Resistance to Subsidence of an Uncemented Femoral Stem After Cerclage Wiring of a Fissure

Objective: To compare: (1) the force required to initiate subsidence, and (2) the relative subsidence, of femoral stems implanted into intact femora, and then into the same femora in which an induced fissure had been stabilized by cerclage. Study Design: In vitro, mechanical study. Sample Population: Femora (n=9) from 9 dogs. Methods: Femora were prepared for implantation of an uncemented stem. Stems were implanted with continuous and impact loading. After axial loading until a fissure occurred, the stems were extracted, and the fissure stabilized with double-loop cerclage. Stems were reimplanted, and reloaded to failure. Results: Mean±SD load to initiate subsidence in intact femora was 1706±584N compared with 2379±657N for cerclaged bones (P=002). Mean relative subsidence of intact femora was 3.99±2.09mm compared with 1.79±2.99mm for cerclaged bones (P=091). Conclusions: The load to initiate subsidence is increased in femora that have fissured, then have been stabilized with double-loop cerclage, when compared with intact femora. The relative subsidence is not different between intact and stabilized specimens.