Penile Prosthesis

The history of phalloplasty has two holy grails: the first being to pass urine from the tip of the phallus and the second to be able to have penetrative sex. The potential problems with the construction of the urethra have already been discussed earlier. To understand the theory behind penile prosthesis for phalloplasty it is first necessary to understand how the natural penis in cis-males functions. 

Normal Male Anatomy

The penis consists of three tubes. The two larger tubes lie side by side on the top and contain the erectile tissue. The smaller tube contains the urethra and also forms the whole glans or head of the penis and lies underneath. The erectile tissue tubes, called corpora cavernosum, are made of a tough but partially elastic fibrous tissue (tunica) that is anchored to the lower end of the pubic bone. Anchorage provides stability of the erect penis and prevents the penis falling back with penetrative sex. The elasticity of the tunica allows some expansion of the width and length of the erect penis. The tough fibrous nature of the tunica allows the pressure inside the erect penis to rise well above the normal blood pressure and makes it hard and rigid. The erectile tissue inside the corpora is like a sponge in that it can expand greatly in size with blood when erect allowing a significant difference in appearance between the flaccid and erect penis. All these factors need to be artificially reproduced in the phallus.

Rigidity and stability

Incorporating pieces of bone or cartilage inside the phallus to make it rigid has been tried. The problem is anchoring it to the pubis as although this could be done one would not then be able to move the phallus around and it would be permanently stiff and in the same position. In any case, cartilage gradually softens so it is ineffective in the long term.

We use permanent stitches to attach the penile prosthesis to the lower edge of the pubic bone. Rather than putting sutures through the prosthesis, we use a Dacron™ (polyester fabric) sock or sheath to recreate the tunica of the corpora cavernosum. This is then attached to the bone with the bone sutures. Dacron is synthetic material used in vascular surgery to replace or repair major blood vessels such as the aorta and is very tough. Over time, it becomes very fibrotic and effectively functions like the real tunica and protects the prosthesis buried inside. If the prosthesis needs replacing, we just open the Dacron sheath and change the prosthesis over without having to reconnect things to the bone again. Our preference is to use a Dacron sock at the base and a Dacron cap at the tip to allow the single cylinder to expand more in the middle and prevent curvature. If the phallus is very wide then we use a complete Dacron sheath to bulk up the cylinder or use 2 cylinders. This covers the anchorage and protective functions of the tunica.

Penile prosthesis

There are two main classes of penile prosthesis, the malleable and inflatable models. The malleable or semi-rigid prostheses consist of a silicone rod with a flexible steel core which allows it to be both stiff and bendable. A newer type has interlocking metal segments with a cable connector instead of a steel core allowing flexibility and when the cable is manipulated, the whole thing locks and becomes rigid. There are no external moving parts and they are to all purposes indestructible. They have been used in phalloplasty, as they are simple to insert. Unfortunately, the drawback is their rigidity, which exerts constant pressure on the skin in spite of the Dacron sheath, and erosions are common. Also having a permanently stiff phallus is very inconvenient.

Because of the above problems with the semi-rigid prostheses we mainly offer inflatable prostheses. This is essentially a balloon that can be filled with fluid to create rigidity when an erection is needed. This is much more like the normal erectile spongy tissue. We cannot however reproduce the elastic function of the tunica because the phallus skin is fixed in size.

Inflatable prostheses come in three basic models from various companies. They all consist of three components which are the cylinders, pump and reservoir. The pump regulates the flow of fluid between the reservoir and cylinders, thereby controlling the erections. The cylinders give the rigidity for penetration and the reservoir stores the fluid when no erection is required. The fluid used is usually saline but x-ray contrast is sometimes used. A one-part inflatable has all three components combined in one cylinder. A two-part inflatable has the reservoir and cylinder combined in the cylinders with a separate pump. The reservoir is at the bone end with the rest of the cylinder being the inflatable component. A three-part inflatable has the cylinders, pump and reservoir as three separate components.

There are a number of advantages of the inflatable over the semi-rigid. Firstly, it functions more naturally. Secondly, in the flaccid state there is much less pressure on the skin and so less likelihood of erosion. The cylinders can expand in girth and with a high pressure of fluid inside can be just as hard as a semi-rigid device. Disadvantages include a higher infection rate because it has more components and also a mechanical breakdown risk as there are moving parts. Our data suggest that about 30% of inflatable prosthesis will fail for mechanical reasons in the first 10 years and require replacement. 

Current technique

Normally only one cylinder is used because together with the Dacron it is quite bulky and gives sufficient rigidity. If there is a urethra then there is very rarely sufficient space for two cylinders. Some of the larger pubic phalluses need two cylinders because of their girth. It is important to leave some fat between the cylinder and the skin to prevent erosion in the future. Patients are advised not to attempt intercourse for at least six weeks to give time for the fibrous capsules to form and more importantly to allow the bone anchoring sutures to become rock solid and provide support for the implants. We also advise all patients to use condoms to help prevent infection getting in through tiny abrasions in the phallic skin and to help with lubrication. Condoms also firm up the fat surrounding the cylinder, thus improving rigidity.

Complications

The two enemies of penile implants are infection and erosion. The latter problem is minimised by all the above techniques. Infection is by far the biggest problem. It is usually introduced at the time of initial surgery from bacteria on the patient’s skin. If there is infection we are fighting a losing battle and the end result is that the whole implant has to come out and we start again. We utilise strict aseptic technique and use perioperative antibiotics for the patients. In addition, patients have an antiseptic bath preoperatively and have nasal antibiotic cream to kill the bacteria in their nose. The space in the phallus is washed with antiseptic solution as well as antibiotics as is the Dacron sheath. We try to avoid the implant touching the skin during surgery which also helps. We use antibiotic impregnated prostheses and in a large series reported from America there has been a significant reduction in infection problems even with patients who have had multiple implant revisions and other high-risk groups.

A sensate phallus is less likely to have erosion problems as innervated skin is tougher and provides early warning signals in the form of pain if the prosthesis is getting too close to the skin.