ÜìˆÁ±‡>ÞØ &(ÞØØØ%ØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØØ“´ç7 ÝÀbjbjUU "7|7| ØØØØØØl¬¬¬¬¬¬¬1Ú4ZZZZf1Ú4– ¦~~~~~~~~p r r r r r r $¤ ‚öÐ ¬~~~~~Ð (¬¬~~Ç (((~ ¬~¬~p (~p (H(p ¬¬p ~rË÷-ƒË1Ú4zÿZö p p ç 0– p O ÕÐO p (1Ú41Ú4¬¬¬¬ôHypothesis 3 Soft Tissue Swelling Impinges on Radial Nerve The foal was subjected to some form of trauma, probably as a result from being kicked in the shoulder by another horse. The trauma may have severed the nerve because it is vulnerable as it passes superficially on the lateral side of the humerus under the lateral head of the triceps brachii muscle. This would explain the loss of function simply due to direct nerve destruction. However, the trauma also led to swelling which acted as a space-occupying lesion, and in turn could have led to disruption of the radial nerve. This later scenario is explained in the following paragraphs. The trauma has led to a variety of occurrences. The trauma caused tissue damage and vascular damage, leading to an acute inflammatory response. The damaged cells released chemical mediators, which were chemotactic to the cells responsible for the inflammatory response. The vasculature also responded by dilating to allow for increased blood flow to the area. Circulation then slows due to the increased permeability of the vasculature. Fluids, phagocytes, and leukocytes leave the circulation and migrate into the damaged tissues. These actions serve to allow the body to clean up the necrotic debris and allow healing to take place. This chain of events continues to amplify the inflammation reaction. The swelling from the inflammation in this case led to the loss of function of the foalÕs right forelimb due to high radial nerve paralysis. The damage to the radial nerve is proximal to its innervation of the triceps brachii muscle. This muscle serves to extend the elbow and flex the shoulder. The triceps can no longer support the limb, and therefore the elbow appears dropped on the right side. The inability to extend the elbow without the use of the triceps brachii, leads to the inability to support weight on the affected limb. As the horse bears weight on the limb, the elbow will collapse the limb by flexing. (This foal appears to be weight bearing on the right side. This may be only an apparent weight bearing as witnessed by the owner. The foal may simply be resting the limb on the ground while not actually placing weight on the limb.) The radial nerve also innervates the extensor carpi radialis, common digital extensor, and the lateral digital extensors. The extensor carpi radialis serves to extend the carpus, while the common digital extensor and the lateral digital extensor serve to extend the carpus and the digit. Due to the loss of innervation of these muscles, the foal looses the ability to extend the distal limb resulting in knuckling over of the carpus and digit. If the loss of function of the radial nerve is attributed solely to the acute inflammation acting as a space-occupying lesion, the loss of function of the radial nerve is presumed to be only temporary. As the swelling in the limb goes down, there will be less pressure on the radial nerve, and the foal will gradually gain control of the limb. However, if the inflammatory process itself leads to damage of the radial nerve (due to release of free radicals and such), full function may not return. Moreover, since this inflammation has lasted well over a week, the radial nerve is also likely injured to pressure necrosis caused by the space-occupying lesion of the swelling. ;