Orthopaedic Surgery - Osteomyelitis

Basics

Osteomyelitis is an infection and inflammatory process involving bone and bone marrow.

It may occur through:

Hematogenous spread

Direct inoculation after trauma or surgery

or

Contiguous spread from adjacent soft-tissue infection.

One of the most commonly used classifications is based on the duration and clinical pattern of infection.

Classification

Acute Osteomyelitis

Acute osteomyelitis most commonly results from:

Hematogenous spread of bacteria.

In children, the infection usually begins in the:

Metaphysis of a long bone.

Causative Organisms in Acute Osteomyelitis

Staphylococcus aureus is the most common organism across most pediatric age groups.

In neonates, other important organisms include:

Group B Streptococcus

Gram-negative bacilli

depending on age and clinical circumstances.

Subacute Osteomyelitis

Subacute osteomyelitis accounts for a substantial proportion of primary bone infections.

It is characterized by:

Insidious onset

Milder symptoms

Longer duration

Less impressive laboratory abnormalities

The most common organisms are usually:

Staphylococcal species.

A localized subacute intraosseous abscess is often referred to as a:

Brodie abscess.

Chronic Osteomyelitis

Chronic osteomyelitis is a longstanding infection characterized by:

Persistent or recurrent inflammation

Necrotic bone

Sinus formation in some patients

Sequestrum formation

Staphylococcus aureus remains an important causative organism.

Chronic disease often requires surgical:

Débridement or curettage of devitalized bone.

Alternative Classification Systems

Osteomyelitis may also be classified according to:

Patient age

Causative organism

Route of infection

Anatomic extent

Categories may include:

Neonatal, pediatric, or adult osteomyelitis

Pyogenic or granulomatous infection

Hematogenous, direct inoculation, or contiguous-spread infection

Synonym

Osteomyelitis is commonly referred to as:

Bone infection.

Epidemiology

Acute hematogenous osteomyelitis occurs more commonly in children than adults.

Peak incidence is generally during:

Later childhood in the first decade of life.

Some historical studies have suggested seasonal variation, with more cases occurring during:

Late summer and early autumn.

Sex Distribution

A slight male predominance has been described.

One possible explanation is greater exposure to:

Minor trauma and activity-related skeletal injury.

Prevalence

Osteomyelitis affects fewer than approximately:

1% of children.

It remains an important diagnosis because delayed recognition can result in major skeletal complications.

Risk Factors

Most children who develop acute hematogenous osteomyelitis are otherwise healthy.

Potential risk factors include:

Recent trauma

Immunocompromise

Malnutrition

Recent systemic infection

Sickle cell disease

Open wounds or surgery

Antecedent Trauma

A history of minor trauma is common but does not necessarily cause the infection.

Trauma may:

Draw attention to the area

or potentially alter local blood flow, facilitating bacterial seeding.

Sickle Cell Disease

Patients with sickle cell disease have an increased risk of osteomyelitis because:

Bone infarction and altered splenic function may predispose to infection.

However, acute bone pain in a patient with sickle cell disease is still more commonly caused by:

Vaso-occlusive infarction

than infection.

Organisms in Sickle Cell Disease

Staphylococcus aureus remains an important pathogen.

Salmonella species are also classically associated with osteomyelitis in patients with sickle cell disease.

Etiology

The exact reason one child develops hematogenous osteomyelitis while another does not is often unclear.

Possible contributing factors include:

Transient bacteremia

Minor trauma

Altered local blood flow

Impaired host defenses

Most affected children have no major underlying disorder.

Associated Conditions

Nearly half of affected children may have a recent or concurrent infection, such as:

Upper respiratory infection

Viral illness

or another transient infectious process.

This may provide a source for transient bacteremia.

Diagnosis

Diagnosis requires a combination of:

Clinical suspicion

Laboratory testing

Imaging

and, when possible,

Microbiologic identification of the organism.

Signs and Symptoms

The most common symptom is:

Localized bone pain.

Other findings may include:

Swelling

Warmth

Erythema

Tenderness

Reduced movement of the adjacent joint

Limp

Refusal to bear weight

Fever

Fever may occur, but:

Its absence does not exclude osteomyelitis.

Some children, particularly neonates and patients with subacute infection, may have little or no fever.

Infants and Young Children

Children who cannot describe their symptoms may present with:

Refusal to walk

Limping

Failure to use a limb

Irritability with movement

Pseudoparalysis

A high index of suspicion is particularly important in:

Neonates.

Classical Diagnostic Criteria

Older diagnostic approaches considered osteomyelitis strongly supported when at least two of the following were present:

Pus aspirated from bone

Positive blood or bone culture

Localized pain, swelling, warmth, and restricted movement

Imaging changes compatible with osteomyelitis

Modern diagnosis relies on the overall clinical, microbiologic, and imaging picture rather than a rigid numerical rule.

History

Important questions include:

When did the pain begin?

Was there preceding trauma?

Has there been fever?

Has the child recently been ill?

Is the patient refusing to bear weight?

Was there recent surgery, injection, or penetrating injury?

Is there underlying sickle cell disease or immune compromise?

Physical Examination

The goal is to:

Localize the infected bone

and

Identify associated joint or systemic involvement.

General Appearance

The child may appear:

Well but irritable

or

Systemically ill and lethargic

depending on the severity and duration of infection.

Observation Before Palpation

Before touching the child, observe:

Spontaneous movement

Limb position

Willingness to bear weight

Use of the affected extremity

Reduced spontaneous use may be an important diagnostic clue.

Tenderness

Palpation usually reveals:

Focal metaphyseal tenderness.

In young or frightened children, a parent may help localize the painful region.

Local Inflammatory Findings

Typical findings include:

Warmth

Swelling

Erythema

Tenderness

These are often most pronounced over the metaphysis.

Deeply Located Bones

In areas with substantial overlying muscle, such as the:

Femur

visible erythema may be absent despite significant infection.

Joint Examination

Adjacent joints should be examined carefully for:

Effusion

Pain with passive motion

Reduced range of motion

because septic arthritis may coexist with osteomyelitis, particularly in infants.

Laboratory Tests

White Blood Cell Count

The WBC count is not sufficiently sensitive to rule out osteomyelitis.

A normal value does not exclude infection.

If elevated, however, it supports the diagnosis in the appropriate clinical setting.

Blood Cultures

Blood cultures should be obtained:

Early and preferably before antibiotics are started, provided this does not delay treatment in an ill patient.

Blood cultures are positive in a substantial proportion of cases, historically around:

50%.

A positive blood culture may identify the causative organism without requiring direct bone aspiration.

ESR

The erythrocyte sedimentation rate is a nonspecific marker of inflammation.

It often rises within:

48–72 hours

and may remain elevated for several weeks.

Because it normalizes slowly, it is less useful than CRP for assessing rapid treatment response.

C-Reactive Protein

CRP is particularly useful because it:

Rises earlier

and

Returns toward normal more rapidly

than ESR.

It is therefore valuable for monitoring response to therapy.

Normal ranges vary among laboratories.

Aspiration and Biopsy

Aspiration of the infected site may be performed to identify the organism.

Samples should be sent for:

Gram stain

Aerobic bacterial culture

and additional studies when clinically indicated.

Special Cultures

In selected patients, samples may also be sent for:

Anaerobic culture

Fungal culture

Acid-fast bacilli

This is particularly appropriate in:

Immunocompromised patients

Unusual travel or exposure histories

Chronic or atypical infections

Timing of Cultures

Whenever safely possible, cultures should be obtained:

Before antibiotic administration.

However, antibiotic therapy should not be dangerously delayed in a septic or unstable patient simply to obtain cultures.

Bone Biopsy

Percutaneous bone biopsy may provide material for:

Culture

and

Histologic examination.

Because the infection often involves metaphyseal cancellous bone, the lesion may be accessible with a:

Bone biopsy or marrow-type needle.

Young children commonly require sedation or anesthesia.

Localization Before Aspiration

If the infected site is uncertain, it may first be localized using:

MRI

or, less commonly,

Bone scintigraphy.

Imaging

Plain Radiographs

Radiographs should usually be obtained as an initial study.

The earliest finding may simply be:

Soft-tissue swelling.

Delayed Osseous Changes

Classic bony abnormalities often lag behind symptoms.

These may not become visible for approximately:

1–3 weeks.

Findings include:

Osteopenia

Bone resorption

Cortical destruction

Periosteal new bone formation

CT

CT is not usually the preferred test for diagnosing acute hematogenous osteomyelitis.

It may be useful for:

Chronic cortical abnormalities

Sequestra

Surgical planning

Differentiating certain osseous lesions

such as:

Osteoid osteoma

or

Chondroblastoma.

MRI

MRI is the most useful advanced imaging modality for most suspected osteomyelitis.

It provides excellent sensitivity for:

Early marrow involvement

Subperiosteal abscess

Soft-tissue extension

Adjacent joint infection

Anatomic extent of disease

MRI Sequences

T1-weighted images provide detailed anatomy and show marrow replacement as low signal.

Fluid-sensitive or T2-weighted fat-suppressed/STIR images demonstrate:

Marrow edema

Soft-tissue inflammation

Periosteal elevation

Fluid collections

Neonates

In neonates, broader scout or localizer imaging may help identify the involved region when localization is difficult clinically.

Ultrasound

Ultrasound may identify:

Subperiosteal fluid

Joint effusion

Superficial abscess

It is useful for guiding aspiration.

However, ultrasound cannot adequately assess:

Deep intramedullary metaphyseal infection.

Pathophysiology

Acute hematogenous osteomyelitis in children classically begins in the:

Metaphysis of a long bone.

Vascular Seeding

Bacteria lodge in the metaphyseal circulation, where:

Slow blood flow and vascular architecture

favor bacterial deposition.

Intraosseous Infection

As infection progresses:

Inflammatory cells accumulate

Medullary pressure rises

Small vessels may thrombose

This compromises local blood flow and may produce:

Bone necrosis.

Cortical Spread

Pus follows the path of least resistance and may extend through the:

Metaphyseal cortex.

Subperiosteal Abscess

Once infection exits the cortex, it may elevate the periosteum and form a:

Subperiosteal abscess.

Later, the elevated periosteum may produce:

Periosteal new bone formation.

Chronic Infection

If devascularized bone persists, it may become a:

Sequestrum, serving as a reservoir for chronic infection.

Reactive new bone around the infected segment may form an:

Involucrum.

Differential Diagnosis

Important alternatives include:

Trauma

Septic arthritis

Cellulitis

Ewing sarcoma

Leukemia

Thrombophlebitis

Sickle cell vaso-occlusive crisis

Transient synovitis

Eosinophilic granuloma

Osteoid osteoma

Septic Arthritis

Septic arthritis should be strongly considered when there is:

Severe pain with passive joint movement

Joint effusion

Marked restriction of motion

It may coexist with osteomyelitis, especially in infants.

Malignancy

Ewing sarcoma and leukemia may produce:

Pain

Fever

Elevated inflammatory markers

Abnormal imaging

and can closely mimic infection.

Biopsy may be necessary when the diagnosis remains uncertain.

Treatment

General Principles

Treatment is based on four major principles:

Identify the causative organism

Administer appropriate antimicrobial therapy

Drain or débride infection when necessary

Continue treatment until clinical and inflammatory markers indicate resolution

Early Disease

Surgery may not be necessary when:

The diagnosis is made early

There is no abscess

There is no necrotic bone

The patient responds promptly to antibiotics

Antibiotic Therapy

Antibiotics should initially be chosen empirically according to:

Patient age

Likely organism

Local resistance patterns

Recent hospitalization

Underlying disease

and then narrowed according to:

Culture and susceptibility results.

Empiric Therapy

Because Staphylococcus aureus is the most common pathogen, empiric treatment generally includes antistaphylococcal coverage.

Depending on local prevalence of MRSA, this may require:

An antistaphylococcal beta-lactam

or

MRSA-active therapy such as clindamycin or vancomycin.

Neonates

Neonates require broader coverage because infection may involve:

Staphylococcus aureus

Group B Streptococcus

Gram-negative organisms

The exact regimen should follow neonatal infectious-disease protocols and local susceptibility patterns.

Duration of Antibiotic Therapy

Treatment duration depends on:

Age

Organism

Clinical response

Presence of abscess

Complications

Route of infection

Many uncomplicated pediatric cases can transition from intravenous to oral therapy after:

Clear clinical improvement and falling inflammatory markers.

Total therapy is commonly measured in:

Several weeks, rather than by a rigid IV duration.

Transition to Oral Therapy

Oral therapy can be used when:

The child is clinically improving

CRP is falling

The organism and susceptibilities are known

An effective oral antibiotic with good bioavailability is available

Surgery

Surgery is required when medical treatment alone is unlikely to control the infection.

Indications for Surgery

Common indications include:

Frank pus or abscess

Substantial necrotic or devascularized bone

Failure to improve after approximately 36–48 hours of appropriate antibiotics

Progressive clinical deterioration

Need for diagnostic tissue when the diagnosis is uncertain

Surgical Technique

Operative treatment may include:

Opening and draining the subperiosteal space

Cortical drilling or creating a bone window

Evacuation of pus

Débridement of necrotic tissue

Removal of devascularized bone when present

Multiple deep cultures should be obtained during surgery.

Chronic Osteomyelitis

Chronic infection may require more extensive management, including:

Removal of sequestra

Repeated débridement

Dead-space management

Soft-tissue reconstruction

Long-term culture-directed antibiotics

Follow-Up

Patients should be monitored until there is:

Resolution of pain

Return of function

Normalization or near-normalization of inflammatory markers

No evidence of recurrent infection

Prognosis

Most children treated promptly and appropriately have an:

Excellent prognosis

with no major long-term sequelae.

Poor outcomes are more likely when:

Diagnosis is delayed

Abscess or necrotic bone persists

The growth plate is damaged

Chronic osteomyelitis develops

Complications

Chronic Osteomyelitis

Delayed or inadequate treatment may result in:

Persistent infection

Sequestrum formation

Draining sinus

Recurrent abscess

Growth-Plate Injury

If infection damages or crosses the physis, the child may develop:

Partial or complete growth arrest

leading to:

Angular deformity

or

Limb-length discrepancy.

Pathological Fracture

A severely weakened bone may fracture before sufficient:

Healing and remodeling

have occurred.

Activity should therefore be progressed cautiously when substantial structural bone loss is present.

Septic Arthritis

Spread into an adjacent joint may produce:

Septic arthritis, particularly in infants where metaphyseal blood vessels may cross the physis.

Systemic Complications

Severe osteomyelitis may be associated with:

Bacteremia

Sepsis

Venous thromboembolism

Disseminated intravascular coagulation

Systemic inflammatory response syndrome

Patient Monitoring

Monitoring should include:

Clinical pain and function

Temperature

Local swelling and tenderness

CRP

ESR when appropriate

Repeat imaging when recovery is atypical

CRP is particularly useful for following early treatment response because it changes more rapidly than ESR.

Key Principle

Osteomyelitis is a bone infection that requires early recognition, microbiologic diagnosis, appropriate antibiotic therapy, and surgical drainage or débridement when abscess or devitalized bone is present.

In children, the disease typically begins in the:

Metaphysis of a long bone, and prompt treatment usually results in complete recovery while minimizing the risk of:

Chronic infection, growth disturbance, pathological fracture, and systemic complications.