Septic arthritis is a term used when the joint space is infected with microorganisms which can be bacteria, viruses, mycobacteria, and fungi. Septic arthritis also includes prosthetic joint infections.
Septic arthritis is also called infectious arthritis.
Joints are quite resistant to infection but there are some risk factors that increase the risk increased infection. These are systemic problems like diabetes mellitus, preexisting rheumatoid arthritis, liver disease, chronic renal failure, malignancies, intravenous drug abuse, hemodialysis, alcoholism, HIV infection, hemophilia, organ transplantation, and hypogammaglobulinemia.
Similarly, local factors, such as damaged joint, joint surgery, arthritis, including osteoarthritis, or a prosthetic joint in the knee or the hip are important predisposing factors for septic arthritis.
Newborns and elderly people, especially those older than 80 years of age, are particularly vulnerable.
Septic arthritis is divided into two types
- Gonococcal – Caused by Neisseria Gonorhoeae and most common type in young sexually active males
- Nongonococcal – Nongonoccal septic arthritis is caused by bactereiae other than Neisseria Gonorhoeae mycobacteriae, fungi and viruses.
Pathogens
Monoarticular septic arthritis is more common than polyartiular arthritis. Many of the patients have one or more comorbidities, and some have been intravenous drug abusers. The occurrence of this type of arthritis in patients who have rheumatoid arthritis is high.
Although Staphylococcus aureus is the most common pathogen, group G streptococci, Haemophilus influenzae, Streptococcus pneumoniae, or mixed aerobic and anaerobic bacteria have been responsible for polyarticular infections.
The organisms causing nongonococcal septic arthritis in adults are 75% to 80% Gram-positive cocci and 15% to 20% Gram-negative bacilli.
Group B streptococcal arthritis in adults is rare but can be a serious infection in patients who have diabetes and also in those who have prosthetic hip infections.
Staphylococcus aureus is the most common organism in native and prosthetic joint infections. The next most common group of Gram-positive aerobes is the streptococci, including Streptococcus pneumonia [Streptococcus pyogenes is followed by groups B, G, C, and F] Patients who have immunosuppression, diabetes mellitus, malignancy, and severe genitourinary or gastrointestinal infections usually present non–group A streptococcal disease.
Borrelia burgdorferi [causes Lyme disease], a large variety of viruses like HIV, lymphocytic choriomeningitis virus, hepatitis B virus, rubella virus), mycobacteria, fungi, and other pathogens may produce infectious arthritis.
Prosthetic joint infections may be a consequence of local infection, such as intraoperative contamination (60-80%), or of bacteremias (20-40%) of cases.
The most common organisms of prosthetic joint infections are coagulase negative Staph aureus and S aureus, enteric gram-negative organisms 25% of isolates streptococci cause of cases. Anaerobes are isolated from 10% of patients.
Pseudomonas aeruginosa or Serratia species occurs almost exclusively in persons who abuse intravenous drugs. Persons with leukemia are predisposed to Aeromonas infections.
The most common Gram-negative organisms are E coli and Pseudomonas aeruginosa.
Infections caused by anaerobes occur in 5% to 7% of septic arthritis. Common anaerobes include Bacteroides, Propionibacterium acnes, and various anaerobic Gram-positive cocci.
Numerous conditions that adversely affect the host’s defenses (eg, liver disease, diabetes mellitus, lymphoma, solid tumors, complement deficiencies [C7, C8], immunosuppressive drugs, hypogammaglobulinemia and are more susceptible to septic arthritis.
Pathogenesis of Septic Arthritis
Septic arthritis is most often occurs when bacteria flowing through blood [bacteremia] seeds on synovium. The bacteriae gain access to the bloodstream from their initial innocuous location if the integrity of skin and mucosa natural barriers becomes broken.
Previously damaged joints, especially those damaged by rheumatoid arthritis, are the most susceptible to infection.
The major consequence of bacterial invasion is damage to articular cartilage. As the destructive process continues, pannus formation begins, and cartilage erosion occurs. Large effusions, especially in the hip can impair the blood supply and result in aseptic necrosis of bone.
Viral infections may cause direct invasion or production of antigen/antibody complexes.
Gram-negative septic arthritis probably arises from bacteremia from the gastrointestinal or urinary tracts.
Sometimes, the bacteriae can gain access from penetrating trauma, such as bite wounds, stepping on nails, or illegal injection drug use, thorns, and wood slivers injuries.
Rarely, arthroscopy or therapeutic joint injections with corticosteroids may be complicated by septic arthritis.
Presentation of Septic Arthritis
Acute septic arthritis is most commonly involves a single joint but it can involve multiple joints too.
Nongonococcal arthritis presents with high fever, and hot, swollen and painful joint, More than 50% cases involve knee joint. Twenty percent of cases have more than one joint involved especially in patients who have chronic degenerative diseases, such as rheumatoid arthritis and osteoarthritis.
Not all the features are present in all the patients.
Gonococcal infection presents either in the bacteremic form [which is migratory polyarthralgia, dermatologic lesions, and tenosynovitis often affecting multiple joints] or septic arthritis form. A recent exposure to sexual encounters should raise suspicion of this type of arthritis
Any recent injury to the joint or penetrating or blunt, needle aspiration or injections of corticosteroids into the joint should be ruled out.
Presentations vary slightly with the affecting organism. For more detailed individual presentations please see Lyme arthritis, fungal arthritis, viral arthritis, prosthetic joint infection, reactive arthritis, tuberculous arthritis.
The most commonly involved joint in septic arthritis is the knee (50%), followed by the hip (20%), shoulder (8%), ankle (7%), and wrists (7%). The elbow, interphalangeal, sternoclavicular, and sacroiliac joints each make up 1-4% of cases.
Signs and symptoms of infection may be softened in people who are elderly, who are immunocompromised (especially those with rheumatoid arthritis), and who have intravenous drug abuse.
Differentiating features of Gonococcal and nongonococcal arthritis are given below.
| Characteristics | Gonococcal | Nongonococcal |
| Patient profile | Sexually active young adults, mainly women | Newborns or adults with a chronic disease like diabetes, rheumatoid arthritis, osteoarthritis |
| Presentation | Migratory polyarthritis, dermatitis, tenosynovitis | Single joint involvement |
| Joint involvement | Involves multiple joints in about 50% | Involves single joints in about 90% |
| Culture positivity | Less than 50% | Nearly 90% |
| Prognosis | Good with adequate antibiotic therapy | Usually requires joint drainage and may leave residual problems |
Lab Studies
A combination of clinical and laboratory data and radiologic imaging studies plays an important role.
An evaluation of the synovial fluid (ie, via leukocyte count, appearance on Gram stain, polarizing microscopy examination, culture) can help to differentiate between crystal arthropathies and joint infection.
Gram staining of synovial fluid, however, lacks sensitivity for the diagnosis of septic arthritis. Gram stains are positive in 71% of Gram-positive septic arthritis, 40% to 50% of cases of Gram-negative septic arthritis, and less than 25% of cases of gonococcal septic arthritis.
The culture of the synovial fluid or of the synovial tissue itself is the only definitive method of diagnosing septic arthritis.
For prosthetic joint infections, 3-6 tissue samples should be obtained. The effectiveness of standard culture techniques is much more limited in patients with prosthetic joint infection. Stopping the administration of antibiotics for 2 weeks prior to obtaining cultures may improve the yield
Usually, synovial fluid cultures are positive in 70% to 90% of cases of nongonococcal bacterial arthritis. The rate is quite low for prosthetic joint infections.
Blood cultures are positive in 40% to 50% of cases.
Patients who have the clinical features of gonococcal arthritis should have synovial, skin, urethral, or cervical cultures, and rectal culture.
Foul-smelling synovial fluid or air in the joint space should raise the suspicion of anaerobic infection, and appropriate cultures should be obtained and held for at least 2 weeks. This type of infection is most frequent in patients who have wound infections or joint arthroplasty and in immunocompromised hosts.
An elevated erythrocyte sedimentation rate or C-reactive protein is useful in following response to therapy, as well as in detecting an acute process in chronically affected joints.
Obtaining a biopsy of the synovium for diagnosis of fungal or mycobacterial joint infections may be required.
Imaging in Septic Arthritis
Radiographs
Plain radiography is of limited value in evaluating a joint for infection. Periarticular soft-tissue swelling is the most common finding. This imaging modality is most useful in ruling out underlying osteomyelitis or periarticular osteomyelitis caused by the joint infection itself.
In addition, plain radiography can reveal the linear deposition of calcium pyrophosphate. The radiographic findings of reactive arthritis are usually limited to those of soft-tissue swelling. Periarticular osteoporosis may be detected.
CT, MRI, Radionuclide scanning
CT and MRI are more sensitive for distinguishing osteomyelitis, periarticular abscesses, and joint effusions. MRI is preferred because of its greater ability to image soft tissue.
Radionuclide scans may be of use in diagnosing septic arthritis in relatively sequestered areas, such as the hip and sacroiliac joints.
In prosthetic joint infection, plain radiography can reveal new subperiosteal bone growth and transcortical sinus tracts. Arthrography can demonstrate loosening of the prosthesis and abscesses. Fludeoxyglucose-positron emission tomography scans may hold some promise in diagnosing lower-extremity prosthetic joint infection bu approach cannot differentiate aseptic loosening from infection.
Differential Diagnoses of Septic Arthritis
- Vasculitis
- Crystalline arthritides)
- Drug-induced arthritis
- Reactive arthritis (eg, postinfectious diarrhea syndrome, postmeningococcal arthritis, postgonococcal arthritis, arthritis of intrinsic bowel disease).
Treatment
Treatment of bacterial arthritis must begin immediately after the evaluation is complete and appropriate cultures have been taken. Parenteral antibiotics and adequate joint drainage are mainstays of the treatment. Initial antibiotic therapy is broad spectrum until a definite pathogen is isolated and specific antibiotic is chosen.
Duration of parenteral antibiotics should be approximately 15 to 21 days and afterward continue with oral antibiotics to complete 4-6 weeks regimen.
The most frequently used regimens use third-generation cephalosporins followed by oral cefixime.
. Infection with either methicillin-resistant or methicillin-susceptible S aureus [MRSA and MSSA] require parenteral antibiotics for 4 weeks at least.
In prosthetic joint infections with Staph aureus, rifampicin should always be used because of its unique ability to penetrate the biofilm in which these pathogens reside.
Patients with gonococcal arthritis should receive concurrent therapy for chlamydia, such as one dose of azithromycin or doxycycline.
Joint drainage improves joint vascularization, decompresses the joint, removes the organism load. It is done either by repeated aspiration or surgical drainage.
If the joint fails to respond after 5 days of appropriate antibiotic therapy –
- Reculture the fluid and reexamine for crystals
- Perform appropriate serologies for diagnosis of Lyme disease and treat if positive
- If fungal or mycobacterial infection is possible, consider a synovial biopsy
- Consider the possibility of reactive arthritis; nonsteroidal inflammatory agents are the primary therapeutic agents for reactive arthritis
- Perform imaging studies, either radiographs or magnetic resonance imaging, to rule out periarticular osteomyelitis.
Oral antibiotics are usually used in treating gonococcal joint infections.
The joint should be immobilized initially and if the patient’s condition responds adequately after 5 days of treatment, gentle mobilization of joint should be done. Most patients require aggressive physical therapy to allow maximum postinfection functioning of the joint.
Gonococcal-infected joints rarely require surgical drainage.
Surgical drainage is indicated when one or more of the following occur
- Antibiotics and percutaneous drainage fails to clear the infection after 5-7 days
- The infected joints are difficult to aspirate (eg, hip)
- The adjacent soft tissue is infected
Routine arthroscopic lavage is rarely indicated. However, drainage through the arthroscope is replacing open surgical drainage.
Debridement and retention of the prosthesis should be considered in patients who develop a prosthetic joint infection within 30 days of implantation or who present within 3 weeks of the development of symptoms if the prosthesis appears to be well fixed and is without a sinus tract.
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