http://orthoinfo.aaos.org/fact/thr_report.cfm?Thread_ID=150&topcategory=Arm
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American Academy of Orthopaedic Surgeons
When a person falls on a outstretched hand, the sudden impact of their body weight on the hand may cause the end of the lower arm bone (radius) to fracture just above the wrist. This is known as a Colles fracture.