Use of Reverse Radial Forearm Fascial Flap for Median Nerve Coverage

Fig. 20.1

Outline of radial artery and the perforators as identified by ultrasound

For revision carpal tunnel cases, the incision will begin at the site of the previous scar. Perform a carpal tunnel release, ensuring the median nerve is circumferentially freed from any tethering or compressive structures. Debride scar tissue as necessary, taking care not to injure any important adjacent structures. To proceed with the flap, the incision is then extended, directed radially past the wrist crease to the level of the mid-forearm, where it then proceeds longitudinally along the axis of the forearm to within a few centimeters of the elbow crease (Fig. 20.2). Elevate the skin with care not to denude the undersurface completely of fat (Fig. 20.3). Next, develop the flap by elevating the fat and deep fascia overlying the forearm flexors. Make two longitudinal incisions, centered over the intermuscular interval of the FCR and brachioradialis. That is, 2 cm on either side making the flap approximately 4 cm in width. Keep the fat and fascia together to preserve the small perforating vessels (Fig. 20.4). Recall that most of these will be clustered at the proximal third and distal fifth of the forearm [5]. Proximal perforators should be ligated as necessary to ensure flap can be rotated; the distal perforators will maintain the vascularity of the flap. Preserve the lateral antebrachial cutaneous nerve proximally when transecting the flap which will be approximately 5 cm in length. Form the rectangular flap by transecting it proximally so that it remains attached distally. Once the flap is elevated, this distal end is turned 180 degrees toward the median nerve (Fig. 20.5). Ensure that the pivot point is proximal enough so as not to cause any kinks in the flap; this will be at least 4 cm from the radial styloid [13]. The flap should also be twisted such that the fascia is now superficial and the fat is in direct contact with the nerve. Envelop the nerve within the fascia for the full length afforded by the flap, extending both proximally and distally into the palm. Range the wrist to ensure sufficient laxity prior to suturing. The nerve should move freely within the newly created gliding interface. The flap should be sutured in place with fine absorbable sutures. The tourniquet is released at this point to confirm viability of the flap. The incision is then sutured over the flap with a standard skin closure.

Whether ligation of the cephalic vein is necessary or not remains in question. One may ligate it at the beginning or choose to wait until the tourniquet is down to observe the degree of congestion if any [3].
Remember to preserve both the lateral antebrachial cutaneous nerve proximally and the superficial radial nerve distally.
Both the lateral antebrachial cutaneous nerve and the radial sensory nerve may have small branches transected during the procedure. Every effort should be made to be aware of these and bury them within the adjacent muscles to prevent neuromas and skin sensitivity [14].
Obese patients may have larger amounts of fat. In these cases, leave a larger layer of subcutaneous fat attached to the dermis as the skin flaps are elevated. If the final flap is too bulky, trimming should occur on the fat side since the perforators are running along the fascia [13].
A drain may be placed at the surgeon’s discretion.
Postoperative splinting with bulky dressings is recommended for wound protection.

Fig. 20.2

The forearm marked out with the incision and dissection margin

Fig. 20.3

Skin flaps elevated and fascial flap measured and outlined with a marker

Fig. 20.4

Fascial flap elevated with radial perforators preserved

Fig. 20.5

Rotation of the fascial flap into the carpal canal to cover the median nerve

Clinical Results

The need for soft tissue coverage in treating persistent or recurrent median nerve symptoms depends largely on the intraoperative findings at the second operation. If the pathology is found to be due to incomplete release of the transverse carpal ligament distally or the antebrachial fascia proximally, or palmar subluxation of the median nerve, then it is not clear that soft tissue coverage would be beneficial. Interposition of a biological barrier between the median nerve and its surroundings is indicated in those situations where the postsurgical environment is the problem, namely, excessive scar tissue. Compression or tethering of the nerve by this fibrosis and adhesions around the nerve could potentially be avoided by wrapping the nerve in vascularized tissue that will provide a smooth gliding environment for the nerve [15].

Other procedures have been developed and employed for soft tissue envelopment of the median nerve . Two examples that have been successfully applied include the hypothenar fat pad flap [16, 17], the abductor digiti minimi flap [18]. A retrospective study looking at 28 patients undergoing microneurolysis and hypothenar fat pad flap coverage for recurrent carpal tunnel syndrome demonstrated positive outcomes with improved postoperative grip strength and decreased pain levels [15]. However, re-exploration of the carpal canal in these patients will often show fibrosis extending proximally up to the antebrachial fascia. In these cases, more tissue than what is generally available with a hypothenar fat pad would be required to completely isolate the median nerve. Some of the disadvantages of these methods include limited arc of rotation, size limitations in terms of shaping the bulk and area of the flap. Some of these studies also mention the technical challenges with these procedures.

With regard to the radial forearm flap , the perforator-based flap was developed in an attempt to spare the radial artery and create an easily customized adipofascial flap in terms of size and shape . This perforator-based flap has been successfully applied to tendons in recurrent De Quervain’s syndrome [19] where fibrosis within the first dorsal compartment rendered simple surgical decompressions futile. Whether harvested on its own or with the overlying cutaneous tissue, a number of case reports and case series have demonstrated its utility in obtaining soft tissue coverage of both palmar and dorsal defects in the hand [10, 14, 20–23]. It has shown success with nerve coverage as well.

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