Mechanisms of injury

Fractures of the pelvis are the result of three different mechanisms of injury;

• Anteroposterior compression - as may occur when a pedestrian is hit front on by a car. The pubic rami are fractured and the pelvis sprung open with destruction of the symphysis. As the pelvis springs open there is partial tearing of the sacroiliac ligaments and there may be a fracture of the posterior part of the ilium. These injuries are usually stable ones.
  
  
• Lateral compression - as may occur when a pedestrian is hit side on by a car. Anteriorly the pubic rami are fractured. Posteriorly there is severe strain to the sacroiliac ligaments or fracture of the ilium. The stability of these injuries is dependent upon the degree of posterior injury/displacement.
  
  
• Vertical shear - as may occur when falling from a height onto one leg. One of the innominate bones is sheared vertically and displaced. The pubic rami are fractured and there is severe damage to the sacroiliac region on the same side. These injuries are unstable and soft tissue damage and haemorrhage severe.