ROYAL COLLEGE OF PODIATRY
What do we know about VTE prevention in lower limb immobilisation?
Lower limb immobilisation presents clinicians with a widespread but tough question – when does the risk of venous thromboembolism outweigh the risks associated with anticoagulation? Emerging evidence is helping to determine decision-making, but uncertainty remains.
Temporary lower limb immobilisation is common across emergency and musculoskeletal care settings. In the UK alone, it is estimated that around 70,000 patients each year are discharged from emergency departments in casts, braces or walking boots following injury.
For clinicians, however, immobilisation introduces an important clinical issue. While some patients may be at increased risk of venous thromboembolism (VTE), routine anticoagulation is not without consequence.
The challenge is balancing both risks safely and consistently.
VTE, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), remains a significant cause of preventable harm. In 2005, the House of Commons Health Committee estimated that VTE contributed to between 25,000 and 35,000 deaths each year in the UK, exceeding the combined deaths from breast cancer, AIDS and traffic accidents.
Importantly, many VTE events are considered preventable through appropriate assessment and prophylaxis.
Why does immobilisation increase VTE risk?
The development of VTE is commonly explained through “Virchow’s triad” a concept of three interacting factors that contribute to thrombosis formation:
venous stasis
endothelial injury
hypercoagulability
Temporary lower limb immobilisation can contribute to all three.
Reduced mobility may slow venous return, while traumatic injury and surgery can increase inflammatory and coagulation responses. Additional patient factors, including obesity, increasing age and previous thromboembolic disease, may further increase the risk.
For clinicians working in foot and ankle care, this creates a familiar scenario – a patient with temporary immobilisation, multiple comorbidities and uncertainty around whether pharmacological prophylaxis is warranted.
What do the current guidelines say?
Despite the frequency of lower limb immobilisation, international guidance on VTE prophylaxis remains inconsistent.
In the UK, NICE guidance recommends that all patients aged 16 and over who are discharged with lower limb immobilisation should undergo VTE risk assessment.
Similarly, the Guidelines in Emergency Medicine Network (GEMNet) advises clinicians to strongly consider thromboprophylaxis in ambulatory patients with temporary lower limb immobilisation who also have additional VTE risk factors.
Internationally, however, recommendations vary significantly. Some healthcare systems champion more routine pharmacological prophylaxis, while others reserve anticoagulation for patients considered higher risk.
What does appear consistent across most guidance is the importance of:
individual patient risk assessment
minimising unnecessary immobilisation
encouraging early weight bearing where possible
balancing VTE risk against bleeding risk
Routine anticoagulation for all patients with foot and ankle injury is not generally supported by current evidence.
Assessing VTE risk in practice
Several patient-specific factors have been associated with increased VTE risk during immobilisation, including:
advancing age
BMI greater than 30kg/m²
personal or family history of VTE
Achilles tendon rupture
surgical intervention
To support clinical decision-making, several VTE risk assessment tools have been developed. NICE recommends using tools developed by recognised national bodies, professional networks or peer-reviewed sources.
One of the most widely discussed models is the TRiP (cast) score – Thrombosis Risk Prediction following Cast Immobilisation.
Developed using data from the MEGA study and POT-CAST trial, the TRiP (cast) score combines factors relating to:
injury severity
type of immobilisation
individual patient characteristics
The score has now been incorporated into local policy across many NHS trusts.
Recent observational data from the TILLIRI study suggests that patients with a TRiP (cast) score below 7 may have a sufficiently low incidence of symptomatic VTE that thromboprophylaxis could potentially be avoided.
However, risk assessment tools are intended to support, but not replace, clinical judgement.
Anticoagulation is not without risk
A recurring theme throughout the literature is that thromboprophylaxis itself carries important clinical risks.
Low molecular weight heparin (LMWH) remains one of the most used pharmacological interventions for VTE prevention. While generally considered safe, bleeding complications remain the principal concern.
More serious adverse effects, although uncommon, include:
heparin-induced thrombocytopenia (HIT)
osteoporosis
hypersensitivity reactions
hyperkalaemia
For clinicians, the decision to prescribe prophylaxis is therefore rarely straightforward.
The central question is whether the patient’s risk of thrombosis outweighs the potential harms associated with anticoagulation.
Variation in clinical practice
Research suggests considerable variation in VTE prophylaxis practice both within the UK and internationally.
A UK survey of emergency departments identified multiple different risk assessment tools in use, while some clinicians relied on locally developed systems.
Globally, a survey published in the Journal of Foot and Ankle Surgery found that many orthopaedic surgeons reported not using formal VTE risk assessment tools at all.
This variation likely reflects the ongoing uncertainty within the evidence base, differing local policies and the complexity of balancing individual patient factors.
Emerging research and future direction
Research into VTE prevention during lower limb immobilisation has sped up over the past decade.
One of the most significant current studies is the National Institute for Health and Care Research-funded TILLIRI study (Thrombosis in patients with Lower Limb Injuries Requiring Immobilisation).
The multicentre observational study is exploring:
the true incidence of symptomatic VTE following immobilisation
how clinicians assess risk
whether oral anticoagulants may offer comparable efficacy to injectable prophylaxis in higher-risk patients
Early findings have supported the use of the TRiP (cast) score in identifying lower-risk patients who may not require pharmacological prophylaxis.
Further findings are expected as the study progresses towards completion in 2028.
What should clinicians take away?
While evidence and guidance continue to advance, several principles remain central to safe practice:
all patients with lower limb immobilisation should undergo VTE risk assessment
clinicians should understand local policy and national guidance
pharmacological prophylaxis should be individualised
bleeding risk must be considered alongside thrombosis risk
risk assessment tools should support — not replace — clinical judgement
For clinicians working in podiatric surgery, musculoskeletal care and foot and ankle practice, VTE prevention remains an important aspect of safe patient management.
As evidence continues to develop, the emphasis is increasingly moving away from blanket prophylaxis and towards more personalised risk assessment and decision-making.
Key messages
Lower limb immobilisation can significantly increase VTE risk in some patients.
NICE recommends VTE assessment for all patients discharged with lower limb immobilisation.
The TRiP (cast) score is increasingly used across NHS trusts to support decision-making.
Routine thromboprophylaxis is not recommended for all patients.
LMWH and other anticoagulants carry important risks that must be considered.
Emerging research is helping clinicians better identify which patients may benefit from prophylaxis.
Links and references
Journal of Vascular Surgery: Virchow’s triad in “silent” deep vein thrombosis
About the authors
Mr Derek Protheroe is a Specialist Registrar in Podiatric Surgery. Derek qualified as a podiatrist in 2005 and was awarded his Fellowship in Podiatric Surgery (FRCPodS) in 2023 having completed the new Masters in Podiatric Surgery course at Huddersfield University. He is currently working as a specialist registrar in podiatric surgery for Wye Valley NHS Trust while completing his Certificate of Completion of Podiatric Surgical Training (CCPST). He also works in an advanced podiatry practitioner role for Hywel Dda University Health Board, where he has set up an independent diagnostic foot and ankle ultrasound service.
Derek has published several peer-reviewed articles on a range of broad subjects in both podiatry and surgery.
Derek also contributes to undergraduate and postgraduate teaching for both Plymouth and Cardiff Metropolitan universities.
Mr Anthony Waddington is a Consultant Podiatric Surgeon with over two decades of experience in the diagnosis and management of foot and ankle conditions. He provides specialist outpatient care across Herefordshire, Shropshire and Merseyside.
Anthony achieved Fellowship (FRCPodS) in 2005. He was awarded his CCPST in 2009. His interest in sports injuries led to completing a Higher National Diploma in Sports Science at Manchester.
He has previously led children’s podiatry services, working closely with Foot Health Services, Surgical Appliances departments and Orthopaedics and Trauma teams.
Anthony continues to contribute to undergraduate and postgraduate teaching across multiple clinical topics and acts as a mentor to orthopaedic and trauma colleagues at the University of Salford.
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