Deep Venous Thrombosis Following Knee Surgery

Clinical Probability Scoring

The Wells score is most often employed to detect the probability of DVT. This is done on the basis of the physical examination and the patient’s medical records (Wells et al., 1997; National Institute for Health and Care Excellence, 2012). Early on, few diagnostic markers may be present and help in the diagnoses of DVT.

A high Wells score usually highlights the clinical probability of DVT. However, to rule out or confirm the presence of DVT, a CT venography, MRI, or compression ultrasonography must be used. D-dimer testing is sometimes employed to rule out DVT inpatients.

The flow diagrams given below show the pathways through which a DVT can be confirmed or ruled out after the Wells score has been determined in the United Kingdom specified by the National Institute of Health and Care Excellence (NICE) and ACCP (Kearon et al., 2012; Kearon et al., 2016).

Diagnostic Imaging

Venous ultrasonography or compression ultrasonography is the most commonly used method to analyze and determine the presence of DVTs (Turpie et al., 2002). Thisis a noninvasive and safe method for the diagnosis of suspected DVTs. The technique allows the compression and imaging of the femoral veins down to the calf veins that are the most proximal (Sternet la., 2002). When a Wells score is above 2 as in the case scenario of Mr. John Grant, this technique can be used.

The alternative to ultrasound is MRI or CT venography.

CT venography is invasive and expensive, but helps to detect distal and proximal DVT (Saad, 2007). As it is a painful procedure, it does not have to be applied to detect the DVT in MR. Grant’s case.

Magnetic resonance imaging uses a powerful magic field (Kluge, 2006). It helps in the generation of high-resolution images of anatomy. It is noninvasive and, hence, is the preferred method to detect DVT as in the case of Mr. Grant.

D-dimer is a fragment of protein formed when thrombus disintegrates and the fibrins are dissolved by the action of plasmin on the thrombus. Negative predictor values are obtained with D dimer and it helps in ruling out DVT presence as ruled out previously by the negative ultrasound scan. This D-dimer testing is not implied in Mr. Grant’s case, as he had previously tested positive for DVT presence by the other methods of diagnosis.

Deep Vein Thrombosis Following Elective Knee Surgery

The occurrence rates of venous thromboembolism have been previously investigated by scientists, who found the incidence decrease by 60% in patients receiving total knee replacements and on prophylaxis. The authors here highlight the case of an ipsilateral deep vein thrombosis in three hundred and twelve patients, who underwent a number of elective knee operative procedures. These patients had not received any prophylaxis against thromboembolism. Total knee replacements were proven to be associated with ipsilateral deep vein thrombosis in 56.4% of the patient’s studies.

On the basis of various findings of the high incidenceof DVTs in knee surgeries, the authors advise prophylaxis against venous thromboembolism in the patient who is undergoing elective knee surgery and is 40 years of age and above.

Scientists originally highlighted that venous thromboembolism was the main cause of morbidity in patients undergoing both elective and emergency orthopedic surgeries. In hip surgeries, it was found that there was a 51% incidence of deep veinthrombosis. Also, pulmonary embolism was the single largest cause of mortality in patients of hip surgery after the operation was performed. However, when it comes to knee surgery, the few studies that have been performed highlight a 59% incidence of DVT in patients that underwent total knee replacements.

The authors of this study undertook a proactive study to understand and analyse the incidences of DVT following a wide variety of knee elective operations under tourniquet ischemia. Such studies, according to the authors, are required to determine the need for prophylaxis.

It is a well-known fact that the diagnosis of DVT is inaccurate clinically. People affected by DVTs have no conspicuous signs or symptoms normally. However, the first indication of thrombosis may be obtained by the presence of fatal pulmonary embolism. The phlebography is the gold standard technique used in the diagnosis of DVT. When phlebography was implemented in the 312 patients, who underwent elective knee surgery, the overall occurrence of DVT was found to be 28% in those patients who obtained no prophylaxis.

Thus, the study highlights the high occurrence of DVT in patients, who have undergone knee replacement surgeries. When patients received prophylaxis, they reported lower incidences of DVT than those who had received no prophylaxis for DVT.

Mechanical Method for Prevention of DVT

In reduction of incidences of DVT, mechanical methods are used as an adjunct to anticoagulants and have been found to be effective. Passive devices are the knee-high GCS or graduated compression stockings (Patel et al., (2103); active such as the intermittent pneumatic compression tools or IPCs, or the VFPS or the venous foot pumps.

A 2012 systemic review study found that thigh- and knee-high GCs arenot different in their abilities to reduce DVT incidence in patients, who were hospitalized. Cost, patient compliance, and ease of use determine what type of stocking the patient would need (Sajid et al., 2012).

In a study that observed DVT incidence in a group with no prophylaxis and a group with IPC, DVT incidence was reduced by 60% by the IPC use. In high-risk cases of developing DVT after knee surgery, mechanical methods are not to be used alone as a measure of prophylaxis.

Pharmacologic Methods

Many pharmacologic agents exist hat help to prevent DVT. Anticoagulants are agents that inhibit the process of coagulation. Antithrombolytics that include antiplatelet and anticoagulant drugs prevent formation of thrombi, while the thrombolytic drugs help in the lysis of thrombi that exist.

Platelet-Active Drugs

Thrombosis has for long been prevented by the use of platelet-active drugs such as aspirin and COX inhibitors. Low-dose aspirin was found to decrease DVT by 30% as compared to placebo in a study performed in Europe. Aspirin doses were 160 mg/day as compared with placebo.

According to reports from scientists, reducing pulmonary embolism by the use of aspirin along with IPC devices is the best method to be employed.

Coumarins

Coumarins are anticoagulant drugs and are antagonists to Vitamin K. Vitamin K is a cofactor to factors II, VII, IX, and X. The coumarins work to interfere with the interaction between these cofactors and vitamin K. Carboxylation is inhibited by coumarins in bringing about their anticoagulant activity.

Warfarin is an anticoagulant and is a mixture of the R and S isoforms.The prothrombin time or the PT is used as a measure to check the anticoagulation effect of warfarin. In hospitals, the International Normalized Ratio or INR is supplanting the PT. INR employs a standardized PT, which enables to compare warfarin effects between laboratories and hospitals. Warfarin for the patient Mr. Grant, given in the case study, can be started the night before surgery and postoperatively continued.

Heparins

Heparin was discovered in 1916, and has even since been used as an anticoagulant. The unfractionated heparin or UFH inactivates factors Ila, IXa, and Xa by acting in conjunction with anti-thrombin.

By the inactivation of thrombin, heparin helps in the prevention of fibrin formation. Heparin has both antithrombotic and anticoagulant activities.

Postoperative DVT prophylaxis with the help of UFH can be achieved by administering a bolus of 5000 U every eight hours. This is a low-dose heparin regimen and can effectively prevent DVT by 60% in the patient to whom it has been administered.

Low-molecular-weight heparins or LMWHs

Low-molecular-weight heparins are obtained by the action of enzymes on heparin. While the usual heparins are of 15 kg molecular weight, that of LMWHs is 4.5 kg.

Combination Therapies

It has been reported by some scientists that early mobilization with a combination of short-duration warfarin and IPC in patients with hip surgery was found to be very effective. A low incidence of clinical DVT was found on postoperative days 3 and 4. This combination can used in the patient referred to in the case study.

Conclusion

Mr. Grant by virtue of his old age and the presence of conditions such as angina developed DVT after total knee replacement surgery. The best option is the use of combination therapy in Mr. Grant who has a Wells score of two. The combination therapy uses IPC and short-duration low-dose warfarin.

References

• Sajid, M. S. et al. (2012). Knee length versus thigh length graduated compression stockings for prevention of deep vein thrombosis in postoperative surgical patients. Cochrane Database Syst Rev, 5, CD007162.
• Kearon, C., Akl, E. A., Comerota A. J. et al. (2012). Antithrombotic therapy for VTE disease: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians evidence-based clinical practice guidelines. Chestvol. 141, e419S–e494S.
• Kearon C., Akl E. A., Ornelas J. et al. (2016). Antithrombotic therapy for VTE disease: CHEST guideline and expert panel report. Chest ,149, 315–352.
• Kluge, A., Mueller, C., Strunk, J. et al. (2006). Experience in 207 combined MRI examinations for acute pulmonary embolism and deep vein thrombosis. AJR Am J Roentgenol, 186, 1686–1696.
• National Institute for Health and Care Excellence (2012). Venous thromboembolic diseases: the management of venous thromboembolic diseases and the role of thrombophilia testing. Clinical guidelines, CG144. 2012
• Patel, N., Khakha, R., Gibbs, J. (2013). Review Article: Anti-embolism stockings. J OrthopSurg (Hong Kong), 21, 361-364.
• Saad, W. E., Saad, N. (2007). Computer tomography for venous thromboembolic disease. Radiol Clin North Am, 45, 423–445.
• Stern, J. B., Abehsera, M., Grenet, D. et al. (2002). Detection of pelvic vein thrombosis by magnetic resonance angiography in patients with acute pulmonary embolism and normal lower limb compression ultrasonography. Chest, 122, 115–121.
• Turpie, A. G. G, Chin, B. S. P., Lip, G. Y. H. (2002). Venous thromboembolism: pathophysiology, clinical features, and prevention. Br Med Jvol. 325, 887–890.
• Wells, P. S, Anderson, D. R, Bormanis, J. et al. (1997). Value of assessment of pretest probability of deep-vein thrombosis in clinical management. Lancet, 350, 1795–1798.

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