Fracture fragments can also be rotationally displaced. After fracture, the distal fragment is rotated along the long axis of the bone by muscle spasm or by the pull of gravity, resulting in either an internal rotation or an external rotation deformity.

A third type of displacement is a change in limb length. After a fracture, the surrounding muscles go into spasm, contracting to produce limb shortening.

Finally, translation occurs when the distal fragment shifts medially, laterally, anteriorly, or posteriorly in relation to the proximal fragment.

Frequently the displacement is a combination of several types of the patterns described. For example, a displaced intertrochanteric fracture of the hip due to a fall typically causes both shortening and external rotation of the limb. Often, a varus angulation is present as well.

TYPES OF FRACTURE

Many terms are used to describe the numerous fracture patterns (see Plate 7-23). Transverse, oblique, and spiral describe the pattern of fracture seen on the radiograph. A comminuted fracture has more than two fragments. A segmental fracture is a type of comminuted fracture in the shaft of a long bone in which there are three (or more) large, well-identified fragments. In an impacted fracture, two fracture fragments are telescoped on each other; usually, this pattern of injury is quite stable. Avulsion fractures frequently occur at the site of attachment of a musculotendinous unit to bone; they are caused when a sudden muscular pull tears the bony attachment loose from the rest of the bone. Compression fractures are common in the cancellous flat bones, particularly the vertebrae. The cancellous trabeculae are compressed, or impacted, together. A pathologic fracture occurs at a site in a bone that is diseased or weakened, most commonly through areas weakened by tumor or by a metabolic bone disease such as osteoporosis.

Two specific terms are used to describe fractures that are unique to children. A greenstick fracture occurs in the shaft of the bone, with the cortex fractured on the convex side of the deformity but intact on the concave side. This pattern is identical to the way a green stick reacts when bent. A torus, or buckle, fracture occurs in the metaphysis of the long bones in response to compressive loading. Most frequently seen in the distal radius, the buckle fracture usually results from a fall on the outstretched hand.