Effect of a cerclage or a crosslink on internal fixator mechanical stability

This study was performed to evaluate the effect of a cerclage or a crosslink on internal fixator mechanical stability in an unstable spine injury model. Nine human thoracolumbar spine specimens were instrumented either with an internal fixator alone (T12-L2) or together with a cerclage or a crosslink. Four modes of loading were used: flexion, extension, lateral bending, and axial rotation. Moments itself were generated using a specially designed loading jig and loading system. The maximum moment applied was 10 Nm, three load-unload cycles were performed. The flexibility was measured by a motion tracker and range of motion (ROM), elastic zone (EZ) and neutral zone (NZ) were calculated. Statistical analysis was performed using the paired t-test (p < 0,05). For flexion, extension and lateral bending all devices were significantly more stable (p < 0,01), for axial rotation all devices were significantly less stable compared to the intact specimen (p < 0,01). But the crosslink provided significantly more stability compared to the internal fixator alone (p < 0,001). The complete device, i. e. internal fixator + crosslink, was significantly more stable compared to internal fixator + cerclage (p < 0,05). In this study the use of a cerclage had no additional effect in stabilizing the internal fixator. The operative and financial expenditure using a crosslink seems to be justified in fractures with a high rotationally instability, i. e. in type A-3-, B-, and C-injuries according to Magerl et al. [18].