Ghogawala 2016.

Methods	Multi‐centre RCT Setting: 5 hospitals Country: USA Period: March 2002 to August 2009
Participants	Number: 66 patients (35/31) Diagnosis: standardized radiographic and magnetic resonance images Included: patients with grade I lumbar spondylolisthesis (degree of spondylolisthesis: 3 to 14 mm) with lumbar stenosis and neurogenic claudication with or without lumbar radiculopathy Excluded: radiography revealed lumbar instability (motion of > 3 mm at the level of listhesis, as measured on flexion–extension radiographs of the lumbar spine), previous lumbar spinal surgery, severe systemic disease Age (years): mean (SD) 66.5 (8.0)/66.7 (7.2)
Interventions	Group 1: decompression alone by a complete laminectomy with partial removal of the medial facet joint Group 2: decompression plus fusion. Patients in the fusion group underwent a lumbar laminectomy as well as implantation of pedicle screws and titanium alloy rods across the level of listhesis, with a bone graft harvested from the iliac crest Follow‐up: 24 months
Outcomes	Pain: SF‐36 bodily pain subscale Disability: ODI Operation time Perioperative blood loss Reoperations Length of hospital stay
Notes	Surgeon's experience: all surgeons routinely performed both operations tested in the trial; each of the surgeons had performed at least 100 laminectomies and 100 posterolateral fusions for lumbar spondylolisthesis before joining the trial. Funding: There was no industry funding or any other industry involvement in the trial
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not mentioned.
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	Low risk	Quote: "independent study coordinator who was not aware of the study hypothesis"
Incomplete outcome data (attrition bias) All outcomes	Low risk	88% 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 Table 1.
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: "There was no industry funding or any other industry involvement in the SLIP trial."