The gracilis muscle: A versatile muscle for the colorectal surgeon

Dear Editor The gracilis muscle is a long, thin muscle in the medial compartment of the thigh which is a part of the medial hamstring group that provides rotational stability to the knee [1]. The gracilis muscle has a unique arrangement of muscle fibres in 5– 7 spiral bundles as each bundle has nerve branches, implying multifocal neuromuscular compartment functioning [2]. The main innervation of the gracilis muscle derives from the anterior branch of the obturator nerve whereas the blood supply is from multiple arteries, including the medial circumflex femoral, superficial and deep femoral, descending genicular, and obturator arteries [3]. The gracilis muscle is commonly harvested and used as a ligament for reconstruction, including anterior cruciate ligament reconstruction, restoration of muscular functioning of digits facial palsy, and brachial plexus injuries [4]. Furthermore, since the gracilis muscle has a single easily identifiable proximal neurovascular pedicle, it can be used as a free flap to repair perineal and pelvic wounds and complex fistulas [5]. The versatility of the gracilis muscle may be attributable to the independent neuromuscular compartments and the proximal location of the single main neurovascular pedicle [3]. The main indications for the gracilis muscle in colorectal surgery are the treatment of intractable faecal incontinence (FI), repair of complex perineal fistulas, and reconstruction of pelvic and perineal defects. The use of the gracilis muscle can be employed as a adynamic or dynamic approach in the treatment of FI. The latter method entails the implantation of stimulating electrodes and a pulse generator to replace the voluntary contraction with a sustained contraction, converting the type II fatigueprone fibres of the gracilis into type I fatigueresistant fibres [6, 7]. In a recent metaanalysis of 14 studies, including 450 patients, dynamic and adynamic graciloplasty achieved similar success as the pooled rates of continence after both techniques were similar (69.1% vs. 71%). However, while dynamic graciloplasty had a lower rate of shortterm complications, it was associated with a much higher rate of longterm complications (59.4% vs. 30%), as compared to adynamic graciloplasty [8]. The findings of this collective study attest that adynamic graciloplasty, having similar success and less longterm morbidity, has a role in the management of intractable FI. The use of gracilis muscle to restore continence after proctectomy was also examined. A caseseries study [9] investigated the use of adynamic bilateral graciloplasty to create a continent perineal colostomy after abdominoperineal resection (APR) with ‘S'trap arrangement of the colon in 42 patients. Approximately 81% of patients could hold more than 1 L of saline and only eight patients experienced occasional nocturnal soiling. Another promising and documented indication for the gracilis muscle is the repair of complex perineal fistulas [10– 12]. A metaanalysis of 25 studies, spanning a 20year period, reported a pooled rate of success of the gracilis interposition procedure of 79.4% while the pooled rates of shortterm complications and 30day reoperation were 25.7% and 3.6%, respectively [13]. Half of the fistulas were rectovaginal and onethird were rectourethral, both types constitute a unique management challenge. Having a pooled success rate of approximately 80%, gracilis muscle interposition should be considered a useful tool used for complex fistulas. Gracilis muscle interposition also proved safe and feasible as redo procedure for recurrent complex fistulas [14]. A further indication for the gracilis muscle in colorectal surgery is in the immediate reconstruction of the perineal wound after APR. One study [15] found immediate pelvic reconstruction with gracilis myocutaneous flap after APR or pelvic exenteration and irradiation for recurrent rectal cancer was followed by fewer major complications (12% vs. 46%) as compared to primary closure. A more recent study [16] assessed the use of bilateral gracilis muscle flaps in pelvic reconstruction in 50 patients who underwent extralevator APR. Complete perineal wound healing was achieved in 86% of patients at 2 years of followup and donorsite and reconstructedsite complications were recorded in 14% and 22% of patients, respectively. Despite its remarkable versatility, the gracilis muscle also has several limitations that should be considered. The small muscle bulk of gracilis muscle may preclude its use in filling largesize defects and may limit its ability to exert enough pressure to achieve satisfactory continence, particularly in patients with small or atrophied muscle mass. The lack of direct perforators and short pedicle may limit the excursion of the flap into the pelvis and compromise the reliability of skin paddle perfusion [17]. In conclusion, the satisfactory outcomes in restoration of continence, healing of fistulas, and closure of gracilis muscle are compelling. Thus, the gracilis muscle transfer should be considered for the treatment of complex fistulas, perineal wounds, and FI. Moreover, the relatively low morbidity of gracilis muscle is appealing.