Bone is composed of minerals, which provide rigidity, and collagen, which provides tensile strength. When bone is subjected to an excessive stress, it will fail. There are many extrinsic factors that are important in causing the injury. These are the magnitude, duration, and direction of the force acting on the bone and the rate at which this force is applied.
A force may have a direct impact on the bone or may produce a fracture indirectly. We discuss these one by one.
Directly Applied Forces
- Tapping Fracture: It is an application of a small force to a localized area of bone. it generally produces a transverse fracture. In such cases most of the energy is absorbed by the bone and damage to soft tissue damage is minimal.
- Crush Injury: When a large force is applied to a larger area of bone, it will cause comminution or a transverse fracture, with extensive soft tissue damage.
- Penetrating Injury: A large force- as via a gunshot wound- will cause extensive comminution and soft tissue damage in high-velocity impacts and moderate damage in low-velocity impacts.
Indirectly Applied Forces
Indirect force is one which is away from the fracture site. This kind of force produces fracture by indirect mechanism.
- Traction or tension fracture: A muscle that forcibly contracts and pulls away a piece of bone attached to its musculotendinous unit (i.e., avulsion fracture) will produce a transverse fracture.
- Angulation Fracture: A force causing bending of the bone such that one side is under compression and the other under tension will cause a transverse fracture. The side under tension fractures first.
- Rotational Fracture: A combination of horizontal and vertical stresses will cause fracture lines at 45 degrees to the long axis of the bone.
- Compression Fracture: Excessive axial loads will cause either impaction fractures of cancellous bone or longitudinal fracture of cortical bone.
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