Orthopaedic Surgery - Septic Hip

Basics

Septic arthritis of the hip is:

An infection of the hip joint

most commonly caused by:

Bacteria.

It can occur in:

Infants

Children

Adults

and

Older adults.

Although traditionally more common in the pediatric population, septic hip is increasingly encountered in:

Older

and

Immunocompromised patients.

Clinical Importance

Septic hip is an:

Orthopaedic emergency

because infection can rapidly damage the:

Femoral head

Acetabulum

and

Articular cartilage.

Early diagnosis and drainage are essential for:

Joint preservation.

Common Predisposing Factors

Important risk factors include:

Previous hip surgery

Hip arthroplasty

Intravenous drug use

Alcohol misuse

Corticosteroid therapy

and other causes of:

Immunosuppression.

Epidemiology

In children, the hip is one of the:

Most common sites of septic arthritis.

In adults, septic arthritis more commonly affects the:

Knee

than the hip.

Prosthetic Hip Infection

Historical estimates have reported infection after total hip arthroplasty in approximately:

2% of cases

although rates vary according to:

Patient factors

Procedure type

and

Definition of infection.

Risk Factors

Risk factors may be divided into:

Local

and

Systemic factors.

Local Risk Factors

These include:

Previous hip surgery

Previous total hip arthroplasty

Intra-articular hip injection

Femoral or iliac osteomyelitis

Osteoarthritis

Avascular necrosis

Previous trauma

Systemic Risk Factors

These include:

Bacteremia

Immunosuppression

Intravenous drug use

Hemophilia

Seronegative inflammatory arthritis

Sickle cell disease

Pathophysiology

In adults, infection may develop through:

Direct inoculation

particularly after:

Surgery

or another invasive procedure.

Hematogenous Spread

In children, infection more commonly reaches the hip through:

Hematogenous spread.

Bacteria circulating in the bloodstream may lodge in the highly vascular:

Synovium

and subsequently invade the joint.

Possible Primary Sources

Sources of bacteremia may include:

Urinary tract infection

Pulmonary infection

Skin and soft-tissue infection

or another systemic infectious focus.

Direct Extension

Infection may also spread directly from adjacent:

Femoral osteomyelitis

Iliac osteomyelitis

Psoas infection

or surrounding soft tissues.

Etiology

Bacteria may enter the hip joint through:

Bloodstream seeding

Direct inoculation

or extension through abnormal or inflamed:

Synovium

or

Joint capsule.

Staphylococcus aureus

The most common organism in both:

Children

and

Adults

is:

Staphylococcus aureus.

Other Causative Organisms

Additional organisms include:

Streptococcus species

Neisseria gonorrhoeae

Pseudomonas species

Escherichia coli

Salmonella species

Klebsiella species

Mycobacterium tuberculosis

Brucella species

Kingella kingae

Kingella kingae

Kingella kingae is particularly important in:

Young children.

It may be difficult to isolate on routine culture and sometimes requires:

Molecular testing.

Sickle Cell Disease

In patients with sickle cell disease, organisms such as:

Salmonella

should be considered, particularly when associated:

Osteomyelitis

is present.

Associated Conditions

Conditions frequently associated with septic hip include:

Osteomyelitis

Hemophilia

Sickle cell disease

Intravenous drug use

Immunosuppression

Diagnosis

Diagnosis requires a combination of:

Clinical suspicion

Laboratory testing

Imaging

and, most importantly,

Hip aspiration.

Signs and Symptoms

Typical symptoms include:

Hip pain

Groin pain

Medial thigh pain

Fever

and

Reduced hip motion.

Groin and Thigh Pain

Pain is commonly localized to the:

Groin

or

Inner thigh.

Referred Knee Pain

Some patients, especially children, may present primarily with:

Ipsilateral knee pain.

Therefore, unexplained knee pain should prompt examination of the:

Hip.

Systemic Symptoms

Patients may have:

Fever

and occasionally:

Chills

or other evidence of:

Systemic infection.

However, fever may be absent in:

Immunocompromised

or

Older patients.

Gait

Patients may demonstrate:

Antalgic gait

or may be completely:

Unable to bear weight.

Guarding

The hip is frequently:

Guarded

with marked resistance to passive motion.

Physical Examination

Position of Comfort

Patients often hold the hip in:

Flexion

and

External rotation.

This position increases intracapsular volume and may reduce painful:

Joint pressure.

Tenderness

Tenderness may be present around the:

Hip

Groin

or proximal:

Thigh.

Range of Motion

Passive hip motion is:

Restricted

and typically causes significant:

Pain.

Pain with even small arcs of passive movement is an important finding.

Weight Bearing

Inability or refusal to:

Stand

Walk

or

Bear weight

is particularly concerning in children.

Laboratory Tests

Laboratory abnormalities are variable and may be less pronounced in:

Immunocompromised patients.

ESR

The:

Erythrocyte sedimentation rate

is commonly elevated.

It is useful as a supportive test and for:

Monitoring treatment response.

C-Reactive Protein

CRP is often elevated and is particularly useful because it responds relatively quickly to:

Active infection

and subsequent:

Clinical improvement.

Peripheral White Blood Cell Count

The peripheral WBC count may be:

Elevated

or

Normal.

A normal value does not exclude:

Septic hip.

Neutrophils

When leukocytosis is present, there is often an increased percentage of:

Polymorphonuclear leukocytes.

Blood Cultures

Blood cultures should be obtained before antibiotics whenever possible.

They may identify the causative organism when the:

Joint culture is negative.

Hip Aspiration

Hip aspiration is the:

Most important diagnostic test.

Synovial fluid should be sent for:

Cell count

Differential

Gram stain

Culture

and susceptibility testing.

Synovial White Blood Cell Count

Septic hip often produces a markedly elevated synovial WBC count.

Historical descriptions include values between approximately:

100,000 and 250,000 cells/µL.

However, lower counts may still occur, and the diagnosis should not depend on:

A single threshold.

Gram Stain

Gram stain may occasionally demonstrate the infecting organism, but its sensitivity is:

Limited.

A negative Gram stain does not exclude:

Septic arthritis.

Culture-Negative Infection

A substantial proportion of septic hips may remain:

Culture negative

even when the clinical diagnosis is convincing.

Possible reasons include:

Prior antibiotic exposure

Low organism burden

or

Fastidious organisms.

Pediatric Considerations

Diagnosis in:

Neonates

and

Children

can be particularly difficult because symptoms may be nonspecific.

Clinical Prediction Features

Features that increase concern for septic arthritis in a child include:

Fever above approximately 38.5°C

Inability to bear weight

Elevated ESR

and

Elevated CRP.

These findings are often incorporated into:

Kocher-type clinical prediction criteria.

They help estimate probability but do not replace:

Hip aspiration.

Imaging

Plain Radiographs

Early radiographs may remain:

Normal

for up to approximately:

2 weeks.

Early Radiographic Findings

Possible early changes include:

Increased joint-space width

or widening of the:

Teardrop interval

caused by joint effusion.

Late Radiographic Findings

Delayed or advanced infection may cause:

Bone erosion

Femoral head destruction

Acetabular destruction

Subluxation

and other destructive changes.

Ultrasound

Ultrasound is especially useful in:

Neonates

and

Children.

It can identify:

Hip joint effusion

and guide:

Diagnostic aspiration.

MRI

MRI is highly useful for evaluating:

Joint effusion

Synovitis

Soft-tissue infection

Osteomyelitis

Pelvic fracture

Psoas or retroperitoneal collections.

Nuclear Imaging

Nuclear medicine studies may occasionally be used when:

The diagnosis remains uncertain

or multiple sites of infection are suspected.

Diagnostic Procedure

Image-guided:

Hip aspiration

is the key diagnostic procedure.

Because the hip is a deep joint, aspiration is generally performed using:

Ultrasound

or

Fluoroscopic guidance.

Pathological Findings

Untreated infection can cause rapid destruction of:

The femoral head

and

Acetabulum.

Late Pathology

Advanced cases may develop:

Septicemia

Hip subluxation

Dislocation

Deformity

Ankylosis

and permanent:

Cartilage destruction.

Differential Diagnosis

Important alternatives include:

Crystal arthropathy

Inflammatory arthritis

Rheumatoid arthritis

Hemarthrosis from hemophilia

Transient synovitis

Lyme arthritis

Psoas abscess

Sacroiliac joint infection

Femoral or iliac osteomyelitis

Pyomyositis

Leukemia

Lymphoma

Transient Synovitis

Transient synovitis is an important pediatric differential diagnosis.

It generally causes less:

Systemic illness

and lower inflammatory markers than:

Septic arthritis.

Osteomyelitis

Osteomyelitis of the:

Proximal femur

or

Pelvis

may mimic septic hip or coexist with it.

MRI is especially useful for distinguishing or identifying:

Combined infection.

Psoas Abscess

A psoas abscess may produce:

Hip pain

Flexion posture

and

Pain with extension.

Cross-sectional imaging is required when this diagnosis is suspected.

Treatment

Initial Stabilization

Early diagnosis is critical to:

Preserve the hip joint.

Cultures Before Antibiotics

When the patient is clinically stable, obtain:

Synovial fluid

and

Blood cultures

before beginning antibiotic treatment.

In a septic or unstable patient, treatment should not be dangerously delayed.

Empiric Antibiotics

After cultures are obtained, begin:

Empiric intravenous antibiotics

directed toward likely organisms based on:

Age

Risk factors

Gram stain

and

Local antibiotic resistance patterns.

Definitive Antibiotics

Once cultures and sensitivities are available, therapy should be changed to:

Organism-specific antibiotics.

Surgery

The traditional cornerstone of treatment is:

Surgical drainage and débridement.

Open Irrigation and Débridement

Open surgery allows:

Complete drainage

Removal of purulent material

Synovectomy when necessary

and inspection of the:

Hip joint.

Arthroscopic Débridement

Hip arthroscopy may be used in selected patients to:

Irrigate

and

Débride the joint.

Its appropriateness depends on:

Age

Disease severity

Surgeon expertise

and

Associated pathology.

Serial Aspiration

If a patient is too medically unstable to tolerate surgery, repeated:

Image-guided aspirations

may sometimes be used as temporary or alternative drainage.

Close monitoring is essential.

Prosthetic Joint Infection

Management of an infected total hip arthroplasty differs from treatment of a native-joint septic hip.

Suppressive Antibiotics

Long-term suppressive antibiotics alone are generally reserved for patients who:

Cannot tolerate surgery

or in whom definitive reconstruction is not possible.

Débridement With Implant Retention

Débridement, antibiotics, and implant retention may be considered when:

The infection is acute

Implants are stable

and symptoms have been present for only a:

Short period.

One-Stage Revision

A one-stage revision removes the infected components, performs thorough:

Débridement

and places a new prosthesis during the:

Same operation.

This may be appropriate in carefully selected patients.

Two-Stage Revision

Two-stage revision historically has been considered one of the most reliable strategies for chronic:

Periprosthetic hip infection.

The first stage involves:

Removal of components

Débridement

and often placement of an:

Antibiotic spacer.

Definitive reconstruction is performed later after infection control.

Late Sequelae in Children

Children with residual deformity may eventually require procedures such as:

Pelvic osteotomy

Hip reconstruction

Hip fusion

or, in severe destructive cases,

Resection procedures.

Late Sequelae in Adults

Adults with severe joint destruction may require:

Resection arthroplasty

or staged:

Total hip replacement.

Referral

A patient with a painful hip and concern for infection should be referred:

Urgently to an orthopaedic surgeon.

Delay in diagnosis substantially increases the risk of:

Permanent joint damage.

Prognosis

If treatment begins:

Early

the prognosis is generally:

Good.

Delayed Diagnosis

Outcomes become significantly worse when diagnosis and treatment are:

Delayed.

Persistent infection may rapidly destroy the:

Femoral head

and

Acetabulum.

MRSA

Infections caused by:

Methicillin-resistant Staphylococcus aureus

may be associated with:

More severe disease

and more complicated treatment than infections caused by susceptible organisms.

Complications

Osteomyelitis

Infection may spread into the:

Proximal femur

or

Pelvis

producing:

Osteomyelitis.

Septicemia

Bacteria may enter the bloodstream and cause:

Systemic sepsis.

Subluxation and Dislocation

Accumulation of pus and destruction of supporting structures may cause:

Hip subluxation

or

Dislocation.

This is particularly concerning in:

Children.

Avascular Necrosis

Severe infection may compromise blood supply to the:

Femoral head

and lead to:

Osteonecrosis.

Physeal Injury

In children, infection may damage the:

Proximal femoral physis

and result in:

Growth disturbance

Angular deformity

or

Limb-length discrepancy.

Degenerative Joint Disease

Cartilage destruction may ultimately cause:

Secondary osteoarthritis

and chronic:

Pain and stiffness.

Deformity

Delayed or inadequately treated childhood infection can result in permanent:

Hip deformity

and loss of:

Joint congruity.

Ankylosis

Advanced destruction and healing may result in:

Severe stiffness

or

Ankylosis.

Patient Monitoring

Patients should be monitored closely for:

Fever

Pain

Range of motion

Weight-bearing ability

CRP

ESR

and other signs of response to treatment.

Failure to Improve

Persistent:

Pain

Fever

Joint effusion

or worsening inflammatory markers should raise concern for:

Inadequate drainage

Resistant infection

Associated osteomyelitis

or another undrained:

Abscess.

Repeat:

Aspiration

MRI

or

Surgical débridement

may be necessary.

Key Principle

Septic hip is a serious infection of the hip joint that can occur at any age and can rapidly destroy the femoral head and acetabulum.

The most common organism is:

Staphylococcus aureus, while hematogenous spread is particularly important in children and direct inoculation after surgery is a major mechanism in adults.

The most important diagnostic test is:

Image-guided hip aspiration for synovial fluid analysis and culture.

Treatment requires:

Prompt antibiotics after appropriate cultures and urgent joint drainage, usually by surgical irrigation and débridement.

Delayed treatment may result in:

Osteomyelitis, sepsis, subluxation or dislocation, osteonecrosis, growth disturbance, deformity, and secondary degenerative joint disease.