1601. Increased axial facet angle correlates with poor percutaneous pedicle screw placement

Authors: Sheeraz Qureshi; Guang-ting Cong, MD; James Dowdell, III, MD; Avani Vaishnav, MBBS; Steven McAnany, MD; Todd Albert, MD; Sravisht Iyer, MD; Catherine Himo Gang (New York, NY)

Introduction:

To test the hypothesis that axial facet angle correlates with poor pedicle screw placement (and especially facet violation) in percutaneous fluoroscopy-guided pedicle screw placement.

Methods:

95 consecutive patients who underwent minimally-invasive instrumented fusion of the lumbar or lumbosacral spine with percutaneous fluoroscopy-guided pedicle screw placement between L4 and S1 were included. Axial facet angles associated with poorly placed screw were calculated and compared to the global mean axial facet angles at L4 and L5 using the two-tailed t-test. Sub-group analysis was finally performed for facet violation alone as cause for poor pedicle screw placement.

Results:

 A total of 349 pedicle screws were analyzed. Of the total, 38 (10.7%) were categorized as poor placement, and of these 31 (82%) were due to topmost unfused facet level violation. Global axial facet angle means were 36.8 degrees for L4 (σ = 11.3, n = 115), 45.8 for L5 (σ = 11.4, n = 161), and 50.5 for S1 (σ = 11.4, n = 73). Mean axial facet angles associated with poorly placed screws were 42.7 degrees for L4 (σ = 11.6, n = 15) and 51.4 degrees for L5 (σ = 10.2, n = 23). These means were higher than the global means (Figure 2) at L4 (p = 0.063) and L5 (p = 0.028). Sub-group analysis demonstrated that the mean axial facet angles associated with topmost unfused facet level violation was 44.0 degrees for L4 (σ = 10.9, n = 14) and 53.2 degrees for L5 (σ = 9.61, n = 17). These means were significantly higher than the global means (Figure 2) at L4 (p = 0.027) and L5 (p = 0.009).

Conclusion:

Increased axial facet angle significantly correlates with poor screw placement and especially with facet violation in percutaneous fluoroscopy-guided pedicle screw placement.