The Thrombosis in Patients with Lower Limb Injuries Requiring Immobilisation Study . (TILLIRI study)

Background: Patients requiring temporary lower limb immobilisation after injury have an increased venous thromboembolism (VTE) risk. The extent of this risk in published studies varies. The TRiP(cast) model (Thrombosis Risk Prediction following cast immobilization) quantifies VTE risk using clinical risk factors. Delineating low from high VTE risk patients is challenging in the clinical setting.

Aims: To determine the 90-day incidence of symptomatic VTE following temporary lower limb immobilisation after injury in an undifferentiated patient population. To prospectively collect data on VTE risk factors, including those incorporated in the TRiP(cast) model, to retrospectively calculate TRiP(cast) scores.

Methods: TILLIRI is a prospective multicentre cohort study including 10 sites within the Irish Network for VTE Research (INViTE). Patients ≥ 18 years with an immobilised injured lower limb following injury were included. Twenty-one clinical variables were collected at presentation. Thromboprophylaxis was prescribed according to clinical gestalt. Patients were followed up at 90-days to determine if a VTE occurred.

Results: Between November 2018 and February 2023, 1243 patients were recruited. Follow up was complete for 1200 patients. 43 patients (3.5%) were lost to follow up. 44 (3.6%) patients and 126 (10%) patients were prescribed an anticoagulant and aspirin respectively. VTE incidence at 90-day follow-up was 7/1222 (0.57%; CI 0.15%-0.99%). TRiP(cast) scores were calculated for 1177/1222 patients. 846 patients (71.9%) had a TRiP(cast) Score < 7, received no prophylaxis and had no VTE.

Conclusion: TILLIRI indicates a low incidence of VTE in an undifferentiated patient population following lower limb immobilization with low rates of anticoagulation and aspirin use. The proportion of patients with low TRiP(cast) scores and no symptomatic VTE rate suggests that thromboprophylaxis may potentially be avoided in patients with a TRiP(cast) score < 7, with a low risk of VTE at 90 days. Future studies examining targeted strategies to identify low-risk patients can help safely avoid unnecessary anticoagulation.