Page 528 - Adams and Stashak's Lameness in Horses, 7th Edition

494 Chapter 4

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A B
Figure 4.67. In medial or lateral asymmetrical displacement (A), arrow). Additionally, the DIP joint becomes asymmetrical when
one side of the distal phalanx descends (white open arrow in B). viewed on a dorsopalmar radiograph; the joint space is increased
The distance between the wall and the distal phalanx increases on the affected side (white arrowhead) and decreased on the
(black double arrow), and the distance between the distal phalanx unaffected side (black arrowhead).
and the sole and ground decreases on the affected side (white open

A B
Figure 4.68. (A and B) In horses with early chronic laminitis, the dorsal distal parietal surface of the distal phalanx and hoof capsule
surface of the hoof wall is unchanged, but the distal phalanx rotates increases (white double arrow) while it remains close to normal
about the DIP joint (the joint flexes, black lines in B); consequently, the proximally (black double arrow), i.e. there is divergence of the surfaces
normal alignment of distal phalanx with the other phalanges is (capsular rotation). Also, the distance between the dorsal margin of
changed (phalangeal rotation). Additionally, the distance between the the distal phalanx and the sole and ground is decreased (open arrow).

left between the hoof wall and the displaced distal pha- THE CLINICAL PRESENTATION: THE HORSE AT
lanx is likely to fill with blood and necrotic tissue (this RISK OF LAMINITIS
area on radiographs may appear radiolucent for a short
time after displacement). As we can now place most laminitis cases into one of
After separation of the lamellae, some germinal epithe- the three types of the disease, we realize that the clinical
lial cells remain on the deep surface of the separated epi- presentation can differ greatly not only between animals
dermal lamellae, and some remain attached to the surface but also between the different types of laminitis.
of the dermal lamellae. Similar to wound healing in other Classically, the literature has attempted to fit the laminitic
tissues, remaining viable germinal epithelial cells prolifer- horse into one of three categories: developmental, acute,
ate. However, the underlying damaged dermis is unable to or chronic laminitis. The developmental/prodromal stage
exert normal control of epithelial proliferation. 60,71 was defined as the stage prior to the horse exhibiting clin-
Therefore, remaining epithelial cells undergo aberrant ical signs (i.e. the septic horse not exhibiting digital signs);
proliferation in the space created by displacement of the the acute stage has been defined as the animal exhibiting
distal phalanx, resulting in a lamellar wedge of disorgan- clinical signs of digital pathology but no radiographic
ized epithelial tissue, the apex of which is proximal and signs of displacement of the distal phalanx; and the
the broader base distal (Figure 4.69). This wedge most chronic stage describing the animal in which displace-
likely impedes the ability of the clinician and farrier to ment of the distal phalanx is present on radiographs.
realign the distal phalanx with the dorsal hoof wall. The authors do not find these categories useful for two