Fig. 3.—Showing (1) Oblique fracture of Tibia; (2) Oblique fracture with partial separation of Epiphysis of upper end of Fibula; (3) Incomplete fracture of Fibula in upper third. Result of railway accident. Boy æt. 16.
A bone may be broken at several places, constituting a multiple fracture ([Fig. 1]).
Separation of bony processes, such as the coracoid process, the epicondyle of the humerus, or the tuberosity of the calcaneus, may result from muscular action or from direct violence. Separation of epiphyses will be considered later.
(2) According to the Direction of the Break.—Transverse fractures are those in which the bone gives way more or less exactly at right angles to its long axis. These usually result from direct violence or from end-to-end pressure. Longitudinal fractures extending the greater part of the length of a long bone are exceedingly rare. Oblique fractures are common, and result usually from indirect violence, bending, or torsion ([Fig. 3]). Spiral fractures result from forcible torsion of a long bone, and are met with most frequently in the tibia, femur, and humerus.
(3) According to the Relative Position of the Fragments.—The bone may be completely broken across, yet its ends remain in apposition, in which case there is said to be no displacement. There may be an angular displacement—for example, in greenstick fracture. In transverse fractures of the patella or of the olecranon there is often distraction or pulling apart of the fragments ([Fig. 35]). The broken ends, especially in oblique fractures, may override one another, and so give rise to shortening of the limb ([Fig. 2]). Where one fragment is acted upon by powerful muscles, a rotatory displacement may take place, as in fracture of the radius above the insertion of the pronator teres, or of the femur just below the small trochanter. The fragments may be depressed, as in the flat bones of the skull or the nasal bones. At the cancellated ends of the long bones, particularly the upper end of the femur and humerus, and the lower end of the radius, it is not uncommon for one fragment to be impacted or wedged into the substance of the other ([Fig. 28]).
Causes of Displacement.—The factors which influence displacement are chiefly mechanical in their action. Thus the direction and nature of the fracture play an important part. Transverse fractures with roughly serrated ends are less liable to displacement than those which are oblique with smooth surfaces. The direction of the causative force also is a dominant factor in determining the direction in which one or both of the fragments will be displaced. Gravity, acting chiefly upon the distal fragment, also plays a part in determining the displacement—for example, in fractures of the thigh or of the leg, where the lower segment of the limb rolls outwards, and in fractures of the shaft of the clavicle, where the weight of the arm carries the shoulder downwards, forwards, and medially. After the break has taken place and the force has ceased to act, displacement may be produced by rough handling on the part of those who render first aid, the careless or improper application of splints or bandages, or by the weight of the bedclothes.
In certain situations the contraction of unopposed, or of unequally opposed, groups of muscles plays a part in determining displacement. For example, in fracture immediately below the lesser trochanter of the femur, the ilio-psoas tends to tilt the upper fragment forward and laterally; in supra-condylar fracture of the femur, the muscles of the calf pull the lower fragment back towards the popliteal space; and in fracture of the humerus above the deltoid insertion, the muscles inserted into the inter-tubercular (bicipital) groove adduct the upper fragment.