Phalloplasty is one of the most complex procedures in plastic surgery. The criteria for an ideal neophallus include an aesthetic and erogenous phallus that allows for sexual intercourse, with a functional neo-urethra enabling standing urination. The free forearm flap has become the gold standard for phallic reconstruction. Various modifications have been made to improve vascularization and reduce urinary complications, such as fistulas and urethral stenosis. Each design has its advantages and disadvantages, with the goal of minimizing functional and aesthetic sequelae in the donor area while achieving the most satisfactory result in the recipient area. Over the years, several prominent surgeons have proposed different forearm flap designs, always with the aim of improving outcomes and patient satisfaction.

La phalloplastie est l’une des procédures les plus complexes en chirurgie plastique. Les critères d’un néo-phallus idéal incluent un phallus esthétique et érogène, autorisant les rapports sexuels, avec un néo-urètre fonctionnel permettant la miction en position debout. Le lambeau libre de l’avant-bras est devenu le gold standard pour la reconstruction phallique. Diverses modifications ont été apportées pour améliorer la vascularisation et réduire les complications urinaires, telles que les fistules et les sténoses urétrales. Chaque dessin a ses avantages et ses inconvénients, avec pour objectif de limiter les séquelles fonctionnelles et esthétiques de la zone donneuse, tout en obtenant un résultat le plus satisfaisant possible au niveau de la zone receveuse. Au fil des années, plusieurs grands chirurgiens ont proposé différents schémas de lambeaux de l’avant-bras, toujours dans un but d’améliorer les résultats et la satisfaction des patients.

# Introduction

Phalloplasty is one of the most challenging procedures in plastic surgery. In 1993, Hage and De Graaf attempted to describe an ideal neophallus as one that can be reproduced in a single step, that is aesthetically pleasing, with tactile and erogenous sensation, that has a functional neo-urethra allowing urination in a standing position, with minimal complications and morbidity at the donor site, and that allows for penetrative sexual intercourse [1].

More than 98% of trans men seeking gender-affirming surgical interventions indicate that urinating in a standing position is an important goal [2].

Although various surgical techniques are available to construct a functional and aesthetic neophallus, none yet meet all the stated objectives, and only a discussion of the patient's needs and expectations allows for an informed decision.

The emergence of various phalloplasty techniques has followed the evolution of flaps themselves. Initially, random pedicled skin flaps were used. Then, pedicled island flaps and myocutaneous flaps were introduced. With the advent of microsurgery, free flaps developed, particulary the radial forearm free flap. The flap remains a mainstay in 21st-century phallic reconstruction. The initial “tube in tube” design by Chang and Hwang has undergone numerous modifications to address various existing complications (fistula, meatal and anastomotic urethral stenosis) [3].

The flap offers the advantages of sensitivity and the inclusion of a vascularized urethra. Although excellent results have been achieved with the use of this flap among Orientals, in non-Oriental populations, the forearm tends to be bulkier and more hirsute, leading to complications: distancing the urethral part of the flap from its arterial pedicle results in a higher incidence of urethral complications. Therefore, modifications have been made to center the urethral part of the flap on the central arterial distribution.

Some techniques include designs to improve blood supply to limit necrosis (Biemer flap), others to eliminate the circumferential meatal suture line to reduce the risk of stenosis (Gottlieb flap). The aim of this article is to present the various designs known to date for phallic reconstruction using a forearm flap, with their respective advantages and disadvantages.

# History of the free radial forearm flap

Initially developed in 1978 by Chinese surgeons at the Military Hospital of Shenyang for the correction of severe burn contractures of the neck, it was described in a Chinese medical journal in 1981 by Yang [4] (Fig. 1
                     ). In 1982, Song in Beijing and Muhlbauer popularized it in the West [5,6]. In 1984, Chang and Hwang, as well as Kao, independently described the same “tube in tube” concept in a single stage using the free radial forearm flap in phalloplasty [7,8].

# Theories on urinary complications

The components of the neophallus urethra can be divided into distinct segments: the native urethra, the fixed urethra (pars fixa), the pendulous urethra (pars pendulans), and the urethral meatus. Complications such as strictures and/or fistulas occur predominantly at the anastomotic zones between the native urethra and the fixed urethra, as well as between the fixed urethra and the pendulous urethra (referred to as the anastomotic urethra) [9].

A large series reported that 41% of strictures occur in the anastomotic urethra between the pars fixa and the pars pendulans, 28% in the phallic urethra, 15% at the meatus, 13% in the fixed urethra, and 8% in multiple urethral segments [10].

Therefore, additional support with vascularized tissue is preferred in all cases [11].

Typically, the type of phalloplasty performed determines the type of urethral reconstruction.

Urethral fistulas and stenosis are the two main complications encountered in patients who have undergone total phallic reconstruction.

Many authors have hypothesized that these urinary complications result from inadequate vascular supply to the neo-urethra [12–14]. The most common urethral complication is the development of a urethral fistula, which occurs in 22 to 75% of cases. Fistulas are primarily urethro-cutaneous. They can occur anywhere along the urethral path, although the risk is higher at the sites of anastomosis between different portions of the urethra. The anastomosis between the fixed urethra and the phallic urethra is the most common site for a fistula. The second most frequent urethral complication is stenosis, occurring in 12 to 50% of cases. Stenoses most commonly occur at the anastomotic site.

The majority of urethral stenosis are associated with fistulas. Indeed, stenosis causes increased pressure, leading to fistulization. Forty percent of patients develop both fistulas and stenosis, with the fistula usually being proximal to the stenosis. The anastomosis between the fixed and phallic parts of the urethra is the most exposed to stenosis [9]. It is also the most prone to fistulas. Most of these fistulas close spontaneously, but sometimes with excessive scarring, leading to the formation of a new stenosis. Relative ischemia at the anastomotic sites is also a contributing factor to stenosis and fistula formation, occasionally with a relative twist of the phallus at its base. The anastomosis between the phallic urethra and the meatus is also a site of stenosis.

At the meatus, a circular anastomosis is performed between the skin of the urethra and the skin of the flap, with contraction of this anastomosis potentially leading to meatal stenosis. In contrast, the fixed part of the urethra is the least affected. It consists of well-vascularized tissue and is in well-vascularized environment, through the perineal muscles [15].

# Chang and Hwang radial flap

In 1984, Chang and Hwang [16] proposed a transverse rectangular design, revisiting Gillies’ “tube in tube” concept [17] (Fig. 2
                     ).

A 1cm-wide de-epidermized strip divides the radial forearm flap into a smaller, glabrous ulnar skin strip, that becomes the neo-urethra, and a larger radial skin strip, that becomes the phallic shaft. The neo-urethra is tubularized around a Foley catheter, and then the radial skin strip is tubularized around the neo-urethra.

The lateral extent of the design results in a large defect at the donor site, corresponding to approximately 2/3 of the wrist circumference.

The neo-urethra is positioned away from the radial vascular pedicle, which can lead to hypovascularization of the urethra, causing urinary complications.

This transverse design may not be suitable for all populations, particularly those with a significant cutaneous fatty panniculus, leading to difficulties in tubularization and suturing under tension. Matti et al. reported a high rate of complications, including partial necrosis and fistula formation [19].

# Biemer radial flap

In 1988, Biemer described a modification in which the neo-urethra is centered on the radial artery to provide the best possible perfusion [20] (Fig. 3
                     ).

The extra-long urethral part is designed as a strip bounded by two de-epidermized strips, which are in turn bound by two para-urethral fascio-cutaneous flaps. The urethra is tubularized, and the two lateral flaps are sutured together to form the phallic shaft.

Centering the neo-urethra on the radial artery limits ischemia, due to better urethral vascularization. The design, with the urethral part extending beyond, both proximally and distally, the phallic shaft allows for a tension-free proximal anastomosis with the native female urethra and the creation of a distal neo-glans [21].

However, centering the urethra on the radial pedicle corresponds to the hairiest area of the forearm. Additionally, the closure of the two para-urethral flaps results in the appearance of two external suture lines, which can be sources of stenosis.

# Semple, Farrow and Boyld radial flap or “cricket flap”

To attempt to eliminate the meatal suture line and its potential for stenosis, Semple et al. described the “cricket flap” in 1991 [22] (Fig. 4
                     ). They positioned the neo-urethra at the center of the pedicle, reducing the width of the forearm flap and ensuring optimal vascularization.

In this design, the urethra and phallic shaft are longitudinally aligned in tandem. The distal narrow “handle” (3cm) forms the urethra, while the wider “paddle” (9cm) constitutes the phallic shaft. The urethra is tubularized over a Foley catheter. The paddle is folded at 180°, at the paddle-handle junction. The paddle is then tubularized around the neo-urethra and sutured on the central face, eliminating the suture line. The handle is designed slightly off-center relative to the paddle. This limits the twisting of the arterial pedicle during the 180° inversion and also avoids overlapping suture lines. The folding of the flap creates a normal urethral opening and a more natural-looking glans. The thin and hairless skin of the handle near the wrist is minimally bulky, facilitating its wrapping by the proximal, thicker and, wider paddle. Thus, the sutures are placed without tension. Additionally, the handle near the wrist is less hairy compared to the paddle on the forearm, which is preferable to avoid intra-urethral hair. The narrow width of the handle limits exposure of the tendinous structures at the wrist. The main drawback of this design is the short phallic length obtained, as the paddle is folded in half. The size of the phallus is thus limited to about half the forearm. Due to the short female urethra and the absence of a bulbous part, the neo-urethra in a transgender male needs to be long enough to anastomose with the native female urethra. Otherwise, either an extension of the native female urethra or the neo-urethra must be performed. However, with the “cricket flap” design, the neo-urethra is often too short.

# Gilbert ulnar flap or “cricket bat transformer”

The ulnar forearm flap was first described in 1987 by Lovie [23] for intra-oral reconstruction, in order to benefit from thin, glabrous skin (Fig. 5
                     ).

In 1992, Gilbert adopt Biemer's concept of centering the urethra on the vascular pedicle, placing the urethra above the ulnar vascular pedicle, and Semple's “cricket bat” concept, by expanding the distal design to form a longer neo-urethra and a neo-glans [24].

The neo-urethra, centered on the ulnar pedicle, is bordered by two de-epidermized strips, which in turn border the cutaneous-fat strips of the future phallic shaft. There are also de-epidermized strips at the distal and of the strips for the future phallic shaft. The neo-urethra is tubularized over a Foley catheter, and the lateral strips are sutured to the ventral and dorsal parts to form the phallic shaft.

The strips are sutured around the urethra, buried under the skin of the phallic shaft, defining the distal end of the phallus, resulting in a more aesthetic glans [18]. These strips also play a protective role for the glans against prosthetic erosion. The neo-glans is proximally sutured to the dorsal neophallus to create a conical-shaped neo-glans.

A circumferential sub-coronal skin graft enhances the projection of the glans. Over time, there may be a decrease in the projection of the neo-glans.

The ulnar flap of the forearm is sensitive, thin, malleable, sensory, with very satisfactory aesthetic results. The appearance of the glans is improved by increasing its projection via the de-epidermized strips. The caliber and length of the ulnar artery are superior to those of the radial artery. The ulnar skin, being hairless, limits intra-urethral hair growth. These hairs are promote bacterial colonization and the formation of urethral stones, although such complications have become rare with the advent of laser hair removal.

Gilbert's design favors width at the expense of phallic length, which can result in a short neo-urethra and neophallus. The main flaw in the design described by Giebert or Biemer is a double scar on each side of the shaft, which makes it less aesthetically pleasing.

# Gottlieb's radial flap

In 1993, Gottlieb adopted Semple's concept of meatal suture elimination, incorporating a distal extension. In his design, the neo-urethra is centered on the arterial pedicle, with a distal extension, in continuity, folded upon itself to form the neo-glans. This eliminates the need for a circumferential meatal suture line and reduces the risk of stenosis, while maintaining an adequate phallic length [25]. Two strips of skin, each 1cm wide, surrounding the neo-urethra are de-epidermized from the proximal edge of the flap. The neo-urethra is laterally defined by 1cm wide de-epidermized lateral strips. The de-epidermization is extended to the proximal part (approximately 3–5cm) of the planned neo-urethra. This proximal extension of the neo-urethra facilitates tension-free urethral anastomosis. The neo-urethra is tubularized over a Foley catheter, and the lateral strips that will constitute the future phallic shaft are sutured together. The wings of the neo-glans are folded over the shaft and shaped accordingly.

This design allows for the creation of the neo-glans during the same procedure. However, the width of the flap is significant, creating a large defect to cover and substantial scar. Additionally, the neo-urethra is designed on hairier skin.

# Discussion

Few studies comparing different designs have been published to date. Scholten et al. [26] report an incidence of fistulas reaching nearly 80% and an incidence of stenosis up to 14% after phalloplasty by Chang and Hwang.

The incidence of partial flap necrosis after Chang and Hwang's phalloplasty varies remarkably, ranging from 3.6 to 25% [27–29].

Wirthmann et al. [30] report high rates of revision surgery for urological complications, with up to 1.3 revisions per patient after phalloplasty by Gottlieb and Levine, without further information on the distinct incidence of fistulas and stenoses. They report a rate of 3 to 4% flap necrosis.

Spennato et al. [31] demonstrated a lower incidence of partial flap necrosis using the Gottlieb and Levine technique, compared to Chang and Hwang (50%). This supports the hypothesis that positioning the neo-urethra at the center of the flap, above the radial artery, limits neo-urethra necrosis. Indeed, in Chang and Hwang's phalloplasty, the neo-urethra, in addition to being located on the ulnar edge and separated from the rest of the flap by a de-epidermized strip, is tubularized, leading to vascular compromise with hypoperfusion of the distal neo-urethra. This contributes to partial flap necrosis. A wider neo-urethra (4cm instead of 3cm) and tension-free sutures could increase flap perfusion and thus reduce the risk of partial necrosis. Conversely, this same study did not find significant differences regarding the occurrence of fistulas and stenoses between the two techniques: 80% fistulas and 30% urethral stenoses for Chang, 92% fistulas and 52% urethral stenosis for Gottlieb.

Several techniques have been described for reconstructing portions of the urethra. The fixed and bulbar urethra can be reconstructed using local vaginal or labial flaps, extra-long urethral segments from the phalloplasty flap, or grafts of skin or buccal mucosa [32].

Among the local flaps used to reconstruct the fixed (pars fixa) or bulbar urethra, vascularized genital flaps from the labia minora, clitoral tissue, or anteriorly-based vaginal flaps have been employed separately [11] or in combination for one-stage urethral lengthening [33].

With vaginectomy, the bulbospongiosus muscle, which lines the vestibule, is preserved to form an additional layer over the newly created fixed urethra. Massie et al. emphasized the importance of this layer by demonstrating that omitting additional layers of vascularized muscle tissue, especially in phalloplasty without vaginectomy, increased the risk of urethro-cutaneous fistula by 40%, from 14 to 56% [34].

In cases of incomplete vaginectomy, there may remain a communication between a persistent vaginal cavity and the neo-urethra. Symptoms that should raise suspicion for this complication include prolonged post-void dribbling, pelvic pain or a feeling of fullness, and recurrent urinary tract infections. A persistent vaginal cavity can lead to fistulas and strictures [35].

Two-stage urethral lengthening has also been described using the Johanson technique, employing a buccal mucosa graft [36].

Buccal mucosa offers several advantages: minimal morbidity at the donor site, straightforward harvesting, a hairless graft, viability in a moist environment, the ability to harvest it as a full-thickness graft, and a thin lamina propria, which facilitates neovascularization [37].

The penile urethra can be reconstructed using various methods, including prelamination, prefabrication, the “tube-in-tube” technique, or free flaps.

Prelamination involves reconstructing the urethra by using a full-thickness skin or mucosal graft to prelaminate the urethra. Better outcomes have been reported with prelamination, though these reports often come from small case series with short-term follow-up [38].

Prefabrication incorporates a free radial forearm flap into a lateral arm flap, enabling the coexistence of a penile prosthesis alongside a vascularized urethra. Both prelamination and prefabrication are secondary procedures performed after creating the neophallus [39].

Urethral reconstruction using free flaps was originally described in oncological cases but is also an option for salvage after partial necrosis of the neo-urethral segment in a “tube-in-tube” phalloplasty or for patients ineligible for “tube-in-tube” phalloplasty who wish to urinate standing up. This approach is known as a double-flap phalloplasty, where one flap is used for phallic reconstruction and another for urethral reconstruction.

The double-flap phalloplasty concept aims to overcome blood flow issues by creating independently vascularized urethral and skin flaps. Radial, gracilis, ulnar, and superficial circumflex iliac perforator (SCIP) flaps have been described for urethral reconstruction. This technique allows for one-stage urethral lengthening [40,41].

In the study by Koshima et al., two SCIP flaps were used to construct a neophallus [42].

Unfortunately, double-flap phalloplasty with an independently vascularized urethra does not appear to improve outcomes.

A retrospective study of 19 transgender men who underwent ALT (anterolateral thigh) phalloplasty with urethral reconstruction using a radial free flap showed long-term urinary complications in 10 patients (53%), with 9 (47%) developing urethral strictures. In the study by Van Der Sluis et al., an ALT pedicled flap combined with a radial free flap was used to construct a neophallus. However, long-term urethral complications, including strictures and fistulas, were reported in over 50% of cases [40].

# Conclusion

Neophallus urethroplasty remains a significant reconstructive challenge. A wide range of tissues and techniques are employed to create a long, functional neo-urethra extending from the native meatus to the tip of the neophallus.

All these designs appear to be reliable from a vascular standpoint, whether they are based on the radial or ulnar artery (Fig. 6
                     ). The tissues of the forearm have a predictable vascular pedicle, which supplies a thin, malleable, and minimally hairy sensory flap, allowing for custom sculpting.

The risk of neo-urethra necrosis is reduced by positioning the neo-urethra at the center of the flap, along the path of the radial artery [43].

Major urinary complications, namely stenosis and fistulas, seem to affect nearly all techniques. Stenoses tend to occur along circumferential suture lines. A tight closure of the neo-urethra and tension on the suture line are contributors to stenosis and fistula formation. Inadequate vascularization between the native urethra and the neo-urethra promotes the formation of fistulas and stenoses.

The ideal flap would be one without a meatal suture line, with a neo-urethra of satisfactory length and centered on a vascular pedicle.

A powerful, prospective, comparative study comparing the different designs and evaluating urethral and vascular complications would allow us to determine the superiority of one design over others. Anatomical studies with perfusion assessments of flaps could help identify the most vascularly reliable designs.

However, the design of the flap and the resulting quality of neo-urethra perfusion are not the only confounding factors to consider: urethral anastomosis technique, prior lengthening of the female urethra, excessive tension due to post-vaginectomy edema, the operator and their experience, are additional variables that can influence urological complications. The ultimate goal is to provide optimal care and improve surgical outcomes for transgender individuals seeking phallic reconstruction.

Tissue engineering holds promise but faces numerous technical and bioethical challenges yet to be resolved [44]. The absence of spongy tissue and structural support, the frequent occurrence of urethral complications, and the common inability to achieve a strong urinary stream while standing make urethral lengthening the greatest reconstructive challenge in gender-affirming phalloplasty.