Supplemental information

Table 1: Search strategy

Database / Terms
OVID version of Medline / 1.  hernia, ventral/prevention AND control*
2.  exp surgical mesh/mt, ut [methods, utilization]
3.  abdominal wound closure techniques/instrumentation*
4.  1 OR 2 OR 3
Embase / 1.  hernia OR abdominal wall hernia OR incisional hernia exp.
2.  mesh OR surgical equipment OR surgical material exp
3.  abdominal AND wall AND closure
4.  1 AND 2 AND 3
Pubmed / Searches:
1.  “incisional hernia” AND “prevention”
2.  “incisional hernia” AND “prophylaxis”
3.  hernia, ventral/prevention AND control
4.  related citations for relevant studies
Cochrane/ clinicaltrials.gov / 1.  “incisional hernia” AND “prevention”
2.  “incisional hernia” AND “prophylaxis”
3.  hernia, ventral/prevention AND control

Table 2: Jadad scale, domains

Item / Maximum points / Description / Guidelines
Randomisation / 2 / 1 point if randomisation is mentioned / A method used to generate the sequence of randomisation will be regarded as appropriate if it allowed each study participant to have the same chance of receiving each intervention and the investigators could not predict which treatment was next. Methods of allocation using date of birth, date of admission, hospital numbers, or alternation should be not regarded as appropriate.
1 additional point if the method of randomisation is appropriate / The method used to generate the sequence of randomization was described and it was appropriate (table of random numbers, computer generated, etc.)
Deduct 1 point if the method of randomisation is inappropriate (minimum 0) / The method used to generate the sequence of randomization was described and it was inappropriate (patients were allocated alternately, or according to date of birth, hospital number, etc.)
Blinding / 2 / 1 point if blinding is mentioned / The method of double blinding was described and it was appropriate (identical placebo, active placebo, dummy, etc.) / A study must be regarded as double blind if the word “double blind” is used. The method will be regarded as appropriate if it is stated that neither the person doing the assessments nor the study participant could identify the intervention being assessed, or if in the absence of such a statement the use of active placebos, identical placebos, or dummies is mentioned.
1 additional point of the method of blinding is appropriate / Participants who were included in the study but did not complete the observation period or who were not included in the analysis must be described. The number and the reasons for withdrawal in each group must be stated. If there were no withdrawals it should be stated in the article. If there is no statement on withdrawals, this item must be given no points.
Deduct 1 point if the method of blinding is inappropriate (minimum 0) / The study was described as double blind but the method of blinding was inappropriate (e.g., comparison of tablet vs. injection with no double dummy)
An account of all patients / 1 / The fate of all patients in the trial is known. If there are no data the reason is stated why.

Table 3: age, BMI and losses to follow-up

Age / BMI
study / Mesh / Range/ SD / Non-mesh / Range/ SD / Mesh / Range/ SD / Non-mesh / Range/ SD / Losses to follow-up
Bevis / 74 / range 59-84 / 72 / range 59-89 / 5 perioperative deaths
Curro / 38 / range 27-64 / 39 / range 23-66 / 45 / range 40-60 / 46 / range 40-65
El-Khadrawy / 47.9 / SD 13.8 / 47.6 / SD 14.1 / 1 perioperative death, 2 early re-operations excluded, 9 losses to follow-up
de la Pena / overall: 64.3 / overall range 42-83
Llaguna / 43.7 / range +/-11.8 / 39.4 / range +/-11.1 / 52.6 / range +/-10.6 / 50.4 / range +/-9.3 / 24 short follow-up, 4 re-operation due to other reason other than incisional hernia
Strzeczyk RCT / 39.4 / SD 12.3 / 38.9 / SD 11.8 / 46.2 / SD 7.1 / 46.8 / 7.6 / 3 patients consent withdrawn
Strzeczyk non-RCT / overall: 37.3 / overall range 18-63 / overall: 45.1 / overall range 35.8-61.3

BMI = body mass index; SD = standardised deviation

Table 4: co-morbidities

Study
Co-morbidity / Bevis / Curro / El-Khadrawy / de la Pena / Llaguna / Strzeczyk RCT / Strzeczyk non-RCT
Previous midline incision / 8
Previous abdominal incision / 13 / 43
Any previous hernia / 21
Cardiovascular disease / 54 / 26* / 8 / 49 / 52
Respiratory disease / 21 / 6 / 24 / 6
Diabetes/ impaired glucose tolerance / 10 / 21 / 8 / 35 / 16
Renal dysfunction / 13 / 1
Obesity / 95 / 17 / 74 / 60
Malnutrition / 3
Multiparity
Malignancy / 9 / 76
Liver disease / 16
Hypersplenism / 4
Gallstones / 8
Crohn's disease / 3
Gastric ulcer / 2
Hypothyroidism / 9
Pancreatic cystadenoma / 2
Diverticulosis / 9

*minimum 26 patients (overlap uncertain): 26 hypertension, 12 hypercholesterolaemia, 9 hypertryglycerides

Table 5: incisions, intention to treat and antibiotics

Study / Incision / Actually completed ITT mesh position / Antibiotics
upper / Lower / Complete/ unstated / Midline / Paramedial
Bevis / 0 / 0 / 0 / 85 / 0 / 39* (97.5%) / Prophylactic antibiotics routine
Curro / 95 / 0 / 0 / 0 / 0 / 45 (100%) / Prophylactic antibiotics routine
El-Khadrawy / 33 / 7 / 0 / 0 / 0 / 20 (100%) / Unclear
de la Pena / 22 / 28 / 0 / 73 (total) or 51 (both) / 27 / Not stated / Prophylactic antibiotics routine
Llaguna / 0 / 0 / 134 / 0 / 0 / Not stated / Not stated
Strzeczyk / 0 / 0 / 0 / 74 / 0 / 36** (97%) / Not stated
Strzeczyk non-RCT / 60 / 0 / 0 / 0 / 0 / 12 (100%) / Not stated

*one patient underwent onlay mesh placement as a plane could not be developed

** one patient withdrew consent

Table 6: Risk of bias assessment: Newcastle Ottawa Scale for all studies

Selection / Comparability / Outcome
Representativeness of exposed cohort / Selection of non-exposed cohort / Ascertainment of exposure / Demonstration that outcome was not KNOWN at start of study / Comparability of groups on the basis of analysis / Assessment of outcome / Was follow up long enough for outcomes to occur? / Adequacy of follow up of cohorts / Total
Study / High-risk cohorts selected / Same hospital and/or surgeon? / Prospective data collection or surgical records? / Prospective assessment? / Study controls for co-morbidities (e.g. randomisation) / Controls surgical technique / Blinded assessment? / Minimum 6 months / Complete or >90% follow-up / Notes
Bevis / 1 / 1 / 1 / 1 / 1 / 1 / 0 / 0 / 1 / 7
Curro / 1 / 1 / 1 / 1 / 0 / 1 / 0 / 1 / 1 / 7
El-Khadrawy / 1 / 1 / 1 / 1 / 1 / 1 / 0 / 0 / 1 / 7
de la Pena / 1 / 1 / 1 / 1 / 1 / 1 / 0 / 0 / 0 / Losses to follow-up unexplained / 6
Llaguna / 1 / 1 / 1 / 1 / 0 / 1 / 0 / 0 / 0 / Large losses to follow-up excluded (28/134) / 5
Strzeczyk RCT / 1 / 1 / 1 / 1 / 1 / 1 / 1 / 1 / 1 / 9
Strzeczyk non-RCT / 1 / 1 / 1 / 1 / 0 / 1 / 0 / 1 / 0 / 6

Table 7: Cochrane tool for assessment of bias of randomised trials

Random sequence generation / Allocation concealment / Blinding of participants and personnel / Blinding of outcome assessment / Incomplete outcome data / Selective reporting / Anything else, ideally pre-specified
Study / Accepted method used to generate random sequence? / Detail / Pre-operative allocation? / Detail / All patients accounted for? / Details / Minimum of hernia outcome / Details / Controls for surgical technique? / Other / OVERALL RISK
Bevis / low / block randomisation / low / pre-operative / high / high / low / all accounted for / low / low / low
El-Khadrawy / high / not stated / high / unclear when randomised / high / high / low / all accounted for / low / low / high
de la Pena / high / not stated / high / unclear when randomised / high / high / high / loses not accounted for / high / early losses unexplained and excluded / low / nine patients lost to early follow-up (reasons not given); 2 early re-operations (reasons not given) / high
Strzeczyk RCT / low / computer generated tables / low / done pre-operatively by no-surgical staff / low / low / low / all accounted for / low / low / low

Table 8: Jadad scale, scores

Study / Randomisation / Blinding / An account of all patients / Total
Bevis / 2 / 0 / 1 / 3
El-Khadrawy / 1 / 0 / 1 / 2
de la Pena / 1 / 0 / 0 / 1
Strzeczyk / 2 / 2 / 1 / 5

Figure 1: Funnel plot analysis of the primary outcome

All studies
High quality RCTs only

Figure 2: study specific results and meta-analysis of secondary outcomes from all studies

Surgical site infection
Haematoma
Duration of surgery
Length of stay
Chronic wound pain
Surgical repair of hernia