Biomechanical comparison of same size transfacet screws versus pedicle screws across the L5-S1 native disc

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Objective: There is resurgence in facet screw use; however, there is a paucity of data comparing the stability of transfacet pedicle screws (TFPS) to standard pedicle screw-rod constructs at L5-S1. The authors aim to compare the stabilizing potential of TFPS compared to pedicle screws of the same length and diameter at L5-S1 with an intact native disc. Methods: Flexibility of human cadaveric lumbar spine segments was biomechanically tested in vitro to provide a comparison of two types of posterior stabilization across L5-S1. Fourteen cadaveric spine specimens (T12-S1) were tested in intact condition, then after, surgical procedures performed at L5-S1 using 5.0 × 40 mm transfacet pedicle screws (Group #1) and same sized pedicle screw-rod construct (Group #2). Specimens were studied using standard non-destructive pure moment flexibility tests. Results: Transfacet pedicle screws (TFPS) allowed less motion in all loading modes than bilateral pedicle screw-rod (BPSR) construct, with a significantly smaller range of motion allowed during extension and axial rotation (p < 0.05). Transfacet pedicle screws allow less lateral bending than BPSR compared to the intact specimen, although the magnitude of the difference was less than during flexion or extension. Conclusion: Bilateral transfacet screws provided better immediate postoperative stability in vitro intact posterior element facets without osteophytes than equivalent-sized unilateral or a bilateral standard pedicle screw at L5-S1. These are limited to a biomechanical application as larger sized pedicle screws are used in the clinical setting. Further biomechanical and clinically relevant studies are warranted to verify these points.

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West Indian Medical Journal







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