Davis 2013.

Methods	Multi‐centre RCT Setting: 21 sites in the United States Country: USA Period: 2006 to 2010
Participants	Number: 322 patients (215/107) Diagnosis: central, foraminal or lateral stenosis; more than 25% reduction of the anteroposterior dimension compared with the next adjacent normal level, with nerve root crowding compared with the normal level, as determined by the investigator on CT or MRI Included: patients with moderate radiographical diagnosis of spinal stenosis with low back pain; spondylolisthesis up to Meyerding grade I; minimum ODI of 20 (0‐50), and VAS back pain score of 50 or more (0‐100); minimum 6 months of conservative care Excluded: prior lumbar surgery; trauma or tumour; isthmic spondylolisthesis; spondylolysis; scoliosis > 25 degrees; disc herniation; serious disease Age (years): mean (SD) 64.1 (9.0)/62.1 (9.2)
Interventions	Group 1: decompression plus transpedicular screw fixation Group 2: Coflex interspinous process spacer device (Paradigm spine, LLC, New York, NY) Follow‐up: 24 months
Outcomes	Pain: 100 mm VAS leg pain Disability: ODI Operation time Perioperative blood loss Complications Reoperations Length of hospital stay
Notes	Surgeon's experience: not reported Funding: "Paradigm Spine, LLC (New York, NY) funds were received in support of this work. Relevant financial activities outside the submitted work: consultancy, royalties, payment for lecture, payment for manuscript preparation, patents, payment for development of educational presentations"
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "computer generated randomization codes"
Allocation concealment (selection bias)	Low risk	Quote: "centralized by the study sponsor"
Blinding of participants (performance bias) All outcomes	Low risk	Quote: "study subjects were blinded until after surgery"
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	Low risk	Quote: "site study personnel were blinded to the treatment assignment up until 5 days prior to surgery"
Incomplete outcome data (attrition bias) All outcomes	Low risk	89% of the patients completed the follow‐up. The number of drop‐outs is unlikely to affect the results.
Intention‐to‐treat analysis (attrition bias)	Unclear risk	No information about intention‐to‐treat analysis.
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 4 to 9.
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	Unclear risk	Quote: "Paradigm Spine, LLC (New York, NY) funds were received in support of this work. Relevant financial activities outside the submitted work: consultancy, royalties, payment for lecture, payment for manuscript preparation, patents, payment for development of educational presentations."