[Biomechanical analysis of the medullary bone nail and its locking]

By mechanical definition an intramedullary nail is not a nail but rather a bendable feather, subject to longitudinal tension and to a lesser degree to transverse pressure. Reaming the medullary canal is necessary for centralization of the nail as well as to increase the area of contact with the bone. However, this procedure is detrimental to the bone metabolism and reduces its elasticity against torsional forces. The dynamic locking nail-system is more biologic than conventional nailing and it reduces rotatory instability with the help of additional components, such as transverse screws. Only static locking allows true static weight bearing with crutches, but not dynamic mobilisation. Nails with conventional strength and in leaf of trefoil formation are superior to other designs. However, an improved angle in the proximal locking is suggested, as this would allow for a three to four times greater weight bearing.