What is the appropriate initial evaluation and management for a 7-year-old male presenting with bilateral red knees?

Bilateral Red Knees in a 7-Year-Old Male

Immediate Priority: Rule Out Septic Arthritis

The most critical first step is to determine if this child has septic arthritis, which is an orthopedic emergency requiring immediate intervention. 1

Key Clinical Assessment Points

Assess for infection indicators immediately:

• Fever and systemic symptoms strongly suggest septic arthritis 1
• Refusal to bear weight or move the joint are red flags for infection 1
• Check for recent bacteremia or infection elsewhere in the body 1
• If C-reactive protein >2.0 mg/dL in a child <5 years, this predicts >90% probability of septic arthritis 1

If septic arthritis is suspected, perform urgent ultrasound-guided joint aspiration immediately - do not delay for imaging 1. The bilateral presentation makes infection less likely than trauma or inflammatory arthritis, but it must be excluded first given the potentially devastating consequences of missed septic arthritis 2.

Determine Trauma History

Ask specifically about:

• Any fall, twisting injury, or significant mechanism of injury 1
• Timing of symptom onset relative to any trauma 3
• Ability to bear weight - inability to take four weight-bearing steps suggests fracture or serious pathology 1

The bilateral nature makes traumatic injury less likely unless there was a mechanism affecting both knees 3.

Physical Examination Essentials

Perform systematic examination looking for:

• Focal bony tenderness at the patella, fibular head, and tibial plateau 1
• Ability to flex knee to 90 degrees - inability suggests fracture or serious pathology 1
• Gross deformity or palpable mass - these mandate immediate radiographs 1
• Joint effusion presence - indicates significant pathology 1, 3
• Dactylitis ("sausage digits") or heel/Achilles tenderness - suggests psoriatic arthritis 4
• Skin examination for psoriatic plaques on knees, elbows, genitals, scalp, or nail changes, as 25-30% of psoriasis patients develop psoriatic arthritis 4

Always compare the affected knees with each other and assess symmetry of findings 3.

Initial Imaging Strategy

Obtain plain radiographs (anteroposterior and lateral views at 25-30 degrees flexion) as the initial imaging study 1. This is recommended by the American College of Radiology as first-line imaging 5, 1.

Radiographs should be obtained if any of the following are present:

• Age >55 years (not applicable here)
• Focal tenderness at patella or fibular head
• Inability to bear weight for 4 steps
• Inability to flex knee to 90 degrees
• Gross deformity or palpable mass 5, 1

Additional views to consider: cross-table lateral with horizontal beam, patellofemoral view, and internal/external oblique views for comprehensive assessment 1.

Differential Diagnosis Considerations

Given the bilateral presentation with redness in a 7-year-old, consider:

Inflammatory arthritis (most likely given bilateral presentation):

• Juvenile idiopathic arthritis - bilateral knee involvement is common 2
• Psoriatic arthritis - look for skin manifestations and dactylitis 4
• Reactive arthritis - ask about recent infections 3

Overuse syndromes:

• Osgood-Schlatter disease or other apophysitis - common in this age group 3

Less likely but must exclude:

• Septic arthritis - bilateral is rare but catastrophic if missed 1, 2
• Lyme disease - can cause bilateral knee arthritis 3

Management Based on Initial Findings

If radiographs show fracture: orthopedic consultation for fracture management 1

If radiographs normal but atraumatic effusion present: urgent ultrasound-guided joint aspiration if infection cannot be clinically excluded 1

If radiographs normal with trauma history and child can bear weight: conservative management with close follow-up 1

If inflammatory arthritis suspected:

• Check inflammatory markers (ESR, CRP) 4
• Consider rheumatoid factor (may be negative in psoriatic arthritis) 4
• Rheumatology referral for definitive diagnosis and management 4

MRI consideration: Not routinely indicated initially 1, but consider at 5-7 days if significant persistent effusion, inability to fully bear weight, mechanical symptoms, or joint instability present 1.

Critical Pitfall to Avoid

Do not assume bilateral presentation rules out septic arthritis - while uncommon, bilateral septic arthritis can occur, and the consequences of missing it include joint destruction, sepsis, and death 2. The threshold for joint aspiration should be low if any clinical concern for infection exists 1.