Paediatric Bone and Joint Infection

Paediatric bone and joint infection is time-sensitive because bacteria, pus and inflammatory pressure can damage cartilage, physis and bone quickly. The two core diagnoses are acute haematogenous osteomyelitis and septic arthritis, but many children sit between these categories: metaphyseal infection may spread to an adjacent joint, a subperiosteal abscess may mimic a joint problem, or pyomyositis may present as a painful limb with fever.

Acute haematogenous osteomyelitis often starts in metaphyseal bone around the knee, hip, ankle and shoulder. Septic arthritis is an orthopaedic emergency because pus within a joint can rapidly damage cartilage and because joint drainage is a source-control decision, not merely an antibiotic decision.

Presentation varies with age. Neonates and infants may present with irritability, poor feeding or pseudoparalysis rather than a classic fever. Toddlers with Kingella kingae infection may have a subtler systemic response than children with Staphylococcus aureus. Children with sickle cell disease, immunosuppression, penetrating wounds or unusual exposures need organism-specific thinking.

The key management question is not "which antibiotic first?" It is "does this child have pus that needs drainage, and have we obtained cultures without delaying treatment?" Antibiotics treat bacteria, but undrained pus can keep the child febrile, painful and systemically unwell.

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Bacteria seed metaphyseal vessels where sluggish flow and vascular loops favour bacterial deposition. Infection raises intramedullary pressure, compromises perfusion and can break through cortex into a subperiosteal abscess.

Delayed or inadequate source control can lead to abscess expansion, pathological fracture, chronic osteomyelitis, sinus formation, growth disturbance, angular deformity, limb-length discrepancy, joint stiffness, chondrolysis, dislocation or avascular necrosis after septic hip.

A key anatomical reason a metaphyseal osteomyelitis becomes a septic joint is the position of the metaphysis relative to the joint capsule. At most joints the metaphysis is extracapsular, so a metaphyseal abscess that breaks through the cortex forms a subperiosteal collection. At a handful of joints the metaphysis lies inside the capsule, and there a metaphyseal abscess can rupture directly into the joint, converting osteomyelitis into a secondary (combined) septic arthritis.

This intracapsular-metaphysis route operates at any age. In infants up to around 18 months a second route also exists: transphyseal vessels that cross the physis connect the metaphysis, epiphysis and joint (as noted above), adding to the risk of combined bone-and-joint infection in this age group.

Infection in the neonate behaves as a distinct entity and is easy to miss because the classic signs are usually absent. A septic neonate may simply feed poorly, be irritable or lethargic, or stop moving a limb (pseudoparalysis), often without fever or a raised white-cell count.

History

The history should establish severity, likely source, organism clues and whether cultures may already be compromised.

Examination

Examine the whole child first. Tachycardia, fever, toxicity, dehydration and reduced interaction change urgency. Then localise the problem.

Always assess adjacent joints and the spine when the child will not walk. Document neurovascular status and look for skin portals, puncture wounds, cellulitis, surgical scars, bites and pressure areas.

Blood tests and cultures

FBC, ESR and CRP support diagnosis and trend response. CRP is particularly useful for monitoring because it changes faster than ESR. Obtain blood cultures before antibiotics when safe, but do not leave a septic child untreated for ideal culture timing. Joint aspirate, bone aspirate or operative tissue should be sent for Gram stain, culture and sensitivity when drainage or biopsy occurs.

Imaging

Plain radiographs are useful first-line imaging because they may show alternative diagnoses, advanced bone change, fracture or tumour, but they can be normal early in osteomyelitis. Ultrasound is useful for joint effusion and superficial collection. MRI is the best escalation test for marrow oedema, subperiosteal abscess, intraosseous abscess, pyomyositis, soft-tissue spread, multifocal disease and adjacent joint involvement.

Response monitoring

Clinical response should be visible: falling fever, decreasing pain, improved limb use and falling CRP. Failure to improve should trigger a search for undrained pus, resistant organism, wrong diagnosis, adjacent septic joint, multifocal infection or inadequate drug delivery.

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The treatment plan has three linked goals: stabilise the child, identify and treat the organism, and obtain source control when pus is present. Antibiotics without source control may fail; surgery without microbiology may make definitive treatment harder.

Early

• Sepsis and clinical deterioration.
• Abscess formation or spread to adjacent joint.
• Pathological fracture in severe osteomyelitis.
• Joint dislocation or cartilage injury in septic arthritis.
• Need for repeat drainage.

Late

• Growth arrest or angular deformity.
• Avascular necrosis after septic hip.
• Chronic osteomyelitis or sinus formation.
• Joint stiffness, chondrolysis or degenerative change.
• Limb length discrepancy after physeal injury.

Paediatric bone and joint infection management is source-control thinking. Antibiotics are essential, but the child improves only when the organism, anatomical source and any pus under pressure are addressed.

The most important fork is septic arthritis versus osteomyelitis without joint sepsis. Septic arthritis is a cartilage emergency. Osteomyelitis may be managed medically if the child is stable and there is no collection requiring drainage, but abscess, adjacent joint spread, toxic sepsis or failure of inflammatory markers to fall should trigger repeat imaging and source control.

Kingella kingae has changed the interpretation of the well-looking toddler with osteoarticular infection. Fever and blood tests may be less dramatic, so age, joint symptoms, PCR where available and clinical trajectory matter. Staphylococcus aureus remains central, and local MRSA prevalence should guide empiric therapy.

Common pitfalls

• Calling it transient synovitis in a febrile non-weight-bearing child.
• Using normal X-ray to exclude early osteomyelitis.
• Forgetting Kingella in toddlers.
• Not imaging the adjacent joint.
• Continuing antibiotics without looking for undrained abscess when CRP rises.
• Stopping follow-up before growth risk is clear.

Paediatric bone and joint infection is managed worldwide, but organism prevalence, imaging access and antibiotic resistance differ markedly between settings. A globally valid answer states the principle, then flags the local variable that changes it.

Global epidemiology

• Acute haematogenous osteomyelitis has an estimated incidence of roughly 1 to 13 per 100,000 children per year in high-income countries, with higher rates reported in some low- and middle-income and Indigenous populations.
• Septic arthritis incidence is broadly similar in magnitude, peaking in children under 3 years; boys are affected more often than girls.
• Staphylococcus aureus is the dominant pathogen at all ages worldwide. Kingella kingae is the leading cause in the 6 to 24 month group where blood-culture-bottle inoculation and PCR are used. Group B streptococcus and Gram-negative organisms feature in neonates.
• Community-associated MRSA prevalence varies enormously by region and is the single most important driver of empiric antibiotic choice.

Side-by-side guideline comparison

Registry and surveillance notes

• Unlike arthroplasty, paediatric infection has no single global implant registry; evidence comes from national surveillance, MRSA resistance monitoring and multicentre cohorts such as the Finnish trials.
• Antimicrobial resistance surveillance networks (for example regional MRSA and Kingella susceptibility data) effectively function as the registries that shape empiric protocols.

High- vs limited-resource practice variation

Several long-held teachings have softened as randomised and registry data have accumulated. Examiners reward candidates who can state where genuine equipoise exists rather than reciting dogma.

These cards are the landmark evidence and current society guidelines that should anchor any viva answer on paediatric bone and joint infection. Two Finnish randomised controlled trials by Peltola and colleagues reshaped global practice by showing that most children can be treated with short antibiotic courses and minimal surgery, while the Kocher prediction rule remains the most cited tool for the irritable hip.