Lower Extremity

Anatomy of the Lower Extremity Arteries

• Overview of the arterial system in the lower extremity.

Arterial System

• Abdominal aorta

• Common iliac artery

• Internal iliac artery

• External iliac artery

• Common femoral artery

• Deep femoral artery

• Superficial femoral artery

• Popliteal artery

• Anterior tibial artery

• Posterior tibial artery

• Peroneal artery

• Dorsalis pedis artery

Detailed Anatomy

• External iliac artery:

  • Branch from the common iliac artery at the level of the sacroiliac joint.

  • Supplies the lower extremity.

  • Courses inferiorly and is located medial to the psoas muscle.

  • Terminates at the level of the inguinal ligament and becomes the common femoral artery.

• Common femoral artery:

  • Formed at the level of the inguinal ligament.

  • Courses inferiorly in the thigh.

  • Gives rise to two branches:

    • Superficial femoral artery (SFA), also known as the femoral artery.

    • Deep femoral artery (profunda femoris artery).

• Superficial femoral artery (SFA):

  • Courses on the medial aspect of the thigh.

  • On the distal aspect of the thigh, it passes through the adductor canal (Hunter canal) and becomes the popliteal artery.

• Deep femoral artery:

  • Located posterior lateral to the SFA in the thigh.

  • Provides potential collateral circulation when the femoral artery is diseased.

• Popliteal artery:

  • Continuation of the SFA.

  • Gives rise to the gastrocnemius and genicular arteries.

  • Gives two terminal branches: the anterior tibial artery and the tibio-peroneal trunk.

• Anterior tibial artery:

  • Passes through the interosseous membrane toward the anterior aspect of the leg.

  • At the level of the ankle, it becomes the dorsalis pedis artery.

• Tibio-peroneal trunk:

  • Branches into the posterior tibial artery and the peroneal artery.

• Posterior tibial artery:

  • Courses medially in the posterior compartment of the leg.

  • Passes posterior to the medial malleolus.

  • Branches into the medial and lateral plantar arteries.

• Peroneal artery:

  • Courses laterally in the posterior compartment of the leg.

  • Terminates into branches that communicate with the anterior and posterior tibial arteries.

• Plantar arch of the foot:

  • Formed by the merging of the lateral and medial plantar arteries.

  • Gives rise to metatarsal arteries, which terminate in digital arteries.

Duplex Ultrasound of the Lower Extremity

Vessels Evaluated

• Common femoral artery (CFA)

• Superficial femoral artery (SFA)

• Profunda femoris artery (PFA)

• Popliteal artery

• Posterior tibial artery (PTA)

• Anterior tibial artery (ATA)

• Dorsalis pedis artery (DPA)

• Peroneal artery

Normal Duplex Image

• B-mode ultrasound appearance:

  • Arterial wall appears smooth and uniform, with no focal lesion or dilation present.

• Color ultrasound appearance:

  • Normal color flow should completely fill the vessel lumen.

  • Color should be uniform and limited to the lumen only.

  • Abnormal color findings include:

    • Aliasing

    • Reduced flow channel

    • Color bruit

• Spectral Doppler:

  • Used as the primary tool to categorize disease.

  • Peak systolic velocity (PSV) recorded in all major vessels.

  • Triphasic high-resistance spectral waveform (biphasic also considered normal):

    • Sharp upstroke

    • Rapid deceleration

    • Retrograde flow in early diastole

    • Antegrade flow in mid-to-late diastole

Normal Values

• Mean arterial diameters and peak systolic velocities (PSVs):

  • External iliac artery: Diameter = $0.79 \pm 0.13$ cm, PSV = $119 \pm 22$ cm/s

  • Common femoral artery: Diameter = $0.82 \pm 0.14$ cm, PSV = $114 \pm 25$ cm/s

  • Superficial femoral artery (proximal): Diameter = $0.60 \pm 0.12$ cm, PSV = $91 \pm 4$ cm/s

  • Superficial femoral artery (distal): Diameter = $0.54 \pm 0.11$ cm, PSV = $94 \pm 14$ cm/s

  • Popliteal artery: Diameter = $0.52 \pm 0.11$ cm, PSV = $69 \pm 14$ cm/s

Peripheral Arterial Disease

• Atherosclerotic disease:

  • Appearance can be homogenous or heterogeneous.

  • Can be smooth or irregular.

  • Calcifications may be present, creating acoustic shadowing.

• Spectral Doppler Changes:

  • Proximal to stenosis: Spectral Doppler recording will depend on the degree of stenosis.

  • At stenotic site: Increase in velocity.

  • Distal to stenosis: Monophasic dampened waveform (low resistance caused by dilated distal arterioles), increased acceleration time, turbulent flow (post-stenotic turbulence).

• Example Values:

  • Left CFA (proximal to stenosis): Normal velocity (140 cm/s) and high-resistance flow pattern.

  • Left SFA (at stenosis): Elevated velocity (308 cm/s) and a monophasic flow pattern.

  • Left SFA (distal to stenosis): Low velocity (38 cm/s) and lower-resistance monophasic flow pattern.

• Determining Degree of Stenosis:

  • Calculating velocity ratio: PSV at stenosis divided by PSV proximal to stenosis.

  • Normal: Less than 2.0.

  • $PSV \ velocity \ ratio \geq 2.0$ = $\geq 50\%$ stenosis.

  • $PSV \ velocity \ ratio \geq 3.0$ = $\geq 70\%$ stenosis.

Arterial Disease Classification

• Proximal to an Occlusion:

  • Spectral waveform will display a very high-resistance pattern.

  • Antegrade flow component only during systole.

  • No flow during diastole.