A Prosthetic Device Infection (PDI), or Prosthetic Joint Infection (PJI) for orthopedic hardware, is a serious medical challenge distinct from routine infections. These infections occur when bacteria colonize the surface of a non-living medical device, such as an artificial hip, knee, dental implant, or pacemaker. Because the infection is physically attached to the device, it resists the body’s natural defenses and standard antibiotic treatments. Addressing this condition requires specialized diagnostic methods and complex, multi-stage treatment plans.
Understanding How Implant Infections Begin
The unique challenge of treating these infections stems from the ability of bacteria to form a protective structure called a biofilm. This self-produced matrix adheres firmly to the implant surface, shielding the microorganisms within. Once established, the biofilm acts as a physical barrier, preventing immune cells from reaching the bacteria and reducing the effectiveness of antibiotics.
Bacteria colonize the implant surface through two main pathways. Direct contamination typically occurs during the surgical procedure or in the immediate post-operative period due to issues like poor wound healing. These acute infections usually present within weeks of the operation.
Hematogenous spread occurs when bacteria travel through the bloodstream from a distant site of infection, such as a skin infection or a urinary tract infection. These infections can occur months or years after the implant was placed. This leads to a chronic infection that may take a long time to become symptomatic.
Recognizing the Physical Signs
Acute infections, which develop shortly after surgery, display clear signs of inflammation. These symptoms include a fever, severe pain localized to the implant area, and visible signs such as redness, warmth, or swelling around the incision site. The presence of purulent drainage or pus coming from the wound is a definitive acute sign.
In contrast, chronic infections appear months or years after the procedure and present more subtly. The primary indicator is persistent pain that progressively worsens over time, sometimes accompanied by joint stiffness or a feeling of the implant loosening. Patients may also experience vague, intermittent symptoms, such as a low-grade fever or general fatigue.
A sinus tract, which is a channel of infected tissue extending from the implant to the skin surface, indicates a long-standing infection.
Medical Procedures for Confirmation
When an implant infection is suspected, the diagnostic workup begins with specialized blood tests to detect systemic inflammation. These tests measure the Erythrocyte Sedimentation Rate (ESR) and the C-Reactive Protein (CRP) level, markers that become elevated in the presence of infection. While useful for screening, these markers are not specific to the implant and may be elevated due to other conditions.
The definitive step for confirmation involves aspiration, where a needle is used to draw a fluid sample directly from the joint or surrounding tissue. The collected fluid is sent for culture to identify the specific pathogen causing the infection. Identifying the exact species of bacteria is important, as this guides the selection of the most effective long-term antibiotic regimen.
Imaging studies, such as X-rays, computed tomography (CT) scans, or bone scans, are also used to assess for structural damage or evidence of implant loosening caused by the infection. However, these techniques are less specific for infection than the laboratory analysis of the aspirated fluid.
Strategies for Treating Established Infections
Treatment for an established implant infection is complex, guided by the infection’s duration, the specific pathogen, and the extent of biofilm formation. Antibiotic therapy requires long-term, high-dose administration, often starting with intravenous (IV) antibiotics for several weeks, followed by an extended course of oral antibiotics. Antibiotics alone are rarely curative for chronic infections because the protective biofilm prevents the drugs from reaching the bacteria effectively.
For acute, early infections caught before the biofilm is fully mature, Debridement, Antibiotics, and Implant Retention (DAIR) may be attempted. This involves surgically cleaning the joint, removing infected and necrotic tissue, and exchanging any modular parts of the implant while retaining the main components. DAIR is most successful when performed early and the infection is caused by a susceptible organism.
For most chronic or late-stage infections where the biofilm is firmly established, the standard of care is a Two-Stage Revision surgery. The first stage involves the complete removal of the infected implant and all foreign material. An antibiotic-loaded cement spacer is temporarily placed in the joint space to deliver a high concentration of antibiotics directly to the infected tissue while maintaining joint space.
After a period of several weeks or months, during which the patient receives systemic antibiotics and inflammatory markers normalize, the second surgery is performed. This involves removing the antibiotic spacer and implanting a brand-new, sterile prosthesis. This approach is necessary to physically eliminate the biofilm, which allows the infection to be fully cleared with a high rate of success.
Steps for Reducing Infection Risk
Reducing the risk of an implant infection begins with pre-operative optimization. Patients must ensure any existing infections, such as urinary tract or dental issues, are fully treated before surgery. Conditions that compromise the immune system, such as poorly controlled diabetes, should be managed aggressively to create a favorable healing environment.
After the procedure, meticulous wound hygiene is necessary to prevent skin bacteria from entering the surgical site. In the long term, patients should remain vigilant for any signs of a new infection elsewhere in the body and seek prompt treatment. The greatest long-term risk comes from transient bacteremia, where bacteria from a distant site enter the bloodstream and can potentially seed the implant.
Patients should inform their dentist or other healthcare providers about the presence of an implant before undergoing any invasive procedure that involves manipulating the gums or breaking the skin. While routine prophylactic antibiotics are no longer recommended for all patients with prosthetic joints undergoing dental work, they may be considered for those at high risk or for specific procedures after consultation with the orthopedic surgeon. Good oral hygiene reduces the overall bacterial load in the mouth, lowering the risk of bacteremia.