Trauma and orthopaedic emergencies

Bone and joint infection

Overview and approach

Septic arthritis and osteomyelitis require rapid diagnosis and source-control planning.

  • Conditions covered: osteomyelitis, septic arthritis, and hand flexor tenosynovitis (see Flexor sheath infection and hand bites under Plastics).
  • Children: mostly haematogenous; adults: haematogenous, contiguous (diabetic foot, pressure sores), or post-surgical/implant-related (including prosthetic joint infection, see that page)1.
  • Why children's metaphyses: blood flows slowly through the capillary loops beside the growth plate, so circulating bacteria settle there, and few white cells reach the spot. Pus then builds under pressure, cuts off blood supply and kills bone, and the infection tracks through the cortex to lift the periosteum4,5.
  • Site changes with age: in neonates, vessels cross the growth plate, so metaphysis, epiphysis and joint are often infected together; in children the metaphysis is typical; after the growth plate closes, adults tend to get epiphyseal and subchondral infection5.
  • Key terms: sequestrum is a piece of dead bone; involucrum is the shell of new living bone that forms around it; a Brodie abscess is a walled-off metaphyseal abscess that grumbles along with pain and little fever; a sinus can drain pus to the skin4,5.
  • Bone to joint: where the metaphysis lies inside the joint capsule (proximal femur, proximal humerus, proximal radius, and at the ankle), osteomyelitis can spill straight into the joint4.

Likely organisms by setting4,5.

SettingThink of
Most agesStaphylococcus aureus (80-90% of culture-positive cases)
NeonatesGroup B streptococcus, E. coli (plus S. aureus)
Under about 2 yearsKingella kingae (often culture-negative; found by PCR), S. pneumoniae
Sickle cell diseaseSalmonella
Nail through a shoe; IV drug usePseudomonas; Gram-negatives
Sexually active adolescent, several jointsNeisseria gonorrhoeae
  • Learning goals: discuss symptoms and signs of bone and joint infection, and list the diagnostic work-up used to reach a definitive diagnosis.
Assessment and clinical features

Assess fever, local pain, reduced motion, wounds, prosthesis, diabetes and immunosuppression.

  • Children: fever, localised pain, limited movement, refusal to weight-bear or pseudoparalysis of a limb1,2.
  • About half of cases are under 5 years, and a quarter of those are infants. Neonates may have fever alone with no local sign4.
  • Osteomyelitis: feel for point tenderness over the metaphysis. Redness and swelling are late and suggest an abscess. Femur, tibia, humerus and calcaneus are the usual sites4.
  • About a third give a history of minor trauma to the area; this should raise, not lower, suspicion4.
  • Septic arthritis: warm, tender joint with an effusion and a dramatically reduced range. Hip and shoulder show little visible swelling early, so are easily missed4.
  • Suspect both bone and joint in children under 18 months, delayed presentation, prior antibiotics, or a slow clinical or CRP response4.
  • Adults: hot swollen painful joint with painful restricted active and passive movement; osteomyelitis may be subacute with local pain, sinus, or non-healing ulcer. Risk factors: diabetes, immunosuppression, IV drug use, joint disease, prosthesis, recent procedure.
Differentials and investigations

Blood cultures, inflammatory markers, joint aspiration and appropriate imaging; sample before antibiotics when safe, without delaying sepsis treatment.

  • Differentials: transient synovitis, crystal arthritis (gout, pseudogout), inflammatory arthritis, haemarthrosis, trauma, malignancy, Perthes/SUFE.
  • Tests: FBC, CRP/ESR, blood cultures; ultrasound for effusion; MRI when osteomyelitis or abscess is suspected; plain films often normal early1,2.
  • Bloods: white cell count is normal in at least half, but CRP or ESR are raised in over 90%. CRP rises within hours and normalises in about 2 weeks, so it tracks response better than ESR. Look at the blood film to exclude leukaemia4.
  • Cultures: blood cultures are positive in only 30-50%; bone aspirate or biopsy in 50-70%. Many cases never grow an organism4,5.
  • X-ray timeline: normal for about the first 3 days, then deep soft tissue swelling, with periosteal reaction or lysis from about day 10-21. Changes present at the first visit mean the infection is not new4. A lytic area with a sclerotic rim suggests established osteomyelitis5.
  • Bone scan: over 90% sensitive and shows multifocal disease, but an abscess can make it falsely cold4.
  • Mimics: bone tumours and leukaemia (the key one to exclude), cellulitis, bone infarction in sickle cell disease, and chronic recurrent multifocal osteomyelitis (sterile, relapsing, often the clavicle)4.
  • Several sites at once: look for a persisting source of bacteraemia such as endocarditis or an occult abscess4.
  • Joint aspiration for cell count, Gram stain, culture and crystals before antibiotics when this does not delay treatment of a septic patient1.
  • Child's hip: Kocher criteria (non-weight-bearing, fever above 38.5 C, ESR above 40, WBC above 12,000); a score of 2-4 warrants urgent orthopaedic assessment, aspiration or MRI2.
Management and follow-up

Urgent orthopaedic/infectious-diseases management, antibiotics and drainage/debridement as indicated.

  • Urgent orthopaedic review; septic arthritis needs urgent aspiration and/or arthroscopic or open washout1,3.
  • Do not delay antibiotics in an ill or rapidly deteriorating patient; start after cultures. Empiric choice depends on age and risk (for example IV cefazolin, adding vancomycin if unwell or MRSA risk in one paediatric guideline)2.
  • Osteomyelitis: bone biopsy/culture, prolonged therapy, debridement of dead bone or abscess; involve infectious diseases.
  • Follow-up: CRP trend, clinical review, rehabilitation and surveillance for chronic osteomyelitis or growth disturbance.
Red flags and clinical pearls

Normal early inflammatory markers do not exclude infection. A child refusing to weight-bear or a painful prosthetic joint needs prompt review.

  • Septic arthritis is an emergency: cartilage destruction begins within days.
  • Bacterial enzymes and the inflammatory response damage articular and growth cartilage. Late results include dislocation, avascular necrosis of the epiphysis and a destroyed joint4.
  • Acute osteomyelitis becomes chronic in 5-25%, usually after delayed diagnosis, extensive dead bone or inadequate treatment. Chronic disease can flare after years and cause pathological fracture, amyloidosis, endocarditis, or squamous cell carcinoma in a long-standing sinus5.
  • Joint replacement, immunosuppression or IV drug use: lower threshold for aspiration and urgent review.
  • Septic hip in a child can mimic transient synovitis: use criteria and low threshold for aspiration.
  • Viva: work-up, aspiration before antibiotics, organisms by age.
References
  1. Royal Children's Hospital Melbourne: Bone and joint infection
  2. Texas Children's Hospital: Acute haematogenous osteomyelitis and/or septic arthritis guideline (2025)
  3. Royal Children's Hospital Melbourne: Osteomyelitis and septic arthritis
  4. South M, Isaacs D, editors. Practical Paediatrics. 7th ed. Edinburgh: Churchill Livingstone Elsevier; 2012. Chapter 12.2, Bone and joint infections.
  5. Kumar V, Abbas AK, Aster JC, editors. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philadelphia: Elsevier Saunders; 2015. Chapter 26, Bones, joints, and soft tissue tumors.

Last updated from Sen’s notes on 22 October 2026.