Differential Diagnosis of a Patient Presenting With a Knee Effusion

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knee joint effusion에 관하여

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Patients presenting with knee effusions within 6 hr of injury may signify an articular fracture, knee dislocation, or cruciate ligament tear (Levy, 2006). Patients presenting with edema after 6 hr usually have meniscal injuries. Recurrent knee effusions after activity are likely meniscal injuries (Levy, 2006).

Differential Diagnosis of a Patient presenting with a knee .pdf

Knee effusions are seen in patients with bursitis (e.g., prepatellar bursitis), meniscal derangement, popliteal cyst (i.e., Baker cyst), or arterial pathology (e.g., popliteal-artery aneurysm; Levy, 2006). 

Knee joint swelling may contribute to traumatic, inflammatory, noninflammatory, and infectious disease processes. 

Traumatic Injuries 

A traumatic knee effusion can occur with valgus (i.e., knee is turned outward and away from the midline of the body) or varus (i.e.,knee is turned inward toward the midline of the body) stress and can be direct or indirect (Levy, 2006). One half of patients with ligamentous injuries will have localized swelling of the knee (Levy, 2006). Knee effusions are seen when there is complete ligamentous or capsular disruption, with synovial fluid exuding through the tear (Levy, 2006). 

Patients presenting with knee effusions within 6 hr of injury may signify an articular fracture, knee dislocation, or cruciate ligament tear (Levy, 2006). Patients presenting with edema after 6 hr usually have meniscal injuries. Recurrent knee effusions after activity are likely meniscal injuries (Levy, 2006).

Noninflammatory Diseases 

Osteoarthritis is an example of a noninflammatory, chronic, progressive, degenerative disease. Patients with osteoarthritis generally do not have knee effusions.

Inflammatory Diseases

Inflammatory diseases include, but are not limited to, gout, pseudogout, and rheumatoid arthritis (Joseph & McGrath, 1995; Zhang et al., 2006). Gout is defined as an inflammation caused by monosodium urate monohydrate crystals (Joseph & McGrath, 1995; Zhang et al., 2006). Pseudogout is defined as an inflammation where there are calcium pyrophosphate crystals (Joseph & McGrath, 1995; Zhang et al., 2006). The disease is also called calcium pyrophosphate disease (Kaplan, 2007). Patients presenting with gout or pseudogout may display a warm, erythematous, painful single joint with asymmetric edema. Desquamation of the skin may be present if there is severe inflammation (Kaplan, 2007).

Rheumatoid arthritis is a chronic, progressive, systemic inflammatory disease that involves the synovial membranes and articular structures of multiple joints. Patients may present with joint tenderness, stiffness, and swelling (King, 2006).

Infectious Arthritis Infectious or septic arthritis is most frequently caused by Staphylococcus aureus, especially if more than one joint is involved (Brusch, 2005). Eighty percent (80%) of septic arthritis cases are caused by Grampositive

aerobes while S. aureus occurs 60% of the time; betahemolytic streptococci is the cause in 15% of cases and  streptococcus pneumoniae 5%. Gram-negative anaerobes account for the remainder of the cases (20%) (Munoz & Raycraft, 2006). 

Septic arthritis can also be caused by other pathogens (Table 2) (Baraboutis & Skoutelis, 2004; Holder, 2007;

Munoz & Raycraft, 2006; Read & Peacock, 2004). The pattern of joint involvement is an extremely important diagnostic feature when diagnosing a septic joint (Brusch, 2005). In nongonococcal septic arthritis, 85–90% of the joint effusions are monoarticular. In gonococcal disease, various viral infections, Lyme disease, reactive arthritis, and various noninfectious processes, polyarticular arthritis, usually is reported (Brusch, 2005). Septic arthritis can spread from a distant source to a joint (e.g., in cases of pneumonia, wound infection), and direct seeding can occur after a surgical procedure, a traumatic injury, or via the transmission from an infection (e.g., osteomyelitis, cellulitis; Holder, 2007). 

PATHOPHYSIOLOGY

S. aureus is the most common microorganism associated with acute bacterial arthritis in adults. It is also the most common pathogen in children greater than 2 years of age. This pathogen is also the cause of nearly 80% of the infected joints in patients with rheumatoid arthritis. The remaining 20% of patients culture out Streptococcus viridans, S. pneumoniae, and group B streptococci (Baraboutis & Skoutelis, 2004). Most of the infections occur in individuals who are

young, old, or at high-risk (e.g., immunosuppressed, IV drug user, sexually active young adults ages 15–24). Gonorrhea is the second most commonly reported infectious disease in the United States, after Chlamydia (Bennett, 2007). Neisseria gonorrhoeae is the most frequent pathogen occurring 75% of the time in young sexually active individuals who present with a knee effusion (Brusch, 2005; Figure 1). N. gonorrhoeae produces white blood cells that enter the joint, ultimately causing joint destruction (Brusch, 2005).

The invasion of microorganisms can occur via inoculation (i.e., microorganism directly enters the body, spread from infected tissue or through the bloodstream). The bloodstream is the most common route (Brusch, 2005). Bacterial

invasion results in damage and breaks down articular cartilage. This may be due to the microorganism’s pathological properties (e.g., S. aureus) and is also due to the polymorphonuclear leukocyte response of the patient (Brusch, 2005).

The knee joint is protected in several ways. Synovial cells provide phagocytic activity and synovial fluid has bactericidal activity (Brusch, 2005). However, when septic arthritis occurs, pathogens will begin to invade the knee joint space. Large effusions impair the blood supply and result in aseptic necrosis of bone (e.g., hip). These processes can occur within 3 days of an untreated infection (Brusch, 2005).

Polymicrobial joint infections occur in 5– 10% of cases (Brusch, 2007). Anaerobic organisms are implicated in  polymicrobial joint infections 5% of the time. They are usually the result of an abdominal infection or trauma (Brusch, 2007). Lyme disease (i.e., Borrelia burgdorferi), viruses (e.g., HIV, lymphocytic choriomeningitis virus, hepatitis B virus, rubella virus),mycobacteria, fungi (e.g., Histoplasma species, Sporothrix schenckii, Coccidioides immitis, Blastomyces species), and other microorganisms may invade the joint causing an infection (Brusch, 2007).

Prosthetic joint infections are primarily a result of local infection (e.g., intraoperative in 60–80% of cases; Zimmerli et al., 2004).  Bacteremias (e.g., gingival disease, secondary to manipulation in 20–40% of cases) can also cause joint infections. and those that occur later than 24 months following a joint implantation. Most cases of early prosthetic joint infections (within 3 months of implantation) are caused by S. aureus, whereas delayed infections (e.g., within 3–24 months of implantation) are due to operating room (OR)–acquired coagulase-negative S. aureus and Gram-negative aerobes (Zimmerli et al., 2004). Prosthetic joint infections that occur after a 2-year period are usually the result of the formation of red blood cells in the body (hematogenesis) causing an infection (Brusch, 2005; Zimmerli et al., 2004).

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