Ethics
This clinical trial was conducted in strict accordance with a predefined protocol that was approved by all researchers and the institutional review board at each respective site [see Additional file 1]. This research followed the recommendations of the Helsinki Declaration and each patient provided written, informed consent before any study-related procedures were performed. This trial was prospectively registered at ClinicalTrials.gov (NCT00692276).
Subjects
Inclusion criteria for this trial included: (a) age ≥ 45 years, (b) persistent leg, buttock, or groin pain, with or without back pain, that was relieved by lumbar flexion, (c) persistently symptomatic with unsuccessful response to at least 6 months of conservative treatment, (d) diagnosis of moderate LSS, defined as 25% to 50% reduction in central canal, lateral recess, or foraminal diameter compared to adjacent levels, and radiographic evidence of thecal sac compression and/or nerve root impingement by either osseous or non-osseous elements, and/or hypertrophic facets with canal encroachment, (e) Zurich Claudication Questionnaire Physical Function score ≥ 2.0, (f) able to sit for 50 minutes without pain and to walk ≥ 50 feet, and (g) able to provide voluntary informed consent and to comply with the study procedures. Exclusion criteria included: (a) LSS at three or more levels, (b) concomitant surgical procedure required, (c) grade II or greater spondylolisthesis, (d) unremitting back pain in any spinal position, (e) significant lumbar instability, defined as ≥ 3 mm translation or ≥ 5° angulation, (f) active systemic disease that may affect the welfare of the patient, (g) vertebral osteoporosis or history of vertebral fracture, (h) body mass index ≥ 40 kg/m2, (i) previous lumbar spine surgery, (j) pregnant or lactating female, and (k) any disease or condition that, in the investigator’s opinion, may affect subject safety or confound trial outcomes.
Pre-treatment procedures
Pre-treatment evaluations included a physical examination, medical history, and assessment for study eligibility based on the inclusion/exclusion criteria. Radiographic assessments included x-rays (standing A/P, lateral lumbar, flexion/extension lateral lumbar) and magnetic resonance imaging or computed tomography of the lumbar spine. Self-reported measures included the Zurich Claudication Questionnaire (ZCQ) [7], a 100 mm visual analogue scale for extremity and axial pain severity, and the Oswestry Disability Index (ODI) (version 2) [8].
Devices
Patients were randomized to treatment with the Superion Interspinous Spacer (VertiFlex, Inc., San Clemente, CA, USA) or a Control spacer (X-Stop Interspinous Process Decompression System; Medtronic, Inc., Sunnyvale, CA, USA). The Superion device (Figure 1A and 1B) is an investigational device that is composed of titanium 6AI-4 V ELI alloy, a material that conforms to ASTM standards for surgical implants and commonly used in a variety of orthopedic applications [9]. Five device sizes are available, ranging from 8 to 16 mm, with each size corresponding to the magnitude of desired distraction between the two spinous processes. This single-piece, self-expanding implant is delivered via minimally invasive access and deployed between the spinous processes of the involved vertebral levels. The Control spacer was approved for use in the United States by the FDA in November 2005 [10]. Procedural details have been described elsewhere [11]. Interspinous spacers were implanted at 1 (51%) or 2 (49%) levels, with a comparable distribution between groups.
Follow-up
Subjects were followed through discharge and returned for visits at 6 weeks and 3, 6, 12, 18, and 24 months. Radiographic evaluations included standing A/P, lateral lumbar, and flexion/extension lateral lumbar x-rays. Postoperative care was prescribed according to individual subject needs and typically included medications, bracing, and/or physical therapy.
Randomization and blinding
Treatment groups were randomly assigned using computer-generated codes. Site personnel accessed a web-based system to obtain treatment assignment before each subject was enrolled. Treatments were not concealed to investigators, outcome assessors, or trial participants.
Data analysis
Data were analyzed using Predictive Analytics Software (v. 18, SPSS, Inc., Chicago, IL, USA). Continuous data were reported as mean ± SD and categorical data were reported as frequencies and percentages. Longitudinal changes in clinical outcomes were assessed with two-way (time x treatment) repeated measures analysis of variance. Clinical success was defined as a ≥20 mm improvement in pain scores [12, 13] and a ≥15 percentage point improvement in ODI [12, 14]. The Kaplan-Meier method and log-rank tests were used to analyze freedom from interspinous process fracture and reoperation at the index level.