Sunday, November 2, 2008

Penile Prostheses (Implants)

The concept of the penile prosthesis dates back to early times when it was noticed that several species of animals had what was termed as an os penis or biaculum. This is a cartilaginous support noted to keep the penis erect. The first penile prosthesis was actually a rib graft implanted into the corporal body.

The recent history of penile prosthesis dates back to 1950, when Dr. Scardino implanted the first synthetic material into the penis. Penile implants improved dramatically with subsequent work of many investigators, and penile implant surgery has progressed to a very high level.

The indications and contraindications for penile implant surgery include vascular disease, diabetes, bladder or prostate cancer surgery or for benign prostate disease, Peyronie's disease, neurologic disease, hypogonadism, pelvic fractures and impotence related to many medical diseases including chronic renal disease, alcoholism, multiple sclerosis, genital trauma, Parkinsonism, drug therapy.

Some of the relative contraindications for penile implant include a poorly controlled diabetic, mostly because of the patient's high susceptibility to infection and significant symptoms of bladder outlet obstruction because a prosthesis
can cause a relative increase in the outflow obstruction and, thereby, produce urinary retention.

When choosing a penile prosthesis, it is important to recognize the major categories. These include:

1) rigid, semi-rigid and malleable rods, which produce varying degrees of rigidity and

2) inflatable prostheses which include two types; a) the multi-component inflatable prosthesis, and b) the self contained inflatable prosthesis. The main objective is to leave the patient with a penis that when sexual intercourse is desired it is
achieved with no complications and with a penis that satisfies both him and his partner.

There is no single penile prosthesis that is best for all patients. It is, therefore,
imperative that the urologist sit down and very carefully review the risks, benefits, and drawbacks to each of the different types.

When discussing the semi rigid prosthesis, the balance sheet includes an erection sufficient for penetration. This is termed axial rigidity in the urologic spectrum and means the amount of torque that can be placed on the penis. Most of the rigid prostheses are associated with a low mechanical failure rate because there really are no moving parts and a fairly simplistic implantation is possible. The down side
is that they produce an erection that may be noticeably unsightly, and because these are the most obstructing of the devices can interfere with urination. Also prostate surgery if needed in the future can be very difficult in this situation. The rigid protheses is however good for men with poor hand mobility, who are relatively elderly, or who do not wish to have the increased risk of malfunction because there are more moving parts.

The one-piece inflatable penile prosthesis offers a compromise between the multi-component inflatable and the semi-rigid device. The downside to this device is that it can sometimes be difficult to manipulate. It doesn't get as erect as the rigid and it doesn't deflate as much as the multi-component inflatable. Additionally,
this device is very limited to the "average size penis," and if the patient has an extremely long penis is not an adequate device.

The multi-component inflatable prosthesis is what we term the "Cadillac" device. It gives the best appearance when erect and is the softest when deflated. It is probably the most popular and there are several major manufacturers including
American Medical Systems and Mentor.

Several penile prostheses are no longer in vogue and do not have a place in modern implant surgery.

The small carrying prosthesis introduced in 1973 was available in numerous sizes and lengths was a reasonable device, but really failed to produce the axial rigidity necessary for intercourse and was supplanted by better models.

The Jones Prosthesis was a malleable rod consisting of an outer silicone shell and silver wires and a twisted configuration that allowed some degree of torquing and thus causes some loss of axial rigidity. This was implanted with a trimable version to ensure adequate sizing.

American Medical Systems introduced the malleable prosthesis. This gives a very adequate erection, but one that can be very unsightly. That the normal erection
is a hydraulic event was really the rationale behind the inflatable device. It has three pieces including a reservoir to store the fluid, cylinders, and a pump which is placed in the scrotum. The pump transfers fluid from the reservoir into the cylinders, thus creating erection and when one desires to end the erection this process is reversed with a releaser deflate valve.

Another American Medical Systems product is the controlled expansion inflatable penile prosthesis which increases the actual rigidity. It has reinforced non-kinking tubing, revised pump, and a rear-tip system to allow adequate sizing. Mentor also
has an inflatable prostheses with both a two-piece and three-piece inflatable prostheses.

The type of surgery used for the implant is generally left to the surgeon's experience and type of device, but can include:

1) a perineal approach which is under the scrotum;
2) a penoscrotal approach which is at the base of the penis on top of the scrotum,
3) the protheses may be placed in the penile shaft, or
4) an infrapubic incision, which is an incision above the penis.

There are advantages and disadvantages to each device, and the most important part of penile prosthesis includes the proper selection of length and diameter to fit the corpus cavernosum, general dilation of the corporal body to avoid perforation proximally, with meticulous attention to detail to avoid infections, including preoperative preparation, intraoperative antibiotics, and copious irrigation during the procedure.
Complications of the penile implant include infections, which can be disastrous and treating an infected prosthesis actually can exceed the cost of the original prosthetic implant. Attempts to avoid infection include use of a surgical
bubble system to prevent particles and bacteria from getting access to the device.

Other complications include perforation of the corporal body which is the area where the prosthesis is held which can cause migration of the device. Management for this includes creating a Dacron graft to prevent migration. Perforation into the
urethra or glans penis can be disastrous and any perforation to a potentially infected area, such as the urethra, should require termination of the procedure.

Other problems include tubing kinks, fluid leaks, aneurysm, dilatation of the cylinders, breakage of the wire, the Silicone spillage, loss of rigidity to the prosthesis, erosion of the reservoir, spontaneous deflation, spontaneous inflation, penile curvature, which is a variant of Peyronie's disease, pump or pump reservoir
migration, phimosis, paraphimosis, things that go along with circumcisions.
All of these can be tremendous problems during the placement of a penile implant.

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