Fractures Caused by Indirect Application of Force

Indirect fractures are produced by a force acting at a distance from the fracture site. In this regard, it should be noted that bone is weaker to tension (stretching) than compression. Indirect fractures can be classified into six types (Figure 4.15):

1. Traction

2. Angulation

3. Rotational

4. Vertical compression

5. Angulation and compression

6. Angulation, rotation, and compression fractures

In traction fractures, the bone is pulled apart by traction. An example would be violent contraction of the quadriceps muscle with resultant transverse fracture of the patella. In angulation fractures, the bone is bent until it snaps. The concave surface is compressed and the convex surface is put under traction. This usually results in a transverse fracture.

In rotational fractures, the bone is twisted and a spiral fracture is produced. Spiral fractures occur only when the bone is subjected to torsional force. In the femur, most spiral fractures occur in the proximal third. The proximal and distant ends of a spiral fracture are connected by what Porta et al. call a "hinge."8 The hinge distinguishes it from an oblique fracture. To determine in which direction a bone was twisted, ascertain the direction the spiral runs from the end twisted. This indicates the direction of torque.

Vertical compression fractures produce an oblique fracture of the body of long bones, with the hard shaft of the long bone driven into the cancellous end. In femurs, a T- or Y-shaped fracture is typically seen at the distal end of the femur. Such fractures may occur following impaction of the end of the femur into the instrument panel in motor vehicle crashes.

Figure 4.15 Indirect fractures. (A) Traction. (B) Angulation. (C) Rotational. (D) Vertical compression. (E) Angulation and compression. (F) Angulation, rotation, and compression.

In angulation and compression fractures, the fracture line is curved, with an oblique component due to compression, and a transverse component due to angulation. The last category is angulation, rotation, and compression fractures. The angulation plus rotation produces an oblique fracture, with the compression increasing the tendency toward fracture.

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