Novel penile prostheses for transmen: surgical outcomes of ZSI FTM penile implants after musculocutaneous latissimus dorsi neophalloplasty

INTRODUCTION

There are various surgical techniques for neophalloplasty in transgender men, each with its own advantages and disadvantages. A primary goal of neophalloplasty is to enable penetrative sexual intercourse. Since the neophallus lacks native erectile tissue, implantation of a penile prosthesis is necessary to obtain erectile rigidity. At our center, the musculocutaneous latissimus dorsi (MLD) free flap technique is the method of choice as it provides a neophallus with excellent volume and length, enabling safe penile prosthesis implantation. Its main drawback, however, is the lack of sensation in the neophallus^[1-3].

Neophalloplasty is a multi-stage procedure; prosthesis placement is usually the last step in patients who require urethroplasty. Insertion of the penile implants is performed at least six months after the initial neophalloplasty to ensure adequate tissue healing and maturation before proceeding with further surgical intervention^[2]. Although multiple techniques exist for prosthesis placement, current literature has not demonstrated the superiority of any one approach over others^[4]. Device selection is often based on a combination of patient-specific factors, surgeon preference, and device availability. In neophalloplasty, erectile devices are associated with high complication rates that may directly compromise the neophallus^[5]. Common complications include infection, migration, and protrusion, often resulting in prosthesis rejection and removal. One of the reasons for frequent complications is the lack of supportive tissue in the neophallus that would normally cover the implant, as is the case with cavernosal bodies in cismen. Until recently, only penile prostheses designed for cismen were available for transgender men, making high complication rates inevitable.

Despite numerous described techniques, no universal solution exists to achieve ideal penile rigidity in transgender men^[2-5]. Even with significant surgical advances and improved knowledge, complications remain frequent. Therefore, the search for better solutions continues. Recently, penile implants specifically designed for transmen have been developed^[6].

This study aimed to assess the surgical outcomes of novel malleable and inflatable penile prostheses specifically designed for transgender men, following MLD neophalloplasty.

METHODS

This retrospective, observational, descriptive study included all patients who underwent insertion of the specifically designed penile prostheses after primary MLD neophalloplasty at our center between January 2022 and January 2025, yielding a total of 20 patients. Patients who underwent other types of neophalloplasty or had a different type of prosthesis inserted were excluded. The mean age was 34.3 years (range 23-58). Data were collected from medical records and outpatient examinations, including patient demographics, age at surgery, type of surgical correction, complication rates, and sexual function. The dorsal neophallic approach was used in all cases.

The study was approved by the institutional review board, and informed consent was obtained from all patients.

Sexual function was assessed using the International Index of Erectile Function (IIEF) questionnaire, which evaluates five domains: erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction^[7].

Descriptive statistical analyses were performed using IBM® SPSS® Statistics 20.

Erectile devices

While a variety of penile implants are available, devices specifically designed for transgender men are limited. The differences between conventional penile implants and those tailored for transgender patients are summarized in Table 1^[8-13].

Table 1

Comparison of penile prostheses devices

Feature	ZSI 100 FTM (malleable)[10]	ZSI 475 FTM (inflatable)[11,12]	Traditional malleable[13]	Traditional inflatable[8,9]
Base plate	Silicone-covered stainless steel	Silicone-covered stainless steel	N/A*	N/A*
Glans shape	Ogive-shaped removable glans stopper	Realistic glans shape	Cylindrical	Cylindrical
Size/Adjustability	Adjustable length (130-200 mm)	Multiple sizes available	Fixed length	Variable by cylinder size
Components	One-piece cylinder with fixation plate	3-piece (cylinder, pump, reservoir)	Two separate cylinders	Cylinder, pump, reservoir
Primary application	Transgender men undergoing neophalloplasty	Transgender men undergoing neophalloplasty	Cisgender men with ED*	Cisgender men with ED

^*N/A: Not applicable, as they do not include base plates. ED: Erectile dysfunction; FTM: female-to-male.

Malleable penile implant (ZSI 100 FTM)

The ZSI 100 FTM is a one-piece malleable penile implant consisting of an adjustable cylinder, 22 mm in diameter, which can be shortened from 200 to 130 mm by sequentially trimming 5 mm from the distal end (ZSI 100 FTM). The distal tip features an ogive-shaped removable glans stopper. At the base of the cylinder, a silicone-coated, stainless-steel plate allows the prosthesis to be anchored to the pubic bone [Figure 1]^[10]. Another variant, the ZSI 100 D13 FTM, has a 13 mm diameter and can be adjusted up to 220 mm in length^[10].

Figure 1. Four sutures are placed through the periosteum via a specially designed plate. The dorsal approach is used for penile implant insertion.

Inflatable penile implant (ZSI 475 FTM)

The ZSI 475 FTM is a 3-piece inflatable penile implant consisting of a cylinder with a realistic glans shape, a fixation plate at the base, a testicle-shaped pump, and a reservoir. In this study, the penile prosthesis comprises a single cylinder engineered to provide both stability and optimal cosmetic outcomes in both inflated and deflated states^[11]. The device is available in four lengths - 120, 150, 180, and 210 mm - and has diameters ranging from 20 to 22 mm. Size selection was individualized based on patient anatomy and surgical planning to ensure proper fit and function. The fixation plate, made of silicone-coated stainless steel, allows the prosthesis to be anchored to the pubic bone^[11,12].

Surgical technique

Patients are positioned supine. The genital region is scrubbed with chlorhexidine and povidone-iodine for 5 min, followed by placement of sterile drapes. A semicircular 4 cm incision is made on the dorsal aspect of the neophallus [Figure 2A]. Blunt dissection is performed through the subcutaneous tissue until the pubic symphysis is identified, creating a space for the prosthesis fixation plate. The space within the neophallus is then created using metal dilators up to 10 mm, making sure to avoid getting too close to the distal tip, maintaining the midline and taking care not to injure the urethra [Figure 2B]. The appropriate length of the cylinder is determined using a Furlow measurement. The prosthesis is immersed in a gentamicin and rifampicin solution prior to insertion.

Figure 2. Approach for penile prostheses insertion in MLD neophalloplasty. (A) Semicircular incision marked on the dorsal aspect of the neophallus; (B) Adequate space for the penile implant created with proper dilation, reaching the tip of the neophallus. MLD: Musculocutaneous latissimus dorsi.

In cases with excessive girth or length of the neophallus, several strategies are considered, including shortening the neophallus, or reshaping the base of the neophallus simultaneously with its width. The specific approach is tailored to the individual patient’s anatomy and desired outcome.

Inflatable prosthesis

A hemiscrotal space is created through the same infrapubic incision on the contralateral side of the vascular pedicle using blunt dissection. In cases with a previously placed testicular implant, the implant is removed, and a new space is created next to the capsule.

A second horizontal incision is made in the left iliac fossa, followed by blunt dissection of the Retzius space. The reservoir is then inserted and filled with saline. The prosthesis plate is anchored to the pubic symphysis with four interrupted sutures through the periosteum [Figure 3A and B]. The pump is positioned in the previously created hemiscrotal pocket [Figure 3C]. The cylinder is then inserted into the neophallus [Figure 3B]. The reservoir tubing is connected to the pump and cylinder tubing. Inflation is tested to confirm the proper functioning of the prosthesis. The prosthesis is inflated to 60% to maintain the dissected space. The incisions are closed, and a compressive dressing is applied.

Figure 3. Inflatable penile implant placement. (A) The periosteum of the pubic symphysis is identified, and four sutures are placed for subsequent fixation; (B) The cylinder is inserted into the neophallus, and sutures are prepared for implant fixation; (C) The testicular implant in the left hemiscrotum is removed, and a pump is placed. The cylinder is inflated, with the neophallus in an erect state.

RESULTS

The mean follow-up was 21 months (range 4-36) [Table 2]. Malleable ZSI 100 FTM and inflatable ZSI 475 FTM penile prostheses were implanted in 15 (75%) and 5 (25%) patients, respectively. In one case, a ZSI 475 FTM was implanted following the explanation of a prior inflatable prosthesis designed for cismen. The standard ZSI 100 FTM was placed in 12 patients, while the ZSI 100 D13 variant was used in 3 patients. Among the ZSI 475 FTM implants, 150 mm prostheses were used in 3 patients, and 180 mm prostheses in 2 patients. No modifications to the prosthesis glans cap were required for any of the patients.

The median time from neophalloplasty to prosthesis implantation was 44 months (range 6-120 months). No intraoperative complications or issues with glans dilatation occurred. In this type of phalloplasty, the vascular bundle passes to the right of the pubic symphysis toward the groin; therefore, the pump is placed in the contralateral hemiscrotum to avoid potential vascular injury.

There were 6 cases (30%) with postoperative complications in total [Table 3]. Three cases (15%) of wound dehiscence were successfully treated conservatively. Three additional cases (15%) required revision surgery: two due to implant fracture and one due to implant detachment. Implant fractures occurred 6 and 9 months after implantation [Figure 4]. In this follow-up period, no complications such as rejection, protrusion, erosion, malfunction, or infection were encountered.

Figure 4. Revision surgery via the same dorsal approach revealed a fracture of the malleable penile implant.

In those two cases with penile implant fracture, we had initially inserted ZSI 100 D13. Patients requiring revision received new penile implants, all of which were replaced with the ZSI 100 FTM device. One patient in this group requested removal of the penile implant, expressing a preference to avoid additional surgery in case of future complications. In one patient (5%), prosthesis detachment occurred 16 months after the primary implantation, requiring an additional surgical procedure for refixation. In this study group, three cases (15%) experienced mild complications (Grade I according to the Clavien-Dindo classification), including partial wound dehiscence, which was managed conservatively. In one case, there were some difficulties with pump manipulation, which were resolved through reinforced patient training after confirming that there was no mechanical failure of the device. No complications related to the MLD flap or any other further complications developed.

Intercourse with complete penetration was feasible in all cases. All patients completed the IIEF questionnaires (100%) and reported satisfactory penetration, with a mean IIEF of 21.1. Average scores were 21.3 (range 19-26) in the erectile function domain and 8.7 (range 7-10) in the overall satisfaction domain. Three patients (15%) scored below 21 in the erectile function domain, indicating erectile dysfunction. At the end of the follow-up, 19 patients (95%) still had prostheses, with an overall revision rate of 15% [Figure 5A and B].

Figure 5. Outcomes after penile prosthesis implantation. (A) Outcome one year after malleable penile implant insertion; (B) Outcome four months after inflatable penile implant placement. Rigidity of the neophallus was achieved.

DISCUSSION

Adequate erectile function is an important aspect of many men´s quality of life^[14-16]. Consequently, achieving penetrative sexual function is a key surgical goal for transmen undergoing neophalloplasty^[16]. An erectile device is usually necessary to attain this goal; however, it is associated with a high complication rate^[16,17]. Transgender men and surgeons dealing with these shared goals have to grapple with complications that jeopardize the patient’s quality of life.

Recognizing the specific needs of transmen, specific erectile devices were developed in the form of a single cylinder device with a fixation plate, which better conforms to the anatomy of a neophallus^[6].

This study assessed the initial surgical outcomes after implantation of the malleable ZSI 100 FTM and the inflatable ZSI 475 FTM prostheses in transgender men after MLD neophalloplasty. Several previous studies have reported outcomes for prostheses specifically designed for transgender men following radial free forearm flap and anterolateral thigh flap neophalloplasty^[14,18-20]. However, no information is available on the implantation of these innovative erectile devices after MLD free flap neophalloplasty.

In a native penis, overall complication rates (infection, erosion or device dysfunction) for penile prosthesis implantation are < 2%, significantly lower than the rates observed in neophallus implants^[21]. In transgender men, studies of penile prostheses designed for cismen following neophalloplasty report overall complication rates of 23.9%-47.6%, while the rates for transmen-specific prostheses were 28.4%-44%^[15,22,23].

Challenges in penile prosthesis implantation in the neophallus begin with understanding the unique anatomy, which guides the selection of the appropriate erectile device and the safest approach to minimize potential intraoperative complications. Inadequate supportive tissue compared to the native penile anatomy is a major contributor to severe and devastating complications after erectile device implantation in transgender men.

Unlike a native penis, the neophallus lacks corpora cavernosa and tunica albuginea (native erectile tissue), structures generally used for prosthesis fixation and coverage. The ZSI 100 and ZSI 475 FTM devices address this anatomical difference with a fixation plate at the base, allowing anchoring to the pubic bone.

Malpositioning with transmen-specific erectile devices has been reported in 4.7%-7% of cases, compared to 12.6%-14.6% for prostheses developed for cismen^[17,19,22]. In this series, there was one case of prosthesis detachment with malpositioning and two cases of implant fracture.

Reported revision rates range from 19%-44% for transmen-specific devices and 19%-43.4% for cismen devices^[17-27]. However, follow-up periods were considerably shorter in studies of transmen-specific prostheses (6.3-16 months) than in studies of devices designed for cismen (20-48 months)^[17-27].

In contrast to an encouragingly low number of complications related to malpositioning and cylinder protrusions, infection rates after prosthesis implantation in a neophallus, either with standard (4.2%-11.9%) or transmen-specific (12%-14.2%) devices, are higher compared with the 1.1% infection rate observed after prosthesis implantation in a native penis^[25-28]. The restricted vascular supply and significant scarring associated with neophallus free flaps hinder the healing process and increase infection risk^[6]. No infections were observed during the follow-up period in our study.

In a recent study by Marchand et al., a high complication rate of 53.1% was reported following ZSI475 FTM implantation^[14]. However, their study primarily evaluated outcomes after inflatable penile implant insertion, whereas in our cohort, most of the patients underwent implantation of malleable penile prostheses. Consequently, we observed a lower overall complication rate. Marchand et al. also reported a high rate of urethral complications (71%) and noted a correlation between urethral and mechanical complications. The discrepancy in complication rates between the studies may be attributable to differences in surgical technique and study populations: Marchand et al.’s cohort primarily underwent radial forearm free flap neophalloplasty (56.2%), whereas all patients in our study underwent MLD free flap neophalloplasty, with other types of neophalloplasty excluded. Marchand et al. (2025) additionally described improvements in implant design, including tubing reinforcement and adjustments to the anchoring plate, which may contribute to reduced mechanical dysfunction. The lower complication rates observed in our study may also reflect the inherent advantages of the MLD flap, which provides substantial neophallus volume and muscular support for the implanted prosthesis, potentially reducing stress on the device and surrounding tissues. Implant placement behind the muscle further minimizes the risk of urethral injury. Nonetheless, detachment of the penile cylinder remains a significant concern. It is important to acknowledge that our study’s smaller sample size (n = 20) and shorter follow-up period, compared to Marchand et al.’s larger cohort (n = 89), may limit the detection of less frequent or delayed complications. Despite differences in complication rates, both studies highlight the role of penile prosthesis implantation in achieving satisfactory sexual function for transmen following neophalloplasty. Longer-term studies with larger cohorts are needed to fully elucidate the long-term outcomes of ZSI 475 FtM implantation.

Evaluation of patient satisfaction is limited by the lack of validated questionnaires designed specifically for this population. In this study, we used the IIEF, a commonly used questionnaire for evaluating sexual satisfaction. While informative, the IIEF may not fully capture the nuances of the transgender experience. Since this study was initiated, the GENDER-Q - a trans-specific series of patient-reported outcome measures (PROMs) has been developed and could provide a more comprehensive assessment in future studies^[29]. Most previous studies (66%) have reported results based on non-validated questionnaires^[16,17,30]. In our cohort, a median IIEF score of 21.1 was recorded, which is consistent with normal erectile function. Additional analyses and longer-term follow-up are needed to obtain more information about satisfaction and long-term complications following this complex reconstructive procedure.

Limitations of this study include its retrospective design, small sample size, absence of a standardized, validated questionnaire, and lack of a control group, which restricts comparative analyses. Long-term outcomes remain to be determined.

Overall, penile prostheses specifically designed for transmen in our cohort appeared to have enabled favorable surgical outcomes and high patient satisfaction. MLD free flap neophalloplasty provided adequate neophallus volume and sufficient blood supply for safe penile prosthesis implantation. The most significant complication observed was penile implant fracture. Long-term studies are needed for further analysis.