Blood Supply of the Forearm

Radial Artery

• Origin: Smaller terminal branch of Brachial Artery.
• Course:
  1. Runs distally on the lateral side of the forearm.
  2. Covered by the belly of Brachioradialis (proximal 2/3).
  3. Becomes superficial in the distal 1/3 (site of palpation/ABG).
  4. Winds around the lateral aspect of the wrist (Anatomical Snuffbox).
• Branches:
  • Radial Recurrent: Ascends to anastomose with Radial Collateral.
  • Muscular: To lateral extensors/flexors.
  • Superficial Palmar Branch: Completes superficial arch.

This artery is the direct continuation of the direction of the brachial artery, though smaller in caliber.

Ulnar Artery

• Origin: Larger terminal branch.
• Course:
  1. Leaves cubital fossa deep to Pronator Teres (Deep head).
  2. Runs obliquely downwards and medially.
  3. Lies on Flexor Digitorum Profundus.
  4. Covered by Flexor Carpi Ulnaris (satellite muscle).
  5. Enters hand via Guyon's Canal.
• Major Branch: Common Interosseous Artery.

The Ulnar artery is the "Workhorse" of the forearm supply.

Common Interosseous Artery

• Origin: Ulnar Artery (just below tuberosity of radius).
• Divisions:
  • Anterior Interosseous Artery (AIA): Runs on the anterior aspect of the interosseous membrane. Supplies deep flexors (FPL/FDP) and nutrients to Radius/Ulna. Pierces the membrane distally to join the dorsal network.
  • Posterior Interosseous Artery (PIA): passes backwards between the radius and ulna (above the interosseous membrane) to supply the extensor compartment.

The AIA is critical in "Volar Compartment Syndrome".

Elbow Anastomosis

Ensures collateral circulation around the joint.

• Radial Recurrent joins Radial Collateral.
• Ulnar Recurrent (Ant/Post) joins Ulnar Collateral (Inf/Sup).
• Interosseous Recurrent joins Middle Collateral.

Clinical Note: This rich network allows ligation of the brachial artery distal to the Profunda in emergency, though not recommended appropriately.

Carpal Arches

• Palmar Carpal Arch: Formed by palmar carpal branches of radial and ulnar. Supplies carpal bones.
• Dorsal Carpal Arch: Formed by dorsal carpal branches. Supplies dorsal wrist.

These arches are smaller than the digital arches (Superficial/Deep Palmar Arches of the hand).

Adachi Types (Radial Artery Origin)

• Type I: Normal (Bifurcation in Cubital Fossa).
• Type II: High Origin from Axillary Artery.
• Type III: High Origin from Brachial Artery.

Remember: High takeoff vessels often run superficial to the fascia ("Brachioradial Artery").

Allen's Test

• Purpose: Assess patency of the Ulnar artery and the Palmar Arch connectivity before harvesting the Radial Artery (ABG or CABG/Flap).
• Steps:
  1. Patient clenches fist (exsanguinate).
  2. Occlude both Radial and Ulnar arteries.
  3. Patient opens hand (should be pale).
  4. Release Ulnar Artery.
• Result:
  • Positive (Normal): Hand flushes within 5-7 seconds.
  • Negative (Abnormal): Hand remains pale (Ulnar supply insufficient).

A negative Allen's test is a contraindication to Radial Artery harvest.

Pulse Palpation

• Radial: Lateral to FCR tendon.
• Ulnar: Lateral to FCU tendon (harder to feel due to overlying fascia).

Only the radial pulse is routinely palpated, but the ulnar pulse is vital in vascular trauma.

Hand-Held Doppler

• Indication: Assessing flow in trauma or pre-harvest.
• Triphasic: Normal flow.
• Monophasic: Indicates proximal stenosis or collateral flow.
• Allen's Confirmation: Audible signal change during compression.

Use a standard 8MHz vascular probe.

CT Angiogram

• Gold Standard for vascular trauma.
• Mapping: Essential for free flap planning (RFFF or ALT perforators).
• Run-off: Assessment of distal vessels (Hand arches).

3D reformats are helpful for surgical planning.

Vascular Injury Management

Radial Forearm Free Flap (RFFF)

• Type: Fasciocutaneous flap (Type B).
• Supply: Septocutaneous perforators from Radial Artery.
• Anatomy:
  • Passes in the septum between Brachioradialis and FCR.
  • Venous drainage is via the Venae Comitantes or Cephalic Vein.
• Harvest: Raises the artery with the flap. Requires confirming Ulnar competency (Allen's Test).

This is the "Workhorse" flap for Head and Neck reconstruction.

Volar Approach (Henry)

• Interval: Between Brachioradialis (Radial Nerve) and Pronator Teres/FCR (Median Nerve).
• Vessel at Risk: Radial Artery.
• Branches: The "Recurrent Leash" of vessels (Recurrent Radial) must be ligated proximally to mobilize the muscle belly laterally.

Failure to ligate these vessels results in troublesome bleeding and obscured view.