Osteomyelitis and Bone Infection

📋 Key Information Summary

📋

Osteomyelitis is infection of bone; classification includes acute haematogenous, chronic, vertebral/discitis, and diabetic foot osteomyelitis.
Staphylococcus aureus (including MRSA) is the most common pathogen across all types; MRSA prevalence varies by Australian region and setting.
MRI is the investigation of choice for diagnosis; sensitivity >95% for bone marrow oedema. Bone biopsy with culture is the gold standard for pathogen identification.
Acute haematogenous osteomyelitis: most common in children <5 years. Requires urgent IV antibiotics and surgical drainage if subperiosteal abscess present.
Chronic osteomyelitis: defined by >6 weeks of symptoms or radiographic sequestrum. Requires surgical debridement combined with prolonged antibiotics.
Vertebral osteomyelitis: presents with insidious back pain and fever. Most common in lumbar spine. Blood cultures positive in ~60%.
Diabetic foot osteomyelitis: present in up to 20% of diabetic foot ulcers. Probe-to-bone test has 87% specificity. Can often be managed with oral antibiotics alone if no sepsis.
Empirical IV therapy: flucloxacillin (or vancomycin if MRSA risk). Directed therapy after culture results. Total duration typically 4–6 weeks (6 weeks for vertebral).
IV-to-oral switch: possible after 2–7 days of IV therapy if clinical improvement, organism identified, and effective oral agent available (e.g., cephalexin, trimethoprim/sulfamethoxazole).
CRP and ESR are key monitoring markers; CRP should normalise by 2 weeks. Serial imaging not routinely required.
Aboriginal and Torres Strait Islander populations have higher osteomyelitis incidence; remote community access and delayed presentation are barriers to optimal care.
Surgical referral is essential for abscess drainage, debridement, dead-space management, and hardware removal in prosthetic joint infection.

Introduction & Australian Epidemiology

Osteomyelitis is infection of bone caused by bacteria, fungi, or mycobacteria. In Australia, Staphylococcus aureus accounts for approximately 50–70% of cases, with increasing prevalence of community-associated MRSA (CA-MRSA), particularly in northern Australia and remote Indigenous communities.

Key Australian epidemiological points:

Acute haematogenous osteomyelitis: incidence ~8 per 100,000 in children <5 years; male predominance (2:1).
Chronic osteomyelitis: rising incidence linked to diabetes, peripheral vascular disease, and prosthetic joint infections.
Vertebral osteomyelitis: incidence ~2.4 per 100,000; median age 65 years; staphylococci in ~60%.
Diabetic foot osteomyelitis: affects 10–20% of patients with diabetic foot ulcers during their lifetime.
CA-MRSA rates in Australia: ~15–20% nationally, up to 50–70% in some remote Indigenous communities.

Acute Haematogenous Osteomyelitis (AHO)

AHO results from bacteraemic seeding of bone. Predominantly affects children, with the metaphysis of long bones (femur, tibia, humerus) most commonly involved.

Risk Factors

Age <5 years; male sex; recent bacteraemia or soft-tissue infection
Sickle cell disease (rare in Australia), immunosuppression
Indwelling IV catheters, trauma, recent surgery

Clinical Features

Fever, bone pain, reluctance to bear weight/use limb, local warmth and swelling
Infants may present with pseudoparalysis
Erythema may be absent early; high clinical suspicion required

Microbiology

Organism	Frequency	Notes
S. aureus	50–70%	Most common; consider CA-MRSA in remote communities
Streptococcus spp.	10–15%	Group A, Group B (neonates), S. pneumoniae
Kingella kingae	5–10%	Children 6 months–4 years; use BHI enrichment broth
Gram-negatives	5%	Neonates (E. coli), sickle cell, immunocompromised

Initial Management

🚨

Urgent surgical referral if subperiosteal/intraosseous abscess on imaging, failed 48 h of antibiotics, or systemic toxicity (sepsis).

IV antibiotics within 1 hour of diagnosis; obtain blood cultures and CRP first.
Empirical IV: flucloxacillin 50 mg/kg (max 2 g) IV 6-hourly in children; 2 g IV 4–6-hourly in adults.
If MRSA risk (remote community, prior MRSA): add vancomycin (paediatric 15 mg/kg IV 6-hourly; adult 25–30 mg/kg loading then 15–20 mg/kg IV 12-hourly).
Consider adding clindamycin 10 mg/kg IV 8-hourly for toxin-mediated strain cover (CA-MRSA).
IV-to-oral switch after clinical improvement + CRP declining (typically 2–5 days IV).

Oral Step-Down Options

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Cephalexin

Generic · 1st-generation cephalosporin

Paediatric dose25 mg/kg (max 500 mg) PO 6-hourly

Adult dose500 mg PO 6-hourly

PBS status✔ PBS General Benefit

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Flucloxacillin

Generic · Antistaphylococcal penicillin

Paediatric dose12.5–25 mg/kg (max 500 mg) PO 6-hourly

Adult dose500 mg PO 6-hourly

PBS status✔ PBS General Benefit

💊

Clindamycin

Dalacin C® · Lincosamide

Paediatric dose7.5 mg/kg (max 450 mg) PO 6–8-hourly

Adult dose450 mg PO 8-hourly

PBS status✔ PBS General Benefit

Chronic Osteomyelitis

Defined as osteomyelitis lasting >6 weeks, with sequestrum (dead bone), involucrum, or sinus tract formation. Often polymicrobial. Requires combined surgical and medical therapy.

Classification — Cierny-Mader Staging

Stage I

Medullary

Infection confined to endosteal surface

Stage II

Superficial

Cortical surface infection; adjacent soft-tissue defect

Stage III

Localised

Full-thickness cortical necrosis; sequestrum

Stage IV

Diffuse

Mechanical instability; may require reconstruction

Management Principles

Surgical debridement of necrotic bone and soft tissue is essential — antibiotics alone are insufficient.
Obtain deep bone/tissue cultures during debridement (not superficial swab).
Pre-operative IV antibiotics should be withheld until intraoperative cultures obtained (if clinically stable).
Duration: 6 weeks total (IV + oral) for adequately debrided bone; consider 3–6 months if hardware retained.
Negative-pressure wound therapy (NPWT) for soft-tissue defects; free-flap coverage may be required.

⚠️

Sinus tract cultures correlate poorly with deep-bone cultures. Always obtain intraoperative bone biopsy rather than relying on sinus swabs.

Vertebral Osteomyelitis & Discitis

Vertebral osteomyelitis accounts for ~2–7% of all osteomyelitis cases. Discitis often co-exists in adults (contiguous spread). The lumbar spine is most commonly affected, followed by thoracic and cervical.

Clinical Features

Insidious back pain (weeks to months), localised tenderness, low-grade fever (absent in ~30%).
Neurological deficit in 10–30% (epidural abscess or vertebral collapse).
ESR and CRP elevated in >90%. Blood cultures positive in ~60%.

🚨

Emergent MRI if new neurological deficit — possible epidural abscess requiring urgent surgical decompression.

Microbiology

Organism	Frequency	Risk Factors
S. aureus (incl. MRSA)	50–60%	IVDU, haemodialysis, prior hospitalisation
Gram-negatives	10–15%	UTI, GU procedures, elderly
Mycobacterium tuberculosis	5–10%	Endemic regions, immunocompromise — consider in all cases
Brucella spp.	Rare in Australia	Overseas travel, occupational exposure

Management

CT-guided biopsy if blood cultures negative — diagnostic yield ~70%.
Empirical: flucloxacillin 2 g IV 4–6-hourly + cover gram-negatives if risk factors (add ceftriaxone 2 g IV daily).
If MRSA: vancomycin 25–30 mg/kg IV loading then 15–20 mg/kg 12-hourly.
Total duration: 6 weeks minimum (IV 2–4 weeks then oral switch).
Surgical referral for epidural abscess, progressive neurological deficit, or vertebral instability.

Diabetic Foot Osteomyelitis

Osteomyelitis complicates 10–20% of diabetic foot ulcers. Early diagnosis and appropriate antibiotic duration can avoid amputation in many patients.

Diagnosis

Probe-to-bone test: sensitivity 87%, specificity 83%. Positive test in the setting of ulcer raises pre-test probability significantly.
Plain X-ray: low sensitivity early (<50%); may show cortical erosion or periosteal reaction after 2–4 weeks.
MRI: sensitivity 90%, specificity 80%. Recommended if X-ray equivocal.
Bone biopsy: gold standard. Perform via cortical window or CT-guided. Yield highest if antibiotic-free for 48 h.

✅

Oral-only treatment for diabetic foot osteomyelitis without sepsis is supported by the OVIVA trial (2019) and may be appropriate in selected patients with good vascular supply.

Antibiotic Regimens

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Trimethoprim/Sulfamethoxazole

Bactrim® · SXT

Adult dose160/800 mg PO 12-hourly (1–2 DS tablets BD)

Paediatric dose4/20 mg/kg (max 160/800 mg) PO 12-hourly

Renal adjustmentAvoid if eGFR <30 mL/min

PBS status✔ PBS General Benefit

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Amoxicillin/Clavulanate

Augmentin® · Co-amoxiclav

Adult dose875/125 mg PO 12-hourly (or 500/125 mg TDS)

Renal adjustment500/125 mg 12-hourly if eGFR 10–30

PBS status✔ PBS General Benefit

Management Approach

If no systemic sepsis: consider oral antibiotics alone after bone biopsy.
If soft-tissue infection present: IV antibiotics until soft-tissue infection controlled, then oral switch.
Duration: 6 weeks if bone infected (shorter courses if bone resected at surgery).
Offloading and wound care are critical adjuncts; multidisciplinary diabetic foot team referral essential.

MRI & Bone Biopsy

Imaging Strategy

Modality	Sensitivity	Role	Availability
Plain X-ray	43–75%	First-line screening; changes lag 2–4 weeks	All centres (MBS)
MRI with contrast	90–100%	Gold standard for diagnosis; assess abscess, sinus tracts	Major/metropolitan centres
CT	67–80%	Sequestrum detection; guided biopsy	Most centres
Bone scan (Tc-99m)	73–95%	Screening when MRI unavailable; limited in diabetic neuropathy	Nuclear medicine centres

Bone Biopsy — Practical Points

1

Timing

Ideally before antibiotics commenced. If already on antibiotics, withhold for 48 h if clinically safe.

2

Technique

CT-guided percutaneous for vertebral/deep bone; open biopsy at debridement for chronic/diabetic foot.

3

Samples

Send for culture (aerobic, anaerobic, mycobacterial, fungal) and histopathology. Use BHI broth enrichment for paediatric cases (Kingella).

4

Yield

CT-guided biopsy diagnostic in ~70%. Repeat biopsy warranted if negative and clinical suspicion high.

Antibiotic Therapy & Duration

Empirical Therapy — Quick Reference

Setting

Empirical Regimen

Duration

AHO — low MRSA risk

Flucloxacillin IV then PO

3–4 weeks total

AHO — high MRSA risk

Vancomycin IV → clindamycin PO

4–6 weeks total

Chronic osteomyelitis

Pathogen-directed post-debridement

6 weeks (up to 3–6 months)

Vertebral osteomyelitis

Flucloxacillin ± ceftriaxone IV

6 weeks minimum

Diabetic foot — no sepsis

SXT or amox/clav PO

6 weeks (shorter if bone resected)

Directed Therapy by Organism

Organism	IV Agent	Oral Agent
MSSA	Flucloxacillin 2 g IV 4–6-hourly	Flucloxacillin 500 mg PO 6-hourly or cephalexin 500 mg PO 6-hourly
MRSA (susceptible)	Vancomycin IV (trough 15–20 mg/L)	SXT 160/800 mg PO BD or doxycycline 100 mg PO BD or clindamycin 450 mg PO TDS
Streptococcus spp.	Benzylpenicillin 1.2 g IV 6-hourly	Amoxicillin 500 mg PO TDS
Gram-negatives	Ceftriaxone 2 g IV daily or meropenem 1 g IV 8-hourly	Ciprofloxacin 500–750 mg PO BD (bone penetration good)
Kingella kingae	Ceftriaxone 50 mg/kg IV daily	Amoxicillin 15 mg/kg PO TDS

IV-to-Oral Switch Criteria

Afebrile ≥48 hours and improving clinically
CRP declining (at least 25% fall from peak)
Organism identified with susceptible oral agent available
Adequate oral intake and compliance expected
No evidence of deep abscess requiring further drainage

Monitoring

CRP: check at baseline, 48–72 h, weekly during treatment. Should normalise by 2 weeks (acute) or show progressive decline.
ESR: slower to normalise (may remain elevated for months). Less useful for treatment response.
Vancomycin: monitor trough levels (target 15–20 mg/L for bone infection); adjust for renal function.
Repeat imaging only if clinical deterioration — early inflammatory changes on MRI may persist for months.
LFTs if on flucloxacillin >2 weeks; FBC if on SXT or clindamycin.

⚠️

PBS Authority: Vancomycin IV requires Specialist/Authority PBS listing. Ciprofloxacin for osteomyelitis is a Restricted Benefit. SXT and clindamycin are General Benefits.

Special Populations

👶 Paediatric

Pathogen: Kingella kingae in 6 months–4 years; S. aureus dominant overall.

AHO duration: 3–4 weeks (recent evidence supports 3 weeks in uncomplicated cases).

BHI enrichment broth improves Kingella culture yield significantly.

IV switch: May switch after 2–4 days IV if CRP falling and clinically well.

🤰 Pregnancy

Safe agents: Flucloxacillin (Category A), cephalexin (Category A), clindamycin (Category A).

Avoid: SXT (Category D — 1st trimester; Category C otherwise), tetracyclines (Category D).

Vancomycin: Category B2 — use if MRSA confirmed, monitor levels closely.

🫘 Renal Impairment

Flucloxacillin: Reduce dose if eGFR <10 (max 500 mg TDS).

Vancomycin: Extended interval dosing; target trough 15–20 mg/L; consult pharmacy.

SXT: Avoid if eGFR <30 mL/min (hyperkalaemia, bone marrow suppression risk).

Ciprofloxacin: Reduce to 250–500 mg BD if eGFR 20–50.

🛡️ Immunocompromised

Broader empirical cover required: consider gram-negatives, fungi, atypical mycobacteria.

Longer duration: Typically 6–12 weeks; tailored by immunology/infectious diseases team.

HIV: Higher risk of S. aureus bacteraemia and vertebral osteomyelitis.

🫁 Hepatic Impairment

Flucloxacillin: Hepatotoxicity risk; avoid if severe liver disease. Use cefazolin IV or cephalexin PO.

Clindamycin: Use with caution; monitor LFTs closely.

SXT: Hepatotoxicity risk; consider alternatives if significant liver disease.

👴 Elderly

Higher prevalence of vertebral osteomyelitis and prosthetic joint infection.

Atypical presentation: May lack fever; confusion, functional decline may be only signs.

Polypharmacy: Check drug interactions (e.g., warfarin + SXT).

Frailty: May limit surgical options; focus on conservative management where appropriate.

Aboriginal and Torres Strait Islander Health Considerations

Aboriginal and Torres Strait Islander Health

Higher Incidence

ATSI Australians have significantly higher rates of osteomyelitis, particularly acute haematogenous osteomyelitis in children. AIHW data show a 2–4× increased incidence compared to non-Indigenous Australians.

CA-MRSA Prevalence

Community-associated MRSA rates in remote ATSI communities range from 50–70%. Empirical therapy must include MRSA cover (vancomycin, clindamycin, or SXT) from the outset in these settings.

Delayed Presentation

Skin infections (scabies, impetigo) are endemic and serve as the portal of entry for S. aureus bacteraemia and subsequent osteomyelitis. Access barriers and distance to hospital contribute to delayed presentation and more advanced disease.

Remote & Rural Access

MRI availability limited in remote communities. Transfer to regional centres for imaging and surgical debridement may be required. RFDS and telehealth ID consultations can support management.

Oral Antibiotic Challenges

Compliance with prolonged oral courses may be difficult. Pharmacy access, refrigeration (for some liquids), and culturally safe engagement are important. Consider depot IV antibiotics via Hospital in the Home (HITH) or community nursing where available.

Skin Infection Programmes

Scabies treatment programmes and community skin infection control (e.g., RHDAustralia Healthy Skin Programme) are critical upstream interventions to reduce osteomyelitis burden. Coordinated approaches with local Aboriginal Medical Services are essential.

📚 References

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3. Lew DP, Waldvogel FA. Osteomyelitis. Lancet. 2004;364(9431):369–379.
4. Li HK, Rombach I, Zambellas R, et al. Oral versus intravenous antibiotics for bone and joint infection (OVIVA). N Engl J Med. 2019;380(5):425–436.
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9. Lipsky BA, Berendt AR, Cornia PB, et al. 2012 IDSA clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clin Infect Dis. 2012;54(12):e132–e173.
10. Tong SYC, Davis JS, Eichenberger E, et al. Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management. Clin Microbiol Rev. 2015;28(3):603–661.
11. Berbari EF, Kanj SS, Kowalski TJ, et al. 2015 IDSA clinical practice guideline for the diagnosis and treatment of native vertebral osteomyelitis in adults. Clin Infect Dis. 2015;61(6):e26–e46.
12. Australian Indigenous HealthInfoNet. Overview of Aboriginal and Torres Strait Islander health status 2023. Perth: AIHW; 2023.