When a bone is broken into two or more parts it is said to be fractured. Fractures assume a variety of forms, each of which presents some feature requiring special consideration, either in regard to diagnosis or treatment. They may be either partial or complete; simple or compound; comminuted or impacted.
When a bone is broken, but the breach only extends through a portion of its substance, the fracture is said to be partial. If, however, the bone is divided into two separate parts, it is a complete fracture.
A simple fracture is one in which the broken bone is not connected with an external wound; where such a wound exists and communicates with it the fracture becomes a compound one (fig. 329).
If instead of the bone being broken into two parts it is divided into three or more - smashed - a comminuted fracture results (fig. 325).
It sometimes happens that when a bone is broken the broken end of one piece is driven into that of the other. Such a fracture is said to be impacted (fig. 328).
Bones break in various directions; hence fractures are spoken of as transverse, longitudinal, or oblique (fig. 326).
A transverse fracture follows a line at a right angle with the shaft of the bone. This is a comparatively rare form of breakage, but is sometimes seen in the scapula, the ilium, the olecranon or elbow, and the calcaneus, or point of the hock.
Great importance attaches to the relations which the two or more broken pieces maintain towards each other after the fracture has taken place. In some instances they continue to remain in their natural position throughout the healing process, a condition favourable of course to reparation, and very much to be desired.
Fig. 325. - Fractures 1, Simple. 2, Comminuted.
In others, however, the fracture is accompanied or followed by more or less displacement of the divided parts, and all the bad consequences which attach to it.
This separation of the broken pieces may result from the same cause, and at the same time, as the fracture, or it may occur some time afterwards by the weight of the body forcing the parts asunder; or by movement, or as a result of the contraction of muscles which are attached to them.
The liability to displacement is much greater in some bones than in others. In the canon it is almost invariable, while in the pastern it is comparatively rare. This difference will be best understood by reference to fig. 327, where it will be seen that nearly the whole of the front and back of the pastern bones, and to a less extent the sides, have attached to them strong ligaments and tendons, so that when either of them is broken the parts are held firmly in their position, and unless the force acting upon them is very considerable, displacement is prevented.
Displacement of the broken fragments may be immediate, i.e. may occur at the time of the accident, or it may be deferred for a period varying between a few hours and a few days, and during the interval between the fracture and the separation of the broken pieces many animals have been known to continue to perform ordinary work without showing inconvenience.
Two classes of causes are recognized as conducing to the fracture of bones, viz., predisposing and exciting.