Radial Forearm and Rectus Abdominis Free Flaps in Reconstruction
SOURCE: UTMB, Grand Rounds Presentation
DATE: October 14, 1998
RESIDENT PHYSICIAN: Ravi Pachigolla, MD
FACULTY: Anna Pou, MD
SERIES EDITOR: Francis Quinn, MD
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"This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."
Over the past two decades, there has been a steady advance in the available surgical techniques for reconstruction of head and neck defects. Prior to this time, efforts had mostly included defects that were closed with local tissues or with random pattern skin flaps that were pedicled and transferred to the head and neck region in long, tedious staged procedures. Panje and colleagues first published use of a free cutaneous flap for use in head and neck reconstruction in 1976. He used a groin flap for this purpose. From this point on, the evolution of free cutaneous flaps continued. By the late 1970s, microvascular transfer of free flaps to the head and neck region had become commonplace but the technique did not capture widespread support due to the advent of pedicled myocutaneous flaps. The free flaps designed thus far had pedicles that were relatively short or vessels with small diameters, not entirely suitable for head and neck reconstruction. During this period, pedicled musculocutaneous flaps dominated while efforts were continuing in finding better and more reliable free flaps. The Chinese surgeons Yang and colleagues described the radial forearm fasciocutaneous flap as early as 1981 with subsequent introduction of the rectus abdominis muscular and musculocutaneous free flaps.
Patient selection is important in determining whether a particular patient is a candidate for free tissue transfer. Advanced age alone does not contraindicate free tissue transfer but aging may be associated with diabetes mellitus, hypercholesterolemia, and arteriosclerosis which may result in thickening of the walls of small arteries and overall increased vessel fragility. Generally, patients with blood coagulopathies, collagen vascular diseases, and other vascular disorders are not candidates for free tissue transfer. Malnutrition presents a problem because patients are at risk for wound healing problems including flap failure. Prior irradiation can lead to decreased patency of vessels and poorer tissue survival rates. Irradiation leads to loss of smooth muscle, vessel fibrosis and endothelial cell disruption.
RADIAL FOREARM FREE FLAP
The radial forearm flap is supplied by the radial artery and venous drainage is provided by the paired vena comitantes (deep venous system) which accompany the artery as well as the various subcutaneous veins of the forearm including the cephalic vein. The radial artery arises from the brachial artery just distal to the antecubital fossa and travels between the brachioradialis and flexor carpi radialis as it runs distally in the forearm. It runs in the lateral intermuscular septum which separates the flexor and extensor compartments of the forearm. It supplies the skin over the volar aspect of the forearm from elbow to wrist as well as portions of the radius. Generally, the skin is thin, pliable, and usually hairless while the vascular pedicle may be up to 18 cm in length and the vessel diameters are usually large (2 - 4 mm). Medial and lateral antebrachial cutaneous nerves can also be made part of this flap (the lateral antebrachial cutaneous nerve is the primary sensory nerve to the forearm) and is most commonly used to create a sensate flap.
Preoperative evaluation includes examination of the forearm to see where a hairless skin paddle can be taken (generally the skin paddle can be taken anywhere along the length of the pedicle). An Allen test should be performed with compression of the radial artery to insure collateral circulation via the ulnar artery. Both radial and ulnar arteries are occluded and the patient raises their hand over their heads and opens and closes their palm to exsanguinate their blood. Then the hand is brought down to a neutral position and the ulnar pulse is released and blood should flow into the thenar area. Venipuncture should not be performed on the on the forearm that is being harvested. Any evidence of intravenous drug abuse or evidence of allen test failure should preclude a radial free flap even though interpositional vein grafts have been described for the radial artery. Defects should be handled that can be managed with the thin pliable skin of the forearm which allows not necessarily bulk to any particular defect but permits mobility of the underlying structures and draping. This flap is ideally designed for this purpose.
The vascular pedicle can be easily identified and marked before flap elevation because of its subcutaneous location. The flap should be designed such that the skin paddle overlies the distal radial artery although any island of skin over the volar aspect of the forearm may be designed because of the numerous muscular perforators. Islands may be created to allow for two skin paddles. The arm is exsanguinated and a tourniquet is inflated to about 70 to 90 mm Hg greater than the patients systolic blood pressure. The flap is first incised along the ulnar border down to fascia and a subfascial dissection is begun heading radially towards the flexor carpi radialis tendon. Preserve paratenon over this tendon to allow skin graft take. The distal flap is then incised and the brachial artery and paired vena comitantes are isolated. The two venae comitantes are ligated and divided while the radial artery may be divided and a microvascular clamp applied distally. Then the radial margin of the flap is incised down to brachioradialis with care to preserve the small branches of the superficial portion of the radial nerve which allows postoperative sensation to the anatomical snuffbox. Working from distal to proximal, the surgeon should be able to visualize the lateral intermuscular septum and vascular pedicle separating the flexor and extensor compartments of the wrist. Continue to develop this plane between the brachioradialis and flexor carpi radialis and the vascular pedicle may be followed to the bifurcation of the radial artery just distal to the antecubital fossa. The proximal vascular pedicle is isolated with vascular loops. The microvascular clamp may be released at this point with reveals retrograde flow through the radial artery indicating palm perfusion. Important in this dissection is a relatively bloodless dissection with warm irrigant and precise handling of the vessels to prevent thrombus formation. When the recipient site is prepared, the flap may be transferred with an ischemia window of about 6 hours. Donor site care may include removal of the palmaris longus (the palmaris is absent in about 14% of patients) and imbrication of the flexor carpi tendon to allow for a smooth bed to receive a skin graft. The donor site defect may be reduced by attaching skin edges to the muscle. A thick split thickness skin graft is applied (0.018 in) over defect and the wrist placed in a plaster splint kept in place for 5 to 7 days. The wrist should be kept slightly extended with fingers in their functional position. The flap itself is usually insetted prior to microvascular anastomosis. Microvascular anastomosis occurs in the usual fashion of donor vein being connected to recipient vein (usually internal jugular) in an end to side fashion and arterial connection in an end to end connection to any of the branches of the external carotid. Postoperatively, antibiotics may be given for 5 to 7 days and low molecular weight dextran at 25 cc/hr to decrease vascular occlusion. The viability of the flap should be monitored with doppler pencil probe every 1 to 2 hours for the first 72 hours. Alternatively, pricking the flap can also be performed which should reveal a slow egress of bright red blood. Any deviation from normal should prompt a thorough search for vascular occlusion including taking the patient back to the operating room to investigate the anastomosis. The splint may be removed on day seven and a resting splint kept in place for the next several days. Range of motion exercises can be begun for the wrist to prevent scar contracture and decreased motion of the wrist. Whether to use a single or dual system of venous drainage from the radial forearm free flap remains a topic of controversy. Arguments exist on both sides that including the relatively larger diameter subcutaneous veins (cephalic and basilic) would presumably decrease venous congestion and lead to increased flap survival but these veins have more anatomic variability than their venae comitantes counterparts. Also, some studies have shown that despite including multiple venous anastomoses, this does not persay increase flap survival with the added cost of increased operative time and morbidity. Also, to include dissection until the venae and superficial veins communicate with each other into a common vein is not entirely practical. Sometimes, these connections do not occur until quite proximal making this pedicle extremely long and unweildy. The dissection sometimes has to proceed dorsolaterally over the upper arm in order to reach this connection. Basically, sound surgical technique, precise microvascular anastomosis, strict postoperative monitoring prevent flap failure more than multiple anastomoses.
ADVANTAGES AND DISADVANTAGES
The significant advantage of this flap is its consistent arterial anatomy and long vascular pedicle with large diameter vessels which facilitate microsurgical anastomoses. The skin paddle as mentioned earlier is thin, usually hairless and quite flexible in placement into defects where bulk is not required. It may be tubed for pharyngoesophageal reconstruction and the medial and lateral antebrachial cutaneous nerves (particularly the lateral) provide the ability for a sensate flap. A two team approach may be used since the flap is distant to the operative site. Disadvantages are usually minor and involve scarring over the forearm especially if the skin graft extends radially. Occasional ischemic hands may be encountered although the Allen test preoperatively will document any untoward events. Even this test is not 100% accurate though. Also, slight decrease in wrist range of motion, strength and sensation can sometimes occur although with proper physical therapy and preservation of nerves to the anatomic snuffbox, this is not usually a problem. Donor site skin graft take should approximate 100% although if paratenons over the flexor carpi radialis tendon are not preserved, skin graft take may decrease over a dry tendon. Treatment with moist dressing changes allows this to re-epithelialize in time.
RECTUS ABDOMINIS FREE FLAP
The rectus abdominis muscles are paired, vertically oriented muscles that arise from the symphysis pubis and pubic crest and insert into the fifth through seventh costal cartilages. The three fascial layers of the abdominal wall join to form the posterior and anterior rectus sheaths. Above the costal margin, the anterior sheath is formed by the external oblique aponeurosis and no posterior sheath exists so the anterior sheath and deep surface of the muscle directly opposes the costal cartilages. Between the costal margin and arcuate line which usually lies at the anterosuperior iliac spine, the anterior sheath is composed of the external oblique and portions of the internal oblique aponeurosis. The posterior sheath in this region is formed by the the remaining portions of the internal oblique aponeurosis and the transversus abdominis. Below the arcuate line, the anterior sheath is composed of fascial extensions of all three layers. Below this line, no posterior sheath exists and only the transversalis fascia separates the peritoneal cavity from the muscle. The arcuate line assumes importance in donor site closure. Other important anatomic landmarks include the linea alba which is the condensation of fascia that forms the midline between the paired rectus muscles and the linea semilunaris which marks the lateral extent of the rectus muscles. Finally, there are between two to seven tendinous inscriptions that are located at regular intervals that adhere the anterior rectus sheath firmly to the underlying rectus. The deep inferior epigastric artery arises from the medial aspect of the external iliac artery and passes upward lateral to the rectus about 3 to 4 cm below the arcuate line and then above the arcuate line is where the major muscular perforators arise. The superior and inferior epigastric vessels anastomose above the umbilicus through intricate connections and this area is referred to as the watershed area. Most of the large perforators supplying the skin are found in the paraumbilical region. These paraumbilical perforators send out a wide array of vessels which permits safe transfer of skin on either side of the rectus. The dominant orientation is 45 degrees from the horizontal in an upward and lateral direction extending toward the scapula.
Factors used in the assessment of whether to use a rectus abdominis free flap are similar to those involved in the decision to use a radial forearm free flap. Additional criteria that warrants close attention in rectus free flaps is prior history of abdominal surgery and in particular whether the vascular pedicle was ligated thus preventing its use. Also obesity may contraindicate flap usage to the extreme bulk of the flap although defatting may be performed at the time of surgery. Due to the rich subdermal vascular plexus, defatting may be performed.
The primary considerations in designing a rectus abdominis free flap are the size, shape, vascularity, and thickness of tissue that is to be transferred. This flap can be harvested as a muscular flap, myofascial or muculocutaneous flap. If a thick flap is needed, a vertically oriented segment of skin overlying the rectus may be harvested but if thinness is desirable, the muscle componenent can be limited to a small paraumbilical cuff which allows capture of the dominant perforators. Most commonly the flap is designed with a skin island lateral to the rectus in a 45 degree fashion and this skin may be harvested to the ipsilateral midaxillary line and the contralateral semilunaris. A two team surgical approach may be used in elevating the flap. The flap is harvested through a midline or paramedian incision. A paramedian incision is used when a muscle only flap is designed. The skin, subcutaneous tissue and anterior rectus sheath are incised along the entire length and from superior to inferior where the rectus muscle is elevated after detachment of the anterior rectus sheath. When designed as a myocutaneous flap with a vertically oriented skin paddle, the paddle is outlined in the periumbilical area overlying the muscle and above the arcuate line. The skin paddle is incised down to and through the anterior layer of the rectus sheath. From the inferior aspect of the paddle, an incision is made through the skin, subcutaneous tissue, and the anterior layer of the rectus sheath. Then the muscle, with its overlying skin paddle, is elevated out of the rectus sheath after transection of the superior-most aspect of the muscle flap. The vascular pedicle is again dissected to the external iliac vessels. The obliquely designed skin paddle is outlined with its base again in the paraumbilical area. The skin paddle is incised down through the anterior rectus sheath except laterally where a fasciocutaneous flap is elevated to the lateral border of the rectus. Here, anterior rectus sheath may be incised vertically and the flap may be elevated as previously described. The pedicle is easily located at the lateral margin of the muscle below the arcuate line where it lies in the adipose tissue. It is identified and traced to its origin from the external iliac artery and a pedicle can be up to 10 cm in length. The pedicle is divided and after analysis of the defect, the deep portion of the flap is inset first which stabilizes the flap. Repair of the anterior rectus fascia is essential especially below the arcuate line to prevent ventral hernia formation. Some authors use synthetic mesh to reconstitute the fascia but many simply suture the anterior fascia below the arcuate line to the posterior fascia above the arcuate line. Also, the anterior fascia above the arcuate line may be reapproximated. Generally, all fascia should be left behind except that immediately underneath the skin paddle. Skin grafting is not usually necessary if sufficient undermining has been performed. A suction drain is placed above the fascia.
Advantages of the rectus free flap include the fact that a two team approach may be used in surgery. This free flap probably allows for the greatest bulk of tissue and the largest skin paddle of all free flaps. Flap elevation is relatively easy and it is quite versatile in head and neck reconstruction. Separate skin islands may be based on a single pedicle to allow for closure of full thickness defects. The tendinous inscriptions allow for tight closure at recipient sites. The vascular pedicle is lengthy and of a large diameter that permits microvascular anastomosis. By varying the amount of muscle in the flap, it can be made thicker or thinner depending on what is required. Additionally, the rich vascularity of abdominal wall skin permits flexibility in skin paddle design. Generally donor site morbidity is minimal.
Disadvantages include the fact that sometimes the flap is too bulky however this can also be managed by defatting and only using paraumbilical rectus muscle. Ventral hernia formation can occasionally occur but that may be due to technical error. Abdominal weakness has generally not been appreciated but the risk nonetheless exists. Color match is not ideal for the face and sensation is absent in this flap.
Recipient sites for these flaps are numerous throughout the head and neck region but some generalizations can be drawn. Where bulk is necessary along with precise anatomic contouring for large head and neck and cranial base defects, the rectus flap may be used. The rectus flap is particularly useful in orbitomaxillary defects and in total glossectomy defects. In cranial base surgery the most important aspect of reconstruction is to seal the intradural space from the extradural space. The rectus provides an ideal barrier of well vascularized tissue to prevent cerebrospinal fluid leak. Pedicled flaps may be tethered with a long reach to the cranial base and the distal portions of these flaps are often in the most crucial areas thus the need for rectus free flaps. Oncologic surveillance may be difficult with the bulk of a rectus flap but with sophisticated imaging, this is not a major concern. Also for large oromandibular defects involving tongue, retrmolar trigone and soft palate defects, the rectus flap also may be used since it maintains its bulk over time above the level of the fascia. The radial forearm free flap has become the preferred choice for reconstruction involving the anterior and lateral floor of mouth, the buccal mucosa, retromolar trigone, pharynx and partial tongue defects. With partial tongue defects and some hypopharyngeal and pharngeal defects after laryngectomy and partial pharyngectomy, the radial forearm free flap may be used as it is extremely thin, pliable and provides the potential for sensate flap possibly decreasing aspiration. Particularly for partial tongue, floor of mouth and other oral cavity defects, the ability of the thin radial forearm flap to contour allows easier speech, deglutition and helps with other functional disabilities. By no means does it allow the tongue normal mobility, but it allows for bolus propulsion from the normal oromandibular structures left behind.
SUMMARY AND CONCLUSION
In summary, the radial forearm and rectus free flaps both provide reliable, workhorse flaps in the management of reconstructive defects. These flaps complement each other in use in reconstruction but both have proven to be effective, safe and reliable with relative safety to the donor sites. A wide array of head and neck defects can be effectively dealt with due to the advent of these flaps.
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