Abstract
PurposeSacropelvic fixation is frequently used in combination with thoracolumbar instrumentation for the correction of severe spinal deformities. The purpose of this study was to explore the effects of the triangular titanium implants on the iliac screw fixation. Our hypothesis was that the use of triangular titanium implants can increase the stability of the iliac screw fixation.MethodsThree T10-pelvis instrumented models were created: pedicle screws and rods in T10-S1, and bilateral iliac screws (IL); posterior fixation and bilateral iliac screws and triangular implants inserted bilaterally in a sacro-alar-iliac trajectory (IL-Tri-SAI); posterior fixation and bilateral iliac screws and two bilateral triangular titanium implants inserted in a lateral trajectory (IL-Tri-Lat). Outputs of these models, such as hardware stresses, were compared against a model with pedicle screws and rods in T10-S1 (PED).ResultsSacropelvic fixation decreased the L5-S1 motion by 75–90%. The motion of the SIJ was reduced by 55–80% after iliac fixation; the addition of triangular titanium implants further reduced it. IL, IL-Tri-SAI and IL-Tri-Lat demonstrated lower S1 pedicle stresses with respect to PED. Triangular implants had a protective effect on the iliac screw stresses.ConclusionSacropelvic fixation decreased L5-S1 range of motion suggesting increased stability of the joint. The combination of triangular titanium implants and iliac screws reduced the residual flexibility of the sacroiliac joint, and resulted in a protective effect on the S1 pedicle screws and iliac screws themselves. Clinical studies may be performed to demonstrate applicability of these FEA results to patient outcomes.
Highlights
Sacropelvic fixation is frequently used in combination with long thoracolumbar fixation for treating adult spinal deformities in order to reduce specific complications including pseudarthrosis of the L5-S1 joint, and implant failure and loosening
pedicle screws and rods in T10-S1 (PED) resulted in only a minor decrease in range of motion (ROM), whereas sacropelvic fixation induced a further decrease in the motion of the sacroiliac joint
We compared the biomechanical effect of two innovative sacropelvic fixation techniques, in which iliac screws were supplemented with triangular titanium implants, in conjunction with thoracolumbar pedicle screw fixation
Summary
Sacropelvic fixation is frequently used in combination with long thoracolumbar fixation for treating adult spinal deformities in order to reduce specific complications including pseudarthrosis of the L5-S1 joint, and implant failure and loosening. IL screw fixation, which consists of special connectors joining the distal end of the longitudinal rod to screws entering the ilium at the posterior superior iliac spine [13], represented an advancement over the Galveston technique in terms of pseudarthrosis risk (14%) [12, 14]. Another technique that was introduced more recently and was widely adopted is the fixation with S2AI screws, which was first described in 2007 by Sponseller and Kebaish and validated by biomechanical studies in human cadavers [15]. S2AI screws are inserted at the S2 level from the sacrum to the ilium, through the SIJ, and they are connected to the posterior rods without connectors [16,17,18]
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