Fractures are a result of both trauma and decreased bone strength.
Trauma depends on factors related to falling and to the force of the impact. For example, bones will break more easily when subjected to torque than compression. The relative risk of a fracture is between 1.3 and 2.6 for each standard deviation of bone density below the age-matched mean. The risks vary depending on the populations studied and on the technique of measuring the bone density. The bone density results are in standardized units.