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Biomechanical Comparison of Same Size Transfacet Screws Versus Pedicle Screws Across the L5-S1 Native Disc



Objective: There is a 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 x 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 screws 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. 

12 May, 2017
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e-Published: 24 May, 2017
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