Introduction: This in‐vitro biomechanical study served to investigate the multidirectional flexibility and load to failure properties of a new S2‐Alar‐lliac fixation technique versus conventional methods of lumbosacral fixation.
Methods: A total of twenty‐one human lumbopelvic spines were equally randomized into three groups based on reconstruction condition: 1) S1+S2 screws (S12); 2) S1+lliac screws (S11), and 3) S1+S2 alar‐iliac screws (S2AI). Non‐destructive multi‐directional flexibility was performed and utilized moments of ±12Nm for axial rotation, flexion‐extension and lateral bending. Fatigue loading was performed for 10,000 cycles and static analysis repeated. Final destructive testing included anterior flexural load to failure. Quantification of lumbosacral and sacroiliac range of motion (ROM) were normalized to intact spine (100%) and failure loads reported in Nm.
Results: Iliac fixation significantly reduced ROM in axial rotation at L4‐L5 and L5‐S1 compared to S12 screws (29% vs. 59% vs. 36%) and at L5‐S1 (28% vs. 37% vs. 41%) (p<0.05). S2AI significantly lowered flexion‐extension ROM at L5‐S1 (42%) vs. S12 (18%) and S11 (10%) (p<0.05). The S1+S2 reconstruction produced significantly higher SI joint flexion and lateral bending ROM compared to intact(p<0.05), while S2AI and S1I demonstrated minor decreases in sacroiliac motion. The S12 group failed under destructive testing at 105±24Nm while S2AI and S1I failed at 119 and 120 Nm (p>0.05). S12 failed by fracture through the SI joint or screw pullout; S2AI by iliac wing fracture away from screw, and S1I by delamination of the ilium or lumbar screw pullout.
Conclusion: Based on the current results, conventional S12 fixation increases sacroiliac motion, while S2AI and S1I significantly reduce flexibility at L4‐L5‐S1 (p<0.05). The latter two methods have similar biomechanical features while S2AI reduces flexion‐extension motion at L4‐L5‐S1 compared to all other treatments (p<0.05). From a biomechanical standpoint, the use of the S2‐Alar‐lliac fixation technique is biomechanically equivalent to S1‐iliac screws and offers lower prominence and ease of assembly compared to conventional sacroiliac stabilization.