Septic Arthritis & Osteomyelitis
Septic arthritis is infection of a synovial joint, and osteomyelitis is infection of bone. Both are rare but potentially life-threatening and should always be treated as red flag conditions requiring urgent assessment.
Clinical presentation
Children may present with fever, bone or joint pain, and reduced use of a limb. Typical features include unexplained limp or refusal to walk, reluctance to use a limb or inability to weight bear, a hot swollen joint with tenderness, and pain on movement.
In infants, presentation may be subtle. Discitis may present with crying on spinal flexion (e.g. during nappy change), and neonates may appear only mildly unwell and not be febrile. In very young or immunosuppressed children, more than one joint may be involved.
Septic arthritis
Septic arthritis is most common in children under 2 years. The knee, hip and ankle are most frequently affected. Infection is usually haematogenous but may also occur following direct inoculation or local spread.
In neonates and infants, the metaphysis lies within the joint capsule, allowing infection to spread easily from bone to joint. In adolescents, sternoclavicular or shoulder joint infection should prompt consideration of intravenous drug use.
Osteomyelitis
Osteomyelitis most commonly affects infants and young children, with metaphyseal bone involvement. Infection is usually haematogenous but may follow trauma or local soft tissue infection.
Disease may be acute, subacute or chronic, and abscess formation may occur. Chronic recurrent multifocal osteomyelitis (CRMO) is a diagnosis of exclusion and is now considered an autoinflammatory condition.
Special considerations
Tuberculosis should be considered in children from endemic areas or who are immunosuppressed. Atypical infections including mycobacterial disease are more likely in immunosuppressed children and may mimic inflammatory arthritis.
Common pathogens
|
Age group |
Common organisms |
|
<12 months |
Staphylococcus aureus, Group B Streptococcus, Gram-negative bacilli |
|
1–5 years |
Staphylococcus aureus, Group A Streptococcus, Streptococcus pneumoniae, Haemophilus influenzae, Enterobacter |
|
5–12 years |
Staphylococcus aureus, Group A Streptococcus |
|
12–18 years |
Staphylococcus aureus, Neisseria gonorrhoeae |
Principles of management
Management requires urgent multidisciplinary care involving paediatrics, orthopaedics and microbiology. Key principles include urgent joint washout and drainage, empirical intravenous antibiotics tailored once culture results are available, appropriate investigations, prolonged antibiotic therapy and supportive care including analgesia and limb rest.
Kocher’s criteria – septic arthritis of the hip
Fever >38.5°C, non-weight bearing or pain on passive movement, ESR >40 mm/hr and WCC >12 ×10⁹/L increase the likelihood of septic arthritis.
|
Number of predictors |
Probability |
|
0 |
<0.2% |
|
1 |
3% |
|
2 |
40% |
|
3 |
93% |
|
4 |
99.6% |
Lyme disease
Lyme disease is a tick-borne infection and an important cause of chronic arthritis in children in endemic areas. It typically presents with erythema migrans in early disease and may progress to neurological, cardiac or joint involvement. Diagnosis is based on clinical features, serology or PCR testing, and prognosis is excellent with antibiotic treatment.
Differentiating causes of arthritis
|
Feature |
Lyme arthritis |
Septic arthritis |
Juvenile idiopathic arthritis |
|
History |
Tick bite or travel |
Acute severe illness |
>6 weeks symptoms |
|
Joint pattern |
Large joint monoarthritis |
Any joint, very painful |
Variable |
|
Systemic |
Rash or neuro/cardiac features |
Fever, unwell |
May have rash, uveitis |
|
Labs |
Often normal |
Raised ESR/CRP/WCC |
Variable |
|
Course |
Intermittent |
Acute |
Chronic relapsing |
Key points for healthcare professionals
- Septic arthritis and osteomyelitis are medical emergencies
- Presentations may be subtle in neonates and immunosuppressed children
- Kocher’s criteria help distinguish septic arthritis from transient synovitis
- Consider TB, atypical mycobacteria and Lyme disease in the right context
- Early antibiotics, surgical management and MDT care are essential
Further Reading
