Section 1: Epidemiology and aetiology
Septic arthritis, also known as 'acute suppurative arthritis', is an acute infection of one or more joints and is usually caused by bacteria.
Septic arthritis is an orthopaedic emergency. Early diagnosis and appropriate treatment are essential for optimum results. Any age group can be affected.
There are around two to ten cases of septic arthritis per 100,000 in the general population. In children, 50 per cent of cases occur under the age of five years and 30 per cent under the age of two years.
Typically one joint is involved but 10 per cent of cases involve more. The most common joints involved are the hip, knee and wrist followed by elbow, ankle and shoulder, but any joint can be affected.
Staphylococcus aureus1 is the usual organism involved but other organisms, such as Streptococcus, Escherichia coli, Proteus and Gonococcus, are also important pathogens.
The incidence of Haemophilus influenzae as a cause of septic arthritis in infants has dropped drastically since the introduction of H influenzae type b vaccine. MRSA is a rare cause of septic arthritis but is becoming increasingly common.2,3
Some conditions have an increased incidence of septic arthritis, including rheumatoid arthritis, chronic debilitating conditions (like diabetes), corticosteroids and other immunosuppressive drug int-ake, IV drug abuse and AIDS.
A joint can become infected in the following ways:
- Haematogenous spread from another site of infection (most common).
- Direct spread from adjacent metaphyseal osteomyelitis, especially in children.
- Direct spread from penetrating wounds and procedures, such as intra-articular injections, arthroscopy and arthroplasty.
The organisms first settle in the synovial membrane causing acute synovitis. Later, pus formation and cellular enzymes cause articular cartilage des-truction leading to permanent joint destruction.
Septic arthritis may completely resolve with early diagnosis and treatment (full movements preserved). There may be a partial loss of articular cartilage and joint fibrosis (some movements preserved) or complete loss of articular cartilage and bony ankylosis (no joint movement).
In children, septic arthritis can cause destruction of the epiphysis leading to growth disorders.
Section 2: Making the diagnosis
Septic arthritis has a variety of presentations depending on age and severity. In adults it usually presents as a mono-arthropathy with severely restricted joint movements due to pain, swelling and muscle spasm.
The affected joint becomes acutely inflamed, swollen and hot. Systemic signs of infection include high fever, rigors and malaise. If untreated it can progress to septic shock, which has a significant morbidity and mortality rate.
Attempts should be made to localise the source of infection, for example a UTI or a history of a minor infected superficial wound. However, the source is often not found.
All suspected cases should be urgently referred to hospital. Blood investigations show raised WCC, CRP and ESR. Blood cultures should be taken but the results take up to 48 hours.
Early radiographs are normal or show widening of the joint space suggesting effusion.
Ultrasound can be used but is non-specific as it cannot distinguish categorically between a sterile effusion and pus.4
The most reliable investigation is aspiration of joint fluid. This should be done urgently in all suspected cases under aseptic conditions, preferably in an operating theatre using a wide bore cannula. The aspirate is sent urgently for microscopy and Gram staining for bacteria.
A high leucocyte count of >50,000/ml in joint fluid (normal value 300/ml) is highly suggestive of septic arthritis even if no organisms are seen. The sample is also sent for culture and sensitivity to antibiotics.
|Clinical factor||Common organisms|
(healthy, sexually active)
|Adults, elderly persons||Staph aureus (50 per cent),
streptococci, Gram-negative bacilli
|Early infection||Staph epidermidis, Staph aureus|
|Late infection||Gram-positive cocci and anaerobes|
|IV drug use||Atypical Gram-negative bacilli
for example, Pseudomonas
|Rheumatoid arthritis||Staph aureus salmonella species|
|SLE, sickle cell anaemia||Staph aureus (50 per cent of cases)|
|Haemophilia||Streptococcus, Gram-negative bacilli|
|Immunosupression||Staph aureus, mycobacterium and fungi|
Section 3: Managing the condition
Septic arthritis is a serious problem. Any delay in treatment can lead to irreversible destruction of joint cartilage.
Principles of management
1. Urgent joint aspiration and fluid examination is essential for early diagnosis.
2. Prompt surgical drainage and washout of the joint based on aspiration results is vital.
3. IV antibiotics are started as soon as joint fluid and tissue samples have been obtained.
4. Joint should be splinted and rested (knee in extension, wrist in neutral, elbow in 90 degrees of flexion).6
Role of antibiotics7
- Empirical IV antibiotics are started once the joint has been aspirated.
- Antibiotics can be adjusted later according to culture and sensitivity reports.
- Duration: IV for up to two weeks, oral for four to six weeks.
- Adequate drainage and washout of a septic joint is the cornerstone of successful treatment.
- An arthrotomy is usually performed but arthroscopic washout is equally successful in superficial joints such as knee, shoulder and ankle.
|Choice of antibiotic|
|Recommendations for initial empirical antibiotic choice in suspected
|Patient group||Antibiotic choice|
|No risk factors for atypical organisms||IV flucloxacillin 2g four times a day. Local policy may be to add IV gentamicin.
If allergic to penicillin, IV clindamycin 450-600mg four times daily or a second or third generation cephalosporin IV.
|High risk of Gram-negative sepsis (recurrent UTI, and recent abdominal surgery)||Second or third generation cephalosporin 1.5g three times a day. Local policy may be to add flucloxacillin IV to third generation cephalosporin. Discuss allergic patients with
microbiology. Gram stain may influence antibiotic choice.
|MRSA risk||Vancomycin IV plus second or third generation cephalosporin IV.|
|Suspected gonococcus or meningococcus||Ceftriaxone IV or similar, dependent on local policy or resistance.|
|IV drug users||Discuss with microbiologist.|
|ICU patients, known colonisation of other organs (for example, cystic fibrosis)||Discuss with microbiologist.|
|Antibiotic choice will need to be modified in light of results of Gram stain and culture. This table is a guide and should be reviewed locally by microbiology departments.|
Section 4: Prognosis and follow up
The key to good prognosis is early diagnosis and treatment. Fifty per cent of adults with septic arthritis have significant sequelae of decreased range of motion or chronic pain after infection.9
Poor prognostic factors include:
- Age >60 years.
- Late presentation.
- Rheumatoid arthritis.
- Other comorbidities, for example, diabetes.
Some complications of septic arthritis include:
- Secondary osteoarthritis.
- Avascular necrosis.
- Growth disturbance in children.
Infection of total joint prosthesis (especially knee and hip)
Infection of total joint prosthesis is limb threatening and urgent referral to hospital is vital. The patient must be referred immediately to the surgeon responsible for their care.
Antibiotics should not be started prior to hospital assessment and investigations.
Antibiotics alone cannot usually control the infection and if started in the community setting, they often mask symptoms and signs of an infected joint replacement. They also lessen the chance of subsequently culturing the causative organism successfully.
At operation, joint aspirate and tissue samples are sent for culture and sensitivity as positive cultures are more often successfully obtained from the tissue samples than the fluid itself. Prosthetic joint infections that cannot be resolved by early washout and appropriate high-dose IV antibiotic therapy require removal of the prosthesis and revision surgery.
Although uncommon, the incidence is rising and may need surgical drainage and IV antibiotic treatment for longer periods.
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