Bloemen 2011.

Methods	RCT Methods to control for contributory patient factors: none described
Participants	Age: Group 1 (mean): 63.1 years Group 2 (mean): 63.8 years Gender: Group 1: 40.6% female Group 2: 44.9% female Type of incision: all participants received midline incisions Type of surgery: Group 1: elective 80.1%; colorectal cancer 47.7%, aortic aneurysm 11.3%, benign colorectal 13.3%, gastric cancer 3.5%, cholelithiasis 5.5%, bowel perforation 3.9%, hiatal hernia 3.9%, appendicitis 2.0%, other 9.0% Group 2: elective 85.4%; colorectal cancer 53.2%, aortic aneurysm 10.9%, benign colorectal 12.3%, gastric cancer 4.9%, cholelithiasis 2.6%, bowel perforation 3.4%, hiatal hernia 2.6%, appendicitis 3.0%, other 7.1% Contamination classification of included participants: not described Pre‐operative antibiotic use: not described Prognostic patient factors: Group 1: DM 9.8%; mean BMI 25.6; steroids 6.3%; chronic pulmonary conditions 3.9% Group 2: DM 6.4%; mean BMI 25.8; steroids 7.9%; chronic pulmonary conditions 10.1% Inclusion criteria: elective or emergent laparotomy with midline incision Exclusion criteria: pregnancy, presence of an abdominal hernia, lack of informed consent, age < 18 years or life expectancy of < 1 year
Interventions	Group 1: Suture: 1‐0 polypropylene (monofilament, non‐absorbable) Suturing technique: continuous Closure method: mass Group 2: Suture: 1‐0 PDS (monofilament, slowly absorbable) Suturing technique: continuous Closure method: mass Surgeon characteristics: consultant or resident surgeons
Outcomes	Incisional hernia: defined as "any abdominal wall gap with or without a bulge in the area of a postoperative scar, perceptible or palpable by clinical examination or imaging" Follow‐up duration: up to 54 months Dehiscence: "Early post‐operative fascial dehiscence was distinguished from later incisional hernia, defined by a clinically palpable gap in the abdominal fascia with, or without wound dehiscence during the first 30 days after surgery..." Wound infection: not defined Sinus or fistula: not defined
Notes	Occurrence of incisional hernia at 1 year used in analysis
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomisation
Allocation concealment (selection bias)	Low risk	Sealed, opaque envelopes
Blinding (performance bias and detection bias) All outcomes	Low risk	Outcome assessors blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants accounted for and included in analysis
Selective reporting (reporting bias)	Low risk	Hernia (at least 1 year); dehiscence and wound infection outcomes all reported
Other bias	Low risk	The study appears to be free of other sources of bias