What is a Prosthetic joint infection?
A prosthetic joint infection, or PJI, is a specific and severe form of infection that occurs when microorganisms adhere to and proliferate on the surfaces of an artificial joint, such as a hip, knee, or shoulder replacement. Unlike an infection in the body’s own native tissues, a PJI involves a non-living foreign body. This artificial implant provides an ideal surface for bacteria to attach to, creating a unique and highly protected environment for them to grow.
The central feature of a PJI is the formation of a biofilm. This is a structured, defensive community of bacteria encased in a self-produced slimy matrix that coats the implant components. This microbial shield effectively insulates the bacteria from both the patient’s immune cells and from antibiotics circulating in the bloodstream. This resistance to treatment is what makes a PJI exceptionally difficult to eradicate.
Clinically, these infections are often categorized based on their time of onset relative to the original replacement surgery. Early-onset infections become apparent within the first few weeks to months after the procedure. In contrast, late-onset infections can emerge many months or even years later, long after the initial surgical wound has healed.
Causes:- Intraoperative Contamination: This is the most frequent cause, occurring at the exact time of the initial joint replacement surgery. Microorganisms, most often originating from the patient's own skin flora or the operating room environment, are inadvertently introduced into the deep wound and gain access to the components of the new implant before the incision is closed.
- Hematogenous Seeding: This is a later event, where bacteria from a subsequent infection located elsewhere in the body (such as a urinary tract infection, a dental abscess, or a skin infection) enter the bloodstream. These circulating bacteria then travel throughout the body until they find and adhere to the foreign surface of the artificial joint, establishing a new, remote site of infection long after the original surgery has healed.
- Patients Undergoing Revision Surgery: An individual having a second or subsequent operation on the same artificial joint faces a much greater risk than a patient receiving their first implant. The presence of existing scar tissue from the prior surgery reduces local blood supply and can make the procedure more complex and lengthy.
- Individuals with Certain Systemic Diseases: The presence of poorly controlled diabetes or inflammatory conditions like rheumatoid arthritis significantly impairs the body's natural defense mechanisms. These conditions can disrupt normal immune cell function, weakening the ability to clear away the small number of bacteria that may be introduced during surgery.
- Obesity: A high Body Mass Index (BMI) is a well-established risk factor. It is often associated with longer operating times, more challenging surgical exposures, and a poorer blood supply within the thick layers of fatty tissue, which hinders both wound healing and the delivery of immune cells to the surgical site.
- Post-operative Wound Complications: Any issue that disrupts the normal healing of the surgical incision, such as the formation of a large blood clot (hematoma) beneath the skin or persistent fluid drainage from the wound, creates a perfect nutrient-rich environment for bacteria to multiply and subsequently invade the deeper tissues to reach the implant.
