Orthopaedic Surgery - Septic Arthritis

Basics

Septic arthritis is:

Infection of a synovial joint

caused most commonly by:

Bacteria.

It represents an:

Orthopaedic emergency

because persistent infection can rapidly destroy:

Articular cartilage

and, in children, may damage the:

Epiphysis

and

Growth plate.

Pediatric Anatomy

In young infants, vascular channels may cross the:

Physis

from the metaphysis toward the epiphysis.

These transphyseal vessels persist during approximately the first:

12–18 months of life.

As a result, infection can spread from:

Metaphyseal osteomyelitis

through the:

Epiphysis

and into the:

Adjacent joint.

Growth-Plate Injury

Infection involving the immature joint can cause irreversible damage to the:

Physis

or

Cartilaginous epiphysis.

Potential consequences include:

Growth disturbance

Angular deformity

and

Limb-length discrepancy.

Polyarticular Septic Arthritis

Although most cases involve:

A single joint

multiple joints may be involved.

Historical series have reported polyarticular involvement in approximately:

5% of patients.

Prevention

Preventive measures include prompt recognition and treatment of:

Bacteremia

Skin and soft-tissue infection

Systemic infection

and sexually transmitted infections such as:

Gonorrhea.

The most important preventive principle is:

Early diagnosis and treatment

before permanent cartilage or growth-plate damage occurs.

Epidemiology

Septic arthritis can occur in:

Any joint

and at:

Any age.

Sex

There is no strong sex predominance in most forms of:

Nongonococcal monoarticular septic arthritis.

Gonococcal arthritis has historically been reported more commonly in:

Women

than men.

Incidence

The incidence varies substantially according to:

Age

Immune status

Comorbidities

and presence of:

Prosthetic joints.

Neonatal septic arthritis is uncommon but particularly serious.

Risk Factors

Important risk factors include:

Neonatal age

Prematurity

Concurrent bacteremia

Inflammatory arthritis

Prosthetic joint

Diabetes mellitus

HIV or other immunocompromised states

Hemophilia

Sickle cell disease

Intravenous drug use

Recent joint surgery or injection

Skin infection

Neonatal Risk

Neonates may have several potential portals of infection, including:

Umbilical infection

Intravenous lines

Skin lesions

or systemic bacteremia.

Rheumatologic Disease

Patients with inflammatory arthritis are at increased risk because of:

Underlying joint disease

and frequently:

Immunosuppressive medication.

Prosthetic Joints

Joint prostheses provide a surface on which organisms can form:

Biofilm

making infection difficult to eradicate without:

Surgical intervention.

Sickle Cell Disease

Patients with sickle cell disease have increased susceptibility to:

Musculoskeletal infection.

Historically, both:

Staphylococcus aureus

and

Salmonella species

have been emphasized, particularly in associated osteomyelitis.

Intravenous Drug Use

Intravenous drug use increases the risk of bacteremia with organisms including:

Staphylococcus aureus

and selected:

Gram-negative organisms.

Etiology

The causative organism varies with:

Age

Host factors

and

Exposure history.

Staphylococcus aureus

Across many age groups, the most important pathogen is:

Staphylococcus aureus.

It is particularly important in:

Infants

Children

and

Adults.

Neonates

Potential organisms include:

Staphylococcus aureus

Group B Streptococcus

Gram-negative enteric bacilli

and, less commonly,

Candida species.

Young Children

In young children, important organisms include:

Staphylococcus aureus

Streptococcal species

and

Kingella kingae.

Haemophilus influenzae

Historically:

Haemophilus influenzae type b

was an important cause of septic arthritis in children younger than approximately:

2 years.

Its incidence declined dramatically following widespread:

Hib vaccination.

Kingella kingae

Kingella kingae is particularly important in:

Young children, often between approximately 6 months and 4 years.

It is:

Fastidious

and may be difficult to isolate using routine culture.

Diagnosis may require:

PCR or other molecular testing.

Adolescents and Young Adults

In sexually active adolescents and young adults, consider:

Neisseria gonorrhoeae.

Staphylococcus aureus remains an important alternative.

Other Organisms

Other causes include:

Streptococci

Gram-negative bacilli

Pseudomonas

and less common organisms depending on:

Immune status

and

Exposure.

Culture-Negative Infection

A causative organism may not be recovered in a substantial proportion of cases.

Culture negativity may result from:

Previous antibiotic therapy

Low organism burden

Fastidious organisms

or limitations of conventional culture methods.

Lyme Arthritis

Lyme disease can produce:

Infectious inflammatory arthritis, particularly of the knee.

However, it generally follows a different clinical pattern from:

Acute pyogenic septic arthritis

and is managed differently.

Associated Conditions

Septic arthritis may occur together with:

Osteomyelitis.

This association is particularly important in:

Infants

and when infection involves the:

Hip

or other joints adjacent to metaphyseal bone.

Diagnosis

Diagnosis depends on:

Clinical suspicion

Joint aspiration

Synovial fluid analysis

Culture

and supporting laboratory and imaging studies.

Signs and Symptoms

Children commonly present with:

Fever

Irritability

Pain

Refusal to move the affected extremity

and reduced:

Appetite or activity.

Subtle Presentation

Not every child appears severely ill.

Some may present only with:

Fever of unknown origin

or relatively subtle findings localized to:

One extremity.

Neonatal Presentation

Neonates may show very nonspecific findings such as:

Poor feeding

Failure to gain weight

Reduced spontaneous limb movement

or irritability.

Only a minority may initially demonstrate obvious:

Sepsis.

Earliest Physical Finding

One of the earliest and most sensitive findings is:

Pain with joint movement.

This may precede visible:

Swelling

or

Erythema.

Later Findings

As infection progresses, patients may develop:

Swelling

Warmth

Muscle spasm

Restricted range of motion

and

Joint effusion.

Erythema

Overlying erythema may be:

Absent

because the inflammatory process is located deep within the:

Joint capsule.

Its absence does not exclude infection.

Physical Examination

The affected joint should be examined for:

Tenderness

Pain with passive motion

Swelling

Warmth

Effusion

and loss of:

Active and passive movement.

Position of Comfort

Patients often hold the joint in a position that maximizes:

Capsular volume

and reduces:

Intra-articular pressure.

Hip

A child with septic arthritis of the hip may hold the hip in:

Flexion

Abduction

and

External rotation.

Weight bearing is often:

Painful or impossible.

Systemic Examination

Assess for potential sources of bacteremia, including:

Skin infection

Respiratory infection

Urinary infection

and signs of:

Systemic sepsis.

Laboratory Tests

Synovial Fluid

Joint aspiration is the key diagnostic procedure.

Fluid should be sent for:

Cell count

Differential

Gram stain

Aerobic and anaerobic culture

and additional testing when indicated.

Synovial White Blood Cell Count

A synovial white-cell count above approximately:

50,000 cells/µL

with a predominance of:

Neutrophils

strongly supports septic arthritis in the appropriate clinical setting.

However, no single cutoff absolutely confirms or excludes:

Infection.

Neutrophil Predominance

Purulent septic arthritis often demonstrates:

More than 90% polymorphonuclear leukocytes.

Gram Stain

Gram stain has limited sensitivity.

It may be positive in only approximately:

30–40% of cases.

A negative Gram stain therefore does:

Not exclude septic arthritis.

Synovial Culture

Culture of aspirated joint fluid remains essential for identifying:

The causative organism

and its:

Antibiotic sensitivities.

Blood Cultures

Blood cultures should be obtained:

Before antibiotics whenever this can be done without delaying treatment.

They may identify the organism even when:

Synovial cultures are negative.

ESR

The:

Erythrocyte sedimentation rate

may be elevated.

It is useful mainly as a supportive test and for:

Following response to treatment.

Limitations of ESR

ESR may be less reliable in:

Neonates

Patients with sickle cell disease

and patients receiving:

Corticosteroids.

C-Reactive Protein

CRP is especially useful because it:

Rises relatively early

and falls relatively quickly with successful treatment.

Serial CRP measurement can therefore help assess:

Treatment response.

Peripheral White Blood Cell Count

A high systemic WBC count with a:

Left shift

may support infection but is:

Nonspecific.

A normal peripheral WBC count does not exclude:

Septic arthritis.

Crystals

Synovial fluid should be examined for:

Urate

or

Calcium pyrophosphate crystals

when crystal arthritis is possible.

The presence of crystals does not completely exclude:

Concomitant infection.

Imaging

Plain Radiographs

Early radiographs may be normal or show only:

Soft-tissue swelling

Joint-space widening from effusion

or distention of the:

Joint capsule.

Hip in Infants

In neonatal hip infection, radiographs may occasionally demonstrate:

Lateral displacement of the proximal femur

relative to the:

Acetabulum

because of a large effusion.

Ultrasound

Ultrasound is particularly useful for detecting an:

Effusion

in deep joints such as the:

Hip.

It can also guide:

Joint aspiration.

MRI

MRI is valuable when:

The diagnosis is uncertain

Adjacent osteomyelitis is suspected

or evaluation of deep structures is required.

It can identify infection within the:

Joint

Bone

Muscle

and surrounding:

Soft tissues.

Pathological Findings

The joint typically contains:

Purulent synovial fluid

with a marked:

Neutrophilic inflammatory response.

Synovial Changes

The synovium becomes:

Hyperemic

Inflamed

and

Thickened.

Cartilage Destruction

If infection remains untreated, bacterial toxins, inflammatory cells, and enzymes begin to damage:

Articular cartilage

within a relatively short period.

This can ultimately lead to:

Permanent joint destruction.

Differential Diagnosis

Important alternatives include:

Osteomyelitis

Transient synovitis

Inflammatory arthritis

Crystal arthritis

Rheumatologic disease

Pyomyositis

Trauma

Malignancy

Transient Synovitis of the Hip

Transient synovitis usually occurs in a child who is:

Less systemically ill

and typically has lower:

Temperature

Inflammatory markers

and

Peripheral WBC count.

Kocher-Type Clinical Features

Features favoring septic arthritis of the hip include:

Inability to bear weight

Fever

Elevated inflammatory markers

and

Elevated peripheral WBC count.

No clinical prediction rule should replace:

Joint aspiration when septic arthritis remains a significant concern.

Treatment

Orthopaedic Emergency

Suspected bacterial septic arthritis should be treated as an:

Emergency.

Hospitalization is often appropriate, particularly for:

Children

Systemically ill adults

and infections of:

Large joints.

Core Treatment Principles

Management consists of:

Prompt joint aspiration

Blood cultures

Immediate bactericidal antibiotics

Adequate drainage

and subsequent:

Restoration of motion.

Timing of Antibiotics

When the patient is clinically stable, obtain:

Synovial fluid

and

Blood cultures

before starting antibiotics.

Antibiotic treatment should then begin:

Promptly.

In a septic or unstable patient, antibiotic treatment should not be dangerously delayed for diagnostic procedures.

Empiric Antibiotics

Initial therapy is generally:

Intravenous

and should provide coverage for the most likely organisms according to:

Age

Risk factors

Local resistance patterns

and

Gram-stain findings.

Staphylococcal Coverage

Because:

Staphylococcus aureus

is a common cause, empiric therapy usually includes strong:

Antistaphylococcal coverage.

Local prevalence of:

MRSA

must be considered.

Definitive Antibiotics

Once the organism and antimicrobial sensitivities are known, therapy should be narrowed to:

Targeted antibiotic treatment.

Duration of Therapy

Treatment duration depends on:

Organism

Joint involved

Presence of osteomyelitis

Clinical response

and host factors.

Historical regimens commonly used approximately:

3–6 weeks of total antibiotic treatment.

Many uncomplicated cases can now be treated with shorter individualized regimens under specialist guidance.

Intravenous-to-Oral Transition

Transition to oral treatment may be appropriate when:

Clinical improvement is clear

The organism is identified or adequately covered

An effective oral agent is available

The patient can reliably take oral medication

and inflammatory markers are:

Improving.

Serial Aspiration

In selected superficial or easily accessible joints, early infection may sometimes be managed with:

Repeated aspiration

plus antibiotics.

The patient must be monitored closely for:

Rapid clinical improvement.

Hip Aspiration

Aspiration of the hip should usually be performed with:

Ultrasound

or

Fluoroscopic guidance.

Surgical Drainage

Surgical drainage is particularly important for:

Hip infection

Large-joint infection

Loculated purulent effusion

Failure to improve with aspiration and antibiotics

or extensive:

Synovitis and debris.

Arthroscopic Irrigation and Débridement

Arthroscopic treatment is commonly used for joints such as the:

Knee

Shoulder

Elbow

and

Ankle.

It allows:

Irrigation

Synovectomy

and removal of:

Purulent material and debris.

Open Irrigation and Débridement

Open drainage remains appropriate when:

Arthroscopic access is inadequate

Infection is advanced

The hip is involved in selected patients

or complete clearance cannot otherwise be achieved.

Gonococcal Arthritis

Disseminated gonococcal arthritis may often respond to:

Appropriate antibiotic therapy

and aspiration without formal surgical drainage, provided there is no persistent:

Purulent joint infection.

Immobilization

Initially, the joint may be splinted in a:

Comfortable position

to control pain.

Duration of Immobilization

Prolonged immobilization should be avoided.

Once:

Pain

Swelling

and

Tenderness

begin to improve, gradual:

Range-of-motion exercises

should begin.

Physical Therapy

Rehabilitation is important to prevent:

Stiffness

Contracture

and

Muscle wasting.

Early Exercises

Adults may begin with:

Isometric strengthening

followed by progressive:

Active range of motion.

Continuous Passive Motion

Continuous passive motion has historically been proposed to:

Reduce adhesions

and improve:

Cartilage nutrition.

Its role depends on the involved joint and current rehabilitation protocol.

Surgery

The goals of operative treatment are to:

Drain purulent fluid

Reduce bacterial burden

Remove inflammatory debris

and decrease enzymes that can destroy:

Articular cartilage.

Open Drainage

Open irrigation and débridement allows direct removal of:

Necrotic synovium

Pus

and

Debris.

Drainage may be maintained when clinically necessary.

Follow-Up

Patients require close follow-up until:

Clinical signs resolve

Inflammatory markers improve

and useful joint function returns.

Prognosis

With:

Prompt diagnosis

Adequate drainage

and

Appropriate antibiotics

the prognosis is generally:

Good.

Poor Prognostic Factors

Outcomes are less favorable in:

Premature infants

Immunocompromised patients

Patients with delayed diagnosis

and those with:

Systemic sepsis.

Delay in Treatment

A delay of several days can substantially increase the risk of:

Permanent cartilage destruction

and other complications.

Historical series identified delays beyond approximately:

5 days

as particularly concerning.

Complications

Cartilage Destruction

Ongoing infection may destroy:

Articular cartilage

leading to:

Pain

Restricted movement

Secondary osteoarthritis

or

Ankylosis.

Pathologic Hip Dislocation

In children with delayed treatment of septic arthritis of the hip, a large effusion and structural damage may result in:

Pathologic dislocation.

Growth-Plate Damage

In children, injury to the:

Physis

and

Cartilaginous epiphysis

can cause:

Growth arrest

Angular deformity

and

Limb-length discrepancy.

Femoral Head Necrosis

Severe hip infection may compromise the blood supply to the:

Femoral head

causing:

Osteonecrosis

and subsequent:

Growth disturbance

or

Degenerative joint disease.

Joint Stiffness

Inflammation, prolonged immobilization, and cartilage injury may lead to:

Loss of motion

or permanent:

Contracture.

Hematogenous Prosthetic Joint Seeding

Patients with prosthetic joints elsewhere in the body may develop:

Hematogenous prosthetic joint infection

during episodes of:

Bacteremia.

Patient Monitoring

Patients should initially be monitored in the hospital until:

Hemodynamic and clinical stability are achieved

Appropriate antibiotic therapy is established

and there is clear evidence of:

Treatment response.

Signs of Improvement

Expected findings include:

Resolution of fever

Reduced swelling

Reduced tenderness

Improved range of motion

and declining:

CRP and other inflammatory markers.

Lack of Improvement

Persistent:

Fever

Pain

Effusion

or worsening inflammatory markers may indicate:

Inadequate drainage

Resistant organism

Associated osteomyelitis

or an incorrect diagnosis.

Repeat:

Aspiration

Imaging

or

Surgical débridement

may be necessary.

Key Principle

Septic arthritis is a joint infection that can rapidly destroy articular cartilage and therefore must be considered an orthopaedic emergency.

The diagnosis depends on:

Clinical suspicion and urgent joint aspiration, with synovial fluid sent for cell count, Gram stain, and culture.

Treatment requires:

Prompt antibiotics after appropriate cultures, effective drainage of the infected joint, and early rehabilitation once inflammation begins to improve.

In children, particularly infants, delayed treatment can result in:

Growth-plate injury, deformity, limb-length discrepancy, hip dislocation, osteonecrosis, and permanent loss of joint function.