Liu 2013.

Methods	Single‐centre RCT Setting: Department of Orthopedic Surgery, Qilu Hospital of Shandong University, Jinan, Shandong Country: China Period: not reported
Participants	Number: 56 patients (27/29) Diagnosis: lumbar spinal stenosis diagnosis by an experienced spine specialist Included: patients with lumbar spinal stenosis without degenerative spondylolisthesis or interbody instability Excluded: not reported Age (years): mean (SD) 59.4 (4.7)/61.1 (3.1) Lumbar stenosis duration (years): mean (range) 6.5/5.9 (0.6‐13)
Interventions	Group 1: conventional laminectomy Group 2: spinous process‐splitting unilateral laminotomy. The spinous process and the interspinous ligaments were split longitudinally, preserving the paraspinal muscles. Then unilateral laminotomy was conducted for bilateral decompression with removal of the cranial and the caudal portion of the ipsilateral lamina, ligamentum flavum, and medial part of the facet Follow‐up: 24 months
Outcomes	Pain: 10 cm VAS leg pain Disability: JOA Operation time Perioperative blood loss
Notes	Surgeon's experience: all patients were diagnosed and assessed by experienced spine specialists Funding: "no funds were received in support of this work. No relevant financial activities outside the submitted work"
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "the patients were randomly categorized into 2 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	54/57=94.7% 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 1 and 2.
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: "no funds were received in support of this work. No relevant financial activities outside the submitted work."