Kortbeek 1992.

Methods	Randomized controlled trial
Participants	Patients with chronic anal fissure
Interventions	Open (54) versus closed (58) partial lateral internal anal sphincterotomy
Outcomes	Persistence of the fissure and incontinence to flatus Open sphincterotomy Persistence risk = 0.06; incontinence risk = 0.07 Closed sphincterotomy persistence risk = 0.03; incontinence risk = 0.09
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	pulling classification cards once surgery had been determined to be necessary
Blinding of outcome assessment (detection bias) All outcomes	High risk	inadequate
Drop‐outs All outcomes	Low risk	zero