• This study is aimed at identifying patients at high risk for Venous Thrombo-Embolism (VTE) (clots in the veins of legs or clots in the lungs) who have lower limb injuries treated with immobilisation of the lower limb. The study aims to identify high risk patients, who may benefit from thromboprophylaxis (blood thinning medication) to prevent such clots forming.
• To do this we will collect data on 3500 patients who present with lower limb injury requiring immobilisation to the Emergency Departments of the six hospitals named.
• We will assess their risk factors for venous thrombosis at the time of presentation and contact them at twelve weeks to assess if they have had a VTE in order to develop a risk scoring system which can be used to predict the likelihood of VTE development
• This risk scoring system can then be used to identify high risk patients who may benefit from thromboprophylaxis.

Currently, there is wide variation in the provision of venous thromboembolism (VTE) prophylaxis for patients who suffer lower limb trauma and require lower limb immobilisation. Current United Kingdom guidelines recommend assessing competing risks of VTE and bleeding followed by shared decision-making with the patient on prescription of pharmacological thromboprophylaxis (VTE thromboprophylaxis). However, current American College of Chest Physicians (ACCP) guidelines do not recommend VTE thromboprophylaxis for this group. The largest study carried out to date, the Prevention of Thrombosis after Lower Leg Plaster Cast (POT-CAST) randomised controlled trial 1 identified a very low rate of VTE (1.8%) in the non-intervention arm. This study concluded that thromboprophylaxis was not justified for patients with lower limb trauma who required lower limb immobilisation. However, it recommended that further studies are required to see if it is possible to identify a high risk cohort of patients who may benefit from VTE thromboprophylaxis. No large prospective study has been published to date to assess if it is possible to identify this high risk group.

The Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis (MEGA) study was a case-control study designed to identify risk factors for a first VTE. A sub-analysis of this study reviewed 230 patients who had lower limb trauma with cast immobilisation who developed VTE. Based on this data a risk assessment score was derived (termed "L-TRiP" [Leiden-Thrombosis Risk Prediction for patients with cast immobilization] score) in order to identify high risk patients who may benefit from VTE prophylaxis. However, this risk assessment tool has not been prospectively validated in a study.

We have carried out a pilot study to assess the feasibility of a large scale, adequately powered multi-centre study aimed at prospective identification of a high VTE-risk group of patients. This study was presented at the International Society on Thrombosis and Haemostasis meeting in Berlin in 2017.5 Utilizing data from this pilot study, we now aim to perform a multi-centre study with sufficient power to determine whether it is feasible to identify a high risk group of patients with lower limb trauma requiring immobilisation who will benefit from thromboprophylaxis The POT-CAST study determined that the rate of venous thrombo-embolism (VTE) in patients with lower limb trauma requiring a cast was 1.8%. This low rate does not justify VTE prophylaxis for all patients who require a cast. However there may be a high risk group with a rate of VTE high enough to suggest that consideration of VTE prophylaxis may be appropriate. This study will prospectively gather risk factor data on patients at the time of initial presentation post trauma with follow up at 12 weeks to identify those patients who have experienced a symptomatic VTE episode. This data will then be used to identify a group with a high VTE risk which future studies can utilise to target this high risk group to assess if VTE prophylaxis is of benefit.

Inclusion Criteria:

• All patients who present to the Emergency Department with lower limb trauma requiring lower limb immobilisation. Aged over 18

Exclusion Criteria:

Patient unable to give consent Previous Venous thromboembolism

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All patients who present to the Emergency Departments of participating centres with lower limb injury over 18 requiring lower limb immobilisation.

All researchers will input their centre patient data. The overall committee will review all patient data for review purposes . Individual centres will not be able to access other centres data.

At the end of trial for a limited time.

Only the reviewing committee will have access to all data. Individual centres will have access to their centres data.