Page 110 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 85

VetBooks.ir 1.146 the digit from the normal, near symmetrical form
and the way the hoof relates to the ground. Neither
poor conformation nor imbalance are diseases or
direct causes of pain per se. However, as they influ-
ence the distribution of stress within the limb, they
can cause injury to structures in the limb that do
cause lameness.

Aetiology/pathophysiology
Hoof shape is dependent on hoof growth, the under-
lying conformation of the skeletal structure of the
limb and the distribution of stresses on the distal
limb. For most horses, that is those with average
conformation and distribution of stresses on the dis-
Fig. 1.146 Surgical removal of a keratoma by
resection of the surrounding horn. (Photo courtesy tal limb, the pattern of hoof growth is fairly even
Graham Munroe) around the circumference of the limb, the coronary
band is symmetrical about the sagittal plane of the
limb and the walls are straight. An abnormal distri-
Prognosis bution of stresses on a ‘normal’ hoof capsule leads
The prognosis for horses with keratomas treated by to movement of the coronary band, changes in
surgical excision is good. Approximately 80% return hoof growth and distortion of the capsule. Clearly,
to previous athletic performance. any deviations of underlying conformation from
‘ normal’ will cause redistribution of stresses, as can
FOOT CONFORMATION AND HOOF trimming and shoeing.
IMBALANCE AS A CAUSE OF LAMENESS Hoof growth appears to be inversely related to
load; that is, the greater the load on any given area
Definition/overview of the hoof, the slower the hoof growth and vice
Conformation and balance are both terms that relate versa. By changing the rate of growth in response
to the form of the limb (i.e. its size, proportions and to load, the foot attempts to re-establish a normal
shape). There is much confusion about the precise distribution of load and hence shape. Imbalance is
meanings of these terms, but for the purposes of represented by a change in the shape of the foot or its
this discussion, balance is reserved for the relation- relation to the pastern. It may develop either because
ship between the hoof, the ground and the rest of of an abnormal distribution in load or because of the
the limb. Conformation is used here to describe the structure of the limb. For example, in a foal with a
shape of the limb (and the rest of the body) proxi- flexural deformity, there is too much load on the dor-
mal to the coronary band, which is largely dictated sal wall and a correspondingly reduced load on the
by the shape and size of the individual structures of heels. Subsequently, the dorsal hoof wall growth is
the limb and the way they relate to each other. By reduced and the dorsal wall becomes concave, while
extension, although hidden from view, this includes the wall growth at the heels is increased. Chronic
those structures within the hoof capsule. Balance redistribution of stress to one side of the foot will
is a three-dimensional concept that is traditionally similarly cause that side of the hoof to grow slower
divided into mediolateral and dorsopalmar compo- and flare and the coronary band to move proximally,
nents as well as dynamic and static components. The while the contralateral side of the hoof grows faster,
underlying importance of the concepts of balance and the wall is straighter or underrun and the cor-
and conformation is that they relate to the distribu- onary band moves distally. These changes in the
tion of stress within the distal limb. Poor conforma- shape of the hoof also represent changes in distribu-
tion and imbalance refer to changes in the shape of tion of stress inside the hoof. Therefore, imbalance