 118 - Adams and Stashak's Lameness in Horses, 7th Edition

84 Chapter 2

140 days of age in Thoroughbreds, suggesting that most
carpal deviations (lateral or medial) should be corrected
VetBooks.ir mation changed greatly in Thoroughbred foals up to 18
before this age. However, carpal and fetlock confor­
38
months of age in one study suggesting that the window
of growth may be longer than previously thought. 34

medial deViation oF the CarPus (knoCk knees, CarPus Valgus)
Medial angular deviation of the carpus (or lateral
deviation of the distal limb) can result from abnormali­
ties of the distal metaphysis, physis, and epiphysis of
the radius; from abnormal development and align­
ment of the carpal bones; or from carpal joint laxity
(Figure 2.22B). This deviation contributes to increased
tensional strain on the medial collateral ligaments of the
carpus and compression forces on the lateral (concave)
surface of the carpus. Varying degrees of stresses are also
transmitted to the joints proximal and distal to the car­
pus. Varying degrees of outward rotation of the cannon
bone, fetlock, and foot may accompany this entity. Mild Figure 2.23. Offset knees (bench knees), which are character-
carpal valgus (5°–7°) may have a protective mechanism ized by the cannon bones being set too far laterally.
against carpal injuries, as the odds for carpal fracture
and effusion decreased with an increase in carpal angle
in Thoroughbred racehorses. However, in a study of short uPright Pastern
2
National Hunt racehorses, carpal valgus conformation
was associated with an increased risk for SDF tendon A short upright pastern is believed to increase con­
41
injury. In the same study, valgus deformations of the cussion and injuries to the fetlock and phalangeal joints,
carpus, fetlock, and tarsus were all associated with an the navicular bone region, and soft tissue structures
increased risk of injury and considered to be detrimental within the metacarpus (Figure 2.24). 29,36 If the angle of
to performance. 41 the hoof is more upright than that of the pastern, it is
referred to as a broken‐forward hoof‐pastern axis.
21
This type of conformation is often associated with a
BenCh knees (oFFset knees) base‐narrow, toe‐in conformation and is often seen in
Bench knee is a conformation in which the cannon horses with short limbs and a powerful body and limb
bone is offset to the lateral side and does not follow a musculature. Additionally, a straight shoulder (more
straight line down from the radius when viewed from vertical) usually accompanies a short upright pastern.
the front (Figure 2.23). Increased weight‐bearing on
the medial splint bone is thought to occur in bench‐
kneed horses. This is thought to contribute to increased long sloPing Pastern
stress on the interosseous ligament predisposing to A long sloping pastern is characterized by a normal
“splints.” In a study documenting the conformational or subnormal angulation of the forefoot (less than 50°–
abnormalities in 356 Warmblood horses, more than 54°) with a pastern that is too long for the length of the
50% were bench kneed. The combination of bench limb (Figure 2.25). If the angle of the hoof is more
22
knees and carpal valgus is common, and offset knees acute (lower) than that of the pastern, it is referred to
has been associated with fetlock problems in racing as a broken‐backward hoof‐pastern axis. It is often
21
Thoroughbreds. 2 seen in horses with long toes and/or low heels and may

A B C
Figure 2.24. Examples of pastern conformation. (A) A normal angulation of hoof wall and pastern. (B) A short upright pastern. (C) A long
upright pastern.