Grade IV cases are the bad boys of laminitis. These cases can involve edema and separation of the laminar structures that
surround the dorsal face of the distal phalanx (P3), with seromas that rupture through the coronary band dorsally (Figure
1), medially or laterally or penetrate the sole (solar prolapse). The final sequela is often fatal sinker syndrome with hoof
capsule loss. Complications that I have seen (as if the aforementioned were not bad enough) are rupture of the distal interphalangeal
(DIP) capsule, fatal emboli, P3 fractures, ankylosis of the DIP joint, gangrene and unusual infections within the hoof capsule
such as botulism.
Figure 1: A typical coronary band rupture. Note the use of a reverse wedge tenotomy trailer rail shoe.
For the sake of simplicity, I divide Grade IV cases into two categories—the rotators (cranial rotation cases) and the sinkers
(fatal sinker syndrome, or FSS).
All horses with Grade IV laminitis are in extreme pain. They are recumbent and rarely stand unless asked to. I have seen these
horses walk in on their hind legs, rather than place weight on their forefeet. I have also watched them walk out of their
hoof capsules. Grade IV cases of the forefeet will always have a degree of laminitis in the hind feet as well, so be sure
to radiograph all four feet when starting your work-up.
Cases of Grade IV laminitis of the hind feet (originating there first) are rarely bilateral and are often less complicated
than forefoot cases, but they can also become euthanasia cases rapidly if not taken seriously—especially if the laminitis
has a supporting limb etiology. (Remember to radiograph the forefeet as well.) Horses with a fractured hind leg or severe
pain of any origin are candidates for supporting limb laminitis. I have also seen smooth wire fencing become a tourniquet
when wrapped around the leg during a struggle in the fence line. When the wire is placed in such a way as to allow intermittent
blood flow, laminitis can be a sequela (Figure 2 and Figure 3).
Figure 2: A venogram of an intermittent constriction of smooth wire around a limb that resulted in a Grade IV laminitic event.
The venogram shows complete absence of the dorsal and circumflex circulation.
Grade IV laminitis has a series of pathologic events that avalanche to final cases that may be beyond salvage. The Grade IV
case can present in 24 hours or five or six weeks. The usual course becomes more critical over a longer period as the structures
within the hoof capsule collapse slowly. It is common to see a case "recur" five to six weeks after the acute phase, when
in actuality this is simply the final stage of the original case.
Figure 3: A lateral radiograph of the limb in Figure 2 showing the separation of laminae in the dorsal and solar regions of
the hoof capsule that was prognosticated by the venogram.