Why ZSI implants for FTM?

Discussions of transsexuality used to evoke the image of a man who wanted to convert to being a woman. But it should be noted that one in 15,000 women as well wants to go through the transformation to have the masculine attributes. It is a long and difficult journey for a person making such a transformation, characterized by various stages, including a phalloplasty.

Biological women who wish to make complete transformations to become men are called FtM (female-to-male) patients.

These patients are in general rather young. They receive testosterone injections, which allow the body to transform itself, increase the libido and change the whole metabolism and the physical attributes. In this process, doubts about sex often arise: “Can I have sexual relations with a phalloplasty?”

Despite the efforts of plastic surgeons to give the appearance and sensitivity of a penis, a FtM phalloplasty do not include a glans formed of spongy tissue nor an erectile corpora cavernosa anchored securely to the base of the pubis  that are both essential to achieving erections. A penile implant should be used for this purpose.

In 2016, ZSI created new implants that were specifically designed for FtM phalloplasties — the ZSI 100 FTM and ZSI 475 FTM implants.

Before that, surgeons had stretched their creativity trying to adapt penile implants designed for biological men for use in FtM phalloplasties. They discovered several problems when implanting products designed for biological men into transsexuals. Here we explain the solutions our FtM-specific implants provide.

(Figure of a penis with glans and corpora cavernosa)


The standard penile implant was conceived solely for biological men. There are various categories—malleable implants and inflatable implants of two or three components (see figures)—but they were all designed to be inserted in the corpora cavernosa of the penis. The standard penile implant compensated for the erectile dysfunction of the corpora cavernosa, taking advantage of its firm attachment to the pubic base. There is still no replacement solution for the glans.


Standard penile implants

Malleable implant


Three-component inflatable implant

Although well-adapted for erectile dysfunction in the corpora cavernosa, standard penile implants are not adapted to the phalloplasty question.


ZSI FTM Implants

The ZSI 100 FTM and ZSI 475 FTM implants were designed to be inserted into a phalloplasty to resolve the problems presented by the standard penile implant.

Penile implants for FtM are adapted

The standard penile implant is composed of two elongated tubes more or less conical at their ends for insertion into the corpora cavernosa. They have a diameter between 13 mm and 14 mm. Their framework is not suited for a phalloplasty. Moreover, the distal part of the standard implant is narrow and runs the risk of perforating the phalloplasty during coitus.


“Standard” implant

Both inflatable and malleable FTM implants have the shape of a penis. They provide a framework that gives “structure” to the phalloplasty, without which the implant would be just a tube of inert skin.


Implant ZSI 475 FTM

ZSI 100 FTM malleable implant

Attachment of the ZSI 475 FTM and ZSI 100 FTM implants

A phalloplasty, in contrast to a penis, has no corpora cavernosa. The penile implant must be affixed to the pubis in order to achieve a stable and effective erection.

Standard penile implants present a problem in attaching to the pubis, because they were designed to be inserted into the corpora cavernosa. The standard penile implant does not include any element that can be attached to the pubis.

  • It is not possible to execute a direct attachment of the implant because the suturing tears the silicone of the fragile and conical proximal part.
  • Attaching it indirectly is the only solution. The surgeon must fashion a pouch from a Dacron arterial prosthesis, which generates additional costs for the clinic. This “pouch” is sewed directly to the pubis. The standard penile implant is inserted into the pouch. Given constant use, it is not uncommon for the standard penile implant to escape from its pouch.

Implants for phalloplasty have a squared proximal part that is rigid and perforated, allowing them to be attached securely to the pubic bone using sutures or screws.

The ZSI 475 FTM and ZSI 100 FTM penile implants have a calculated angle of erection

Standard implants press against the pubis without any angle of compensation. During penetration, this generates significant tensions in the implant, which may induce its “exit” from the Dacron pouch or the total separation of the apparatus.

Diagram of the standard implant in erection “fixed” to the symphysis

The FTM penile implant is not aligned with the pubic symphysis (the medial point where the two pubic bones join).

There is an angle between the attachment plate at the pubis and the implant in erection. This angle reproduces the natural angle of the penis’s suspensory ligament. It is adapted for penetration and reduces tension in the penis and thus in the implant.


FTM penile implants have a tested angulation in detumescence

Standard penile implants are not designed to fold when deflated. When deflated, the silicone proximal part affixed to the pubis rubs against the independent inflatable part, which can cause premature wearing of the walls, potentially resulting in a low-pressure rupture. This is a recurrent problem for standard implants when they are used in phalloplasties.

Diagram of the uninflated standard implant “fixed” to the symphysis


ZSI 475, junction of inflatable and rigid parts


The angle formed between the FTM penile implant and the pubis, and the presence of the internal support tongue on the inflatable part, which follows the curve of the deflated implant, reduce the risk of folding and breakage (see the figure).

View of the deflated ZSI 475 FTM implant “sustained” by the internal tongue

The exit angle of the tube of the FTM penile implant is sufficient for phalloplasty

The standard penile implant was designed to be placed in the corpora cavernosa attached to the pubic branches located in the legs. The tubes of the standard penile implant rotate forward and toward the scrotum where the pump is located.

In the case of phalloplasty, the part between the legs is affixed to the pubis. The tubes emerge upward and away from the intrascrotal pump located below. The tubes must form a downward loop. This encourages premature fatigue in the tubes, which can cause them to break.

Finally, by being angled in a “contrary” orientation, the tubes of the standard penile implant may be noticeable below the skin, which can be unsightly. This could be a problem for a patient who wants to be discreet concerning their penile implant.

Standard implant showing the exit angle of the tubes toward the front


With the ZSI 475 FTM penile implant, the angle of the tube that connects the inflatable part with the pump is lateral to avoid injuring the urethra. The tube is positioned underneath in order to place the intrascrotal pump in a natural unobtrusive way. The tube is not folded, which eliminates any risk of rupture.

The glans of the FTM penile implant

The standard penile implant has a distal part with a ogive (pointed) shape made of dense silicone, which can perforate the phalloplasty during coitus. This small-diameter pointed shape doesn’t come close to emulating a glans or filling out the phalloplasty.

The glans of the FTM penile implant allows a proper filling of the distal end of the phalloplasty, which reproduces the look and feel of the glans of a biological man. The silicone used is of low density, which reduces the risk of compressing the cutaneous tissue. The glans also provides a good contact surface for the interior of the remnant during coitus, distributing pressure and reducing the risk of perforation.

In case of fibrosis in the phalloplasty, the surgeon could have difficulty working the glans, 25mm in width, into its final position. The glans is made completely of silicone, and the surgeon can cut it easily with Mayo scissors to reduce its size.

Moreover, this glans is designed to accommodate the urethra. The glans has a flattened covered bottom portion with a groove to accommodate the passage of the urethra and avoid the possibility of pressure zones.


The body of the FTM penile implant is designed to “fill out” the phalloplasty

The standard penile implant is supposed to be inserted into the corpus cavernosum. Once inflated, its diameter is limited to between 14 mm and 16 mm.

In the majority of FtM cases, the surgeon places only one of the two inflatable implants that comprise the prosthesis; the fill volume is not sufficient, because the standard implant “swims” in the phalloplasty and there is no glans.

Placing only one implant in the phalloplasty also creates a reliability problem. The surgeon must cut and seal the extra tube attached to the part of the inflatable prosthesis that has been removed. The pressure in the inflatable prosthesis can reach more than 500 mbar, and leaks of hydraulic liquid are common, with which the functionality of the prosthesis quickly begins to fail.

Some surgeons place both of the standard implant’s inflatable prostheses in the phalloplasty. The level of “fill” improves, but several issues arise:

  • Both ends “link” in the phalloplasty.
  • The prostheses overlap, crisscross, separate, and reverse, because they are loose in the phalloplasty.
  • It is necessary to make two separate attachments to the pubis with two “pouches.”
  • The risk of “detachment” doubles.

The body of the penile implant designed for phalloplasty reaches 22 mm in diameter when inflated. Adding to this the fatty tissue and thickness of the skin of the phalloplasty, the total diameter reaches 40 mm. Along with the glans, this diameter provides the appearance of a penis.

The FTM penile implant has an improved inflatable part

One of the standard penile implants available on the market has a single thin wall made of a mixture of silicone and plastic. Along with the unnatural sound the wrinkling plastic makes as the phalloplasty moves, there is also a significant risk of perforating the wall of the implant when making abrupt movements.

The inflatable part of the FTM penile implant is composed of three layers: an interior cylinder made of silicone, a polyester cylinder, and a silicone cylinder coated with PVP to prevent infections. If a suture needle makes strong contact with the implant, the risk of perforating the interior silicone tube is limited.

The polyester tissue used is a quality-tested arterial prosthesis that takes several folds without weakening or tearing.


Structure of the inflatable part of the ZSI 475 FTM implant

The problem of pump size in standard penile implants

The pump in the standard penile implant, located in the scrotum, is large in order to accelerate the filling of the implant and to accommodate the “one touch” deflation system. This is possible in a biological man because after age 50 the scrotum gets larger and more flexible.

But it is problematic to fit these pumps into transsexuals’ scrotums, which tend to be small because they are formed from the labia majora. The pumps in the FTM penile implants are lower in volume and therefore easier to place.



The diverse complications arising while placing standard penile implants in phalloplasties has allowed us to address their shortcomings and consider how to improve them. Moreover, it has been possible to develop penile implants designed specifically for FtM transsexuals that address these defects.

The ZSI 475 FTM and ZSI 100 FTM penile implants, adapted for phalloplasty, actually solve the problem of attachment to the pubis by giving a “framework” to the phalloplasty. The tubes were correctly “aligned” and the weaknesses were resolved in a positive manner.

The FTM penile implants should significantly reduce the rates of failure and revision, as well as the costs associated with replacing unsuitable implants. Even more important, the FTM penile implants improve patient satisfaction and personal development.

ZSI is the only European manufacturer of artificial urinary sphincters and of malleable and inflatable penile implants, as solutions for male urological problems (incontinence), sexual complications (Erectile Dysfunction), and gender identity procedures (prostheses for trans men and women).