Ashley Davidoff Copyright 2011
Blunt Trauma
Penetrating Trauma
Bending Forces
Bending fractures occur after a force applied to a specific focal region overcomes the elastic limit of the bone, resulting in a cortical break on the opposite side of the force due to tensile forces on the tissues. The periosteum on the side of the compressive force usually remains intact. The resulting fracture is usually transverse or oblique, but may have a butterfly fragment.
Torsional Forces
Torsional forces occur when there is a twisting force applied to the long axis of the bone, such that one end of the bone is fixed, while the force causes the other end to rotate. An example may be a person running in a field and steps into a holeand then falls forward and to one side. The distal tibia and fibula are fixed and the falling to the front and side result in a rotational force that will cause a spiral fracture.
Compression Forces
Compressive forces are often gravity induced forces such as when a person falls from a height and the impact is transferred to the femur or spine. In the case of a long bone the diaphyses or metaphyses projects or impacts into the broader epiphyses and an impaction fracture occurs in the region. Similarly the classical boxer’s fracture where a punch against a wall results in a comprtessive force against the 5th metacarpal and the shaft impoact on the broder distal epiphyses.
Shearing Forces
A shearing force is also a force that occurs along the long axis of a long bone by compressive mechanisms, but the force is then transmitted across a joint to other bones not protected by the longitudinal axis of the bone.
Avulsion Force
An avulsion force is most commonly caused by strong musculat action resulting in avaulsion of a bony protuberance which is a site for attachment of the bone.
Pathological Fracture
A pathologic fracture is a fracture that occurs through weakened bone. Causes include benign conditions such as osteoporosis, focal osteomyelitis, or bone cysts. metatstatic sidease or primary malignant disease can also cause weakening of the bone and predispose the bone to fracture.