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  • Biomechanical Assessment of Gradual Stabilization Using Semi-Rigid Fixation in the Thoracolumbar Spine

    Final Number:

    Ivan Cheng; Frank LaMarca MD; Joseph Pirolo MD; Chad W. Farley MD; Soumya Yandamuri MS; Erika Matheis MS; Brandon Bucklen PhD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2015 Annual Meeting

    Introduction: Long pedicle screw constructs have been associated with a high incidence of proximal junctional kyphosis (PJK) in both adults and adolescents, where there is an abrupt change from rigidity to complete motion in unfused spinal segments. Semi-rigid constructs have been used to bridge the gap between free motion and complete rigidity as a potential solution for gradual motion restoration.

    Methods: Eleven T8-L2 human specimens were tested on a six-degree-of-freedom machine with a motion capture system which monitored the most proximal fixed segments motion in flexion-extension (FE), lateral bending (LB) and axial rotation (AR). Specimens were instrumented from T10-L2 with pedicle screws at T12-L2 and tested in two groups, varying instrumentation at proximal levels (T10-T11). Group 1: 1) Intact; 2) Bilateral pedicle screws (PS); 3) One-level sublaminar 6mm polyethylene terephthalate (PET) band (SILC™, Globus Medical, Audubon, PA) (SL-1); 4) Two-level sublaminar 6mm PET band (SL-2); Group 2: 1) Intact; 2)Bilateral pedicle screws (PS); 3) One-level bilateral dynamic stabilization (Figure 1) (TRANSITION®, Globus Medical, Audubon, PA) (T1); 4) Two-level bilateral dynamic stabilization (T2).

    Results: The general trend in ROM was PS<1-level semi-rigid constructs <2-level semi-rigid constructs, across all loading modes with very few exceptions (Figure 2). At T11-T12, the increase in ROM from the PS construct with SL-1/SL-2 and T1/ T2 constructs showed analogous trends across all bending modes, with two-level treatment (SL-2, T2) having the most increase. However, at T10-T11, subtle differences were seen across both the groups, in FE and LB.

    Conclusions: Both sublaminar PET bands and dynamic stabilization constructs show similar flexibility providing a less rigid option than pedicle screws for gradual stabilization of the thoracolumbar spine. Two-level semi-rigid constructs provide similar increase in ROM with either PET bands or dynamic stabilization across all loading modes. Gradual stabilization may be clinically relevant as a potential prophylactic treatment of proximal junctional kyphosis.

    Patient Care: Biomechanical understanding of different implant choices may lead to better clinical decisions regarding long fusion.

    Learning Objectives: By the conclusion of this session participants should be able to distinguish motion differences between pedicle screws, PET bands, and dynamic stabilization by: 1) Describing the importance of instrumentation choice for long fusion, 2) Discussing in small groups the choice of semi-rigid fixation versus rigid fixation, 3) Identify an effective treatment for long fusion with the possible reduction in PJK through gradual motion stabilization.


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