The Limping Child: A Systematic Approach

The limping child is one of the most common and anxiety-provoking presentations in orthopaedics. The differential diagnosis spans the spectrum from the benign (Transient Synovitis) to the catastrophic (Septic Arthritis, Osteosarcoma, Non-Accidental Injury). The challenge is compounded by the patient: a crying toddler cannot tell you "my hip hurts"; they just refuse to walk.

This guide provides a structured, age-based algorithm to navigate the diagnostic minefield, ensuring you never miss a "Red Flag" condition.

Visual Element: "The Age Wheel of Diagnosis". A circular graphic divided into 3 segments (Toddler, Child, Adolescent), populating the top 3 differentials for each age group.

The Golden Rules

1. It is the Hip until proven otherwise. The obturator nerve provides sensory innervation to both the hip and the knee. Hip pathology (Perthes, SCFE) frequently presents as isolated knee or thigh pain. Always examine the hip. Always X-ray the hip.
2. Examination involves the whole child. Look for rashes (Meningococcal, Henoch-Schonlein Purpura), bruising (NAI), and lymphadenopathy.
3. Night pain is a red flag. Growing pains occur in the evening but do not wake the child. Pain that wakes a child is infection or tumour until proven otherwise.

The Age-Based Differential

1. The Toddler (1 - 3 Years)

• Infection: Septic Arthritis / Osteomyelitis.
• Trauma: "Toddler's Fracture" (undisplaced spiral fracture of the distal tibia). Mechanism is often minor twist. X-rays may be normal initially.
• DDH: Missed developmental dysplasia presents as a painless waddling gait (Trendelenburg) or leg length discrepancy (Galeazzi).
• Discitis: Infection of the disc space. Child refuses to walk or sit.

2. The Young Child (4 - 10 Years)

• Transient Synovitis ("Irritable Hip"): The most common cause. A diagnosis of exclusion.
• Perthes Disease: Idiopathic avascular necrosis of the femoral head. Painless limp. Loss of Abduction and Internal Rotation.
• Leukemia: Can present as bone pain (marrow infiltration) and limp. Look for bruising/pallor.

3. The Adolescent (11 - 16 Years)

• SCFE (Slipped Capital Femoral Epiphysis): The obese adolescent. External rotation gait. Must not miss.
• Osgood-Schlatter: Tibial tubercle apophysitis.
• Avulsion Fractures: ASIS/AIIS avulsion in athletes.

The Critical Distinction: Septic Arthritis vs Transient Synovitis

Distinguishing a surgical emergency (septic hip) from a self-limiting viral reaction (transient synovitis) is the most common dilemma. We rely on the Kocher Criteria (probabilistic algorithm).

The 4 Criteria:

1. Non-weight bearing on affected side.
2. ESR > 40 mm/hr.
3. Fever > 38.5°C.
4. WBC > 12,000.

Probability of Septic Arthritis:

• 1 predictor: 3%
• 2 predictors: 40%
• 3 predictors: 93%
• 4 predictors: 99%

Update: C-Reactive Protein (CRP) > 20 mg/L has been added in modified criteria (Caird et al) as a strong independent predictor.

Visual Element: Flowchart for "The Irritable Hip". Algorithm starting with History/Exam -> X-ray -> Labs -> Ultrasound -> MRI/Aspiration decision node.

Specific Conditions in Detail

Transient Synovitis

• Pathology: Post-viral inflammation of the synovium.
• Presentation: Well child, afebrile, recent URTI. Limp or refusal to walk.
• Management: Rest, NSAIDs. Should improve within 24-48 hours.
• Safety Net: If not better in 48 hours, re-evaluate. It might be Perthes or early sepsis.

Perthes Disease (Legg-Calvé-Perthes)

• Epidemiology: Male > Female (4:1). Age 4-8. Hyperactive small child.
• Signs: Antalgic gait. Stiff hip (Loss of Abduction/Internal Rotation is key).
• X-ray Stages (Waldenstrom): Initial (sclerosis) -> Fragmentation -> Reossification -> Healed.
• Prognosis: "Head at Risk" signs (Herring Lateral Pillar classification). Older age (>8) = Worse outcome.

Slipped Capital Femoral Epiphysis (SCFE)

• Epidemiology: Obese adolescent. Endocrine disorders (Hypothyroid).
• Pathology: The femoral neck slips anteriorly and superiorly relative to the epiphysis (Ice cream falling off the cone).
• Classification (Loder):
  • Stable: Can bear weight. Low risk of AVN.
  • Unstable: Cannot bear weight. High risk of AVN (up to 50%).
• Treatment: In situ screw fixation. Do not attempt to reduce (risk of AVN).

Toddler's Fracture

• Mechanism: Twisting injury (e.g., getting foot caught, sliding down slide).
• Exam: No focal tenderness often. Swelling minimal.
• X-ray: Faint spiral line on AP tibia. Often invisible.
• Management: Long leg cast for 3-4 weeks. If X-ray normal but suspicion high, cast and repeat X-ray in 10 days (callus visible).

Workup Protocol

1. History: Fever? Trauma? Recent viral illness? Night pain?
2. Exam: Gait? Spine (discitis)? Abdominal exam (psoas abscess)? Hip ROM? Knee/Ankle? Neurovascular?
3. X-Ray: AP Pelvis (Frog leg lateral is essential for SCFE). AP/Lat Tibia/Femur.
4. Blood: FBC, ESR, CRP (if red flags or fever).
5. Ultrasound: Highly sensitive for hip effusion. (Note: Transient synovitis and Septic arthritis BOTH have effusions; US cannot distinguish the fluid type, only its presence).
6. MRI: Gold standard for osteomyelitis, early Perthes, stress fractures.

Summary

The limping child requires a detective's mind.

• Filter by Age.
• Apply Kocher Criteria to rule out sepsis.
• Don't miss the Hip in a child with knee pain.
• Believe the parents. If they say the child isn't right, they aren't right.

Pediatric Gait Gallery

Video library showing classic gait patterns: Antalgic, Trendelenburg, Circumduction, and Short Leg gait.