Related Experiment Video
Updated: Jun 2, 2026

Doppler Ultrasound-Based Leg Blood Flow Assessment During Single-Leg Knee-Extensor Exercise in an Uncontrolled Setting
Published on: December 15, 2023
Changes in popliteal vein diameter and flow velocity with knee flexion and hyperextension
Objective:
To compare popliteal vein (PV) diameter and peak flow velocity generated by a calf compressor, when the knee is either flexed or hyperextended.
Method:
Subjects lay supine on a couch with a calf compressor on each leg. Peak flow velocities in the PV were measured by duplex ultrasound during activation of the compressor, when the knee was either flexed or hyperextended. Hyperextension of the knee is seen when the heel is elevated to prevent heel pressure ulcers.
Results:
The results were analysed using the Wilcoxon signed rank test. This showed a significant increase in peak flow measurements related to narrowing of the PV when the knee was hyperextended.
Conclusion:
There is a functional narrowing of the PV during hyperextension of the knee. We developed a model, which postulates an increase in the risk of deep vein thrombosis in patients whose knee is hyperextended. Based on this model, we suggest that the knee should be flexed slightly when patients are supine and anaesthetized.
More Related Videos
Related Concept Videos
Veins of Lower Limbs
Formed by the union of the medial and lateral plantar veins, the posterior tibial vein, rising through the calf muscle, assimilates the fibular vein. The anterior tibial vein, a superior extension of the foot's dorsalis pedis vein, merges with the posterior tibial vein at the knee,...
Venous Thrombosis II: Clinical Manifestations and Diagnostic Studies
Sites for measuring blood pressure
The Brachial Artery: Primary Site for Blood Pressure Measurement
Assessing Blood pressure in the Leg
Preparation:
Peripheral Arterial Disease II: Clinical Manifestations and Diagnostic Evaluation
Assessment of the Cardiovascular System III: Palpation
Jugular Venous Pressure (JVP) Measurement
Position the patient at a thirty- to forty-five-degree angle or in a semi-fowler's position. Look for the highest point of pulsation in the internal jugular vein and measure the vertical distance to the angle of Loius or sternal angle. A normal JVP is 3-4 cm above the...

