Preventing Deep Vein Thrombosis in Total Knee Replacement Patients

This article discusses the risk factors, assessment, and prevention of deep vein thrombosis (DVT) in patients undergoing total knee replacement (TKR) surgery. It covers the importance of DVT prophylaxis, the use of pharmacological agents and mechanical devices, and the timing of prophylaxis. The article also provides information on diagnosing DVT and the various diagnostic modalities available. Overall, it emphasizes the need for proper management and coordination between surgeons and physicians to reduce the risk of DVT in TKR patients.

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Post operative deep vein thrombosis [DVT]
Introduction
DVT or deep venous thrombosis is the formation of a thrombus in the deep veins. In lower limb,
distal DVT refers to thrombosis in infrapoplitial veins [1] and proximal DVT refers to
thrombosis in poplitial, femoral and iliac veins [2]. At the adductor hiatus, poplitial vein
continues as femoral vein. Adductor hiatus is the distal end of the adductor canal, a canal in the
middle third of thigh, which contains femoral vessels [3]. DVT can be provoked due to an
identifiable cause like trauma, surgery or immobilization or it can be unprovoked, wherein no
environmental cause can be identified [2]. Pulmonary embolism is a potentially life threatening
complication of DVT. The common symptoms of DVT of leg are pain, edema, and warmth [2].
Many patients with DVT are totally asymptomatic and unfortunately, a fatal pulmonary
embolism may be the only presentation of DVT.
DVT following Total knee replacement [TKR]
The incidence of DVT in TKR patients not receiving DVT prophylaxis is 40 to 88%. It is less
than or equal to 1% in patients receiving adequate thromboprophylaxis [2]. Thus there is a very
significant, almost 60% decrease in the incidence of DVT in patients receiving
thromboprophylaxis. 2012 ACCP- American College of Chest Physicians guidelines

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recommend pharmacological DVT prophylaxis for all patients undergoing TKR who do not have
excess bleeding risk [4].
Risk factors for DVT
Virchow’s triad consists of slowing or stasis of blood flow, hypercoagulable state of blood and
injury to endothelial lining of blood vessels. It explains the etiopathogenesis of DVT in most
cases [2]. The hypercoagulable state may be inherited or acquired. Factor V Leiden mutation and
prothrombin gene mutation together account for more than half of the cases of inherited
thrombophilias , that is inherited hypercoagulable states.[2]
There are numerous acquired risk factors like surgery, trauma, infection, immobilization etc.
Among surgeries, the risk is more in orthopaedic surgery, neurosurgery and surgery for
malignancies. [2]
The focus of this article is on assessment of DVT risk in a given patient and how to prevent
the occurrence of DVT in a patient of TKR
Various guidelines and scoring systems have been developed to help a clinician in assessing the
risk of DVT and how to prevent it in a particular situation.
The risk of DVT in a given post operative patient not only depends on the patient’s
characteristics but it also depends on the type of surgery and the techniques used in the surgery.
Patient related factors

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Advanced age, past history of DVT, significant co morbidities like ischemic heart disease – IHD,
obesity, hypercoagulable states etc are patient related risk factors for high risk of DVT.
Surgery specific risk factors
Hip arthroplasty, knee arthroplasty, surgery for pelvic fracture or major trauma, oncosurgery etc
are associated with increased risk of post operative DVT [2]
The modified Caprini risk assessment model, modified further by ACCP in the year 2012 is
widely used for the assessment of DVT risk of surgical patients.[2]
The patient is classified in very low, low, moderate and high risk for getting DVT based on
Caprini score.
It should be noted that Caprini scoring covers most of the common surgeries but cannot be used
for each and every surgery. For example, for oncosurgery it should not be used
Total hip and knee replacement surgeries by themselves in any patient carry a high risk for DVT.
That is the reason why elective arthroplasty by itself is given a maximum individual score of five
points in Caprini scoring system.
Assessment of risk for post operative DVT with help of Caprini score for the case study
patient Mr. John Grant: [2]
Age 63 years: 2 points
Elective arthroplasty: 5 points
Total score: 7 points

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It classifies Mr. John as having high risk [a score more than or equal to 5] to get post operative
DVT
Planning of post operative care of Mr. John based on Executive Summary: antithrombotic
therapy and prevention of thrombosis, 9th edition: ACCP evidence based clinical practice
guidelines 2012:
1. Use one of the following pharmacological agent for 10 to 14 days of post operative
period
The available agents are:
 Low molecular weight heparin
 Fondaparinux- factor Xa inhibitor
 Apixaban , Rivaroxaban: Inhibitor of activated factor X
 Dabigatran: Direct thrombin inhibitor
 LDUH- low dose unfractionated heparin
 Adjusted dose VKA- vitamin K antagonist, for example warfarin.
 IPCD- Intermittent pneumatic compression device
 ACCP guidelines give preference to the use of LMWH over and above other
drugs in TKR or THR [total hip replacement] patients with or without IPCD

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Use of both, that is a drug and an IPCD is preferable throughout the course of hospitalisation for
all major orthopaedic surgery patients [Total knee arthroplasty, total hip arthroplasty and hip
fracture surgery.
Early ambulation and avoiding dehydration are general measures that are helpful for any patient
at risk for DVT
Timing of the prophylaxis:
 Preferably start it 12 hours prior to the scheduled surgery
 Some surgeons prefer to start it 18 hours after the surgery
 Patients of major orthopaedic surgery who have a high bleeding risk:
 Use an IPCD for minimum 18 hours daily and do not use pharmacotherapy.
IPCD:
The basic technique used by an IPCD is periodic inflation and deflation of air bladders wrapped
around the leg which prevents venous stasis. The devices also help to improve blood flow
velocity and increase the levels of circulating fibrinolysins [7]. Venous stasis is one of the major
risk factors for DVT [6].
IPCDs may not be widely available and need energy supply. Elastic compression stockings are
easy to use, cheaper than IPCD and do not need any energy supply. They are not as effective as
IPCDs but can be used with some benefit especially when IPCDs are not available. [7] The
stockings should be well fitting for the required benefit.

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Key points related to DVT prophylaxis in a patient of TKR
There is a significant risk of DVT if thromboprophylaxis is not used in any patient of TKR
Combination of pharmacological agent, preferably LMWH and mechanical device- IPCD should
be used. Duration of prophylaxis is minimum 10 to 14 days post operatively. If used correctly,
there is a very significant risk reduction in incidence of DVT in TKR patients.
The guidelines help a clinician to decide correct management of the patient. The plan of action
may need changes depending on characteristic of each patient and the post operative course. For
example, if there is unexpected heavy blood loss during surgery, hematoma, drop in platelet
count, bleeding tendency, gastric stress ulceration causing hematemesis or any other unexpected
complication, the management should be done on case-to-case basis.
There should be good coordination between the operating surgeon and the physician or internist
in charge of the patient. In spite of best care, some patients may still develop DVT.
Diagnosis of DVT
Wells score: It assesses clinically pretest probability of a person getting DVT. Points are given
to various risk factors of getting DVT and few physical findings like leg swelling, tenderness and
comparison of calf circumference.
The total score is used the determine DVT risk
 Score of 0 or less indicates low probability
 Score of 1to 2 indicates moderate probability

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 Score of 3 to 8 indicates high probability [2]
Various diagnostic modalities are used to diagnose DVT depending on the risk stratification,
clinical situation and availability of modalities.
D dimer- It is measured in blood. It is a degradation product of fibrin linked by factor XIII. It
has a very good negative predictive value for DVT in patients with low Wells score
It can be also elevated in many situations other than DVT like pregnancy, trauma, recent surgery
and cancer. In the case of Mr. John Grant, elevated levels of d dimer are of no value for the
diagnosis of DVT due to his recent TKR surgery [8]
Venous Doppler study: It is an ultrasound based technique. It is easily done, non invasive and
there is no risk of radiation exposure or contrast injection. A skilled observer is very important
for correct diagnosis. It is the investigation of choice for many patients.
There are many clues to presence of DVT in ultrasound. The thrombosed vein is not
compressible, thrombus can be directly visualised in the vein, there is loss of augmentation of
blood flow on compression of lower limb etc
Severe obesity reduces the sensitivity of the ultrasound. It is difficult to visualise the proximally
situated iliac veins by ultrasound.
Magnetic resonance venography – MRV with or without contrast has good sensitivity and
specificity for the diagnosis of DVT [9]. It cannot be used if the patient is claustrophobia or has
a MRI incompatible implant. It is a costly test and is many times not available.

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CTV- Computed tomography venography with intravenous contrast: The thrombus is seen
as an intraluminal filling defect. It has a good sensitivity and specificity. The draw backs are
radiation exposure and exposure to contrast agent which can be nephrotoxic.
Angiography and nuclear imaging techniques can be used in selected patients.
Management:
Short term or long term anticoagulation therapy and control of risk factors form the mainstay of
DVT treatment.

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References:
1. Palareti, G. (2014). How I treat isolated distal deep vein thrombosis (IDDVT), Blood,
123(12), 1802–1809.
2. Pai, M. (2017). Deep Vein Thrombosis Overview, Uptodate.com.
3. Dorland. (2003). Dorland’s illustrated medical dictionary, 30th edition, W. B. Saunders
Company.
4. Forsh, F. A. (2016). Deep venous thrombosis prophylaxis in orthopedic surgery,
Medscape.Com.
5. Lo, B. M. (2016). Deep venous thrombosis risk stratification, Medscape.com.
6. Morris, R. J. (2004). Evidence-based compression: prevention of stasis and deep vein
thrombosis, Annals of Surg., 239(2).
7. Szigeti, R. G. (2014). D-dimer, Medscape.com.
8. Hofer, E. K. (2015). Imaging in deep venous thrombosis of the lower extremity,
Medscape.com.
9. D'Alesandro, M. (2016). Focusing on lower extremity DVT, Nursing2017.