Summary It is of practical value to understand the mechanism of injury because each mechanism produces injuries with well defined characteristics, and reporting an injury by mechanism is descriptive. Reduction is usually accomplished by reversing the direction of the forces causing the injury. Thus it is important to recognize the characteristics of the fractures caused by each mechanism. The nature of the injury is determined by the mechanism and in turn determines the method and period of immobilization as well as the prognosis. Each mechanism causes characteristic ligament injury and awareness of the mechanism makes it easier to find the ligament damage and to treat it.