Dahl 1997.

Methods	Study design: Randomised, prospective, double‐blind, placebo‐controlled trial Country: Norway Setting: Multicentre, hospital and home, January 1993 ‐ June 1994 Intention‐to‐treat: Yes, after withdrawals removed. For the purposes of our meta‐analyses we used the reported ITT population
Participants	Number randomised: Total n = 265 (extended LMWH n = 134; placebo n = 131) Exclusions post randomisation: Total n = 38 (extended LMWH n = 17; placebo n = 21) withdrawn for reasons other than DVT or PE (21/38 due to adverse events: 10 extended LMWH and 11 placebo) Losses to follow up: No losses to follow‐up all participants received treatment until the day of final visit Age mean years: Extended LMWH 70.98, placebo 71.4 Sex %F: Extended LMWH 68.5%; placebo 73.6% Inclusion criteria: 18 years or older; admitted to hospital for elective primary or secondary hip replacement; obtained written consent form Exclusion criteria: Known renal or liver insufficiency; cerebral bleeding less than three months before surgery or known haemorrhagic diathesis; eye or ear surgery within one month before surgery; severe hypertension; septic endocarditis; threatened arterial circulation in the leg; body weight less than 40 kg; anticoagulant therapy less than one week before surgery; known hypersensitivity to heparin, low‐molecular‐weight heparin, dextran or contrast media; pregnancy or breastfeeding; inability to comply with study protocol; previous surgery within study
Interventions	Treatment: Dalteparin 5000 IU, injections once daily for four weeks Control: Initial treatment with dalteparin 5000 IU followed by placebo (sodium chloride) injections, once daily Duration: 35 days (7 days initial treatment + 28 days continued treatment)
Outcomes	Primary: Verified VTE on days 7 and 35 Secondary: Haematological assessment; safety: reoperation due to bleeding, wound haematoma and local haematoma at injection site
Notes	Funding: Not reported Method of VTE evaluation/confirmation: DVT verified by bilateral venography and PE verified by perfusion ventilation or chest X‐ray
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient information given to determine adequate randomisation
Allocation concealment (selection bias)	Unclear risk	Insufficient information given to determine adequate allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Described as double‐blinded and gave placebo subcutaneous injections
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Venograms, X‐rays and V‐Q scans evaluated after the study by a blinded specialist
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants accounted for, ITT and PP analysis
Selective reporting (reporting bias)	High risk	VAS patient acceptability reported but not reported as pre‐planned, as was pain at injection site and serious adverse events, bleeding not reported as outcomes
Other bias	Low risk	No evidence of other bias