Two-year clinical outcomes of a multicenter randomized controlled trial comparing two interspinous spacers for treatment of moderate lumbar spinal stenosis

Background: Interspinous spacers are a minimally invasive surgical alternative for patients with lumbar spinal stenosis (LSS) unresponsive to conservative care. The purpose of this prospective, multicenter, randomized, controlled trial was to compare 2-year clinical outcomes in patients with moderate LSS treated with the Superion (R) (Experimental) or the X-Stop (R), a FDA-approved interspinous spacer (Control). Methods: A total of 250 patients with moderate LSS unresponsive to conservative care were randomly allocated to treatment with the Experimental (n = 123) or Control (n = 127) interspinous spacer and followed through 2 years post-treatment. Complication data were available for all patients and patient-reported outcomes were available for 192 patients (101 Experimental, 91 Control) at 2 years. Results: Zurich Claudication Questionnaire (ZCQ) Symptom Severity and Physical Function scores improved 34% to 36% in both groups through 2 years (all p < 0.001). Patient Satisfaction scores at 2 years were 1.8 +/- 0.9 with Experimental and 1.6 +/- 0.8 with Control. Axial pain decreased from 59 +/- 26 mm at baseline to 21 +/- 26 mm at 2 years with Experimental and from 55 +/- 26 mm to 21 +/- 25 mm with Control (both p < 0.001). Extremity pain decreased from 67 +/- 24 mm to 14 +/- 22 mm at 2 years with Experimental and from 63 +/- 24 mm to 18 +/- 23 mm with Control (both p < 0.001). Back function assessed with the Oswestry Disability Index similarly improved with Experimental (37 +/- 12% to 18 +/- 16%) and Control (39 +/- 12% to 20 +/- 16%) (both p < 0.001). Freedom from reoperation at the index level was 84% for Experimental and 83% for Control (log-rank: p = 0.38) at 2 years. Conclusions: Both interspinous spacers effectively alleviated pain and improved back function to a similar degree through 2 years in patients with moderate LSS who were unresponsive to conservative care.