Grob 1995.

Methods	Single‐centre RCT Setting: Schutthess Hospital, Zurich Country: Switzerland Period: November 1989 to November 1990
Participants	Number: 45 patients (15/15/15) Diagnosis: history and clinical examination; CT and MRI (mid‐sagittal diameter of the spinal canal of less than 11 mm) Included: degenerative spinal stenosis Excluded: systemic disease; instability of the spine; previous operation Age (years): mean (range) 67 (48‐87) Lumbar stenosis duration (years): mean (range) 1.3 (0.5‐3.1)
Interventions	Group 1: decompression alone. Decompression involved widening of the lateral recess, undercut of lamina, and discectomy or foraminotomy in some patients Group 2: decompression plus arthrodesis of the most stenotic segment Group 3: decompression plus arthrodesis of all of the decompressed vertebral segments Follow‐up: 28 months
Outcomes	Pain: 10 cm VAS overall pain Disability: walking ability Operation time Perioperative blood loss: Complications Reoperations
Notes	Surgeon's experience: All the operations were performed by the same surgeon Funding: "no funds were received in support to this study"
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "the patients were randomly assigned to the three treatment groups."
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	100% of the patients completed the follow‐up.
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)	Unclear risk	No information about patients characteristics at baseline.
Co‐interventions (performance bias)	Low risk	Only the surgical technique differed between treatment groups. Similar percentage of concomitant discectomy. All participants received the same postoperative care.
Compliance (performance bias)	Low risk	Compliance in both treatment groups: 100% (surgery).
Timing of outcome assessment (detection bias)	High risk	Patients were assessed at different time points. The average duration of follow‐up was 38 months (range: 24 to 32).
Other bias	Low risk	Quote: "no funds were received in support to this study"