**3.2.2 Joint aspiration fluid**

442 Recent Advances in Arthroplasty

Adequate microbiological procedures must reflect the special character of periprosthetic infections in order to identify the causative agents accurately. Although largely interdependent, eight issues which may influence the significance of microbiologic testing are addressed separately in the following: i) patient-specific factors, ii) the sample character, iii) the logistic interface between the clinic and the laboratory, iv) the method of sample processing, v) the means of identification, vi) the culture conditions, vii) the means of discriminating between infection and contamination, and viii) the stage at which sample

Joint aspiration prior to revision arthroplasty is widely utilized. For knee patients the procedure is comparatively straightforward, whereas hip aspiration may impose a higher risk of iatrogenic infection. Thus, it is often argued that invasive diagnostic samples from hip patients should be obtained only if a there is a high probability of infection (Bozic et al.,

Regarding periprosthetic tissue biopsies, the diagnostic sensitivity of pre-operative sampling may be lower in hip infections compared with knee infections (Fink et al., 2008; Meermans & Haddad, 2010; Williams et al., 2004), possibly because infected tissue is more

The definitive identification of microorganisms is especially important in patients with systemic inflammatory diseases because, as mentioned before, inflammation markers can be elevated in aseptic implant failure. At the same time, the differentiation between an

False-negative results of microbiological cultures and even PCR tests have been reported in patients who received antibiotic therapy within 2 weeks prior to obtaining intra-articular sample material (Achermann et al., 2010). Furthermore, it is also suggested that perioperative antibiotic prophylaxis should be withheld if possible until samples for microbiological analysis have been obtained, but that the risk of false-negative sample results also should be weighed against the protective effect of pre-operative administration of antibiotic prophylaxis (Achermann et al., 2010; Engesaeter et al., 2003; Jämsen et al., 2009;

In a report on hip and knee patients organisms cultured from swabs of sinus tracts showed no concordance with the culture results from specimens obtained intra-operatively (Sadiq et al., 2005). There are limited data which suggest that the results of superficial swabs show a reasonable correlation with culture yield from intra-operative tissue biopsy material (Cune et al., 2009). However, other studies have rated results from swab material as both insensitive and unspecific (Font-Vizcarra et al., 2010; Levine & Evans, 2001). Swabs cannot

infecting and a contaminating agent is challenging in these patients (see 3.7).

**3. Microbiological diagnosis: Pros and cons of different approaches** 

materials are drawn (pre-operatively versus intra-operatively).

**3.1 Patient-specific factors** 

2009, 2010).

**3.1.1 Sample origin (hip versus knee)** 

difficult to assess without dislocating the joint.

**3.1.2 Underlying systemic diseases** 

**3.1.3 Previous antibiotic therapy** 

Trampuz et al., 2007).

**3.2 Sample character 3.2.1 Tissue swabs** 

The overall significance of culture from pre-operative synovial fluid to detect periprosthetic infection is valued as high. However, sensitivity may be reduced if the infection does not involve the synovia or if the concentration of planktonic bacteria in the fluid is limited due to a mature biofilm. Furthermore, false positive results from skin flora occur (Barrack & Harris, 1993; Della Valle et al., 2007; Eisler et al., 2001; Fink et al., 2008; Lachiewicz et al., 1996; Malhotra & Morgan, 2004; Williams et al., 2004).
