Indications

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  A reverse pedicled radial forearm flap can be used for acute and chronic soft-tissue reconstruction of the upper limb.

  
  
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  There is no specific age range or time limit for this procedure.

  
  
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  It can be used for coverage of the palm or extensor surface of the carpus, with or without vascularized tendon.

  
  
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  An antegrade flap can be used for coverage of elbow defects. It provides a durable surface for coverage of amputation stumps near the wrist.

Contraindications

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  Underdevelopment of the radial artery or injury to the superficial and deep palmar arches would preclude the use of this flap, as would the absence of a connection between the radial and ulnar arteries.

  
  
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  In a cadaver dissection of 650 cadaver arms, only 3.2% had no communication between the radial and ulnar artery, and 3% had an incomplete deep arch. If both of these variations are present, the thumb will be dependent on the radial artery (~ 1 in 1,100). This can be identified by a preoperative Allen test. Vein graft reconstruction of the radial artery would be necessary in these cases.

  
  
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  Care should be exercised in acute trauma when hematoma extends to the snuffbox.

Examination/Imaging

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  An Allen test with the aid of Doppler ultrasound is needed to assess the patency of the radial artery.

  
  
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  Angiography may be necessary if there is any doubt.

Relevant Anatomy

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  The skin of the forearm flexor surface does not have any truly axial artery. An axial pattern flap is effectively created by raising a flap, including the fascial and subcutaneous vessels with their longitudinal orientation and interconnections.

  
  
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  The entire radial artery from its brachial artery origin to the wrist can be transferred. For most of its course, the radial artery lies under the brachioradialis.

  
  
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  The pronator teres, flexor pollicis longus, and pronator quadratus lie deep to the artery. The superficial radial nerve (SRN) is lateral to the artery under the brachioradialis.

  
  
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  After giving off the radial recurrent artery near its origin, the radial artery has no named branches until it reaches the wrist. Here it gives off a superficial palmar branch and a palmar carpal branch.

  
  
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  One cadaver study demonstrated between 9 and 17 branches from the radial artery to the fascia along the flexor surface of the forearm. The branches supplying the skin are contained in an intermuscular septum between the brachioradialis and the flexor carpi radialis ( Fig. 4.1 ). These branches are arranged into a proximal and distal group, with corresponding zones of perfusion.

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  In the distal half of the forearm, there are branches every 1 to 2 cm. As elsewhere, one vascular zone can be extended into another. The distal zone vessels can perfuse a fasciocutaneous flap as far proximal as the elbow. In a reverse pedicled flap, the skin blood supply is dependent on retrograde flow from the ulnar artery through the deep palmar arch.

  
  
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  Venous drainage of the radial forearm flap is by means of both the superficial and deep veins. There are three subcutaneous veins, including the cephalic, basilic, and median forearm vein, as well as the paired deep venae comitantes of the radial artery.

  
  
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  A reverse pedicled flap is drained by means of retrograde flow through the venae comitantes. Normally, the venous valves prevent backflow. When a distally based flap is raised, the veins are denervated. The veins are kept filled by blood from the wrist and hand, which leads to an increased venous pressure after ligation of their proximal ends. One author postulated that the combination of these factors allows reverse flow through the venous valves.

  
  
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  The SRN, the brachioradialis, flexor carpi radialis, and palmaris longus tendons are each supplied by direct branches and branches off cutaneous vessels.

  
  
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  The medial and lateral antebrachial cutaneous nerves enter the proximal margin of the flap and supply sensibility to the volar forearm.

  
  
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  The radial artery gives off at least two periosteal branches of 0.2 mm to 0.5 mm in size along the lateral aspect of the radius, immediately distal to the pronator teres insertion. These branches are accompanied by two small venae comitantes and pass along the fascial layer deep to the extensores carpi radialis longus and brevis.

  
  
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  Musculoperiosteal vessels form a constant source of blood supply over the anterior aspect of the distal shaft. They are in turn fed by branches of the radial artery supplying the flexor pollicis longus and pronator quadratus.

  
  
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  The skin can be innervated by including the medial or lateral antebrachial cutaneous nerve.

  
  
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  The flap can include the entire volar forearm skin from the subcutaneous border of the ulna around to the radial dorsum of the forearm, extending as far proximal as the antecubital fossa. Forearm flaps as large as 35 × 15 cm have been reported.

Surgical Technique

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  The patient is positioned supine with the arm abducted on an arm board. The surgeon sits facing the volar forearm when harvesting the flap but may switch to the other side when insetting the flap. The procedure is done under brachial block or general anesthesia using loupe magnification, but the operating microscope may be needed for any venous anastomoses or neurorrhaphy. A tourniquet is used for the initial dissection, and the limb is only partially exsanguinated with an Ace wrap rather than an Esmarch bandage to facilitate identification of the vessels.

  
  
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  The courses of the radial artery and the superficial veins are marked. The flap axis is slightly medial to the course of the radial artery.

  
  
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  Using a pattern from the recipient site, outline the size of the defect on the proximal forearm. If the flap is outlined over the proximal ulnar forearm, it will be thinner and less hair-bearing ( Fig. 4.2a–c ).

  
  
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  A thin skin island can be left over the course of the radial artery to prevent the need for skin grafting the pedicle later on and to avoid an overlying skin bridge ( Fig. 4.3 ).

  
  
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  Incise the flap down to the deep fascia. Harvest veins along the proximal medial border of the flap. This allows an easier anastomosis with local veins once the flap has been rotated 180 degrees.

  
  
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  Identify the medial or lateral antebrachial cutaneous nerve, and then make a proximal extensile incision for a longer nerve pedicle ( Fig. 4.4a–c ). The SRN should be protected to preserve sensation to the radial aspect of the hand.

  
  
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  Develop a plane deep to the radial artery at the wrist and find the intermuscular septum between the flexor carpi radialis (FCR) and the brachioradialis. Incise the deep fascia over the FCR muscle belly, well medial to the intermuscular septum.

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  Dissect the interval between the deep fascia and the muscle. Suture the deep fascia to the skin flap to minimize shear on the septocutaneous perforators. Continue the dissection deep to the radial artery on both sides of the septum. The fascia superficial to the radial artery is left undisturbed because it contains the septocutaneous perforators that supply the skin flap ( Fig. 4.5a–e ).

  
  
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  After the flap dissection is complete, apply a micro-vascular clamp to the proximal radial artery prior to releasing the tourniquet. If there is adequate perfusion to the flap and the thumb with the tourniquet deflated, then the artery is divided.

  
  
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  Raise the flap, ligating all the perforators deep to the artery. Transpose the flap to the dorsum of the hand. If desired, perform a venous anastomosis prior to insetting the flap ( Fig. 4.6 ).

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