Non-surgical traumas to the lower limbs that require orthopedic immobilisation (plaster or splint) are a frequent reason for going to accident and emergency. Due to venous stasis caused by immobilisation, hypercoagulable states and vascular injuries brought on by the trauma, these patients are at risk of developing VTE. For this reason, it is current practice in France and Belgium for the majority of patients to receive a preventative anticoagulant treatment. However, the benefit of this treatment, which has a considerable cost, is controversial. Contrary to French recommendations, American recommendations from 2012 actually advise against systematic preventative medicine, with prevention appearing to be effective primarily in studies with restrictive inclusion criteria. The most significant randomised controlled study on the subject did not show the benefit of low-molecular-weight heparin (LMWH) on the rate of symptomatic VTE among 1,435 non-selected patients. Therefore, in 2017, the Cochrane meta-analysis concluded that stratification of the risk of thromboembolism is required.

For this purpose, in collaboration with the Dutch team of Nemeth et al. we have recently developed a risk stratification model that takes into consideration the patient's characteristics, the type of immobilisation and the severity of the trauma: the TRiP(cast) score. This score is applied retrospectively to a large cohort and demonstrates excellent prognostic performances (AUC (area under the curve) of 0.74). In addition, when using a <7 limits, it makes it possible to identify a large group of patients at very low risk of developing VTE (negative predictive value: 99.2%).

The aim of the CASTING study is to prospectively demonstrate the reliability and utility of the TRiP(cast) score by showing that patients with orthopaedic immobilisation of a lower limb who are not receiving preventative treatment on the basis of a TRiP(cast) score of <7 have a very low rate of symptomatic VTE, which allows for a significant reduction in prescriptions of anticoagulants in comparison with prior practices.

Inclusion Criteria:

• Consultation in one of the emergency department participating in the study,
• Isolated trauma from lower limb,
• Rigid (plaster or resin) or semi-rigid immobilization for an assumed duration of at least 7 days,
• Adults (18 years),
• Affiliated patient or beneficiary of a social security,
• Patient with prior informed consent.

Exclusion Criteria:

• Patient with anticoagulant treatment at the time of trauma,
• Trauma requiring hospitalization of more than 48 hours,
• Co-morbidity(s) requiring hospitalization of more than 48 hours at the time of inclusion,
• Any factor making 90-day follow-up impossible,
• Pregnant, nursing or childbearing patient,
• Patient deprived of liberty by judicial or administrative decision,
• Patient undergoing psychiatric care under duress,
• Patient subject to a legal protection measure,
• Patient unable to give free and informed consent.

Individual participant data will not be available. The study protocol, the Statistical Analysis Plan, Informed consent form will be available immediately following publication. No end date.