Septic arthritis

Question 1

What is septic arthritis?

Answer 1

Septic arthritis is an infection producing inflammation in a native or prosthetic joint or more than one joint.

It can be acute or chronic. Prompt diagnosis and treatment of infectious arthritis can help prevent significant morbidity and mortality

Question 2

What are the risk factors for septic arthritis?

Answer 2

S.aureus is the most frequent pathogen.

RF includes:

• Increasing age.
• Diabetes mellitus.
• Prior joint damage - eg, rheumatoid arthritis, gout, systemic connective tissue disorders.
• Joint surgery.
• Hip or knee prosthesis.
• Skin infection in combination with joint prosthesis.
• Immunodeficiency - eg, infection with HIV

Question 3

What is the presentation of septic arthritis?

Answer 3

The classic picture is a single swollen joint with pain on active or passive movement.

The triad of fever, pain and impaired range of motion is typical. Fevers are usually low-grade and rigors are only present in a minority of cases.

Septic arthritis may present as polyarticular arthritis in a minority of patients.

Fevers and rigors are present in the majority of cases but their absence does not exclude the diagnosis. Bacteraemia is a common finding and, when present, may cause prostration, vomiting or hypotension.

Question 4

What is the presentation of septic arthritis in children?

Answer 4

Easily missed in children as localising signs may be absent and may be confused with transient synovitis and trauma.

Patients usually present with fever, joint pain and/or unwillingness to move the affected joint (eg, a limp or refusal to weight bear if the hip joint is affected).

Question 5

What are the signs of septic arthritis?

Answer 5

The joint is usually swollen, warm, tender and exquisitely painful on movement. An effusion may be obvious. The knee is the most common joint involved (about half of cases), followed by the hip, shoulder, ankle and wrists.

Signs may be less marked or poorly localised in the elderly, in the immunocompromised, in drug abusers and in infections of the spine, hip and shoulder joints.

Infection of a prosthetic joint may show few signs until a drainage sinus develops. Occasionally, an abscess around the joint, or loosening of the implant, is indicated by pain.

Question 6

What are the differentials of septic arthritis?

Answer 6

RA
OA 
Vasculitis 
Gout 
Reactive arthritis 
Lyme disease 
Viral arthritis 
IE

Question 7

What are the investigations of septic arthritis?

Answer 7

FBC.
-This may reveal an elevated white cell count. Inflammatory markers (ESR and CRP) are usually elevated in infection, and may be useful in following response to therapy.

Synovial fluid examination:
-If synovial fluid can be aspirated, it should be sent for leukocyte count, Gram staining, polarising microscopy to exclude crystal arthropathy, and culture. Marked leukocytosis may be seen in mycobacterial infection.

Synovial tissue culture.
-This is predominantly indicated where fungal or mycobacterial infection is suspected. Culture is 94% sensitive for tuberculous infection.

Blood cultures. At least two blood cultures should be taken to exclude bacteremia.

Cultures for gonococcal infection. Rectal, cervical, urethral and pharyngeal swabs should be taken if this condition is suspected.

PCR

Tests for Lyme disease.

Immunology. Serological tests for diagnosis of various rheumatological disorders and vasculitides should be arranged as clinically appropriate.

CT and MRI scan for diagnosing periarticular abscesses, joint effusions and osteomyelitis. Also useful for investigating the prosthetic joint

Question 8

What is the management of septic arthritis?

Answer 8

Management involves surgical drainage and lavage of the joint and high-dose intravenous antibiotics

.
• Joints difficult to access (eg, hip, shoulder and sacroiliac joints) may require ultrasound-guided needle aspiration or open arthrotomy.
• Surgical drainage may be required in any infected joint which does not respond to medical treatment.
• The limb should be splinted in the position of function (knees in extension, elbows at 90°, wrists in neutral to slight extension, hips in balanced suspension in neutral rotation). Once the infection is under control, immediate joint mobilisation will promote healing of the articular cartilage and prevent contractures.

Question 9

Which antibiotics are used in septic arthritis?

Answer 9

The antibiotic should at least cover S. aureus and Streptococcus spp. A microbiologist should also be consulted, as the choice of therapy should be based on resistance patterns in the local hospitals and community.

Antibiotics are given intravenously initially (usually for 2-3 weeks) before being switched to oral (often for at least a further 2-4 weeks).

Recommended antibiotic treatments include:

• Seek specialist advice if prostheses are present.
• Flucloxacillin for 4-6 weeks (longer if infection complicated); if penicillin-allergic then use clindamycin instead.
• If meticillin-resistant S. aureus (MRSA) is suspected, vancomycin (teicoplanin may also be used) for 4-6 weeks (longer if infection complicated)
• If gonococcal arthritis or Gram-negative infection is suspected, cefotaxime (ceftriaxone may also be used). Treat Gram-negative infections for 4-6 weeks (longer if infection complicated). Treat gonococcal infection for two weeks.

If the condition fails to respond to five days of treatment with an appropriate antibiotic (as evidenced by persistent fever, positive cultures or synovial purulence), the therapeutic approach should be reassessed.

Synovial fluid should be re-examined for crystals, and Lyme disease serology should be arranged

Question 10

What is the management of septic prosthetic joints?

Answer 10

The prosthetic joints to get infected most commonly are the elbow, shoulder and ankle joints, followed by hips and knees. Early infection (less than 12 weeks after implantation) is usually caused by skin pathogens such as coagulase-negative Staphylococcus spp. It can often be cured medically, providing there is no evidence of periarticular soft tissue involvement or joint instability.

Late-onset infections (more than one year after implantation) are usually caused by haematogenous spread of common organisms such as Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus epidermis and S. aureus.

Prosthetic joint infections are often managed by surgical treatment of irrigation and debridement in acute infections, and 1-stage or 2-stage exchange arthroplasty in chronic infections.