After implantation of a prothesis, infections can develop that are often difficult to diagnose. Acute early infections that develop soon after surgery are differentiated from delayed infections that generally have a chronic course as well as late infections that ususally have an acute course.
A periprosthetic infection (PPI, also known as a prosthetic joint infection) generally manifests as persistent or increasing joint pain and early prosthesis loosening.
Early infections that occur up to three months after surgery usually develop as wound infections wiht acute local and systemic signs of infection. Delayed infections that can occur up to 24 months after surgery are also usually contracted intraoperatively and are caused by slow-growing bacteria. Late infections can develop at any point, even several years after implantation of the prosthesis. In theses cases, the infection develops as a result of the spread of bacteria from a remote infection site, that is, via the blood circulation as a rule (haematogenous).
The following rule of thumb applies the chronic infections:
The later they develop, the more difficult they are to diagnose and treat because the classic signs of inflammation and significantly elevated laboratory values are generally absent.
The bacteria also form tenacious biofilms. A combination of various methods is needed for diagnostics including
- aspiration of joint fluid (puncture)
- biopsies of tissue samples from different sites
- sonication (ultrasound cleaning) of the removed prosthesis to detach the biofilm
In addition to radical surgical excision of the infected and necrotic tissue, the treatment of a prosthetic joint infection includes the systemic and local administration of antibiotics, ideally with combination preparations.
Before therapy, a biofilm-specific antibiogram should be prepared. Identifying pathogens and any antibiotic resistance or susceptibility is a major challenge in clinical microbiology, particulary for slow-growing pathogens.