See also

The limping or non-weightbearing child
The acutely swollen joint
Antimicrobial guidelines
Cellulitis and other bacterial skin infections

Key points

1. Osteomyelitis and septic arthritis should be suspected in any child presenting with fever, pain and limited use of the affected limb or joint
2. Urgent surgical intervention reduces the risk of serious complications in septic arthritis, but should not delay antibiotics
3. Always consider alternate diagnoses such as trauma, non-accidental injury, inflammatory conditions and malignancy

Background

• Septic arthritis is the intra-articular infection of a synovial joint. It may coexist with osteomyelitis, an infection localised to the bone
• Most cases are spread to the bone or joint via the bloodstream. Infection may be introduced via a penetrating injury
• Staphylococcus aureus is the commonest cause, though other organisms should be considered based on age (eg Group B streptococci in neonates, Kingella Kingae in 6 months to 4 years), immunisation status (Haemophilus influenzae) and underlying illness (eg Salmonella in children with sickle-cell disease).
• Discitis is inflammation/infection of an intervertebral disc, typically occurring in pre-school aged children and most often affecting the lumbar spine. Diagnosis requires a high index of suspicion.

Assessment

History

• Site of pain
  • Septic arthritis: most commonly hip or knee but could be any synovial joint
  • Osteomyelitis: most commonly femur or tibia, pelvis and humerus but can be any bone
• Onset and duration of symptoms – eg acute (<2 weeks) or chronic
• Fever – may not be present, particularly in infants
• History of trauma or fall – symptoms may be incorrectly attributed to minor injury
• Functional limitations – eg limited range of motion, refusal to weight bear or non-use of the affected limb or joint
• Irritability in infants – eg when picked up or nappy changed
• Risk factors for development of a severe or disseminated infection include:
• Immunocompromised child
• Neonate
• Delayed presentation
• Delayed diagnosis

Examination

• Fever and signs of sepsis
• Bone and joint examination – using “Look, Feel and Move”
  • Look for resting limb position (eg hip flexed, abducted and externally rotated), swelling and erythema, open wounds or soft tissue infection (potential source)
  • Feel for tenderness, warmth and effusion in all major joints
  • Move:
    • Passively, in all planes of motion, in all joints above and below the site of pain
    • Actively, by asking child to move or by placing an object out of reach
    • Compare with contralateral side
    • Don’t forget the spine
• Assess gait and general posture:
• reluctance to weight bear or to use the affected limb

Differential diagnoses:

• Transient synovitis
• Trauma, including non-accidental injury
• Inflammatory conditions – eg inflammatory arthropathy, chronic recurrent multifocal osteomyelitis, acute rheumatic fever
• Pyogenic myositis
• Discitis
• Malignancy, including leukaemia

Key clinical features of most common differentials

(see also limping or non-weight bearing child)

Management

Recognition and management of the seriously unwell or septic child is the most urgent consideration

Investigations

• Investigations may not be necessary for a child who is systemically well, afebrile and is walking or using the affected limb without significant discomfort – a clear working diagnosis and early follow-up is usually sufficient
• Any child with systemic illness, significant bone or joint pain and limitation of movement requires urgent investigation and discussion with an orthopaedic team

Pathology

• No laboratory test, or combination thereof, is specific for a diagnosis of bone or joint infection
• FBE, ESR, CRP
  • Inflammatory markers may be normal, especially early, in chronic infection, or for infection of the small bones (eg hand, feet)
  • They may also be used to monitor effectiveness of treatment
  • A blood film may help to rule out other causes such as malignancy
• Blood cultures – taken prior to antibiotics if possible
• Synovial fluid aspiration
• Where appropriate, in cases of suspected septic arthritis
• In consultation with an orthopaedic unit
• Should not delay antibiotic treatment

Imaging

• X-ray
  • May exclude other causes of pain (eg fracture, tumour)
  • Often normal until 7 to 10 days in osteomyelitis
• Consider:
• Ultrasound
  • To identify joint effusion in suspected septic arthritis
  • Highly sensitive, but not specific
• MRI with contrast
  • Preferred test for osteomyelitis, especially where symptoms localised
  • May demonstrate sub-periosteal abscess or marrow involvement
  • Highly sensitive for myositis
• Technetium bone scan
  • May be useful where access to MRI is limited
  • A positive bone scan is not a specific finding
  • A negative bone scan cannot rule out infection or other serious pathology
  • May help to identify a multifocal process or infection in ill-defined locations
• CT scan
• Plays a limited role in suspected bone and joint infections. Should not be used in lieu of MRI or bone scan.

Treatment

Septic arthritis requires urgent aspiration +/- arthrotomy and washout. Do not delay antibiotics

Antibiotic treatment

Antimicrobial recommendations may vary according to local antimicrobial susceptibility patterns; please refer to local guidelines

• In uncomplicated cases of both osteomyelitis and septic arthritis, commence:

  
  

  Flucloxacillin 50 mg/kg (max 2 g) intravenous every 6 hours
  
  Or:

• For children under 4 years (higher risk Kingella kingae) consider as a single agent:
  
  Cefazolin 50 mg/kg (max 2 g) intravenous every 8 hours

Criteria for switch to oral antibiotic

• In a child with uncomplicated infection who shows clinical improvement, remains afebrile and has improving inflammatory markers, a switch to oral antibiotics may be considered after 2 to 3 days of IV treatment. Consider:

• Oral cefalexin 45 mg/kg (max 1.5 g) oral, every 8 hours

• Uncomplicated cases of osteomyelitis usually require total treatment duration of 3 to 4 weeks. Septic arthritis usually requires 2 to 3 weeks
• Unusual sites of infection (eg small bones of the hands and feet, vertebra, disc), flat bone infection (eg sternum, skull, scapula) or unusual or resistant organisms will likely need longer intravenous and total duration of antibiotic therapy – discuss with infectious diseases team

Consider consultation with local paediatric team when

• Children with suspected osteomyelitis/septic arthritis should be discussed with an orthopaedic team (in conjunction with general paediatrics)
• Consider infectious diseases consultation in the following circumstances:
• Failure to respond to treatment (either clinically or biochemically)
• Resistant or unusual organism
• Chronic infection (>2 weeks)
• Disseminated infection or unusual site
• Age <3 months
• Immunocompromised

Consider transfer when

Child requires care above the level of comfort of the local hospital

For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services.

Consider discharge when

• Child tolerating appropriate oral antibiotics or has planned outpatient IV therapy, (eg hospital in the home)
• Afebrile, well child
• Improved inflammatory markers and clinical indicators
• Weightbearing/using involved limb
• The family has been advised to return to emergency in the presence of fever or a deterioration in symptoms 

Parent information

Septic arthritis 
Osteomyelitis 
Parent resources

Additional notes

Potential causative organisms

Last updated August 2021