Lonne 2015.

Methods	Multi‐centre RCT Setting: 6 different Norwegian hospitals Country: Norway Period: June 2007 to September 2011
Participants	Number: 96 patients (49/47) Diagnosis: symptoms of neurogenic intermittent claudication and magnetic resonance images and radiographs Included: patients with 1 or 2 stenotic levels (from L2 to L5) and with minor spondylolisthesis (Meyerding, grade 1) Excluded: spinal stenosis at more than 2 levels; previous low back surgery; unilateral radiculopathy; severe paresis; cauda equina syndrome; degenerative spondylolisthesis > grade 1; isthmic spondylolisthesis; severe scoliosis, idiopathic or degenerative (Cobb angle > 10° or sagittally imbalanced); osteoporosis or suspected osteoporotic fractures in lumbar spine; symptomatic coxarthrosis; vascular intermittent claudication; polyneuropathy; malignant disease Age (years): mean (SD) 67 (8.7)/67 (8.8) BMI (kg/m²): mean (SD) 28 (3.8)/28 (4.7) Lumbar stenosis duration (years): more than 2 years for the majority of patients in both groups
Interventions	Group 1: minimally invasive decompression (bilateral laminotomy). Decompression was performed by a partial excision of the lower part of the lamina and the medial aspects of the facet joint. Group 2: interspinous process spacer device (X‐Stop). The X‐Stop was inserted between the spinous processes through the interspinous ligament and was secured by the supraspinous ligament posteriorly and by the lamina anteriorly Follow‐up: 24 months
Outcomes	Pain: 11‐point numerical rating scale leg pain Disability: ODI Quality of life: EQ‐5D Costs Operation time Perioperative blood loss Complications Reoperations Length of hospital stay
Notes	Surgeon's experience: not reported Funding: "the study was supported by non‐commercial organisations (South‐East Regional Health Authority, Norway and the National Advisory Unit on Spinal Surgery, St. Olavs Hospital, Norway)"
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "patients were randomized with randomly selected block sizes by a computer‐based web solution."
Allocation concealment (selection bias)	Unclear risk	Not mentioned.
Blinding of participants (performance bias) All outcomes	Unclear risk	No mention of any attempts to blind the participants.
Bliding of personnel/ care providers (performance bias)	High risk	The surgeon could not have been blinded to the intervention.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No mention of any attempts to blind the assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	81/96 = 84% of the patients completed the follow‐up. The number of drop‐outs was similar in each group and the reasons for drop‐out are also reported and are unlikely to affect the results.
Intention‐to‐treat analysis (attrition bias)	Low risk	Quote: "in the main evaluation, not only was an intention‐to‐treat analysis performed..."
Selective reporting (reporting bias)	Low risk	All expected outcomes were reported.
Group similarity at baseline (selection bias)	Low risk	Patients did not differ in their baseline characteristics, based on Tables 2 and 4.
Co‐interventions (performance bias)	Low risk	Only the surgical technique differed between treatment groups.
Compliance (performance bias)	Low risk	Compliance in both treatment groups: 100% (surgery).
Timing of outcome assessment (detection bias)	Low risk	All important outcome assessments for both groups were measured at the same time.
Other bias	Low risk	Quote: "the study was supported by non‐commercial organisations (South‐East Regional Health Authority, Norway and the National Advisory Unit on Spinal Surgery, St. Olavs Hospital, Norway)."