Penile Prosthesis Implantation 

Updated: Aug 31, 2016
Author: Richard A Santucci, MD, FACS; Chief Editor: Bradley Fields Schwartz, DO, FACS 

Overview

Background

Potency has always been something special in human culture. Its effects even have been intertwined within early Common and Church laws in Europe. For instance, laws required that marriages be consummated; unconsummated marriages were grounds for annulment. Considering this happened in an age when divorce was extremely rare shows the magnitude of the "offense" of impotency.

Impotency at that time had far-reaching consequences, which included social stigmatization, societal standing within the community, and legal ramifications on such issues as claims on wills and considerations of the legitimacy of heirs. Although less drastic today, potency still plays a large part in men's self-image and affects the relationship with their partners.

Before 1960, urologic therapy for erectile dysfunction (ED) was rare. ED was branded a psychiatric disorder with little surgical role. More recently, the pathophysiology of male sexual dysfunction has been elucidated, and both medical and surgical treatments of ED are now common.

History of the Procedure

The history of modern ED surgery began with the development of the inflatable penile prosthesis by Scott and Bradley in the early 1970s.[1] This surgical treatment became the treatment of choice in men with significant organic ED. Although the popularity of the inflatable penile prosthesis increased during that time, its design suffered from unacceptable failure rates and the need for surgical revision. Because of this, some urologists began using semirigid intracorporal devices to circumvent the reliability problems of early inflatables.

Today, penile prostheses have proven to be both reliable and durable, with approximately 20,000-30,000 devices implanted annually worldwide. In a 1996 survey, approximately 21,000 prostheses were implanted in North America, with another 5000 worldwide. With new social awareness regarding ED, many experts believe that future device implantations will become more prevalent because of failing medical therapy.

Problem

As defined by Pearman, an early leader in this field, ED is the inability to produce and maintain a functional erection because of pathology of the nervous or vascular system or deformation of the penis.[2] The surgical treatment of ED largely involves the placement of a penile prosthesis, although penile revascularization procedures have been described.

The most fundamentally basic prosthesis is the semirigid rod prosthesis, which consists of 2 rodlike cylinders that are implanted in the corpora cavernosa. The prosthesis can have a mechanically jointed "backbone" or have a malleable one that allows the phallus to be dressed in the upward or downward position. This prosthesis is generally considered for patients who are significantly obese, who have limited manual dexterity, or in whom abdominal hardware such as reservoir balloons cannot be implanted (ie, patients undergoing extensive abdominal/perineal surgery and those receiving peritoneal dialysis).

Models

See the list below:

  • Mechanical rods: Dura II (AMS [formerly produced by Timm Medical Technologies]) prostheses have a series of polyethylene segments that articulate in a ball and socket arrangement and are held in place by a central spring. A silicone membrane covers these devices, and they come in 2 width sizes—10 mm and 12 mm. The standard length of 13 cm is augmented by adding proximal and distal tip extenders.

  • Malleable rods (650/600M [AMS]; Acu-Form [Mentor])

    • The AMS models consist of a wire core surrounded by polyester covering and silicone outer jacket. Model 600 is available in 9.5-mm and 11.5-mm width sizes, and the model 650 is available in 11-mm and 13-mm width sizes. Lengths range from 12–20 cm and can vary with tip extenders.

    • The Mentor Acu-Form has a silver wire backbone with a silicone elastomer outer coat and is available in widths of 9.5 mm, 11 mm, and 13 mm. Cylinder lengths range from 14-27 cm. This prosthesis is chosen for its simplicity of usage and durability due to fewer vital moving parts.

  • Unitary inflatable penile prosthesis (Dynaflex [AMS])

    • In 1990, the Dynaflex model was introduced as a more robust replacement of the Hydroflex. It is a paired cylinder with all operating components contained within each device, and it consists of the distal tip, central chamber, and proximal reservoir. Rigidity is achieved by pumping 2-3 mL of liquid into the central chamber from the reservoir. Bending the cylinder 55° or more from horizontal operates a pressure switch to deflate the device and to return fluid back to the reservoir. These cylinders are available in 2 widths—11 and 13 mm—and various lengths.

    • This was a good attempt to allow for inflation and deflation in a self-contained unit; however, a patient with a broad penis usually has incomplete filling by the Dynaflex cylinders and, thus, may experience shifting and buckling of the device during intercourse. Some patients complain that it is difficult to inflate because of 2 separate distal pumps. In addition, this device is not suitable for patients with a history of distal urethral erosion because of pressure applied to tissue while the implant is operated.

  • Two-piece inflatable devices (Ambicor [AMS] and Mark II [Mentor] [production discontinued in 2000])

    • These devices are marketed to improve the ease of surgical implantation by eliminating the need for reservoir placement in the abdominal region. These prostheses consist of 2 inflatable cylinders that are inserted into the corporal bodies and are connected to a pump-reservoir located in the scrotum. The drawback of these devices is the limited reservoir capacity of 15-20 mL, which is available not only for cycling the 2 cylinders for full rigidity but also for allowing for flaccidity. As much as 5-10 mL of fluid is left in the cylinders during the flaccid state because of limited reservoir space. Patients with larger penises criticize these devices for insufficient volume to fully inflate the cylinders, and those with smaller penises complain of difficulty completely deflating the cylinders because of the limited reservoir capacity and resulting residual cylinder fluid.

    • These prostheses should be considered for patients in whom reservoir implantation is difficult or contraindicated, such as those who have undergone pelvic exenteration or renal transplantation.

  • Three-piece inflatable devices (700 series [AMS], Alpha 1, and Titan [Mentor])

    • These devices tend to be more complex and consist of 2 inflatable cylinders placed in the corporal bodies, a small pump that resides in the scrotum, and a large fluid reservoir located in the abdomen. Three-piece prostheses prove to be the most satisfactory devices because they produce the most natural-appearing phallus in both the inflated and deflated states, produce good rigidity (even for larger penises), and offer good flaccidity for social dress. In addition, the flaccid state of the 3-piece allows removal of pressure against the corpora and tunica albuginea. Thus, patients with diabetes, previous implantation extrusion, and previous infections may benefit from this type of inflatable device.

    • The AMS 700 series offers the Ultrex model, which allows for girth and distal expansion, while the CX imparts only girth expansion. The CX line is most applicable to patients with scar tissue or those with a tendency for penile curvature upon tumescence. A new innovation in this line includes the InhibiZone antibiotic surface treatment (rifampin and minocycline hydrochloride), which has been shown to decrease the incidence of infection by roughly half compared with uncoated devices (down to 0.7% in one large study[3] ).

    • The Bioflex cylinders used in the Alpha 1 and Titan models from Mentor allow expansion in girth with minimal axial elongation. These have proven to be very durable and resistant to cylinder aneurysm formation. The newer Titan model is identical to the Alpha 1, with the addition of a hydrophilic coating (polyvinylpyrrolidone), which decreases bacterial attachment and enables antibiotic absorption onto the implant when soaked in antibiotic solution prior to implantation. Preliminary data suggest a significant reduction in infection compared with the noncoated model. Both Mentor 3-piece devices now come equipped with a reservoir lockout valve, which has been shown to decrease the risk of autoinflation.

In summary, selection of the appropriate device for the individual patient is very important. Considerations include patient's preference and underlying medical condition, surgeon's preference, and cost of the device. The advantages of the semirigid devices include easier placement, less dependence on patient manual dexterity, a smaller risk of mechanical failure, and lower cost. The disadvantages include higher risk for device erosion, less concealability, and inability to change girth. The semirigid devices may suit patients who have dexterity problems such as those with severe arthritis and others with hand limitations that interfere with working a scrotal pump.

The ideal penile prosthesis would result in a normal-appearing penis when flaccid and erect. Younger patients with good hand dexterity often choose the 3-piece prothesis. This is especially important for those engaged in social settings, such as health club showers, or who wear form-fitting clothes. However, prospective patients should be counseled that penile prostheses do not achieve the full length achieved by natural erections.

Epidemiology

Frequency

Studies regarding the incidence of ED have proven difficult. Many experts believe that currently available data are often unreliable, especially when based on patient self-reporting. One study by Massey et al (1984) mentions ED incidence as 17 new cases per 100,000 man-years.[4] In other studies, as many as 40% of men interviewed reported some kind of sexual dysfunction. Interestingly, few respondents indicated that the problem was abnormal for their age, and even fewer stated they would seek medical treatment for their sexual problem.

Among men who seek medical help for sexual dysfunction, ED is the single most common presenting problem. It accounts for more than one half of all sexual complaints.

The Massachusetts Male Aging Study by Feldman and colleagues (1994) estimates that men in their early fifth decade of life have a 20% ED rate, and, by their eighth decade of life, close to 45% of men have impotence problems. They further estimate that, between the fifth and seventh decades of life, the probability of having complete impotence triples.[5]

Etiology

The causes of impotence are multifactorial, but diabetes and vascular disease are the most common etiologies. They are usually classified as hormonal, neurologic, psychological, arterial (ie, insufficiency), and venous (ie, venous incompetence).

Injury to nerves and blood vessels can result from trauma, radiation therapy, pelvic surgeries (including prostatectomy), and longstanding medical conditions (eg, diabetes, hypertension).

Neurologic causes include multiple sclerosis, tabes dorsalis, and other degenerative disease of the nervous system. Hormonal imbalance or deficiency, such as primary testicular failure, Cushing disease, Addison disease, and diabetes mellitus, can cause ED.

Sometimes, adverse effects of drugs such as parasympathetic- and sympathetic-blocking agents, antihistamines, and drugs of abuse may be a cause. Peyronie disease, which is characterized by scarring of the underlying fibrous covering of the erection bodies of the penis, can cause curvature that prevents adequate penetration and requires surgical intervention.

Pathophysiology

Penile tumescence is a complex integration of vascular and neurophysiologic events that culminates in the accumulation of blood under pressure. Fundamentally, the erectile components are surrounded by a thick fibroelastic sheath called the tunica albuginea, which allows a hydraulic effect in which intrapenile blood volume may increase 8-fold. The effect is an increase in intracorporal pressure that approaches systemic blood pressure and produces both penile volume and rigidity.

Blood supply to the penis is derived from the internal pudendal artery, which is a branch of the internal iliac artery. The internal pudendal artery becomes the common penile artery, which then branches into the bulbourethral, cavernosal, and the dorsal penile arteries. Tumescence depends most on the cavernosal arteries.

Penile tumescence is caused by microvascular events in the corpora cavernosa, which allow inflow of blood but restrict outflow. When blood enters the corpora cavernosa, it pressurizes the lacunar spaces within the spongy tissue of the corpora and translates this pressure to the tunica sheath. This pressure impedes venous drainage and results in blood being trapped in the penis and penile erection.

These microvascular events are triggered by neurologic events, which themselves are triggered by sexual stimuli. The parasympathetic nervous system offers the excitatory input to the penis and allows for the vasodilation of the penile vasculature. The parasympathetics originate from sacral spinal cord segments 2-4 and travel via the pelvic plexus into the pelvic nerve. The pelvic nerve joins the sympathetic nerve fibers that originate in the thoracic spine and together become the cavernous nerves as they exit the pelvic plexus. The cavernous nerves travel along the posterolateral aspect of the prostate and are susceptible to damage during pelvic surgery, such as a radical prostatectomy.

The sympathetic nervous system controls ejaculation and detumescence and has a partial role in maintaining erections. Sympathetic preganglionic nerve fibers originate from the intermediolateral cell column to form the thoracolumbar sympathetic pathway (thoracic segment 9 to lumbar segment 2). These preganglionic fibers exit the spinal cord as ventral roots via white rami to become part of the sympathetic chain ganglia. They synapse onto sacral and caudal lumbar ganglion cells. These cells then send postganglionic axons via gray rami to diverge into the pelvic, cavernous, and pudendal nerves that serve the urogenital tract.

Somatic pathways are important for penile sensation and ejaculation. Sensory afferents from the pudendal nerve become the dorsal nerve of the penis, which enters the urogenital diaphragm to innervate the penile skin, prepuce, and glans. The input from these sensory fibers helps maintain erections. These sensory fibers can be damaged by aging and diabetes.

Somatic efferents also originate from the pudendal nerve to innervate motor fibers of the pelvic floor and the bulbocavernous and ischiocavernous muscles. Contraction of these muscles occurs during ejaculation and influences the quality of erections.

Complex synaptic connections of the somatic and visceral neurons facilitate the coordination of erection and ejaculation. The parasympathetic and sympathetic nervous systems were once believed to be in an antagonistic balance to achieve erections; however, parasympathetic and sympathetic pathways are now known to act synergistically. Moreover, well-studied neurochemicals, such as acetylcholine and noradrenaline, are joined by newly discovered ones, such as nitric oxide, vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and serotonin, which are believed to contribute to normal erectile function.

Erectile function is a very complex and highly tiered system. Disruption along this chain of events can cause varying degrees of ED.

Presentation

See Etiology.

Indications

Penile prosthesis placement is indicated in a motivated patient with erectile dysfunction (ED) who desires reconstitution of penile function adequate for intercourse and in whom conservative treatment has failed.

Conservative treatments may include oral medications, such as sildenafil (Viagra); intracavernosal injections of vasoactive substances, such as prostaglandin E1 (PGE1); intraurethral deposition of PGE1 pellets (medicated urethral system for erection [MUSE]); and vacuum-assist devices. Recently, Rosenberg et al (2009) reported on successful results with the phosphodiesterase-5 inhibitor vardenafil. Vardenafil provided erection duration that was statistically superior to that conferred by placebo in men with ED, leading to successful intercourse.[6]

Patients with sickle cell anemia who have stuttering priapism and/or cavernosal scarring are also potential candidates for inflatable penile prosthesis, which offers not only a cure for their priapism but also a close approximation to normal appearance and function.

Men with Peyronie disease, which is characterized by a fibrous scar of the tunica albuginea, who have penile curvature may benefit from an inflatable penile prosthesis. The hydraulic effect of the prosthesis can frequently overcome the scar and help greatly to straighten the penis for adequate intercourse. Surgeons can also place penile prostheses after excision and grafting of the Peyronie plaque.

As discussed below, many preoperative tests can be used to assess ED (see Lab Studies). However, the actual practice of evaluating ED proves to be not only quite varied but also controversial. It depends on the practice of the individual urologists. Some practitioners argue that etiology is insignificant and that ED is treated in a stepwise fashion—from least to progressively more invasive treatments. Others argue that, from a medicolegal standpoint, basic evaluation and documentation should be instituted regarding the diagnosis of ED.

Physicians whose practices focus on treating ED say that many patients who seek treatment are interested in finding the etiology. The more involved and knowledgeable the patient becomes, the more he is willing to continue a particular treatment and report greater satisfaction. Basic tests such as a testosterone level assessment can help diagnose primary or secondary hypogonadism and can allow for possible medical treatment without surgical intervention.

In the authors' experience, a screening testosterone level should be obtained and ED diagnosis confirmed with ultrasound Doppler scan (at the very minimum). In addition to a careful history taking, physical examination, and the combination of biochemical test or tests with radiographic/physical findings, the diagnosis of ED is more reassuring to both patient and physician. Basic evaluation can prevent unwanted and unnecessary intervention.

Relevant Anatomy

To understand the relevant anatomy of erectile function is to understand the tunica albuginea. It is the tough covering of the corpora cavernosa and consists of inner circular layers with intracavernosal pillars that help tether the corporal bodies from overexpansion. Outer longitudinally arranged fibers run from the glans penis to the proximal crura at the base of the penis.

The tunica albuginea is made of elastic tissue with embedded collagen fiber that offers expansile capability and rigidity.

The thinnest area of the tunica is at the ventral 5- and 7-o'clock positions, where the longitudinal outer layers are thinnest. This becomes important intraoperatively during cavernosal dilation because the dilator can extrude out of the corporal body. Postoperatively, the prostheses can herniate out in these weakened regions of the tunica.

Emissary veins run obliquely between the inner and outer layers of the tunica. These veins serve to drain the corporal bodies and are important during erection. Also important is that the septum between the paired corporal bodies is incomplete and has good vascular communication. This communication is why vasoactive substances, such as PGE1, injected intracavernosally into one corporal body elicit an equal response from the contralateral side.

Arterial supply

The main arterial vascular supply to the penis comes from the internal pudendal artery, which is a branch of the internal iliac artery. The vascular anatomy of the internal pudendal artery varies greatly, and many men have accessory internal pudendal arteries. This circumstance can explain why some men with discrete obstruction of their pudendal arteries can still achieve erections.

The internal pudendal becomes the common penile artery, which branches into the dorsal, bulbourethral, and cavernous arteries. The cavernous or cavernosal artery plays the most important role in erectile function because it gives off the helicine arterioles, which supply the spongy trabecular tissue that stores and traps blood for erection. These helicine arterioles are the gatekeepers for erections, and their dilation is the aim of many vasoactive drugs.

Venous drainage

The erectile spongy tissue is drained by venules that later coalesce to form the subtunical venous plexus before exiting the tunica albuginea as emissary veins. After surfacing from the tunica, they eventually form the circumflex, periurethral, and superficial dorsal veins.

Contraindications

Some have listed psychogenic erectile dysfunction (ED) as a contraindication to penile prosthesis implantation. However, patients with severe longstanding psychogenic ED that is resistant to therapy might be considered for implantation as long as they understand the treatment is permanent. Nonetheless, the patient's mental health professional must be consulted prior to serious consideration of penile prosthesis implantation. Psychogenic ED is usually diagnosed based on results from a careful sexual history and diagnostic testing such as nocturnal penile tumescence (NPT) monitoring. Good morning erections with highly variable erection activity suggest a psychogenic factor.

The clinician may also consider the patient's reliability for follow-up care, as well as his manual dexterity. If the patient cannot operate his device, he must have a supportive and willing partner who can help. As mentioned above, the ability to operate the device must be considered when the type of device is chosen. The semirigid devices require less manipulation to operate.

Penile prosthesis implantation should not be performed in the presence of any systemic, cutaneous, or urinary tract infections. Patients with active or chronic infectious processes such as decubitus ulcers and venous stasis ulcers are at high risk for device seeding. In addition, no evidence of dermatitis, wounds, or other cutaneous lesions in the operative field should be present.

Conservative management regarding replacement of an infected prosthesis has mandated removal of the infected prosthesis with a delayed interval, usually 3-6 months, to allow adequate healing and eradication of the offending microorganism before replacement. However, rigorous salvage techniques have evolved that show success of one-stage replacement surgeries when no severe infection is present (eg, extrusion, gross purulence, immune compromise, severe diabetes).

 

Workup

Laboratory Studies

See the list below:

  • The workup of erectile dysfunction (ED) is controversial and not standardized among urologists. Some practitioners do not attempt to perform complex diagnostic procedures to determine the exact cause of the ED, reasoning that all organic impotence is treated in the same manner and that a specific diagnosis is not more helpful to the patient. Others, usually specialists in impotence, have a multitiered approach to the diagnosis of ED.

  • Endocrine disturbances are an important and potentially treatable cause of ED. The hypothalamic-pituitary-testicular axis is a very important and finely balanced force that helps regulate many bodily functions, including sexual drive and behavior. The hypothalamus secrets gonadotropin-releasing hormone that stimulates pituitary production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These in turn stimulate testicular function, including production of androgens such as testosterone and dihydrotestosterone. Both of these hormones are important for male genital fetal development, formation of male secondary sexual characteristics, and libido.

  • In developed adult men, testosterone greatly influences sexual behavior because (1) castrated men report decrease in sexual interest and performance, (2) hypogonadal men can have increased libido if supplemented with exogenous androgens, and (3) antiandrogens, such as those administered to treat prostate cancer, can greatly suppress sexual desire and performance in men.

  • The complete workup of ED should include a biochemical/hormonal profile to help delineate underlying endocrinopathies such as hypogonadism or hyperprolactinemia, which may be able to be managed medically.

  • Many clinicians investigate an initial testosterone level prior to sending a more exhaustive panel. Some specialists who focus on treating ED may elect to send a larger panel.

  • More extensive laboratory tests may include prolactin, free testosterone, and gonadotropin (both FSH and LH) in addition to a screening testosterone.

  • Of course, the first step to help a clinician investigate ED is a careful history and physical examination. In the physical examination, the clinician should be aware of secondary sexual characteristics, such as axillary and pubic hair distribution, as well as body habitus. In some instances, this provides clues about underlying endocrine problems.

  • When low levels of gonadotropins and testosterone are present, the clinician should be suspicious of a hypothalamopituitary cause and consider cranial imaging, such as MRI, to rule out pituitary or hypothalamic tumors or the empty sella syndrome.

  • Patients with thyroid problems experience sexual problems. Hyperthyroidism can cause decreased libido, most likely because of increased levels of circulating estrogens. Hypothyroidism can cause decreased testosterone levels and increased prolactin levels, causing erectile difficulties and decreased libido.

  • Some controversy exists regarding penile prosthesis implantation in persons with diabetes. Early studies indicated a high infection rate in persons with poorly controlled diabetes with elevated hemoglobin A1c levels. Subsequent studies challenged this practice, but, as mentioned above, the practice is not uniform. Persons with poorly controlled diabetes have a higher complication rate due to infection, compliance issues, and tissue healing. Therefore, their satisfaction rates are lower than those of persons without diabetes.

Imaging Studies

Many practitioners do not feel that preoperative imaging studies are required before penile prosthesis implantation. However, others prefer a complete workup of the etiology of ED, which can include arteriography, penile duplex with Doppler flow, and cavernosography.

  • Arteriography

    • This study rarely is performed, and practitioners sometimes pose the question, "Is it worth all the trouble?"

    • Penile arteriography proves to be extremely challenging because of the wide variation in penile arterial anatomy. Often, selective catheterization of the intended pudendal arteries is not only difficult but also extremely time consuming. Over time, the artery can spasm and produce a false reading, and, sometimes, accessory internal pudendal arteries can mislead the true extent of penile inflow.

    • The best arteriograms should be performed with cavernosal arterial distention to view the cavernosal arteries in their entirety and then follow the arteriolar flow.

    • The cavernosal arteries in the flaccid state are 0.2-1 mm in diameter, which can increase to 1-1.5 mm. In most instances, the spatial resolution, even with modern angiographic instruments, can account for a 30% error rate in vessel diameter. Operator inconsistency can further increase the error rate.

    • Many pragmatic experts question the value of arteriography, especially when considering what patients must undergo, its high cost, and the limited information it provides. Most experts do agree that its most useful application is in patients with pelvic trauma who are young and may have discrete lesions that are amenable to vascular intervention, such as to repair steal syndrome or simply to cannulize or bypass an area of obstruction or stenosis.

  • Duplex sonography

    • Urologists specializing in ED often use the duplex sonography modality. It has some clear advantages over other diagnostic tests. It can be performed in an office setting and is noninvasive. Imaging is good, and Doppler blood flow studies can be accomplished on individual cavernous arteries. In addition to its ability to demonstrate the vascular state of penile vessels, it also can reveal a venous leak, high-flow priapism, and calcium deposits characteristic of Peyronie disease.

    • The study entails first obtaining baseline images and measurement on the flaccid penis; then, a pharmacologic agent is injected to induce erection. Cavernous arterial diameter and pulsatility are recorded, as well as any anomalous anatomy or findings. This information allows the urologist objective criteria concerning flow velocity and arterial caliber to gauge vascular health.

    • Some authors agree that a peak systolic velocity of greater than 35 cm/s indicates a normal arterial supply, and those with a velocity of less than 25 cm/s are considered to have severe arterial disease. More subjective is the pulsatility or ability to dilate regarding penile arteries. Most experts agree that, in general, a forceful pulsation with good change in arterial diameter between systolic and diastolic phases indicates normal arterial function and signals a healthy arterial system.

    • Proponents of duplex ultrasonography say that it is an effective modality to evaluate vasculogenic impotence. However, it also has problems that can affect accuracy; the procedure is performed in a nonsexual office setting, patients vary in their response to vasogenic agents in both dosage and time to erection, and the test is very operator-dependent.

  • Cavernosography

    • This study uses radiocontrast solution injected into the corpora cavernosa during an artificial erection. The injection is a percutaneous intracorporal infusion of fluid via a needle or catheter. It should always be performed after a vasoactive agent is injected in an attempt to induce erection.

    • By performing this study, clinicians hope to visualize areas of venous leak, where blood normally trapped during erections leaks out so that arterial inflow cannot maintain adequate erections.

    • Areas of leak include the glans, corpus spongiosum, superficial and deep veins, cavernous veins, and areas of Peyronie plaque. The original thought was that if these areas could be ligated surgically, erectile function could begin to favor arterial inflow. However, enthusiasm for cavernosography and venous ligation has waned because of poor long-term results.

Diagnostic Procedures

See the list below:

  • Nocturnal penile tumescence testing

    • The NPT test takes advantage of the natural sleep-related erections found in potent men during rapid eye movement (REM) sleep. The primary goal of NPT testing is to distinguish organic etiology from psychogenic causes of ED.

    • NPT testing was once associated with a wide assortment of tests, including those for sleep study, such as electroencephalography, electro-oculography, electromyography, and video monitoring. Today, many urologists use an abbreviated portable home model (RigiScan), which a patient can take home after he is instructed on its proper use. Essentially, it entails applying a measuring device to the penis that measures the number of nocturnal erections, axial rigidity at base and tip, duration of erection, and level of maximal rigidity.

    • NPT testing and the introduction of the portable RigiScan for home use in 1985 still have some controversies, particularly regarding the lack of standardized parameters and limited clinical trials.

    • Cilurzo et al (1992) suggest the following for normal NPT parameters:[7]

      • Achieving 4-5 erectile episodes per night

      • Mean duration of erectile episodes greater than 30 minutes

      • Increase in circumference of greater than 3 cm at base and 2 cm at tip during erectile episodes

      • Greater than 70% maximal rigidity at both tip and base during erectile episodes

    • NPT testing, although expensive, can help differentiate organic from psychogenic impotence and thus prevent further unnecessary workup and possible unwarranted intervention.

 

Treatment

Medical Therapy

Nonsurgical treatments for erectile dysfunction (ED), such as vacuum devices, intraurethral alprostadil pellets (MUSE), oral sildenafil (Viagra), and intracavernosal prostaglandin injection, should be attempted prior to penile prosthesis implantation. In the authors' experience, patients in whom conservative treatments have failed tend to be more satisfied with their choice of surgical intervention.

In patients with hypogonadism, long-term androgen replacement can obviate the need for penile implant surgery. Oral or depot testosterone can be administered, and, if sufficient to maintain testosterone level, transdermal patches may be prescribed. At least an annual prostate-specific antigen (PSA) test should be performed because men on testosterone supplementation are at higher risk for developing prostate cancer.

Surgical Therapy

The criterion standard for erectile surgery is penile prosthesis implantation. However, in the rare patient whose discrete and focal arterial lesion can be identified on arteriography, revascularization procedures may be indicated. Further considerations for optimizing outcome include selecting patients whose etiology is previous pelvic trauma and patients who are young, do not have diabetes, do not smoke, and have no underlying neurologic disease.

Many techniques for the placement of penile prosthesis exist, including infrapubic, penoscrotal, perineal, and subcoronal approaches. The subcoronal approach is suitable only for implantation of semirigid devices. The perineal approach for implantation of semirigid prostheses is seldom used. Only the infrapubic and penoscrotal approaches are suitable for implantation of 3-piece inflatable devices. The infrapubic approach has a distinct advantage over the scrotal approach in the ability to place the reservoir under direct vision. However, in the eyes of the authors and many others, the disadvantages undermine this one advantage. These disadvantages include possible damage to the dorsal penile nerves with accompanying sensory loss, limited exposure of the corpora, and inability to fixate the scrotal pump via this approach.

The authors prefer the penoscrotal approach because it provides very good exposure to the corporal bodies, allows for concomitant repair and excision of Peyronie plaque near the base of the penis, and facilitates the placement of scrotal pumps. Although many techniques exist, they generally follow the same principles. This article describes the authors' technique for penile prosthesis placement via the penoscrotal approach.

Preoperative Details

Preoperative preparation entails a detailed checklist of items. The patient should be free of infection in the urine, on the skin, or elsewhere. Perioperatively, many infection control measures have been suggested, but few methods have been evaluated carefully in a randomized fashion.

Some surgeons suggest that the patient shower with a surgical scrub the day before and the morning of surgery to decrease skin bacterial colony count. One hour prior to surgery, a wide-spectrum antibiotic, such as cefazolin (Kefzol or Ancef) 1 g IV and gentamicin 80 mg IV, is administered. Oral fluoroquinolones 1-2 hours prior to surgery have been shown to produce excellent corporal tissue levels and to provide excellent coverage. In the operating room, the patient can be anesthetized either with regional or general anesthesia. The authors prefer spinal or general anesthesia, although some do perform this procedure under local anesthesia, usually in patients at high risk for anesthetic complications. Under anesthesia, the patient is shaved at the surgical site and the hairs are removed from the field.

The authors have adopted a rigid regimen of infection control practices that have resulted in some of the lowest published rates of prosthesis infection (national reported range, 0.6-8%). To decrease the chances of airborne infections, only clean laminar flow operating rooms, such as those used for joint replacement procedures, are used. Iodinated preparation solutions (Baxter iodine scrub and iodine preparation solution) are used to scrub and then paint the lower torso, including the abdomen, genitalia, bilateral thighs, and inguinal folds. Next, the bladder is catheterized to drain the urine; then, it is irrigated with antibiotic solutions (bacitracin 50,000 U and gentamicin 160 mg in 1 L NaCl). Finally, a solution of 50% iodine preparation and 50% antibiotic solution is used to irrigate the urethra as the Foley is removed, taking care to prevent iodine from entering the bladder because it is an irritant.

The surgical team scrubs for at least 15 minutes and returns to scrub and prepare the patient for another 15 minutes with iodine scrub and preparation. The patient is draped carefully in the standard surgical fashion. After draping, the surgical team changes their gloves and double gloves. With this precautionary regimen, the authors have significantly reduced the infection rate to 0.4%.

Intraoperative Details

A 16F caliber Foley catheter is inserted and capped with a catheter plug. A self-retaining circular retractor (eg, Scott retractor by Lone Star Medical Systems) with elastic hooks is placed over the genitalia. A 3-cm incision is made at the penoscrotal junction at the mid raphe and carried down to the superficial/dartos fascia. Once the dartos fascia is divided, the hook elastic retractors are used to hold the surgical field open. The next step is to dissect over, identify, and then avoid the corpus spongiosum by moving laterally to expose the corpora cavernosa on each side of the spongiosum. A small (1-cm) corporotomy incision on the corpora cavernosa is made after placement of 2-0 Vicryl (polyglactin) stay sutures as depicted in the image below. This exposes the corporal spongy tissue.

Exposure of the corpus cavernosum followed by plac Exposure of the corpus cavernosum followed by placement of stay sutures in the walls of the corpus followed by corporotomy in anticipation of placing an intracavernosal rod. (Photograph courtesy of Chirpraya B. Dhabuwala, MD).

A blunt Hegar dilator is used to dilate the spongy tissue of the corpus cavernosa from 8-14 mm proximally and 8-11 mm distally as depicted in the image below. A Dilamezinsert (DMI) instrument is used to measure the corporal length so a prosthetic device of the proper length can be chosen. Meanwhile, throughout the operation, antibiotic solution is misted over the surgical sites and over the instruments at regular intervals and when each anatomical compartment is opened.

Proximal dilation of the corpus with Hegar dilator Proximal dilation of the corpus with Hegar dilator. (Photograph courtesy of Chirpraya B. Dhabuwala, MD)

The appropriate 3-piece prosthesis is selected, the package is opened, and the contents are sprayed copiously with antibiotic solution. The cylinder and pump is checked for integrity, and all air is removed by infusing sodium chloride solution and then back-suctioning to collapse the cylinders. Next, the proximal cylinder is placed gently into the proximal cavernosal body and seated down into its position next to the pubic bone as depicted in the image below.

Seating of the proximal portion of the prosthesis Seating of the proximal portion of the prosthesis into the corpus. (Photograph courtesy of Chirpraya B. Dhabuwala, MD).

The distal half of the cylinder is brought through the distal corporal body with a Furlow inserter. This instrument passes a needle through the glans penis and is designed to avoid the urethra. The needle is removed, and the accompanying thread is used to pull the cylinder snugly against the distal glans (still within the cavernosal body as depicted in the image below. This procedure is repeated for the contralateral side.

Seating the distal portion of the prosthesis into Seating the distal portion of the prosthesis into the distal corpus using the suture attached to the prosthesis. Previously, the suture has been passed out the glans penis using a Furlow inserter. (Photograph courtesy of Chirpraya B. Dhabuwala, MD).

Next, the open corporal bodies (corporotomies) are closed using 2-0 braided dissolvable suture (polyglactin by Vicryl Ethicon), carefully reapproximating the tough tunica albuginea. A P-3 retracting tool is used to push down on and protect the prostheses from the needle when the corpora are being closed. After closure is complete, the tubing from the cylinders is visible coming from inside the corpora and connected to the control pump.

The next consideration is placement of the abdominal reservoir. If the patient has received prior pelvic radiation treatments or has undergone pelvic surgery, placing this through a separate abdominal incision can be prudent. Otherwise, the reservoir can be tunneled from the scrotal area via the external inguinal ring, through the transversalis fascia to place the reservoir into the retropubic space (also called the space of Retzius). Once there, the reservoir is filled to the correct volume (60-100 mL); then, the tubing is brought to the pump, trimmed to length, and connected to the pump. The prosthesis is tested for inflation, deflation, and leaks. It is left in a semirigid state to help tamponade potential bleeding and hold the tissue in the correct shape.

The pump must now be inserted in a scrotal subdartos pouch as depicted in the image below. Using blunt dissection, a subdartos space is created in the anterior dependent area of the scrotum, and the pump is placed there for ease of location and usage. Some have used a nasal speculum to help with this dissection.

Bluntly creating the subdartos pouch, which will h Bluntly creating the subdartos pouch, which will house the pump. (Photograph courtesy of Chirpraya B. Dhabuwala, MD).

If necessary, the process of penile molding can take place at this juncture for patients with asymmetric phallus and Peyronie plaque. In the inflated state, rubber shods are clamped on the prosthesis tubing to take up the extra pressure that would compromise the control pump valves. The surgeon can gently torque and bend the asymmetric penis into a more symmetric shape.

Finally, any light bleeding is detected and electrocauterized. The scrotal/dartos fascia is closed in 2 layers with medium polyglactin (Vicryl) sutures, and the skin is closed with a running subcuticular fine dissolvable suture. Then, the patient is cleaned, the potentially irritating iodine paint is washed away, and the Foley catheter is connected to a dependent drainage bag.

Some key items regarding operative techniques should be remembered. Accurate measurement of the corporal bodies is key to good device performance.[8] Isotonic solution should be used in the device because silicone is semipermeable over time. The phenomenon of autoinflation, which is inflation of the prosthesis caused by differential pressure changes without manually pumping the device, can be inconvenient. It is largely avoided by placing the reservoir in the retropubic space, by performing back-pressure tests when filling the reservoir to ensure the correct volume is added, and by keeping the device deflated and the reservoir full when the pseudocapsule is forming around the reservoir.

Frequently, the authors purposely leave 5-10 mL of the stated reservoir capacity unfilled. This allows for adequate filling of the prosthesis without having to worry about differential pressure. The new Mentor devices with a reservoir valve lockout have proven to be very successful in preventing autoinflation.

Finally, the companies that make penile prostheses often make their technical and sales representatives available to assist in the operating room. This can be particularly useful for surgeons who do not routinely place these devices.

Postoperative Details

The next morning, the Foley catheter is removed, the prosthesis is partially deflated, and the patient is discharged home with a follow-up visit in the office for further instructions and oral antibiotics for approximately 14 days.

Follow-up

The patient is instructed to refrain from sexual activity for 6 weeks. After 6 weeks, the patient is instructed on the usage of the inflatable penile prosthesis.

For excellent patient education resources, visit eMedicineHealth's Men's Health Center. Also, see eMedicineHealth's patient education articles The Male Anatomy, Impotence/Erectile Dysfunction, and Erectile Dysfunction FAQs.

Complications

After the prosthesis is placed, patients may experience modest penile shortening in the range of about 2 cm. This must be discussed with the patient and partner prior to any surgical intervention. Patients also should be aware that they may never achieve their most youthful length and girth due to underlying pathology such as fibrosis and plaque formation. Other issues that should be addressed include possible erosion of the device over time and the possibility of implant infection despite careful preoperative preventive means. An average infection rate ranges from 2%-4% over a 2-year period with a national wider range of 0.6%-8%. Most infections become evident within the first year and are due to seeding during implantation.

Some bacterial species, such as Staphylococcus epidermidis, can lie dormant for as long as 2 years before causing clinical signs of infection. Risk factors for infection include prolonged hospital stay, diabetes mellitus, concomitant surgical procedures such as artificial sphincter implantation and circumcision, spinal cord injury, paraplegia, and the use of additional foreign bodies during implantation. None of these conditions or circumstances are contraindications to implantation but rather emphasize increased attention to infection prevention. Another potential complication is mechanical failure, which can occur with use and may require repeat surgery for revision or replacement. Overall, reoperation rate for mechanical failure is about 5% for the life of the prosthesis (5-10 y).

Intraoperative challenges occur and require good problem-solving skills and creativity. Most difficulties concern prosthesis cylinder placement. Inadequate dilation of the corporal bodies can cause prosthesis migration, unnatural-looking erections, and pain, among other problems.

Corporal crossover due to the thinness of the distal corporal septum that divides the corporal bodies can occur. Vigorous dilation can cause a crossover injury where the prosthesis cylinders occupy the same corporal body. This is most likely due to not dilating in a lateral, but rather in a medial, fashion. If recognized early, it can be corrected by redilating but maintaining a lateral course and keeping another dilator in the contralateral corporal body. Recognizing this problem intraoperatively is important to avoid penile curvature, pain upon inflation, and unnatural-looking erections.

Penile corporal fibrosis is a common finding among patients who have undergone intracavernosal injection therapy, those with history of priapism or Peyronie disease, and those with penile trauma or reimplantation of prosthesis after infection. Multiple dilations are necessary, usually starting with blunt-tipped Metzenbaum scissors to gently spread the corpora. Other dilators, such as Hegar, Brooks, or DMI, may be used in conjunction to carefully and deliberately dilate/dissect the fibrosed corpora. Sometimes, additional incisions must be made, including distal corporotomies to dilate under direct vision and dissect away fibrosed tissue.

Montague and Angermeir (2003) reported on a transverse penoscrotal approach, which they used in men with severe corporeal fibrosis in whom scarring was due to ischemic priapism or removal of an infected prosthesis. An inverted "T" incision was made, exposing almost the entire corpus cavernosum on each side. They found that this incision obviates blind dilation, making the dissection of the corporeal bed much safer.

Pathak et al (2005) also described a novel approach whereby a rectus fascia graft was harvested for corporeal reconstruction. Augmentation of the tunica with autologous rectus fascia and implantation of a penile prosthesis was successfully completed in 15 patients with severe scarring. No evidence of graft infection or erosion was noted after a mean follow-up of 18 months.[9]

In certain instances, defects in the tunica albuginea require patching with material such as Gore-Tex or cadaveric tissue. When extensive fibrosis that may jeopardize the operation is encountered, a viable consideration is to abandon the very fibrosed side and place a single cylinder on the contralateral side. In general, when extensive nondilatable corporal fibrosis is encountered, downsizing the inflatable prosthesis device is important. Certain manufacturers offer a line of prosthetics that have limited lateral girth and may help in this application (eg, AMS 700CXM).

Proximal corporal perforation can occur after vigorous proximal dilation, especially in the presence of extensive fibrosis. To avoid this, careful initial sharp dissection with blunt-tip Metzenbaum scissors should be attempted. The corporotomy incision may require lengthening to achieve adequate exposure. Should perforation occur, it can be recognized with differential measurements of the corporal length greater than 1 cm, feeling of a sudden "give" during the dilation process, and inadequate dilator seating compared with the contralateral side.

Correction of proximal perforation can include securing prosthesis tubing sheath or rear tip extender to the tunica albuginea. Over time, the perforation heals because of scar formation around the cylinder. A better alternative is repair by creating a wind-sock patch with Gore-Tex, Dacron, or autologous/cadaveric fascia. By placing this wind-sock, the defect is covered and fixed in place with nondissolvable suture, and it allows for good seating of the rear-tip of the cylinder.

Urethral perforation is another possible complication of extensive fibrosis. In the authors' institution, the placement of the prosthesis is abandoned and healing is awaited after any necessary repair prior to another attempt after 4-6 weeks. Other surgeons may choose to modify their operation, including stenting the urethra and draining the bladder with Foley catheter and placing a single cylinder on the unaffected side. This injury is usually recognized intraoperatively by blood in the urine, blood at the meatal tip, and irrigation fluid exiting the urethra.

Glans bowing can occur when the prosthesis is inadequately sized. This ventral deflection of the glans is commonly called the "SST deformity" after the Concorde supersonic transport aircraft. The Concorde's nose-cone tips downward during takeoffs and landings to provide pilots better visibility, but urologists have adopted this metaphor for distal glanular penile curvature. SST deformity should be checked intraoperatively to ensure adequate dilation of the distal corporal bodies. If the defect does exist, further dilations may be necessary, and resizing the prosthesis may be in order. In rare instances, a dorsal plication procedure may be necessary.

An important topic that should be addressed is the concept of salvage implantation as pioneered by Mulcahy.[10] He describes removing infected penile implants, cleansing the wound with a series of antiseptic solutions, and then placing a new prosthesis in the same procedure. During the cleansing and irrigation process, the biofilm or slime made by the microorganism (eg, staphylococcal bacteria) should be washed from the newly formed pseudocapsule.

The pseudocapsule is a fibrous sheath that will form naturally around the inflatable prosthesis as the healing process begins. Once formed, it has a very poor blood supply and becomes a barrier to intravenous antibiotics. Bacteria can grow in this protected zone around the prosthesis and can begin to form colonies with their associated biofilm. The mechanical washing with antiseptics, as Mulcahy describes, is the only feasible way to attempt to eradicate an infectious process during a salvage procedure.

His irrigation solution includes a specific protocol of kanamycin-bacitracin, hydrogen peroxide, and iodine solution, followed by pressure washing with vancomycin and gentamicin. This sequence is then repeated. Mulcahy reports about an 80% success rate with his salvage technique. However, he warns that certain conditions make salvage success unlikely. These conditions include infection with a virulent organism and patients with a serious systemic illness (eg, septicemia, diabetic ketoacidosis) or necrotizing infections, including those with frank purulent drainage.

In addition, a mini-salvage procedure, which entails a curtailed version of Mulcahy's irrigation protocol, is espoused as standard practice by many urologists in replacement of uninfected prostheses, as biofilm formation is documented to occur on virtually all explanted prostheses. This biofilm is believed to be responsible for the higher rate of infection seen with replacement, even if the original device was clinically infection-free.

In the care of a skilled and experienced surgeon, most prostheses are placed without difficulty and function well for many years.

Outcome and Prognosis

Generally, the authors' experience at Wayne State University Department of Urology is that the vast majority of patients in whom conservative therapy has failed and who subsequently underwent a penile prosthesis implantation are very satisfied with inflatable penile prostheses. Of men who have undergone this procedure, 95% are happy about their decision to have surgery. Patient satisfaction with surgery is bolstered by supportive staff and low infection and malfunction rates.

National multicenter studies show similar satisfaction rates, ranging from 69%-89%. Using validated questionnaires, Akin-Olugbade et al (2006) reported that predictors of lower satisfaction included Peyronie disease, a body mass index of greater than 30 kg/m2, and previous radical prostatectomy.[11] Of all modes of ED treatment, surgical therapy yielded the highest satisfaction rates. Interestingly, even despite good mechanical function, the satisfaction rating of the patients’ sexual partners is comparatively lower (60%-70%). Some experts attribute this to a psychological factor (ie, unrealistic expectation of the implantation). Jarow et al (1996) recommended counseling the patient and partner on realistic goals of implants and informing them that an implant may not be as satisfying as a natural erection.[12]

A study by Carvalheira et al that interviewed 47 men who underwent penile prosthesis implantation found that the majority of men (79%) reported to be satisfied with penile prosthesis implantation. The four main themes for men’s satisfaction were psychological factors (reported 54 times), improvement of sexual functions (reported 54 times), relationship factors (reported 11 times), and improvement in urinary function (reported 3 times).[13]

On average, patients may wear out their prosthesis in 4-8 years. Revisions become more common as time passes. Some of the older patients have undergone as many as 4 revisions over 2 decades of use.[14]

Goldstein et al (1997), studying the 3-piece Mentor Alpha 1 prosthesis in multicenter trials, reveals a Kaplan-Meier actuarial device survival rate of 98% at 12 months, 93% at 24 months, and 85% at 36 months.[15] Dhar et al (2006) studied the AMS 700CX/CXM and found that the implant mechanical survival rate was 81% after a median follow-up of 91.5 months.[16] Lux et al (2007) reported on 147 patients with newest version of the AMS Ambicor 2-piece device, and only one implant had a mechanical failure over a mean follow-up of 38 months.[17]

A prospective study by Rolle et al found that penile length restoration with the use of the “sliding” technique represents an effective option for end-stage Peyronie's disease associated with erectile dysfunction and severe shortening of the shaft.[18]

With steady improvements regarding prosthesis material and construction, long-term survival of the modern implants shows promise.

Future and Controversies

The popularity and success of sildenafil (Viagra) and it competitors, vardenafil (Levitra) and tadalafil (Cialis), has brought to light the prevalence of erectile dysfunction (ED). Men who would have ignored their ED problem in the past are now realizing the potential help available.

Along with development of surgical/prosthesis improvements, new medical agents are emerging for evaluation. Among them is apomorphine, a direct central dopamine receptor agonist. Used for parkinsonism in the past, it has a lasting side effect of eliciting durable erections in small studies of patients. It has a sublingual formulation, which is currently under clinical investigation, but time will tell if it proves as successful as the phosphodiesterase-5 inhibitors.

When men with ED begin trying conservative therapy (which fails in some), the authors believe that these patients will eventually seek surgical options such as inflatable penile prostheses. With this new influx, urologists may witness a second wave of patients seeking surgical correction for their impotence.

The future holds more promise. Currently, Mentor 3-piece inflatable prostheses come equipped with a lockout valve designed to prevent autoinflation. Initial studies have shown a decreased incidence of autoinflation, from 11% to 2%.[19] The remaining 2% incidence was attributed mainly due to improper usage. The newest AMS 700 devices now also incorporate a lockout mechanism, and anecdotal reports have been positive.

Other mechanical improvements include buttressing of the sites most prone to breakage, notably the tubing junctions. The incorporation of rear-tip extenders that lock onto the prosthesis cylinders are one of the newest improvements for both the Mentor and AMS implants. This innovation is of particular value when explanting or replacing a device, since rear-tip extenders commonly slip off the main body of the cylinder and can be difficult to retrieve from the proximal corpora. Retrieving these old rear-tip extenders is critical before implanting a new device in order to minimize infection. The new locking rear-tip extenders appear promising in avoiding this problem.

Prostheses impregnated with antibiotics, such as the InhibiZone coating (rifampin and minocycline hydrochloride) used in the AMS 700 series, is proving to significantly decrease the incidence of postoperative infection.[3, 20] Similarly, the new Mentor Titan 3-piece device is coated with polyvinylpyrrolidone, a hydrophilic substance that decreases bacterial adherence and absorbs topical antibiotics. This innovation has also been shown to decrease the incidence of infection.[21] Another avenue being explored to increase satisfaction with penile prostheses is dealing with "cold glans," which is expected because the prosthesis does not affect glans engorgement. Topical alprostadil cream is showing some preliminary promise as an adjunct to penile prosthesis in increasing erectile satisfaction by increasing engorgement of the glans.[22]