[Biomechanics of intramedullary nailing and its interlocking]

Mechanically an intramedullary nail cannot be conceived of as a nail but rather as a bendable feather subject to longitudinal tension and, to a lesser degree, to transverse pressure. Reaming the medullary canal is necessary for centralizing of the nail as well as for increasing the area of contact with the bone. However, this procedure is detrimental to the bone metabolism, thus reducing its elasticity against torsional forces. The dynamic locking nail-system is more biologic than conventional nailing, with rotatory instability being reduced by additional components, such as transverse screws. By applying static locking only true static weight bearing with crutches, will be ensured but no dynamic mobilisation. Nails with conventional strength and in trefoil leaf formation are superior to other designs. However, an improved angle in the proximal locking is suggested, as this will allow the weight bearing to be increased three to four times.