Avulsion of skin from the hand or fingers is an injury that has a dramatic presentation. The entire musculo-skeletal unit of the finger is intact, and the patient can often move the parts of his naked hand quite normally. The avulsion of skin from the underlying structures is usually a result of trauma. These injuries occur when the hand is caught by a force and pulled at a low velocity. The force that holds the skin usually has some amount of irregular surface, that holds on to the skin and does not slip. When this then pulls in an outward direction — it may be the force moving outward, like the tyre of a vehicle that has run over the hand or it may be the counter force — the patient pulling his hand outward — for example, from a machine in which his hand has been caught. The most common causes are road traffic accidents, conveyor belt injuries and ring avulsion injuries.
Info can be found here