A comparative biomechanical evaluation of various instrumentation techniques at lumbopelvic junction

Abstract

Objective: A well-supported fixation is generally imperative to stabilize spinopelvic junction in case of sacrectomy or neurologic diseases that deteriorate the spinopelvic balance. A comparative biomechanical study was designed to evaluate various fixation techniques for long spinopelvic stabilization. Material and Methods: A total of 40 in vitro calf spine models were used. Five groups (one control and 4 study groups), each having 8 samples, were created. In the study groups, lumbosacral junctions were stabilized either with L3-S1 bilateral pedicle screws connected to rods (group 1), with L3-S1-iliac screws (group 2), with L3-S1-dual iliac screws (group 3) or with a combination of rods in which the initial L3-S1 fixation was connected to the transiliac bar system with oblique connectors (group 4). The compression behavior of each model and control group were tested under axial loading by using a universal testing system. Statistical analysis was done to compare yield load, displacement at yield and stiffness within groups and to compare study groups with the control group. Results: All groups were significantly stiffer than the control group. Group 4 exhibited the highest (median: 11253 N) yield load (min:11247-max:11259) among the groups. The highest load displacement at yield point (median: 11.4 mm) (11.2-11.6 mm) amongst all tested systems was reached at group 2 (p<0.001). The statistical analysis, however, showed a significant difference between groups 4, 2 and 3 in terms of yield load, displacement at yield and stiffness (p<0.001). Although group 4 had the highest yield load, the stiffness of group 3 was slightly higher than group 4 (p<0.001). However, there was no statistically significant difference between group 2 and the control group in terms of stiffness (p=0.083). Conclusion: The four-rod fixation technique with obtaining additional stability from ilium provides a better yield strength when compared to other techniques. This system not only ensures a more stable construct, but also can lower the need for an anterior support. © 2013 by Türkiye Klinikleri.