Biomechanical Evaluation of Lag Screw versus Cerclage Cable for Treatment of Diaphyseal Femur Fractures

Background Diaphyseal femur fractures are commonly treated with intramedullary nailing; however, plate fixation is required when deformity, existing implants, or limited bone stock preclude nail use. Long lateral locking plates often require adjunct fixation to achieve anatomic reduction. Lag screws provide compression but may be unreliable in osteoporotic bone, whereas cerclage cables offer circumferential fixation independent of bone density. This study compared the biomechanical performance of anatomic fixation of a long spiral oblique femur fracture using either a single lag screw or a single cerclage cable augmented by a lateral plate. Methods Ten synthetic femora were osteotomized at the mid-diaphysis. Five specimens were reduced and fixed with a bicortical lag screw and five with a cerclage cable. All specimens received a lateral 4.5-mm LC-DC neutralization plate with a standardized screw configuration. Constructs underwent cyclic axial loading, and fracture-site micromotion was recorded using optical motion capture. Stiffness was calculated from the linear portion of the load–displacement curve. Mean and maximal interfragmentary displacement were recorded. Statistical analysis included independent-samples t-tests and one-way ANOVA. Results Mean stiffness was similar between lag screw (996.6 ± 138.8 N/mm) and cerclage constructs (988.9 ± 156.8 N/mm; p = 0.12). Mean displacement did not differ between groups (lag screw: 0.56 ± 0.36 mm; cerclage: 0.49 ± 0.66 mm; p = 0.84). Maximal displacement ranged from 0.7 to 1.8 mm with no group difference (p = 0.87). Significant stiffness differences were observed among constructs of the same type (p < 0.0001). Conclusions Both lag screw and cerclage cable fixation provided comparable axial stability and resistance to micromotion in a laterally plated synthetic femur model. Cerclage cables may be a viable alternative when lag screw use is limited. Construct variability highlights the importance of surgical technique.