The use of urologic implantable prostheses has increased since the modern forms became available in the early 1970s. Penile prostheses are generally of two types: semirigid penile prostheses (SRPPs) and inflatable penile prostheses (IPPs).
SRPPs provide rigidity at all times. They are paired cylindrical devices, which are implanted within the corpus cavernosa. The devices are activated by means of a hinged segment or by repositioning a flexible metal core. Two types of SRPP commonly in use are the Finney and the Small-Carrion. These types of prostheses are less expensive and more durable than the IPP type. Disadvantages of the SRPP include reduced ability to conceal the device and need for proper sizing of the device prior to implantation. Incorrect sizing can lead to sagging of the glans if the device is too small or pressure necrosis if the device is too large.
IPPs can inflate and deflate by a hydraulic mechanism. These devices are composed of paired inflatable cylinders within the corpus cavernosa, and a pump and reservoir that are commonly located within either the corpora or the scrotum. Many types of IPPs exist that use different versions of the general concept. As would be expected by the increased complexity of IPP devices, they tend to be more expensive and have a greater rate of mechanical failure. Because of the more natural appearance of this type of device, however, IPPs are still widely used despite their drawbacks.
Erosion, which is a complication of both types of prostheses, occurs through a number of mechanisms, the most prominent being the anatomic relationship of the corpus cavernosa to the urethra. The corpus cavernosa are physically in closest contact with each other in the region of the fossa navicularis. Therefore, the highest degree of pressure exerted by the prostheses to the urethra occurs in this region. Given their constantly rigid state, SRPPs have a higher rate of erosion, which is often worsened by inappropriate sizing of the device. This is particularly the case with either patients who have indwelling catheters or those who perform intermittent catheterizations. Introduction of the catheter into the lumen of the urethra adds to the local pressure and can lead to necrosis.
Because a large percentage of patients requiring penile prostheses have an underlying neurologic deficit, erosions will often present as a prosthetic device protruding from the urethral meatus. Patients with intact sensation frequently complain of pain or discomfort at the site of necrosis. In the case of SRPPs, the protruding device can usually be removed by simple extraction with forceps, followed by careful urethral catheterization and urologic follow-up.
Infection is the most devastating of complications associated with penile prostheses and nearly always results in removal of the prostheses, with long-term antibiotic coverage and wound drainage. Inability to clear the infection fully, as well as scar tissue formation, can limit the possibility of reimplantation of another device.
Penile prostheses incite a foreign body reaction within the host. An inflammatory reaction occurs shortly after implantation and results in the formation of a scar-tissue capsule. Though this capsule helps hold the device in place, it also acts as a potentiator of infection. The surface of the prosthesis provides a site for bacterial adherence, as well as a local environment that is resistant to host defenses. The periprosthetic space created between the prostheses and the capsule acts as an ideal site for the growth of bacteria and the production of an extracellular matrix. This extracellular matrix, along with the relative avascular nature of the capsule, limits the ability of immune cells and antibiotics to penetrate and eradicate infection.
The vast majority of prosthetic infections occur at the time of implantation. This being the case, it makes sense that most infections present within the postoperative period and that the most common infective agents are gram-positive cocci like Staphylococcus epidermidis.8 Reduction of prosthetic infection rates is thus aimed at perioperative precautions, including the use of prophylactic antibiotics. Late infection of established prosthetic devices does occur, however. Hematogenous seeding can occur, so it is currently recommended that patients with penile prostheses be treated in accordance with the American Heart Association's bacterial endocarditis prophylaxis guidelines during procedures likely to induce bacteremia.
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