Measuring stability of wire cerclage in femoral fractures when performing total hip replacement. In vitro study on a standardized bone model.

The stability of wire cerclage was investigated on a wooden model. Two semitubular shells made of hard oak were firmly joined together using cerclage wires of different diameters and with different techniques. A conical test piece was then implanted. The test set-up was subjected once to an axial force of 4 kN and a torque of 20 Nm using a testing machine. Implant excursion at the interface was measured. One hundred forty measurements carried out on test pieces with fissures demonstrated that cerclage wires with the largest diameter possible should be used with a double-loop technique. Wire diameters under 1.2 mm are unsuitable for cerclage of the femur because they rupture easily. The most stable cerclage is obtained with two double cerclages using 1.5-mm stainless steel wires. Although micromotion is greater than for the reference group without fissures, no cases of excursions exceeding 100 microns could be measured. In comparison with a femoral shaft that is not fractured, marked instability remains. It is recommended that a tightening tool be used to tighten the wires, as this achieves considerably more stable cerclage than that achieved with two forceps.