Prosthetic etiologies
• Periprosthetic infection
• Aseptic loosening
• Polyethylene wear
• Periprosthetic fracture
• Flexion instability
• Anterior knee pain—unresurfaced patella, patellar maltracking
Extra-articular etiologies
• Soft tissue pain—bursitis, ligament strain, tendinitis
• Complex regional pain syndrome
• Periarticular neuropathy
• Referred pain—ipsilateral hip, lumbar spine
Unexplained pain following TKA should be evaluated for an infection until proven otherwise. It is important to gauge whether the TKA has always been painful, or if the pain started suddenly. Patients will often report pain at rest, as well as nighttime pain. The pain may also have insidious onset, as is often the case with more indolent, chronic PJIs. The pain may be global around the knee and is often worsened by range of motion and weight bearing on the involved extremity. Careful questioning should elicit whether there is concomitant hip or lumbar back pain referring to the knee.
7.2.1 Risk Factors
Risk factors for the development of PJI following TKA are classified as host factors and surgical factors (Table 7.2). Many of these predictive factors are supported by literature [3, 7–21]. Therefore, it is important to acquire information about past medical and surgical history and to identify which of these factors is potentially modifiable prior to further surgical intervention.
Table 7.2
Host and surgical risk factors for periprosthetic joint infections
Host risk factors | • Obesity (body mass index >30 kg/m2) [7] • Liver disease [8] • Renal disease [9] • Malnourishment [10] • Smoking [11] • Diabetes mellitus [12] • Inflammatory arthropathy [13] • Immuno-compromised state [14] • Corticosteroid use [15] • Excessive alcohol consumption [16] • Other systemic infections (bacteremia, urinary tract infection, etc.) [3] |
Surgical risk factors | • Improper aseptic technique • Prolonged operating room time [17] • Multiple surgeries [18] • Revision TKA [19] • Previous wound complications [20] • Allogenic blood transfusion [21] |
Determining the diagnosis for the index TKA (e.g. primary osteoarthritis, post-traumatic arthritis, inflammatory arthritis, post-septic arthritis) can help predict case complexity, which may contribute to an increased risk of infection [22]. Previous treatment for soft tissue erythema, wound drainage, or other concerns for PJI should be outlined. It is critical to document previous surgical attempts to eradicate infection, as well as the timing of the treatment postoperatively. A classification system exists that categorizes PJIs based on time to diagnosis (Table 7.3). Since management protocols differ based on when the PJI diagnosis is made, concise determination of the presumed onset of the infection is paramount [9].
Categorization | Modifier | Criteria |
|---|---|---|
Type 1 | Positive intra-operative culture | 2 positive cultures at time of revision for reasons other than infection |
Type 2 | Early | Infection diagnosis within 4 weeks of index operation |
Type 3 | Late | Infection diagnosis outside of 4 weeks of index operation |
Type 4 | Acute hematogenous | Infection diagnosis within 4 weeks of symptom onset with concomitant bacteremia |
7.2.2 Host Characterization
A complete history and documentation of the patient’s comorbidities allows the clinician to classify the patient’s host status. Different classification systems exist. The classification outlined by Cierny and DiPasquale [24] classifies patients as type A, B, or C hosts based on comorbid conditions and tissue healing potential (Table 7.4). The staging system by McPherson et al. [25] is more comprehensive, considering timing of PJI diagnosis, host comorbidities, and soft tissue condition (Table 7.5). The timing of PJI diagnosis is classified as early (type 1, diagnosis of PJI less than 4 weeks after index surgery), acute hematogenous (type 2, symptom onset within 4 weeks of bacteremia), and late (type 3, diagnosis of PJI greater than 4 weeks after index surgery). It is important to identify these local and systemic factors whenever a PJI is suspected following TKA. This information can help the surgeon educate their patients regarding the likelihood of treatment success, as well as identify factors that may be modifiable during the treatment course of the infection.
Host type | Local factors | Systemic factors |
|---|---|---|
A | • No healing deficiency | • Healthy |
B | • Venous stasis • Chronic lymphedema • Peripheral vascular disease • Previous radiation • Extensive fibrosis • Retained foreign bodies | • Malnutrition • Immuno-compromised state • Chronic hypoxia • Malignancy • Diabetes mellitus • Chronic or current tobacco use • Major organ dysfunction |
C | • Cannot withstand treatment | • Morbidity and mortality risk of proposed treatment exceeds the risks of living with current illness |
Grade of host/tissue | Definition | Compromising factors |
|---|---|---|
Systemic factors | ||
A B C | No compromising factors 1–2 compromising factors >3 compromising factors | • Age >80 years • Alcohol abuse • Nicotine use • Chronic indwelling catheters • Chronic malnutrition • Diabetes mellitus • Liver/pulmonary/renal insufficiency • Inflammatory disease • Malignancy • Immuno-compromised state |
Local tissue factors | ||
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Related posts: Preoperative Screening and Eradication of Infection
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 The Role of Knee Aspiration in the Infected Total Knee Arthroplasty
 Two-Stage Revision of Infected Total Knee Arthroplasty
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