Page 113 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

88 CHAPTER 1

VetBooks.ir carpus flexed so it is viewed from its palmar/plan- parallel to the ground. In some horses, in which the
distal phalanx is tilted down slightly towards one side
tar aspect, the ligaments in the limb are relaxed and
the foot rests in an unforced position, thus enabling
likely to be a normal variation for that horse. Uneven
the observer to better determine the relationship of of the foot, but the joint space is parallel, it is most
the foot to the rest of the limb. Specifically, with the spacing of the DIP joint may be evident following
foot on the ground, the length and angles of the wall acutely induced mediolateral imbalance, but is rare
at the heel and toe, and the approximate symmetry in horses with chronic mediolateral imbalance. On
of the medial and lateral walls of the hoof, includ- the lateromedial radiograph, the solar margin of
ing the presence of underrun and flared wall, are the distal phalanx should form an angle of 2–10°
observed. With the foot off the ground, the medio- to the ground, although 3–5° is the more common.
lateral symmetry of the ground surface of the foot is Gross misalignment of the foot–pastern axis can be
noted as well as its length and width, which are usu- detected, but subtle misalignment is hard to evaluate
ally approximately equal (Figs. 1.150, 1.151). because it changes as the horse’s weight shifts. One
Horizontal dorsopalmar and lateromedial radio- measure is to observe the proportion of the foot in
graphs can be helpful to determine the relationship front of the centre of rotation of the DIP joint versus
between the hoof capsule and the phalanges. It is that palmar to it; normally, approximately 60% of
important that the horse is bearing even weight on the ground surface of the hoof is dorsal to the centre
both front feet, which necessitates that both feet are of rotation, but in horses with a flexural deformity
on blocks of equal height, and that the metacarpus/ of the joint, it may be only 50% and in horses with a
metatarsus is vertical; uneven weight distribution long toe-low heel, it may be 70%. Regional analgesia
will distort the normal relationship of the distal pha- may be necessary to localise the lameness to the dis-
lanx with the hoof capsule and middle phalanx. On tal limb and often to the heel region.
the horizontal dorsopalmar view, the interphalan- Imbalance per se rarely causes lameness. Lameness
geal joint spaces should be symmetrical and usually associated with hoof imbalance is usually caused by

1.150 1.151

Figs. 1.150, 1.151 Hoof imbalance. (1.150) Assessing the mediolateral balance of the foot with a shoe in place.
Note the asymmetry of the walls and bulbs of the heel. (1.151) Same foot as in 1.150 with a T square in place
demonstrating the asymmetry of the bearing surface (long on the lateral side [left side of picture]). (Photos
courtesy Graham Munroe)