Gender dysphoria is defined as a discomfort or dissatisfaction because of a discordance between the individual\'s assigned sex and their gender identity. A national survey of transgender adults in the United States has shown that 39% of their respondents experience psychological distress, which is eight times the rate in the United States population. Transition-related treatment contains counseling, psychotherapy, hormone therapy and gender-affirming surgery depending on what the individual desires. Gender-affirming surgery aims to change an individual's physical characteristics concordant with their gender identity and results in a reduction of psychological distress.

A part of this population will eventually undergo genital gender affirming surgery (GGAS) to align the appearance of the external genitalia as well. In transgender men, GGAS can be performed as metoidioplasty or phalloplasty with or without the removal of the native external genitalia. In metoidioplasty, the goal is to create anatomically looking but undersized external genitalia in which the clitoris forms the base of a micro-penis. In phalloplasty, anatomically sized external genitalia (phallus with or without urethra, scrotum, and perineum) are created using on the one hand a donor skin flap and on the other hand tissues from the original genitals. As there is no erectile tissue present in the neophallus after phalloplasty, it is usually not possible to penetrate a sexual partner without the use of external or internal erectile aids. In patients having undergone phalloplasty, a multitude of methods for obtaining phallic rigidity are available. One option can be the implantation of an internal erectile prosthesis.

Most types of erectile prostheses used in the transgender community have originally been designed for cisgender men. However, implanting such a prosthesis in the neophallus presents a number of challenges due to the differences with the anatomy of a native penis. As there are no cavernosal bodies with surrounding tunica albuginea that can be used as scaffold for anchoring of the prosthesis to the pubic bone there is an increased risk for distal extrusion, malposition and extensive mobility during use. Furthermore, vascularization of the neophallus is largely dependent on the one or two vessels supplying the flap(s), resulting in relative hypovascularization, delayed healing and an increased risk of infection. Finally, these types of prosthesis were originally made for an older population with erectile dysfunction. Most transgender patients are younger and sexually more active which could lead to mechanical failure of the erectile prosthesis; hence the life expectancy of implants is significantly reduced in this population. Consequently, penile implant surgery is associated with higher complications in a transgender population than in a cisgender population. The revision rate or explantation rate within 4 years follow-up ranges from 37.6% to 44% in several studies. Falcone et al. reported that up to 22% of the prostheses was explanted within 20 months. Within this study the patient and partner satisfaction were surveyed with a non-validated questionnaire. Up to 88% of patients were completely satisfied with the outcome of the phalloplasty and the erectile prosthesis, despite a significant complication rate. However, the partner satisfaction rate is significantly lower and rated at 60%. Without further discussion, Falcone et al. stated that his result should be explored in the future.

Recently, the Swiss company Zephyr Surgical Implants created the ZSITM 475 female-to-male (FTM) (Switzerland, Europe), the first erectile prosthesis specifically designed for transgender men after phalloplasty surgery. It contains several functions such as a large base plate for pubic bone fixation, a glans shaped tip, and a testicle-shaped pump, that have been conceived to answer several of the difficulties of prosthesis implantation. Recent publications on this prosthesis continue to report high complication rates. Verla et al. reported postoperative complications in 32% of the patients. Moreover, 23% of the devices were explanted within 18 months follow-up due to distal cylinder protrusion, infection, malpositioning, mechanical failure and urinary retention. In the paper of Neuville et al., the overall revision rate was 19% with a mean follow-up of 8.9 months, resulting from infection, mechanical failure and malpositioning. However, 92.8% of patients reported to be either satisfied or very satisfied with the erectile prosthesis and a mean EDITS score of 82 of 100.

To date, it is not possible to state which prosthesis is performing better in terms of complications and sexual satisfaction. A more comprehensive questionnaire is needed to understand the reported satisfaction of the patient according to the different types of prosthesis. As observed in the publication of Falcone et al., the low partner satisfaction rate should be explored further as this may impact patients' and partners' relational functioning. The current study aims to explore in more detail the sexual satisfaction in both transgender patients and their partners regarding erectile prosthesis placement using validated and non-validated questionnaires. These questionnaires will be provided to all included patients that are minimum 6 months after placement of an internal erection prosthesis and have a functional erection prosthesis in place