Orthopaedic Surgery - Hip Pain in the Child

Basics

Hip pain in a child usually refers to discomfort arising from structures around the hip and commonly perceived in the groin, lateral hip, anterolateral thigh, or even the knee.

The groin receives sensory innervation largely through branches of the femoral and obturator nerves, which helps explain why pathology within the hip joint is frequently perceived anteriorly.

Pain may originate from numerous structures, including:

The joint capsule and synovium, pelvis, proximal femur, surrounding muscles and tendons, peripheral nerves, blood vessels, buttock, groin, and pelvic structures.

Because several causes of pediatric hip pain require urgent treatment and may cause permanent disability if diagnosis is delayed, every child with significant hip pain or unexplained limp requires a careful evaluation.

Epidemiology

Transient synovitis is commonly reported as the most frequent cause of acute hip pain in children.

Several important pediatric hip disorders show a male predominance.

Historical male-to-female ratios include approximately:

Transient synovitis: 2:1

SCFE: approximately 2.5:1

Osteomyelitis: approximately 4:1

Legg–Calvé–Perthes disease: approximately 6:1

Septic arthritis also demonstrates a slight male predominance.

Incidence

Transient Synovitis

The lifetime risk of at least one episode of transient synovitis during childhood has been estimated at approximately 3%.

Legg–Calvé–Perthes Disease

Peak incidence occurs at approximately 6 years of age.

Historical incidence is approximately 1 per 1,500 children, although rates vary among populations.

Slipped Capital Femoral Epiphysis

SCFE occurs almost exclusively during preadolescence and adolescence.

Its incidence has historically been estimated at approximately 1 per 10,000 children, although prevalence varies substantially with age, sex, ethnicity, and obesity.

Risk Factors

Risk factors depend on the underlying diagnosis.

Important examples include:

Juvenile inflammatory arthritis, trauma, impaired immune function, obesity, and age.

Obesity, adolescence, and mechanical stress are particularly associated with SCFE.

Genetics

Most causes of pediatric hip pain do not follow a simple hereditary pattern.

A minority of patients with SCFE have a positive family history, historically reported in approximately 4% of cases.

Etiology

The two most common acute causes of hip pain in children are transient synovitis and septic arthritis, but the differential diagnosis is broad.

Transient Synovitis

Transient synovitis is a self-limited inflammatory process involving the hip joint.

Age

The average age at presentation is approximately 6 years, with most cases occurring between 3 and 8 years.

Associations

The disorder may follow:

A recent viral illness, minor trauma, or an allergic or inflammatory stimulus.

In many children, no clear precipitating cause is identified.

Septic Arthritis

Septic arthritis is a bacterial infection of the hip joint and represents an orthopaedic emergency.

Approximately two-thirds of cases historically occur in children younger than 3 years.

Mechanism

Infection may reach the hip by:

Hematogenous spread through the synovial blood supply or direct extension from adjacent osteomyelitis.

Infants

During approximately the first 12–18 months of life, transphyseal vascular channels may permit infection to spread from the proximal femoral metaphysis into the epiphysis and hip joint.

For this reason, concomitant proximal femoral osteomyelitis and septic arthritis are particularly important in infants.

Organisms

The causative organism varies with age and immunization history.

Staphylococcus aureus remains a major pathogen across pediatric age groups.

Historically, neonatal infections were also associated with streptococci and other organisms, while Haemophilus influenzae type b was an important cause before widespread vaccination.

Sexually active adolescents may rarely develop gonococcal septic arthritis.

Legg–Calvé–Perthes Disease

Perthes disease is an idiopathic osteonecrosis of the developing femoral head.

Its exact cause remains unknown.

Proposed contributing mechanisms include:

Vascular interruption, thrombosis, hypercoagulability, repetitive trauma, and other disturbances of femoral-head perfusion.

Slipped Capital Femoral Epiphysis

SCFE results from failure of the proximal femoral physis during adolescent growth.

Potential contributing factors include:

Mechanical stress, physeal weakness during rapid growth, obesity, trauma, and hormonal or metabolic influences.

Approximately 80% of affected patients have historically been described as overweight or obese.

Other Causes of Pediatric Hip Pain

Other etiologic categories include:

Infectious, traumatic, neoplastic, inflammatory, hematologic, developmental, and idiopathic conditions.

Associated Conditions

Transient synovitis may occur in association with:

Current or recent viral illness, minor trauma, or an allergic-type inflammatory event.

Diagnosis

Signs and Symptoms

Hip pathology may produce pain in several locations.

Common sites include:

The groin, greater trochanter, anterolateral thigh, medial thigh, or knee.

An important principle is that knee pain in a child may originate from the hip.

Muscle Guarding

Inflammation or pain within the hip frequently causes involuntary muscle spasm or guarding.

The child may hold the hip in a position that maximizes capsular volume and minimizes discomfort.

Loss of Motion

Both active and passive hip motion may become restricted.

The pattern of restriction can provide diagnostic clues.

Perthes Disease and Hip Dysplasia

Loss of abduction and internal rotation is characteristic.

SCFE

A particularly important finding is obligatory external rotation of the hip during attempted flexion.

As the hip is flexed, the thigh progressively rotates outward.

This finding strongly suggests SCFE.

Weight Bearing

Refusal or inability to bear weight is an important red flag.

Possible causes include:

Septic arthritis, osteomyelitis, fracture, severe transient synovitis, or unstable SCFE.

Limp

The child may have either:

An antalgic painful limp or a relatively painless chronic limp, depending on the disorder.

Muscle Atrophy

Long-standing disease may cause wasting of the:

Thigh, gluteal, or other periarticular musculature.

This finding suggests a more chronic process.

Fever

Fever should raise concern for infection, especially:

Septic arthritis or osteomyelitis.

Absence of fever does not completely exclude infection.

Physical Examination

Inspection

Inspect the child at rest and, when possible, during standing and walking.

Look for:

Abnormal limb position, swelling, erythema, bruising, muscle wasting, limb-length discrepancy, or deformity.

Palpation

Palpate the:

Hip, groin, greater trochanter, buttock, lower back, pelvis, and thigh.

Assess for:

Warmth, focal tenderness, swelling, fluctuance, or tenderness over a bursa or bone.

Resting Position

Document the spontaneous position of the limb.

A child with an irritable hip may hold it in slight flexion, abduction, and external rotation to reduce capsular pressure.

Range of Motion

Active and passive range of motion of both the hip and knee should be examined and compared with the opposite side.

Particular attention should be given to:

Internal rotation, external rotation, abduction, and flexion.

Loss of internal rotation is often one of the earliest findings in many intra-articular hip disorders.

Neurovascular Examination

A complete distal motor, sensory, and vascular examination should be documented.

Weakness, numbness, abnormal reflexes, or poor perfusion may point toward neurologic, spinal, or vascular pathology rather than an isolated joint disorder.

Gait Examination

If the child is able to walk safely, observe the gait.

Assessment may include:

Normal walking, toe walking, heel walking, stride length, stance duration, trunk position, and symmetry.

An antalgic gait is characterized by decreased stance time on the painful side.

Hip Aspiration

If septic arthritis is suspected, urgent aspiration of the hip joint should be considered.

Because the hip is deep, aspiration is usually performed with ultrasound or fluoroscopic guidance.

Fluid should be sent for appropriate microbiologic and laboratory analysis.

Laboratory Tests

Routine blood studies may be normal in:

Transient synovitis, Perthes disease, SCFE, and developmental hip dysplasia.

However, laboratory testing is important when infection is part of the differential diagnosis.

Septic Arthritis Laboratory Findings

Common abnormalities include:

Elevated leukocyte count, neutrophilia or left shift, elevated ESR, and elevated C-reactive protein.

No single blood test confirms or excludes septic arthritis.

Synovial Fluid

The synovial white blood cell count is an important diagnostic measure.

A value greater than approximately 50,000 cells/mm³, particularly with a high neutrophil percentage, strongly raises concern for septic arthritis, although lower counts can still occur with infection.

Blood Cultures

Blood cultures should be obtained early when septic arthritis or osteomyelitis is suspected.

Historically, blood cultures have been positive in approximately 40% of children with septic arthritis or osteomyelitis.

Imaging

Plain Radiographs

Radiographs are commonly the first imaging study for persistent or significant hip pain.

Typical views include an AP pelvis and appropriate lateral hip view, depending on the suspected disorder.

Septic Arthritis

Early plain radiographs may show:

Soft-tissue swelling, capsular distension, or displacement of normal fat planes.

They can also help exclude fracture, SCFE, Perthes disease, or advanced osteomyelitis.

Osteomyelitis

Early radiographs can be normal.

As infection progresses, findings may include:

Loss of normal bone density, cortical or medullary lucency, periosteal reaction, sclerosis, and progressive osseous destruction.

Untreated proximal femoral infection may ultimately damage the femoral head.

Transient Synovitis

AP and lateral radiographs are typically normal or nonspecific.

Their main purpose is to exclude other structural disease.

Ultrasound may demonstrate an effusion but cannot reliably distinguish transient synovitis from septic arthritis.

Legg–Calvé–Perthes Disease

Radiographic abnormalities evolve over time.

Early Findings

Early findings may include:

Failure of expected epiphyseal growth, increased density or sclerosis of the femoral head, and subtle loss of normal contour.

Later Findings

Progressive disease may produce:

Subchondral fracture, fragmentation, femoral-neck shortening, flattening, extrusion, and eventual enlargement or deformity of the femoral head.

Slipped Capital Femoral Epiphysis

Radiographs may show:

Physeal widening or irregularity, osteopenia around the physis, and displacement of the proximal femoral epiphysis relative to the metaphysis.

Both hips should generally be evaluated because bilateral disease is not uncommon.

When an unstable SCFE is suspected, forceful frog-leg positioning should be avoided.

Pathological Findings

Septic Arthritis

Early disease causes synovial inflammation and hypertrophy.

Without rapid treatment, bacterial enzymes and inflammatory mediators can destroy the articular cartilage.

SCFE

The femoral head remains seated within the acetabulum while the proximal femoral metaphysis displaces relative to the epiphysis.

The epiphysis is therefore effectively positioned posteriorly and inferiorly relative to the metaphysis.

Perthes Disease

Progressive femoral-head osteonecrosis can result in:

Flattening, extrusion, fragmentation, and deformity of the capital femoral epiphysis.

Differential Diagnosis

Transient synovitis is common but should remain a diagnosis of exclusion, particularly until infection and other serious conditions have been considered.

Infectious Causes

Important infectious conditions include:

Septic arthritis of the hip, proximal femoral osteomyelitis, pelvic osteomyelitis, sacroiliac septic arthritis, discitis, pyomyositis, and psoas infection or abscess.

Developmental and Mechanical Causes

These include:

Legg–Calvé–Perthes disease, SCFE, developmental hip dysplasia, and early degenerative or chondral disease.

Inflammatory Causes

Consider:

Juvenile idiopathic arthritis and other inflammatory arthropathies.

Neoplastic Causes

Tumors involving the:

Pelvis, spine, proximal femur, or surrounding soft tissues may present with hip or referred knee pain.

Hematologic and Malignant Disorders

Consider:

Sickle cell crisis, leukemia, and lymphoma.

Extra-Articular Causes

Other possibilities include:

Iliopsoas bursitis, greater trochanteric bursitis, pyomyositis, referred lumbar or sacroiliac pain, and other nonarticular disorders.

Treatment

Management depends entirely on the underlying diagnosis.

Transient Synovitis

Transient synovitis is usually self-limited.

Treatment focuses on symptom relief.

Rest

Relative rest and temporary reduction in weight bearing are appropriate until pain improves and a normal or near-normal range of motion returns.

NSAIDs

Anti-inflammatory medication may reduce pain and synovial irritation.

Natural History

Symptoms usually resolve spontaneously.

Failure to improve as expected should prompt reassessment of the diagnosis.

Septic Arthritis

Septic arthritis requires urgent treatment because irreversible cartilage injury can occur rapidly.

Drainage

The infected joint should be aspirated and, when indicated, surgically irrigated and debrided.

Antibiotics

Empiric broad-spectrum intravenous antibiotics are started after appropriate cultures are obtained whenever feasible, then narrowed according to culture and susceptibility results.

The route and total duration of treatment depend on:

The organism, clinical response, inflammatory markers, presence of adjacent osteomyelitis, and local infectious-disease protocols.

Rigid historical treatment durations should not replace clinical and laboratory response.

Positioning

When severe capsular distension has occurred, the hip may temporarily be positioned to reduce discomfort, historically including mild abduction.

Range of Motion

After infection is controlled and drainage is no longer required, gentle range-of-motion exercises are begun to minimize stiffness.

Osteomyelitis

Antibiotic therapy is the primary treatment.

Surgical drainage or debridement may be required when there is:

Abscess formation, necrotic bone, failure of medical treatment, or need for diagnostic tissue sampling.

Legg–Calvé–Perthes Disease

Treatment aims to preserve:

Femoral-head containment, hip range of motion, and the most spherical possible femoral-head shape during healing.

Nonoperative Care

Measures may include:

Activity modification, maintenance of hip motion, treatment of synovitis, and temporary reduction in weight bearing when symptoms are severe.

Traction or bed rest has historically been used during painful episodes, although prolonged immobilization is generally avoided.

Surgery

Selected patients with more extensive disease may require femoral or pelvic reconstruction to improve containment of the femoral head within the acetabulum.

Slipped Capital Femoral Epiphysis

SCFE requires prompt stabilization to prevent further displacement.

Initial Management

Once SCFE is suspected, the child should generally be made non–weight bearing until definitive treatment.

Surgery

The standard treatment for most stable slips is in situ percutaneous screw fixation.

Forceful reduction should be avoided because vascular injury to the femoral head can cause osteonecrosis.

Physical Therapy

Formal physical therapy is not routinely needed for every child with hip pain.

Its role depends on the diagnosis and may include:

Gait retraining, maintenance of range of motion, strengthening, and postoperative rehabilitation.

Medication

Septic Arthritis and Osteomyelitis

Appropriate antimicrobial therapy is essential.

Treatment should be tailored to the likely organism initially and then adjusted to culture results.

Transient Synovitis

NSAIDs may be used for symptomatic relief.

Surgery

Septic Arthritis

Surgical treatment may involve:

Irrigation, debridement, and drainage of the hip joint.

An anterior or other suitable approach may be chosen according to surgeon preference and clinical circumstances.

Osteomyelitis

If operative drainage is necessary, a cortical window may be created to permit:

Culture, curettage, and decompression of infected bone.

Chronic osteomyelitis, although uncommon in children with modern treatment, may require more extensive debridement.

Perthes Disease

Severe disease may require reconstructive surgery involving either the:

Proximal femur, acetabulum, or both to improve containment.

SCFE

Percutaneous in situ fixation is performed to prevent progression of the slip and reduce the risk of additional deformity.

Follow-Up

Prognosis of Septic Arthritis and Osteomyelitis

Early diagnosis and treatment can produce a good outcome.

Delayed or chronic infection may result in permanent deformity.

Prognosis of Perthes Disease

Outcome generally improves when:

The child is younger at disease onset, the necrotic segment is smaller, femoral-head extrusion is minimal, and hip range of motion remains good.

Some residual radiographic deformity may persist even when clinical function is satisfactory.

Prognosis of SCFE

Long-term outcome depends substantially on the severity of the slip and development of complications.

More severe deformity is associated with a greater risk of later femoroacetabular impingement and degenerative arthritis.

Complications

Septic Arthritis and Osteomyelitis

Untreated infection can be devastating in a growing child.

Potential consequences include:

Femoral-head or physeal destruction, limb shortening, joint incongruity, stiffness, deformity, growth disturbance, and early degenerative arthritis.

Cartilage injury can begin very early in the course of untreated bacterial arthritis, reinforcing the need for urgent treatment.

SCFE Complications

Major complications include:

Osteonecrosis and chondrolysis.

Osteonecrosis

Disruption of the femoral-head blood supply may occur as a consequence of the unstable slip or overly aggressive reduction.

Chondrolysis

Chondrolysis is rapid loss of articular cartilage and produces:

Joint-space narrowing, stiffness, contracture, pain, and limp.

Degenerative Arthritis

Patients with SCFE have an increased long-term risk of premature hip osteoarthritis, particularly when residual deformity is substantial.

Patient Monitoring

Septic Arthritis and Osteomyelitis

Clinical recovery should be followed together with inflammatory markers such as:

C-reactive protein and ESR.

A downward trend toward normal supports successful treatment.

Antibiotic duration should be guided by the overall clinical course, inflammatory markers, microbiology, and presence or absence of associated osteomyelitis.

Transient Synovitis

Observation is appropriate when symptoms improve predictably and serious alternative diagnoses have been excluded.

Persistent, recurrent, or worsening symptoms require reevaluation.

Legg–Calvé–Perthes Disease

Children with limited femoral-head involvement may be managed with observation and serial clinical and radiographic assessment.

Historically, involvement of less than approximately 50% of the femoral head has been associated with a more favorable course.

Important Clinical Red Flags

Urgent evaluation is particularly important in a child with:

Fever, inability to bear weight, severe pain with passive hip motion, rapidly progressive symptoms, night pain, systemic illness, significant trauma, or suspected unstable SCFE.

These findings may indicate a condition in which delayed treatment risks permanent damage to the hip.