What is the appropriate evaluation and management of posterior knee pain at night in a 3-year-old girl?

Posterior Knee Pain at Night in a 3-Year-Old Girl

This is most likely growing pains, but nighttime pain in a young child is a red flag that requires careful evaluation to exclude serious pathology including infection, malignancy, or inflammatory disease before making this benign diagnosis.

Nighttime pain in a 3-year-old is a critical red flag that mandates systematic evaluation, as it may indicate spinal or musculoskeletal neoplasm (present in 25-30% of pediatric cases), discitis/osteomyelitis, or inflammatory arthritis rather than benign growing pains. 1

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Initial Clinical Assessment

Key History Elements to Obtain

• Duration and pattern of pain: Constant pain or pain lasting >4 weeks increases concern for serious pathology 2
• Associated systemic symptoms: Fever, unintentional weight loss, poor appetite, or vomiting suggest infection or malignancy 1
• Functional impact: Inability to bear weight, refusal to move, or gait abnormalities are red flags requiring immediate imaging 2, 1
• Timing specificity: Pain that awakens the child from sleep or occurs exclusively at rest is more concerning than activity-related pain 2, 1

Critical Physical Examination Findings

• Neurologic examination: Assess gait, strength, reflexes, and sensation; abnormal findings require immediate imaging 1
• Joint examination: Check for effusion, warmth, erythema, and range of motion limitations 3, 4
• Spinal examination: Evaluate for tenderness, abnormal curvature, or paraspinal muscle spasm 2, 1
• Systemic signs: Document fever, tachycardia, or lymphadenopathy 2

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Laboratory Testing Before Imaging

• Obtain baseline inflammatory markers including ESR, CRP, and complete blood count to evaluate for infection or inflammatory disease 1
• ESR ≥40 mm/hour, WBC ≥12,000 cells/mm³, and CRP >2.0 mg/dL are predictive of septic arthritis and warrant urgent intervention 1, 3

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Imaging Algorithm

Initial Imaging Study

• Begin with plain radiographs of the knee (anteroposterior and lateral views only) as the initial imaging study to assess for fractures, joint effusion, tumors, or degenerative changes 2, 5, 4
• Avoid oblique views as they double radiation exposure without added diagnostic benefit 1

When to Proceed Directly to MRI

If any of the following are present, proceed directly to MRI without waiting:

• Nighttime symptoms with systemic signs (vomiting, weight loss, fever) suggesting neoplasm or infection 1
• Normal radiographs but high clinical suspicion based on red flags 1
• Neurologic deficits on examination 2, 1
• Inability to bear weight or refusal to move 1

MRI Specifications When Indicated

• Order MRI of the complete spine with and without IV gadolinium contrast when intraspinal neoplasm or inflammatory process is suspected 1
• MRI has high sensitivity and specificity for detecting primary neoplasms, syringomyelia, transverse myelitis, and discitis/osteomyelitis 1
• Complete spine imaging is essential given the possibility of multifocal disease 1

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Critical Diagnoses to Exclude

Spinal or Musculoskeletal Neoplasm

• Persistent nighttime back or limb pain is the hallmark symptom of spinal neoplasm, present in 25-30% of pediatric cases 1
• Normal knee radiographs do not exclude referred pain from spinal pathology 1

Infection (Discitis/Osteomyelitis/Septic Arthritis)

• Presents with constant pain refractory to rest, may have fever, and requires immediate IV antibiotics targeting Staphylococcus aureus 1
• Urgent joint aspiration with synovial fluid analysis is required if significant effusion is present and infection is suspected 3
• Immediate orthopedic consultation for possible surgical drainage 1, 3

Inflammatory Arthritis

• Juvenile idiopathic arthritis can present with night pain and may affect multiple joints including the knee 1
• Requires rheumatology referral and consideration of disease-modifying therapy 1

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Management Based on Findings

If Serious Pathology is Identified

• Infection confirmed: Immediate IV antibiotics, orthopedic consultation for possible surgical drainage 1
• Neoplasm identified: Urgent oncology referral and advanced imaging 1
• Inflammatory arthritis diagnosed: Rheumatology referral and disease-modifying therapy 1

If Evaluation is Reassuring

• Only after excluding serious pathology, consider diagnosis of growing pains (benign nocturnal limb pains of childhood) 6, 4
• Growing pains typically affect both legs, occur in the evening/night, resolve by morning, and have completely normal examination and laboratory findings 4
• Management includes reassurance, massage, stretching, and acetaminophen or ibuprofen as needed 4

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Critical Pitfall to Avoid

Do not dismiss nighttime pain in a 3-year-old as "just growing pains" without systematic evaluation. Delays in identifying spinal cord compression, epidural abscess, or malignancy can result in permanent neurologic disability. 1 The key is that growing pains is a diagnosis of exclusion that can only be made after red flags have been systematically evaluated and ruled out. 2, 1, 4