Introduction

Osteomyelitis is an infection of the bone and bone marrow caused by pyogenic bacteria, mycobacteria, or fungi, resulting in progressive inflammatory destruction of bone, vascular compromise, bone necrosis, and reactive new bone formation. It may present as acute or chronic disease depending on the duration of symptoms. The condition can occur at any age but is most common in children younger than 12 years because of hematogenous spread to the highly vascular metaphysis of growing bones.

Staphylococcus aureus is the most common causative organism worldwide. In patients with sickle cell disease, Salmonella species are more frequently isolated than in the general population.

Epidemiology

• Commonest in children younger than 12 years

• Male predominance

• Higher incidence among patients with diabetes mellitus

• Common after open fractures and orthopaedic surgery

• Increased risk in peripheral vascular disease

• Increased risk in immunosuppressed patients

• Common in sickle cell disease

Classification

According to duration

• Acute osteomyelitis

• Subacute osteomyelitis

• Chronic osteomyelitis

According to route of infection

• Hematogenous spread

• Contiguous spread from adjacent infection

• Direct inoculation following trauma or surgery

According to host status

• Normal host

• Compromised host (diabetes, peripheral vascular disease, immunosuppression)

Etiology

Common causative organisms

Hematogenous osteomyelitis

• Staphylococcus aureus (most common)

• Streptococcus species

• Kingella kingae (young children)

Sickle cell disease

• Salmonella species

• Staphylococcus aureus

Post-traumatic or post-operative infection

• Staphylococcus aureus

• Coagulase-negative staphylococci

• Gram-negative bacilli

Chronic osteomyelitis

• Mixed aerobic and anaerobic bacteria

Specific infections

• Mycobacterium tuberculosis

• Fungal organisms in immunocompromised patients

Pathophysiology

1. Organisms enter bone through the bloodstream, contiguous spread, or direct inoculation.

2. Bacteria proliferate within the metaphysis, particularly in children.

3. Acute inflammatory response causes increased intraosseous pressure.

4. Blood supply becomes compromised leading to bone ischemia.

5. Bone necrosis results in sequestrum formation.

6. Reactive periosteal new bone forms an involucrum.

7. Chronic infection may develop with sinus tract formation.

Risk Factors

• Trauma

• Open fractures

• Orthopaedic implants

• Diabetes mellitus

• Peripheral vascular disease

• Sickle cell disease

• Intravenous drug use

• Immunosuppression

• Chronic kidney disease

• Recent surgery

• Pressure ulcers

Clinical Presentation

Acute Osteomyelitis

• Fever

• Malaise

• Severe localized bone pain

• Fatigue

• Irritability

• Local swelling

• Erythema

• Warmth

• Tenderness

• Restriction of movement

• Refusal to bear weight in children

• Pseudoparalysis of the limb in neonates

• History of recent trauma, surgery, or infection elsewhere

When infection is adjacent to a joint:

• Sympathetic joint effusion

• Concomitant septic arthritis

• Painful limitation of joint movement

Chronic Osteomyelitis

• Previous history of osteomyelitis

• Recurrent pain

• Persistent swelling

• Erythema

• Draining sinus with or without pus

• Bone deformity

• Low-grade fever

• Recurrent exacerbations

Red Flags

• Rapidly progressive swelling

• Persistent high fever

• Septic shock

• Neurovascular compromise

• Suspected compartment syndrome

• Pathological fracture

• Extensive soft tissue abscess

Diagnostic Criteria

The diagnosis of osteomyelitis is established through a combination of clinical assessment, laboratory investigations, imaging studies, and microbiological confirmation. A high index of suspicion is essential, particularly in children, patients with diabetes mellitus, immunocompromised individuals, and those with recent trauma or orthopaedic surgery.

A diagnosis is strongly supported by the presence of:

Major Criteria

• Positive bone biopsy or bone culture demonstrating a pathogenic organism (gold standard)

• Histopathological evidence of bone infection from bone biopsy

• Presence of pus within bone identified during surgery or aspiration

• Sinus tract communicating directly with bone

Minor Criteria

• Localized bone pain or tenderness

• Fever or other systemic features of infection

• Local swelling, erythema, warmth, or reduced limb function

• Elevated inflammatory markers (CRP and/or ESR)

• Leukocytosis

• Positive blood culture with a compatible clinical presentation

• Imaging findings consistent with osteomyelitis (MRI, CT, bone scan, or plain radiographs)

• Clinical improvement following appropriate antimicrobial therapy

Diagnosis is Considered

Definite Osteomyelitis

One or more major criteria are present.

Probable Osteomyelitis

Typical clinical features together with elevated inflammatory markers and imaging findings suggestive of osteomyelitis, particularly when supported by positive blood cultures.

Possible Osteomyelitis

Compatible clinical features with supportive laboratory or imaging findings but without microbiological confirmation. Further investigations, including bone biopsy where feasible, are recommended.

Diagnostic Principles

• Bone biopsy with culture and histopathological examination remains the gold standard for confirming chronic osteomyelitis and identifying the causative organism.

• Blood cultures should be obtained before initiating antibiotic therapy whenever possible.

• MRI is the most sensitive imaging modality for detecting early osteomyelitis and associated soft tissue involvement.

• Plain radiographs may be normal during the first 10–14 days of acute infection and should not exclude the diagnosis if clinical suspicion is high.

• In chronic osteomyelitis, withholding antibiotics for approximately two weeks before bone biopsy, when clinically safe, improves microbiological yield.

Investigations

Laboratory investigations

• Total and differential white blood cell count

• Erythrocyte sedimentation rate (ESR)

• C-reactive protein (CRP)

• Blood culture and sensitivity

• Urinalysis

• Urine culture and sensitivity

• Aspirated pus for culture and sensitivity

• Bone biopsy for culture and sensitivity (gold standard in chronic disease)

For chronic osteomyelitis, antibiotics should preferably be withheld for approximately two weeks before bone biopsy whenever clinically safe to improve microbiological yield.

Special investigations

• Polymerase chain reaction (PCR) for organisms such as Kingella kingae

Imaging

• Plain X-ray

• Ultrasound

• Bone scan using Technetium-99 (especially early disease)

• CT scan for complex anatomical sites such as the spine, pelvis, and shoulder

• MRI (most sensitive imaging modality for early osteomyelitis where available)

Differential Diagnosis

• Septic arthritis

• Cellulitis

• Bone tumour

• Ewing sarcoma

• Sickle cell vaso-occlusive crisis

• Stress fracture

• Osteonecrosis

Management

Management requires:

• Early diagnosis

• Prompt antibiotic therapy

• Appropriate surgical management

• Immobilization

• Monitoring of inflammatory markers

• Long-term follow-up

Pharmacological Treatment

Acute Osteomyelitis

Cloxacillin

• 1–2 g IV every 6 hours

Then continue with:

Ampicillin + Cloxacillin (fixed-dose combination)

• 500 mg orally every 8 hours

Continue treatment for 3–6 weeks or until CRP normalizes and radiological improvement is demonstrated.

OR

Ampicillin + Sulbactam (fixed-dose combination)

• 3 g IV every 6 hours for two weeks

Then:

Amoxicillin + Clavulanate (fixed-dose combination)

• 625 mg orally every 12 hours for four weeks.

Patients with penicillin allergy

Clindamycin

• IV every 6 hours for two weeks

Then continue orally to complete 4–6 weeks

PLUS

Ciprofloxacin

• 400 mg IV every 12 hours for two weeks

Then continue orally to complete 4–6 weeks

Sickle Cell Disease (Salmonella suspected)

Ciprofloxacin

• 400 mg IV every 12 hours for four weeks

May be switched to oral therapy after two weeks if clinically improving.

Surgical Management

Acute Osteomyelitis

• Surgical drainage

• Bone window procedure when indicated

• Recommended for patients presenting after more than 24 hours of symptoms

• Drainage of abscesses

• Removal of necrotic tissue

• Limb immobilization

• Pain control

• Nutritional support

Chronic Osteomyelitis

• Extensive surgical debridement

• Removal of all devitalized tissue

• Excision of sequestrum

• Dead-space management

• Antibiotic bead placement

• Antibiotic cement spacer

Antibiotic cement

Vancomycin

• 2–4 g per 40 g of bone cement

Monitoring and Follow-up

Patients should be reviewed regularly for:

• Clinical improvement

• Resolution of pain

• Wound healing

• CRP and ESR trends

• Repeat imaging when indicated

• Monitoring for antibiotic toxicity

• Detection of recurrence

Complications

• Chronic osteomyelitis

• Bone abscess

• Sequestrum formation

• Involucrum formation

• Pathological fracture

• Growth disturbance in children

• Septic arthritis

• Chronic draining sinus

• Sepsis

• Limb deformity

• Amputation

• Squamous cell carcinoma arising from chronic sinus tracts

Prevention

• Early treatment of skin and soft tissue infections

• Prompt management of open fractures

• Strict aseptic surgical technique

• Appropriate peri-operative antibiotics

• Good glycaemic control

• Early treatment of bacteraemia

• Proper wound care

Patient Education

Patients should be advised to:

• Complete the full antibiotic course.

• Attend all follow-up appointments.

• Keep wounds clean and dry.

• Report persistent fever, increasing pain, or recurrent drainage immediately.

• Avoid smoking where possible.

• Maintain good diabetes control if diabetic.

• Avoid weight bearing until medically advised.

Prognosis

The prognosis depends on the organism, duration of infection, host factors, and timing of treatment. Acute osteomyelitis treated promptly generally has an excellent outcome. Delayed diagnosis increases the risk of chronic osteomyelitis, recurrent infection, pathological fractures, and permanent disability. Chronic osteomyelitis has a higher recurrence rate and often requires repeated surgical intervention.