**3. Classification of the arthroplasty associated infection**

The arthroplasty associated infection may distinguishes two major types―septic arthritis and osteomyelitis, which both cause serious morbidity and are often difficult to manage. Septic arthritis is a joint disease typified by bacterial colonisation and rapid articular destruction[6]. Infiltration and growth of bacteria within the synovium results in inflammation with infiltration of leukocytes into the joint fluid [4]. The production of reactive oxygen species and host matrix metalloproteinases (MMPs), lysosomal enzymes and bacterial toxins contribute to the destruction of cartilage. This starts with degradation of host proteoglycans followed by collagen breakdown within hours of infection, and is mediated by polymorphonuclear leukocytes[3-5,24]. The containment of the inflammatory process within the joint results in increasing pressure, which impedes blood and nutrient supply to the joint exacerbating joint damage and facilitating destruction of cartilage and the synovium. Permanent destruction of articular cartilage and subchondral bone can occur rapidly, within just a few days[24].

Osteomyelitis describes a range of infections in which bone is colonized with microorganisms, with associated inflammation and bone destruction. Acute osteomyelitic foci are characterized by pus-forming inflammation at the site of microbial colonisation. Damage to bone matrix and compression and destruction of vasculature is also observed as the infection spreads to surrounding soft tissues, which can further exacerbate bone necrosis[7,10].Sections of dead bone, known as sequestra, can form which may then detach to form separate infectious foci which, due to the lack of vasculature, are protected from immune cells and antibiotics[7,10]. Such areas of dead, infected tissues that are inaccessible to antimicrobials or the immune response can lead to chronic persistence of the infection[10].

The principal routes of these infection involve: (I) haematogenous or lymphogenous seed of the pathogen, (II) contiguous, by contact with a neighboring infected site, (III) or direct, resulting from infiltration of bone, often following inj ury, surgery or implantation of a foreign body, such as joint repalcement[25]. The range of environments experienced by the bacterium differs for each route and hence the virulence factors that are involved in pathology may be different for each route of infection.

Another classification of arthroplasty associated infection distinguishes acute, chronic and reactive forms, which differ in their type of joint infection and their triggering bacteria.

Infection with virulent organisms (e.g., S. aureus and gram-negative bacilli) inoculated at implantation is typically manifested as acute infection in the first 3 months (or, with hematogenous seeding of the implant, at any time) after surgery, whereas infection with less virulent organisms (e.g., coagulase-negative staphylococci and P. acnes) is more often manifested as chronic infection several months (or years) postoperatively. The most common symptom of infection associated with a prosthetic joint is pain. In acute infection, local signs and symptoms (e.g., severe pain, swelling, erythema, and warmth at the infected

Staphylococcus Infection Associated with Arthroplasty 463

cause infection include (but are not limited to) Actinomyces israelii, Aspergillus fumigatus, Histoplasma capsulatum, Sporothrix schenckii, Mycoplasma hominis, Tropheryma whipplei, and mycobacterium (including tuberculosis), brucella, candida, corynebacterium,

Some bacteria have preferences for certain infection routes and patterns. Infections not related to injuries or medical interventions (e.g. intraarticular puncture, joint replacement)

S. aureus is the most commonly identified pathogen both in septic arthritis and osteomyelitis, by a substantial margin, regardless of type or route of infection [3,7,28]. Staphylococci (S. aureus and coagulase-negative staphylococcus species) account for more than half of cases of prosthetic-hip and prosthetic-knee infection[29](Fig. 2). Other bacteria

are mostly resulting from often physiologic bacteriaemic periods.

Table 2. Bacteria responsible for (hip) joint infections

granulicatella, and abiotrophia species.

joint) and fever are common. Chronic infection generally has a more subtle presentation, with pain alone, and it is often accompanied by loosening of the prosthesis at the bone– cement interface and sometimes by sinus tract formation with discharge.

Reactive arthritis is a postinfectious complication with no need of presence for viable pathogens in the joint. While reactive arthritis often simultaneously affect several joints, the presence of polyarthritic types of non reactive arthritis occur infrequently and then mostly as a result of several bacteriaemic phases.

Among joint infections, the knee is the most frequent localization than others. Infection occurs in 0.8 to 1.9% of knee arthroplasties[12-14]and 0.3 to 1.7% of hip arthroplasties[14-16]. However, hip joint infections are aggravated by the fact that they can exist over a long time with only poor symptoms. Basically, there are no differences in the bacterial spectrum among large joints.
