Abductor Digiti Minimi Flap for Vascularized Coverage Following Recurrent Carpal Tunnel Syndrome
Peter S. Vezeridis, MD, James T. Monica, MD, Nata Parnes, MD, Jesse B. Jupiter, MD
Massachusetts General Hospital
Hand and Upper Extremity Service
Carpal tunnel syndrome is the most common entrapment neuropathy with an estimated incidence ranging from 0.1% to 10% [1,2]. Carpal tunnel release (CTR) is one of the most common procedures performed by the orthopaedic surgeon, often with good results. However, as many as 14 to 32% of patients have persistent symptoms following CTR [3,4]. The incidence of symptoms following secondary surgery ranges from 25% to as high as 95% [5,6]. Moreover, chronic regional pain syndrome (CRPS) is a known complication of CTR [7,8].
Neurolysis for recurrent carpal tunnel syndrome may not be sufficient to prevent new scar formation or to relieve allodynia and hyperesthesia. Therefore, interposition of well-vascularized soft tissue may be necessary in order to successfully treat cases of recurrent carpal tunnel syndrome. Several techniques have been described to provide increased soft tissue coverage in repeat CTR. These include local fat grafting, intrinsic muscle flap, abductor digiti minimi (ADM) flap, sublimis turn down, pronator quadratus muscle flap, fascial or fasciocutaneous flaps, synovial tissue transposition, and vein wrapping [9-18]. Each technique has unique advantages and disadvantages that guide the decision to utilize a specific method.
The ADM flap in particular has several significant advantages over other soft tissue coverage procedures in treating recurrent carpal tunnel syndrome. In the present correspondence we describe the use of the ADM flap to provide adequate soft tissue coverage around the median nerve during revision surgery to address recurrent CTS, especially in the setting of (CRPS).
The surgical technique is similar to the approach originally described in 1921 by Huber . A volar incision is made starting along the distal forearm over the median nerve and then traced over the prior incision (Figure 1). The incision can be extended distally to the ulnar aspect of the small finger and proximally past the transverse carpal ligament to the volar skin of the forearm. The skin and subcutaneous tissues are incised, taking care to identify and protect all viable surrounding structures. The median nerve is identified, and median neurolysis is performed (Figure 2). A microscope or loupe magnification is used for neurolysis if necessary. Next, attention is turned to the hypothenar musculature. The ADM is identified (Figure 3), and this muscle is dissected and elevated while maintaining the proximal pedicle (Figure 4). Elevation is begun distally, and the muscle is split so as to take only half of the muscle mass. Dissection is carried proximal to the area of pedicle. The ADM is mobilized to provide soft tissue coverage over the median nerve. Once in place, the muscle is sutured to the radial aspect of the transverse carpal ligament (Figures 5 and 6). The skin and subcutaneous tissues are closed in layers in the usual fashion.
From 1996 to 2009, 11 patients (12 cases) with recurrent carpal tunnel syndrome were treated with repeat carpal tunnel release and ADM flap by the senior author (JBJ). Two patients had preoperative CRPS. One patient with bilateral CTR experienced profound pain and CRPS. A post-index surgery EMG testing was normal bilaterally. The second patient with CRPS had EMG evidence of CTS prior to index CTR and did not have repeat EMG testing after index CTR. All patients treated with ADM flaps for recurrent CTR healed without complication. Neurolysis was performed using microscopic magnification in two patients and using loupe magnification in one patient. Seven patients were available at mean follow-up of two years and nine months. Two cases rated improvement as excellent, and five cases rated improvement as good. All patients stated that if given the choice they would have the surgery again. The average postoperative Quick DASH score was 29.7 (range 2.3 – 65.1). When asked specifically about the function of the small finger, no patients reported any complaints.
The ADM flap was first described by Huber as a transfer for thumb opposition . Milward et al. originally described the application of an ADM flap for use in the cases of recurrent nerve compression in 1977 . This study described one patient treated successfully with the ADM flap technique for median and ulnar nerve compression after failed decompression and internal and external neurolysis . Leslie and Ruby have also applied the ADM flap for coverage of an infected wound dehiscence following carpal tunnel release . In their case report, the authors describe the use of the ADM flap for infected wound dehiscence in a 41 year-old man taking prednisone for dermatomyositis.
The ADM flap has also been used in the treatment of carpal bone osteomyelitis  and in the treatment of recalcitrant pain due to volar wrist injury or surgery . Reisman found the ADM flap to be particularly effective when implanting a transected nerve into the flap to prevent neuroma formation . The ADM may also be used as a musculocutaneous island flap for opponens transfer .
The ADM has a number of advantages that make it a good choice to provide soft tissue coverage of the median nerve. One advantage is that vascular muscle is utilized for coverage. Another appealing characteristic is its minimal donor site deficit. Additional advantages to the ADM include its predictable anatomy, its compact neurovascular bundle, and the ability to utilize this flap distal to the wrist crease . In a cadaver study, Spokevicius and Kleinert describe a technique to harvest the ADM flap along with a small skin island from the hypothenar eminence, thus enabling direct closure of the skin following ADM transposition. The authors state that this skin island is much smaller than others previously reported . Potential disadvantages to use of this technique include risk of taking donor muscle and issues stemming from the palmar incision. In our experience, no patients have reported significant difficulties related to the donor muscle site, and no significant complications have arisen related to the palmar incision. The ADM flap is a useful technique to provide adequate soft tissue coverage with minimal donor site morbidity in patients with recurrent carpal tunnel syndrome and may be of particular interest in patients with CRPS.
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