Armando Hasudungan
Biology and Medicine videos

Septic Arthritis


Overview Septic arthritis refers to infection in a joint; it is usually caused by bacteria but can be caused by fungi or mycobacteria. Septic arthritis due to bacterial infection is often a destructive form of acute arthritis

Arthritis: Inflammation of joint
Arthrosis: Degeneration of joint
Septic Arthritis: Infection of joint

Risk Factors

  • Age >80 years
  • Diabetes mellitus
  • Rheumatoid arthritis
  • Presence of prosthetic joint
  • Recent joint surgery
  • Skin infection
  • Intravenous drug abuse, alcoholism
  • Prior intraarticular corticosteroid injection

Signs and Symptoms

Monoarthritic Joint (Oligoarticular or polyarticular infection occurs in approximately 20% of septic joint infections)

  • Severe pain
  • Swelling
  • Warmth
  • Restricted movement
  • Fever
  • Chills
Remember The knee is involved in more than 50 percent of cases
Remember Septic arthritis can result in irreversible joint damage within 48 hours of the onset of infection due to the proteolytic enzymes of the white blood cells that flood the infected synovial space.

Differential Diagnosis

Monoarthropathy Oligoarthropathy Polyarthropathy
Septic arthritis Crystal arthritis Rheumatoid arthritis
Crystal arthritis (Gout) Psoriatic arthritis Viral Arthritis
Osteoarthritis (can be mono-poly) Reactive arthritis Autoimmune connective tissue disease (ie. SLE)
Trauma (Haemarthrosis) Ankylosing spondylititis Vasculitides (ie. Polymyalgia Rheumatica)


  • Transient synovitis
  • Osteomyelitis may also mimic septic arthritis in its presentation
  • Trauma
  • Tumours
Transient synovitis: or Irritable hip, is a common disorder of childhood which presents with the acute onset of hip pain and a limp that gradually resolves. The history is one of an acute onset of hip pain and a limp, followed by knee pain and inability to weight bear. On examination, the affected leg tends to be held in the position of greatest ease, typically, one of flexion, abduction and slight external rotation.
Osteomyelitis: The patient usually presents with pain, malaise and a fever and in neglected cases toxaemia may be marked. Sometimes a history of preceding skin lesion, an injury or sore throat may be obtained, the limb is held still and there is acute tenderness near the largest joint. Even gentle manipulation is painful and joint movement is restricted. Local redness, swelling, warmth and oedema are later signs and signify the presence of pus.


Patients with suspected septic arthritis should be referred urgently and immediately for hospital specialist review

  • Joint aspiration – Synovial Aspiration
  • FBC
  • EUC
  • Blood cultures
  • Urinalyis
  • Anti-streptolysin O titre
Synovial fluid analysis
Aetiology Colour and Clarity WBC (mm³)
Normal Normal Clear and transparent <200
Inflammatory Gout Yellow and traslucent-opaque 2000-100,000
Septic Bacteria Yellow/green and opaque >25,000 – >100,000 
Haemorrhage Trauma Red and Bloody 200-2000

Diagnosis – Identification of bacteria in the synovial fluid



  • Staphylococcus aureus – In patients with comorbid joint disease or recent joint surgery
  • Group A Streptococcus 
  • Neisseria gonorrhoeae – Sexually active adult


  • Anaerobic microbes
  • Fungal
Remember In children Staphylococcus aureus is the most common pathogen. Other causative organisms include group A Streptococcus and Enterobacter species. Haemophilus influenzae septic arthritis may occur in children who have not been vaccinated.


Septic arthritis involves bacterial infection of a synovial joint.

  • Haematogenous bacterial spread is the most common cause of septic arthritis
  • Osteomyelitis of adjacent bones may also result in joint infection
  • Direct inoculation via penetrating injuries or surgery can occur

Proteolytic enzymes released by host inflammatory cells and certain bacteria cause cartilage destruction.


  • Broad Spectrum Antibiotic therapy
  • NSAIDs
  • Joint drainage and lavage of the joint
  • Tailored antibiotic regime following identification of microbe

Complication and Prognosis


  • Antibiotic allergic reaction
  • Osteomyelitis
  • Dislocation – a tense effusion may cause dislocation of a joint.
  • Joint destruction
  • Joint destruction in children:
    • Epiphyseal destruction. In neglected infants, the largely cartilaginous epiphysis may be destroyed, leaving unstable psudeoarthrosis.
    • Growth disturbance – Physeal damage may result in shortening or deformity.
    • Ankylosis – If articular cartilage is eroded, healing may lead to ankylosis.

Prognosis Delayed or inadequate treatment can lead to irreversible joint destruction and subsequent disability (<48hours). There is also an estimated case fatality rate of 11%.


RACGP – Septic arthritis in children 2015