**3. Periprosthetic joint infection (PJI)**

PJI is a serious complication and is considered one of the most common causes of revision surgery following the failure of primary TKA [21]. The incidence of PJI after primary knee replacement is ranging from 0.85 to 2.2 percent [22], with a higher rate up to 9 percent in revision cases [23]. Despite a small incidence of infection following TKA, the trend of revision due to PJI was rising by 2.5-fold in the past decade [22].

*Complications after Total Knee Arthroplasty: Stiffness, Periprosthetic Joint Infection… DOI: http://dx.doi.org/10.5772/intechopen.105745*

This problem illustrates an increasing and substantial treatment burden to both orthopedic surgeons and the patients, as well as the health service system.

A systematic review and meta-analysis by Kunutsor et al. showed patients with smoking, BMI >30 kg/m<sup>2</sup> , diabetes, depression, steroid use, previous joint surgery, and frailty were the significant risk factors associated with the long-term developing PJI [24]. A study by Rosteius et al. demonstrated the most common pathogen found in PJI after TKA was methicillin-susceptible *Staphylococcus aureus* (MSSA) which occurred in 28.2 percent of patients, followed by coagulase-negative *Staphylococcus* (CoNS), methicillin-resistant *Staphylococcus epidermidis* (MRSE), *Streptococcus*, ampicillin-susceptible *Enterococcus faecalis*, and methicillin-resistant *Staphylococcus aureus* (MRSA) with the frequency of 16.4, 13.2, 9.1, 7.1, and 6.6 percent, respectively. However, up to 17.8 percent of patients could not identify any pathogens [25].

#### **3.1 Diagnosis**

Recently, there is no gold standard for the diagnosis of PJI [21]. The Musculoskeletal Infection Society (MSIS) and the Infectious Diseases Society of America (IDSA) have previously developed criteria to standardize the definition of PJI in 2011 and 2013 [26, 27], together with an International Consensus Meeting on PJI in 2013 [28]. The latest consensus in 2018 proposed a new scoring-based definition for PJI after emerging of new diagnostic tests. Two positive cultures of the same organism or the presence of a sinus tract were considered as major criteria and a definite diagnosis of PJI. The minor criteria consisted of laboratory tests either serum or synovial fluid which were weighted differently. An elevated serum C-reactive protein (CRP) or D-dimer received 2 points, whereas an elevation of erythrocyte sedimentation rate (ESR) weighted 1 point. Furthermore, an elevated synovial white blood cell (WBC) count or leukocyte esterase (LE) was considered 3 points. The other diagnostic tests for synovial fluid were a positive alpha-defensin, an elevated synovial polymorphonuclear (PMN) percentage, and synovial CRP which took 3, 2, and 1 point, respectively. Patients with a total score of equal or greater than 6 were suggested infected, while a score between 2 and 5 was classified as inconclusive and required further intraoperative diagnostic score to fulfill the definition, and a score of 0 to 1 was defined as no infection.

The intraoperative diagnostic score consisted of positive histology, purulence, and a single positive culture which scored 3, 3, and 2 points, respectively. In combination with the inconclusive preoperative diagnostic score, patients with an overall score of equal or greater than 6 were considered infected, whereas a score between 4 and 5 was inconclusive and need further molecular findings, and a score of 3 or less was defined as aseptic (**Table 2**). The threshold of each laboratory test is detailed in **Table 3**. The sensitivity and specificity of this new scoring system are 97.7 and 99.5 percent, respectively, which is higher sensitivity than the previous diagnostic criteria [29].

#### **3.2 Treatment**

Management of PJI includes surgical intervention and medical treatment, especially antibiotics therapy, with the goals of eradicating the infection, minimizing pain by restoring the function of the infected joint before performing the revision arthroplasty, as well as reducing morbidity and mortality of the patients [30]. Tsukayama et al. classified characteristics of infection after TKA into four types with the guidance of surgical options among these scenarios (**Table 4**) [31].


*Modified from Parvizi et al. The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria. J Arthroplasty. 2018;33(5):1309–14.e2.*

#### **Table 2.**

*The 2018 International Consensus Meeting on Musculoskeletal Infection scoring-based definition for PJI.*


*Modified from Parvizi et al. The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria. J Arthroplasty. 2018;33(5):1309–14.e2.*

**Table 3.**

*The threshold of laboratory test of the minor criteria.*
