Septic arthritis overview

# Overview
Septic arthritis is the one of the most serious medical emergency of a patient present with one or more hot and swollen joints. It is the most rapidly destructive joint disease. It is most common in patients with longstanding rheumatoid arthritis and it is a an important consideration in adults presenting with monoarticular arthritis in 80 to 90% of patients. It can involve any joint, but most commonly involves knee > hip > shoulder > ankle. Other joints such as sacroiliac joint, sternoclacicular or costoclavicular joints may be involved in patient with history of intravenous drug abuse (IVDA), penetrating trauma, animal or human bites and local steroid injections. Septic arthritis is joint inflammation secondary to an infectious etiology, usually bacterial, but occasionally fungal, mycobacterial, viral, or other uncommon pathogens.  Septic arthritis is usually monoarticular involving one large joint such as the hip or knee; however, polyarticular septic arthritis involving multiple or smaller joints may also occur. Though uncommon, septic arthritis is an orthopedic emergency that can cause significant joint damage leading to increased morbidity and mortality.

# Historical Perspective
- First case of septic arthritis described in literature by Walter Whitehead  in 1902, as "The open method of treating exceptional cases of septic arthritis of the knee".
- An experimental and clinical Study on arthritis deformans described by Nathan PW in 1917.
- Surgical management of septic arthritis by By Captain W. Rankin in 1917.

# Classification
Septic arthritis broadly classified based on the etiology as gonococcal or non-gonococcal arthritis and based on the clinical presentation it is classified as mono articular septic arthritis or poly articular septic arthritis.

# Pathophysiology
Septic arthritis most commonly develop as a result of hematogenous spreading of bacteria into the synovial membrane, that induces inflammatory reactions. Eventually, release of cytokines and activation of both host humoral and immunological response along with bacterial virulence factors cumulatively damages articular surface and cartilage.

# Causes
Septic arthritis caused by bacteria or tiny disease-causing microorganisms that spread through the bloodstream to a synovium. It may also occur when the joint is directly infected with a microorganism from an injury or during surgery. The most common sites for this type of infection are the knee and hip. Most cases of acute septic arthritis are caused by bacteria such as staphylococcus or streptococcus. Chronic septic arthritis (which is less common) is caused by organisms such as Mycobacterium tuberculosis and Candida albicans.

# Differential Diagnosis
Patient present with septic arthritis should be differentiate from other causes of acute monoarticular arthritis.

# Epidemiology and Demographics
- Incidence of septic arthritis approximately varies between 2 to 10 cases per 100,000 per year in the general population.
- Incidence of septic arthritis in patients with history of rheumatoid arthritis and patients with joint prostheses is ~3070 cases per 100,000 per year.
- Incidence of septic arthritis in patients with joint prostheses is 40-68 cases per 100,000 per year.
- The case-fatality rate of septic arthritis is estimated to be 10-25%.
- Even after survival from septic arthritis, 25-50% of the patients suffer from irreversible loss of joint function.

# Risk Factors
Most common risk factors that predisposes septic arthritis are rheumatoid arthritis, prosthetic joint or joint replacement and skin infections. Other common risk factors includes:
- Age >80 years
- Recent history of bacteremia
- Intravenous substance abuse
- Corticosteroid therapy
- Cytotoxic chemotherapy
- Diabetes mellitus
- Alcoholism
- Leukemia
- Granulomatous diseases
- Hypogammaglobulinemia
- Cirrhosis
- Chronic kidney disease

# Natural History, Complications & Prognosis
Septic arthritis commonly present with either mono articular involvement associate with tenosynovitis and dermatitis  (gonococcal) or polyarticular involvement (non gonococcal). It is more common in patients in extreme age groups with pre existing joint disorders such as rheumatoid arthritis or predisposing factors such as skin infection. Prompt diagnosis. rapid initiation of treatment, early physical therapy and mobilization are crucial for the outcome of septic arthritis. Complications of septic arthritis mainly depends on the pre existing joint disease and treatment of current infection. Common complications include Joint degeneration (~ 40%) bacteremia (5-20%) osteomyelitis and growth retardation (in children) Prognosis of septic arthritis depends on various factors such host immune response, pre existing joint disease, presence of risk factors, virulence of the pathogen and the duration between onset of symptoms and diagnosis.

# Diagnosis
Patients with history of chronic joint disease and concurrent septic arthritis can be misdiagnosed as acute flareup of underlying chronic disease which often delays the treatment for septic arthritis. So, patients with acute flare of one or two new inflamed joints with underlying chronic joint diseases or with another connective tissue disease, it should be assumed that the joint is septic until proven otherwise, should always rule out concurrent septic arthritis with appropriate diagnostic studies. In patients with acute effusion of unknown etiology, might have concurrent crystal-induced arthritis and septic arthritis. So, the synovial fluid should always be cultured and examined for crystals in the evaluation of an acute effusion.

## History and Symptoms
Septic arthritis commonly present with joint pain (knee> hip>shoulder>ankle) associate with fever, malaise and local joint symptoms such as swelling, erythema and decreased range of motion at the level of joint. In children, hip is commonly affected. Abrupt onset of a single hot, swollen, and painful joint indicate non gonococcal arthritis. It can involve any joint, but most commonly knee is the site of infection in 50% of cases of adults and elderly patients. Hip infection is the most common site in children. Disseminated gonococcal infection(DGI) often present initially with migratory polyarthralgias, tenosynovitis, dermatitis, and fever. Less commonly, patients with DGI will present with purulent joint effusion, most often of the knee or wrist. Often present with inflamed and tender tendons of the wrist, ankles, and small joints.

## Physical Examination
- Swelling of the joint that involved
- Decreased range of motion such as pseudo paralysis
- Patient hold the hip in flexed and externally rotated position if SA involving hip.
- If child, unwillingness to bear weight on the affected joint (antalgic gait)

## Diagnostic Evaluation

# Imaging Studies

## X-ray
X-ray of the joint with septic arthritis are usually normal in the first few days of infection as there is no joint destruction seen usually or may show a preexisting joint disease such as rheumatoid arthritis or osteoarthritis. So, the initial x-ray may be useful to determine pre-existing conditions, such as osteoarthritis or simultaneous osteomyelitis, or may be useful as a baseline image in monitoring the treatment response. However, in the late stages of septic arthritis, X-ray film may show: swelling of the joint capsule and soft tissue around the joint, fat pad displacement, and joint space widening due to localized edema and effusion.

## CT
Computerised tomography is used to diagnose ambiguous cases of septic arthritis to differentiate it from other causes of acute arthritis or to determine the extent of bone and soft tissue infections. But, it is less sensitive in the early stages of the disease. In the late stages of septic arthritis, CT shows: visualization of joint effusion, soft tissue swelling, para-articular abscesses, joint space widening due to localized edema, bone erosions, foci of osteitis, and scleroses.

## MRI
The role of MRI in the diagnosis of septic arthritis has been increasing in recent years in an effort to detect this entity earlier.  Findings are usually evident within 24 hours following the onset of infection and include: synovial enhancement, perisynovial edema and joint effusion.  Signal abnormalities in the bone marrow can indicate a concomitant osteomyelitis. The sensitivity and specificity of MRI for the detection of septic arthritis has been reported to be 100% and 77% respectively.

# Treatment

## Medical Therapy
Acute nongonococcal septic arthritis is a medical emergency which causes severe joint destruction and may increase both morbidity and mortality. So prompt diagnosis and treatment with antibiotic therapy and  prompt drainage which reduces long-term complications. Vancomycin is recommended as either empirical therapy for patients with Gram-positive cocci on a synovial fluid Gram stain or as a component of regimen for those with a negative Gram stain if methicillin-resistant Staphylococcus aureus (MRSA) is prevalent.  If Gram-negative bacilli are observed, an anti-pseudomonal Cephalosporin (e.g., Ceftazidime, Cefepime) should be administered.  Carbapenems should be considered in conditions such as colonization or infection by extended-spectrum -lactamaseproducing pathogens.  The optimal duration of therapy for septic arthritis remains uncertain.  A minimum 3- to 4 week course is suggested for septic arthritis caused by S. aureus or Gram-negative bacteria.  The use of Corticosteroids or intraarticular antibiotics is not advisable.

## Surgical Therapy
Successful treatment of septic arthritis include both anti microbial therapy and removal of intra-articular pus with surgical management. Surgical or arthroscopic management will increase the risk of infections when compared to diagnostic athroscopic procedures without further procedures. Infection rate depends on the type of procedure (open procedures ~17% and arthroscopic procedures 1~1%), duration of the procedure and prior joint disease.
Surgical management options include:
- Closed needle aspiration
- Open drainage
- Tidal irrigation
- Arthroscopy
- Arthrotomy

## Primary Prevention
Prevention of septic arthritis is possible by intensive treatment of risk factors such as old age patients having rheumatoid arthritis, diabetes mellitus, joint prostheses or joint surgery and skin infection.