Are We Accurately Assessing Risk For Deep Venous Thrombosis?

A majority of foot and ankle surgeries and injuries involve some form of immobilization. To assist with patient independence and mobility, clinicians universally emphasize the use of ambulatory aids such as crutches, knee scooters, and knee walkers. However, the act of limiting weightbearing or immobilization may place a relative risk for the development of a deep venous thrombosis (DVT), which would embolize into the pulmonary arteries, causing a pulmonary embolism (PE).

Virchow’s Triad for the development of thrombosis includes venous stasis (i.e., immobility, congestive heart failure), endothelial injury (i.e., surgery, trauma), and hypercoagulability (i.e., cancer, thrombophilia).¹ Venous stasis is the most important factor and can contribute to the formation of a DVT. Risk factors for venous thromboembolism (VTE) include comorbidities such as diabetes mellitus, hypercholesterolemia, tobacco use, active infection, cancer, increased age, obesity, a previous history of VTE, oral contraception use, trauma, recent surgery and immobilization.²  

Pharmacologic prophylaxis addresses the hypercoagulability of the patients. The incidence of clinically apparent VTE following foot and ankle surgery with pharmacologic prophylaxis is 0.6 percent and without prophylaxis is 1 percent.³ Interestingly, the American College of Chest Physicians (ACCP) produced a set of guidelines in 2012, recommending no prophylaxis rather than pharmacologic prophylaxis in patients with isolated lower-leg injuries requiring leg immobilization.³ This recommendation comes after the guideline authors analyzed data from six randomized trials, involving 1,500 patients who required lower-leg immobilization for at least 1 week, that compared once-daily low molecular weight heparin (LMWH) versus no thromboprophylaxis until the cast or brace was removed. The ACCP guideline authors suggest that these results did not establish the benefit of pharmacologic prophylaxis and that no prophylaxis is a more cost-effective option than pharmacologic prophylaxis.

In regard to mechanical prophylaxis, clinicians can combat venous stasis with the use of intermittent pneumatic compression (IPC) pumps for the foot and calf as well as elastic compression stockings. These modalities appear to provide effective means of thromboprophylaxis in postoperative patients.⁴ Additionally, active and passive ankle plantarflexion help increase venous return from the lower limb via the muscular-venous pump system. However, utilizing any of these methods is often impractical or impossible following foot and ankle surgery or injury, specifically when the extremity is immobilized in a cast, splint, or walking boot.⁴

The knee scooter is a useful ambulatory aid for patients who cannot tolerate the use of crutches. However, recent studies have shown that the venous flow rate is decreased in a seated knee-flexed position.⁵ Knee scooters and walkers require a flexed-knee position, albeit with an extended hip and weightbearing borne to the affected knee. In fact, a recent level II study demonstrated a significant decrease in mean venous velocity and volumetric venous flow rate in the study participants using a knee scooter device with a flexed knee.⁵ From this, one can assume that patients may be at a greater risk for developing a DVT secondary to non-weightbearing with the assistance of a knee scooter.

The ACCP guidelines do recommend using an intermittent pneumatic compression device (IPC) as a means of mechanical thromboprophylaxis but this poses a challenge if the patient is immobilized with a cast, splint or even boot to the lower leg. In a 2016 study, researchers examined the effects of placing IPC on the thigh alone to observe the peak blood velocity (PBV) in the lower legs.⁶ They found that intermittent pneumatic compression to the thigh in sitting patients resulted in a 2.3-fold increase in peak blood velocity in the superficial femoral veins and a 3.0-fold increase in peak blood velocity in popliteal veins, respectively, in comparison to patients resting in supine positioning. Intermittent pneumatic compression to the thigh alone increases peak blood velocity significantly in both supine and sitting positions, and could be a useful means of thromboprophylaxis in patients with lower leg immobilization.

Final Notes

Patients who are immobilized to the lower limb have an estimated VTE rate of 2.5 percent without prophylaxis.⁶ Although venous stasis is a known risk factor for DVT, venous flow rate thresholds for developing a DVT and, consequently, a PE are not well-defined in the literature. The duration of knee scooter use or flexed-knee positioning seems to have some effect on the degree of venous stasis, but this too remains ill-defined. Further studies should evaluate the average duration of knee scooter use. It would be beneficial to define how long a patient should use the knee scooter device as extremity positioning can decrease venous flow rate. Placement of IPC on the thigh for mechanical thromboprophylaxis produces an increase in venous blood velocity but cost-effectiveness remains in question as does patient adherence.

As there exists a constellation of factors which could potentially raise the risk of DVT formation, we should more closely and individually assess our patients post-operatively and post-injury. Considering that a clinical consensus recommends foregoing pharmacological prophylaxis in a majority of patients and the inability to mechanically prophylax patients that are immobilized and/or non-weightbearing, developing a cost-effective and practical means of mechanical thromboprophylaxis is a priority, especially in patients who are immobilized in the lower leg.

This blog was co-authored with Sokieu Mach, DPM, and Jayson N. Atves, DPM, CO, AACFAS.

References

1. Badireddy M, Mudipalli VR. Deep Venous Thrombosis (DVT) Prophylaxis. StatPearls [Internet]. StatPearls Publishing. Treasure Island, Fla. 2018.
2. Carr P, Ehredt D, Dawoodian A. Prevention of deep venous thromboembolism in foot and ankle surgery. Clin Podiatr Med Surg. 2019;36(1):21-35.
4. Craik J, Hendry J, Hamilton P. The effect of ankle joint immobilization on lower limb venous flow. Foot Ankle Int. 2015;36(1):18-23.
5. Ciufo D, Anderson M, Baumhauer J. Impact of knee scooter flexion position on venous flow rate. Foot Ankle Int. 2019;40(1):80-84.
3. Prevention of VTE in orthopedic surgery patients. Antithrombotic therapy and prevention of thrombosis, 9th edition: American College of Chest Physicians evidence-based clinical practice guidelines. Chest. 2012;141(2 Suppl):e278S-e325S.
6. Nakanishi K, Takahira N, Sakamoto M, Yamaoka-Tojo M, Katagiri M, Kitagawa J. Effects of intermittent pneumatic compression of the thigh on blood flow velocity in the femoral and popliteal veins: developing a new physical prophylaxis for deep vein thrombosis in patients with plaster-cast immobilization of the leg. J Thromb Thrombolysis. 2016;42:579-584.