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

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
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