Septic arthritis

• RED FLAG – permanent joint damage can occur in <2 weeks 
• Most commonly knee and hip joint in children
• An acute monoarthritis (rarely an oligoarthritis)

Causes

• Haematogenous spread
• Osteomyelitis of adjacent bones
• Direction – injury, surgery

Aetiology:

• Haematogenous (adults)
• Osteomyelitis (children)
• Direction inoculation via skin/trauma
• Iatrogenic (surgery, arthroscopy, arthocentesis)

Predisposing factors

• Extra-articular infection (e.g. GU tract, skin, lung)
• Chronic illness (e.g. RA, DM, malignancy)
• Prior drug use (e.g. antibiotics, immunosuppressives)
• Prior joint damage (e.g. OA, RA, prosthetic joints)
• Suppressed immune status (e.g. SLE, HIV)

Differentials

• transient synovitis
• osteomyelitis, trauma
• tumours
• Perthes
• SUFE
• inflammatory arthropathy
• acute rheumatic fever

Clinical

• Passive movement extremely painful
• Non weight bearing
• Fever
• Preceding bacteraemia with skin lesions and migrating polyarthritis settling to monoarthritis often of a large joint (usually knee)
• Systemic symptoms of sepsis
• Local symptoms in involved joint – swelling, warmth, pain, inability to bear weight, ↓ROM
• Gonococcal triad:
  • Migratory arthritis
  • tenosynovitis next to inflamed joint
  • maculopapulovesicular skin changes

Diagnosis:

• XR and USS for effusion
• Aspiration: Culture and sensitivity (blood, urine, endocervical, urethral, rectal, oropharyngeal). Arthrocentesis is essential.
• Infection = opaque, ↑ wbc cell, PMNs >85, culture positive
• Surgical drainage and lavage
• Complications:Systemic sepsis, cartilage destruction, growth plate damage, avascular necrosis of femoral head