A sprain is an injury to a ligament, a tendon, a muscle, or a joint, in which there is over-extension and sometimes laceration of fibres and maybe displacement of parts.

Bog spavin Truss or Compress.

Fig. 364. - Bog-spavin Truss or Compress.

Ligaments and tendons, with one or two notable exceptions, are inelastic, and tear rather than stretch when a force is applied beyond their power of resistance. The apparent elongation in a "break down" is due to the rupture of a number of fibres in more than one place, and not to actual fracture across the ligament. In the case of strain so violent as to dissolve the connection of one part with another, the separation will usually be found close to the bone and not in the middle or seemingly weakest portion. The ligament or tendon tears away from its attachment, or carries with it a thin layer of bone.

The rarity of complete rupture of a ligament in the middle portion is due to the close weaving of its fibres into a dense rounded bundle, whereas at the ends the fibres spread out to afford a wider attachment to the bones, and are consequently more loosely connected with each other. The great strain put upon certain ligaments, when a draught-horse exerts himself to start a load, is easily borne while the pull is a straight one, but if he be suddenly turned, and a twisting and unequal force is applied to the fibres, rupture is very likely to occur. The force which will extend the fibres of a tendon, or ligament, or muscle will of necessity injure the nerves and blood-vessels concerned in their innervation and nutrition; the pain suffered is due to pressure upon, or else laceration of, the former, and the swelling which follows to the escape of fluid from the latter into the structure of the part.

In the process of repair additional enlargement results from the deposition of new matter, which may be in excess of that actually required. Some of this surplus matter will in time be removed, but it frequently happens that a considerable amount remains behind as a chronic swelling after all active disease has ceased.

This undue development of reparative tissue will in some instances interfere with the action of the part and impair its function. In whatever manner he attempts it, the surgeon's chief concern is to get rid of superfluous growth and to restore the parts as nearly as possible to their normal state.