However, the commoner form of injury done tendons, is strain or sprain. Because of the sudden tensile strain brought to bear upon tendons in the shocks of concussion, as well as in propulsion of the body, there frequently occurs a rupture of fibers and this we know as sprain.
Sprains may be considered as fibrillary fractures of soft structures and since this form of injury is subsurface, and limited to fractional portions of tendons, the inflammation occasioned usually remains an aseptic one. Reaction to this form of injury is characterized by inflammation, the course of which is erratic and variable. In chronic inflammation of tendons, where animals are continued in service, the usual sequel is contraction, or shortening of these structures.
The degree of contraction as well as its import varies in different subjects and in the various tendons which may be affected. Contraction is a slow-going process that is progressive, gradually causing a decrease in the length of the affected structure and eventually rendering the animal useless.
The practice of applying shoes with extended toe-calks for the purpose of “stretching” contracted deep digital flexor tendons (flexor pedis perforans) cannot be too strongly condemned. While the addition of an extension such as is ordinarily employed to the toe of a shoe of this kind, prevents for a time, frequent stumbling in such cases, the increased tensile strain which is thus occasioned hastens further contraction and subjects animals so shod to much unnecessary pain.
Because of their being protected by other structures, nerve trunks, which supply muscles of locomotion, are not subjected to frequent injuries such as contusions. However, they do become injured at times and the result is lameness, more or less severe.
Lameness originating from nerve affection, may involve central structures as, for example, the spinal cord, medulla oblongata or parts of the brain. In making an examination of some lame animals it is necessary to distinguish between cases of lameness that are of central origin and marked by incooerdination of movement, and disturbances caused by other affections. Tetanus in its incipiency should not be confused with laminitis involving all four feet, or with certain forms of pleuritis, when careful examination is made, yet, in a way, to one not trained, the clinical symptoms are similar.
Disturbances of nerve function are caused in a variety of ways. It is not within the scope of this work to discuss central nervous disturbances caused by ingestion of mouldy provender, or disturbances of the brain or cord occasioned by infectious diseases, but mention of the existence of such conditions is appropriate.
By direct injury the result of blows, certain nerves are injured and muscles supplied by such nerves are rendered inactive. Depending upon the nature and extent of an injury thus inflicted, so the manner in which the affection is manifested varies. The suprascapular nerve is rather frequently injured causing partial or complete loss of function of the structures supplied by this nerve, and abduction of the scapulohumeral joint naturally results.