Classification and aetiology of arthroplasty device infections

Arthroplasty device infections are classified according to the timing of the infection following joint implantation and the duration of symptoms. This classification indicates the likely aetiology of the infection and has implications for how it is managed (see Approach to managing arthroplasty device infections).

Arthroplasty device infections can be classified as:

• early postoperative—infections occurring within 30 days of joint implantation
• late acute—infections occurring more than 30 days after joint implantation and symptoms present for 7 days or less with no evidence of a sinus communicating with the joint
• late chronic—infections occurring more than 30 days after joint implantation and symptoms are prolonged or there is a sinus communicating with the jointManning, 2020.

Early postoperative infections are caused by a broad range of pathogens. Although Gram-positive organisms (Staphylococcus aureus, coagulase-negative staphylococci and enterococci) predominate, at least a quarter of infections will involve Gram-negative enteric organisms, including those of the ESCAPPM group¹. Polymicrobial infection is commonManning, 2020.

Late acute infections are the most common type of arthroplasty device infection. In contrast to early postoperative infections, the majority of late acute infections are monomicrobial and involve Gram-positive organisms (S. aureus and beta-haemolytic streptococci). Late acute infections are often presumed to be haematogenous and around half of patients presenting with late acute infection are expected to be bacteraemicManning, 2020.

Late chronic infections are predominantly monomicrobial. The aetiology is varied with a greater contribution of less virulent organisms, such as coagulase-negative staphylococci, than in late acute infectionsManning, 2020. Organisms are often present in low numbers, with a patchy distribution focused around the periprosthetic interface. Infections of prosthetic shoulder joints are usually late chronic infections and more frequently involve Cutibacterium acnes; see Postoperative infections of the shoulder.