The Effects of Cerclage Wiring on the Immature Canine Diaphysis A Biomechanical Analysis

When cerclage wiring is used in skeletally immature dogs, the wires become imbedded in the cortical bone due to radial appositional bone growth.
Six groups of five dogs each received one or two extraperiosteal cerclage wires at the mid-diaphysis of the left femur at the age of five months. Ten dogs were killed immediately, ten dogs were killed at eight weeks postoperatively, and ten at twelve weeks. Both femora from each animal were collected and subjected to torsional loading to failure within.5 seconds. The maximum torque, shear stress, energy absorption, angular deformation, and torsional stiffness were determined and subjected to í test analysis.
Application of the wires predictably caused an increase in weight and cortical bone thickening at the implant site, which was primarily due to endosteal bone deposition in the 8-and 12-week groups. The 8-and 12-week wired bones were stiffer and failed at a lower angular deformation than did their corresponding control femurs, but the zero-time bones did not show this tendency. Significantly less shear stress accumulation and energy absorption at failure were present In the 8-and 12-week implants, but no difference was seen in the zero-time femora. The 8-week groups showed a greater difference between the wired and control femurs than did the 12-week groups. No significant difference was found between one-and two-wire implants in the study.
The results indicate that confinement of dogs with clinically wired fractures of immature canine femurs should extend past eight weeks.