Background: Supplementary iliac screws have the highest potential to protect S1-pedicle-screws from loosening in long fusion constructs. However, this technique bridges the iliosacral joint with potential disadvantages for the patient. This study aimed to evaluate if two different established fixation techniques can be used in addition to pedicle screws as alternative to iliac screws, and if these two techniques can provide similar stability when S1-pedicle-screws are loosened.
Methods: Flexibility testing with pure moments of 7.5Nm was performed with six human osteopenic/osteoporotic L4-pelvis specimens. The following conditions were investigated: 1. Intact; 2. Destabilization L5/S1; 3. Fixation with rigid L4-S1 pedicle-screw-system; 4. Condition 3- loosening of S1-screws; 5. Condition 4- L5-S2-lamina-hooks; 6. Condition 4- L5/S1-translaminar-screws; 7. Condition 4- S2-ala-ilium screws.
Findings: Application of compressive L5-S2-lamina-hooks or L5/S1-translaminar-screws next to pedicle screws in L5 and S1 was feasible in all specimens. L4-S1-pedicle-screw-instrumentation reduced the Range of Motion significantly compared to the destabilized condition. After simulation of S1 screw loosening, lamina hooks only reduced the Range of Motion in flexion/extension significantly. L5/S1-translaminar-screws had a higher stabilizing effect in lateral bending and axial rotation, but the effect of both systems was smaller than with an instrumentation extension to the os ilium.
Interpretation: In long lumbar pedicle screw instrumentations including L5/S1, additional ilium screws have the highest potential to protect the S1-anchorage. Additional L5/S1-translaminar-screws can increase stability of the lumbosacral junction without bridging the iliosacral joint, whereas lamina hooks showed no significant biomechanical benefit.
Keywords: Biomechanics; Fixation techniques; In vitro; Lumbar fusion; Lumbosacral instrumentation.
Copyright © 2017 Elsevier Ltd. All rights reserved.