What Is an Infection of Prosthetic Devices?
Implantable and prosthetic devices have grown in use recently due to research and development and better availability. Electronic and mechanical implantation has been used in many specialties successfully.
Types of implants and prosthetics vary in indications and materials used:
- Breast implants and dermal fillers for cosmetic or reconstructive purposes
- Intrathecal (cerebrospinal fluid) shunts and pumps, and epidural neurostimulators
- Cochlear implants
- Artificial joints
- Intraocular lenses
- Mesh used in urogynecology
- Cadaver, animal (porcine, bovine), and human donor tissues
- Arteriovenous shunts for dialysis
- Contraceptive and hormonal subdermal and intrauterine delivery capsules
- Wearable prosthetics (limb-replacement)
Problems associated with implantable devices arise from the following:
- Rejection due to a foreign body response
- Infection introduced by the device or the device acting as a reservoir for infection
- Device failure
The two complications of rejection and infection are often simultaneous, each synergistic with the other. Rejection induces an immune response which attracts transudates (fluid) which can be a nidus of infection. Overt infection can create an exudate (inflammatory fluid such as pus) that can hasten the rejection process. Device failure in an otherwise sterile environment is limited to the cessation of device benefit, which in the case of drug delivery can be important to health.
With wearable devices such as prosthetic limbs, improper fitting or sizing can cause pressure points that are prone to breakdown and subsequent infection.
Infection in Implantables and Prosthetics
Sterile procedure is a methodical process, and infection risks increase with breaks in sterile procedure during the implantation process. Besides the risk of device malfunction in a septic environment, there is the risk of infectious spread to adjacent or target tissues.
For example, an intrathecal pain pump, which is filled via percutaneous injection, communicates with the cerebrospinal fluid and can be a source of bacterial meningitis. Infection of an artificial joint risks further joint damage which can negatively impact the success of future attempts to implant prosthetics. Infected heart valves can seed the entire arterial tree with septic emboli, risking distant organ infection and systemic sepsis.
Timing of Diagnostics
The timing in diagnosing prosthetic device infection is usually straightforward in that most occur due to the implantation process itself. Otherwise, infection distant from the time of implant can be caused by exposure to infectious agents in the environment, as in refillable pumps or due to changes in the immediate implant environment that encourages opportunistic infections, such as in prosthetic heart valve endocarditis.
Initial Diagnostic Approach
The diagnostic approach is directly related to the prosthetic suspected. Diagnostics include investigating the type and source of the infectious agent which will drive treatment, as well as testing for device function that may drive the decision to remove or replace it.
- A focused physical exam: Centering on the device can assess function as well as symptoms associated with malfunction or device-related infection
- Blood Tests: general testing includes a complete blood count to assess the leukocytosis (white blood cell count) to determine the general severity of infection. More specifically, blood cultures are done to identify or rule out bacteremia and the risk of sepsis.
- Aspiration of fluid for culture from suspected sites of infection: Such as joints, tissue spaces around the implanted device, or obvious pockets of exudate or transudate
- Cerebrospinal fluid: Via lumbar puncture can determine the markers for intrathecal infection (altered protein and glucose) as well as retrieve samples for culture
- Diagnostic imaging: echocardiography (in the case of heart valves), ultrasound (arteriovenous grafts, breast implants, etc.), and CT/MRI to evaluate in-situ placement and function
Later Diagnostic Testing
The success of the device relies on eradication of infection, so treatment testing using the above modalities is crucial to document a “test of cure.”
Management and treatment depends on identifying the infection and an appraisal of prosthetic or implant function.
Management of Infection
Culture of the infecting organism is crucial for a rational choice of antimicrobials (antibiotics, antivirals, or antifungals). There are statistical flowsheets that recommend specific antimicrobial regimens for specific prosthetics. Close surveillance, necessary to judge treatment efficacy, is via many of the diagnostic tests done initially: blood tests and cultures, fluid aspiration, lumbar puncture, and imaging studies such as X-rays, ultrasound, CT, and MRI.
Management of Device Failure or Malfunction
Failure of implantables can be subtle initially. Clinicians involved in their insertion and maintenance require a heightened sensibility for even small functional variations. Identification and treatment of infection or overt rejection requires a functional assessment via measurements of the desired outcome of function (homeostasis, as in artificial heart valves) and possibly electronic “interrogation” (as with intrathecal pumps, neurostimulators, or cardiac pacemakers).
Devices that have failed or which are at risk for failure or increase the likelihood of adjacent tissue jeopardy should be removed. If survival is jeopardized without the prosthetic, removal should be accompanied by immediate replacement; if not, definitive (“test of cure”) clearance of the infection should be evident before re-introducing the foreign body.
Considerations for Wearable Prosthetics
The loss of a limb alters the entire dynamic of bodily function, from the altered balance and center-of-gravity from lower extremity loss to repetitive strain injuries from compensating for upper extremity loss. These compensatory changes are multiplied with the use of prosthetic limbs. If fitting for a limb is not perfect, pressure points will indicate the faulty sites where refining the fit is necessary. The friction against the tissues or the pressure ulceration will cause necrosis of exposed tissues that necessitate antibiotic prophylaxis or treatment.
Prevention of Infections of Prosthetic Devices
Prevention begins with following sterile procedure for implantable devices or proper fitting for wearable prosthetics; likewise, patient compliance with post-operative or post-fitting instructions is part of the procedure itself.
After that, the patient is his or her own best expert: self-reports are the basis of prevention of infections associated with internal prosthetic devices, implants, and wearable prosthetics. Rejection and/or infection will be noticed first by the patient and the prompt reporting to the responsible physician is the best preventative strategy at addressing problems early that may develop from these complications.
A heightened level of surveillance for possible complications related to these devices is crucial for the managing physician or primary care provider. Scrupulous physician interaction, in tandem with the patient’s self-reports, works synergistically to prevent, mitigate, or address any infection or malfunction.