Page 96 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 71

VetBooks.ir wall defects and displacement of the distal phalanx have displaced distally on only one side of the foot,
most commonly the medial side, one side of the dis-
(e.g. white line disease).
Diagnosis tal phalanx is significantly closer to the ground, the
ipsilateral side of the DIP joint space increases and
In acute laminitis, diagnosis is usually straightfor- the distance from the distal phalanx to the surface
ward based on the history, characteristic stilted gait, of the adjacent wall increases (Figs. 1.117, 1.118).
increased digital pulses, heat in the feet, withdrawal In horses with more chronic rotation other changes
response to hoof testers or reluctance to lift a limb. occur, including remodelling of the distal phalanx,
However, when the hindlimbs alone are affected, especially at the tip, and flexural deformity of the DIP
acute laminitis may be hard to identify. Initially, joint (also known as phalangeal rotation in laminitic
radiographs indicate no changes except slight thick- horses). Horses without characteristic symptoms or
ening of the dorsal hoof due to lamellar oedema. gross morphological changes of the hoof capsule may
In horses with chronic laminitis, the characteris-
tic concavity of the dorsal hoof wall, convergence of
growth rings dorsally (laminitic rings), dropped sole, 1.116
widened white line and coronary band depression may
be sufficient to make a diagnosis. Lightly paring the
sole may indicate poor horn quality and demonstrate
bruising distal to the solar margin of the distal pha-
lanx, often seen as an arc just in front of the apex of the
frog. Radiographs are useful to determine the severity
of the disease. Prior to radiography the foot should be
marked with a radiodense marker on the dorsal hoof
wall in the median plane that extends from the coro-
nary band distally. Lateromedial and horizontal dor-
sopalmar/plantar radiographic views are necessary to
evaluate the position of the distal phalanx in relation
to the hoof capsule. The radiographic beam should Figure 1.116 Laminitis. Distal displacement of the
be centred on the approximate location of the solar distal phalanx demonstrated by decreased depth of
margin of the distal phalanx, approximately 1–1.5 cm sole and a prominent ‘sinker line’ at the coronary band
from the ground surface of the foot. Digital radiogra- (arrows).
phy permits assessment of both skeletal and soft tis-
sues of the foot on the same image, and in particular, 1.117
the junction of the hoof capsule and the underlying
dermis. A 45° dorsoproximal/palmarodistal oblique
view is useful to evaluate the solar margin of the distal
phalanx for osteolysis and remodelling. In horses that
develop capsular rotation, the dorsal parietal surface
of the distal phalanx diverges from the dorsal hoof
wall, the DIP joint flexes so that the angle the solar
margin of the distal phalanx makes with the ground
increases and the distance from the dorsal solar mar-
gin of the distal phalanx to the ground decreases.
In contrast, in horses in which the distal phalanx
displaces distally, the thickness of the dorsal hoof
increases, the depth of sole decreases and the extensor Fig. 1.117 Laminitis. Radiograph after rotation
process of the distal phalanx moves distally in rela- of the distal phalanx, both capsular and phalangeal.
tion to the coronary band (Fig. 1.116). In horses that Note the gas line in the dorsal hoof wall.