[Comparative biomechanical studies of internal stabilization of trans-foraminal sacrum fractures]

A new method of internal stabilization of transforaminal sacrum fractures in unstable pelvic ring fractures was developed by modification of standard AO small-fragment implants. The rationale of this type of stabilization is the use of an unilateral dorsal approach and avoidance of transfixation of the uninvolved SI joints. In a comparative biomechanical study on 8 human cadaver pelvises two types of the new type of stabilization were compared to stabilization with Harrington sacral bars and transiliosacral screw fixation. The fracture model represented a Tile C1 type injury (symphysis disruption and transforaminal sacral osteotomy) on a complete pelvic ring. The anterior stabilization was performed with a 4-hole AO 4.5 mm DC plate in all cases. The load simulation used a one-leg standing model in an upright position with abductor muscle simulation. The pelvises were loaded in 4 load stages of 50%, 80%, 100% and 130% body weight. In each load stage 4 load-unload cycles were completed. With a three-dimensional measurement system (Polhemus 3 Space Motion Tracker) translations an rotations in the fracture plane could be analyzed. Typical behavior in the load-displacement curve was seen in all implants, with settling during the first cycles and permanent displacement after exceeding a specific failure load. The failure load showed no significant differences between implants (99.6-113.6% body weight). The analyses of the persistent displacement, the elasticity and the direction of displacement and rotation showed a typical behavior in the implants, but no differences, which can be interpreted as a significant difference in the stability of the fixation methods. In an additional test the new fixation method showed no loosening in 10,000 cycle loading with 60% body weight. The new stabilization method showed biomechanical results comparable to clinically successful methods of stabilization in the chosen fracture model. Thus, clinical applications of this type of stabilization may be successful.