Rapid pre-tension loss in the Ilizarov external fixator: an in vitro study.

Background and purpose Wire pre-tension in the Ilizarov frame is considered to be important in order to reduce movements that can impair fracture healing. Wires will eventually lose part of their pre-tension, however. In order to gain more insight into the need for wire pre-tension, we investigated: (1) the amount of pre-ten-sion loss, (2) the relationship between pre-tension loss and bolt-tightening torque, (3) the cause of a possible loss of pre-tension, and (4) the effect of pre-tension on cyclic micromotions and total displacement of the bone segments.Methods 3 Ilizarov configurations, with various wire pre-tensions and bolt-tightening torques, were tested 3 times with an MTS machine. For each wire, slippage and tensions were measured for the duration of the whole experiment.Results A loss of wire pre-tension (up to 75%) due to slippage was found. Higher bolt-tightening torques significantly reduced the amount of pre-tension loss. Furthermore, a higher wire pre-tension reduced the maximal axial displa...