A biomechanical study of three wiring techniques for cerclage-plating.

Transverse fractures at the distal tip of a well-fixed femoral prosthesis are difficult to stabilize using plates and screws due to the presence of the underlying intramedullary stem. The attachment of plates using cerclage wires obviates the need for screws, but the stability provided by cerclage plating is a clinical concern. In this study we compared the mechanical performance of three wire-cerclage plating techniques: (a) simple cerclage (each wire wrapped around the bone and plate once); (b) double cerclage (each wire wrapped around the bone and plate twice); and (c) a new method that used small stainless steel inserts that fit into the plate holes and permit the direct coupling of the cerclage wires to the plate. To compare the performance of the three fixation constructs, synthetic femora were osteotomized, stabilized with a wire cerclage plating technique, and subjected to monotonic and cyclic loading using a Materials Testing System (Minneapolis, MN) servo-hydraulic testing system. The performance of each construct was evaluated using seven different mechanical parameters (four monotonic, three cyclic). Double cerclage performed significantly better than did simple cerclage for three of the seven mechanical parameters. The insert technique performed significantly better than did the simple and double cerclage techniques for all seven of the measured mechanical parameters. For both monotonic and cyclic loading, the use of inserts resulted in an improvement in fixation strength and stability in comparison with conventional simple and double cerclage plating techniques. The insert technique shows promise in the treatment of this difficult type of fracture at the distal tip of a well-fixed femoral prosthesis.