What is the appropriate investigation and management for a 4-year-old child with mild genu varum (knocked knee)?

Management of Mild Genu Valgum (Knocked Knee) in a 4-Year-Old

This 4-year-old child with mild knocked knee requires only clinical observation and reassurance, as this represents physiological genu valgum that will spontaneously resolve without intervention. 1

Immediate Clinical Assessment

No investigation is needed for this child. The presentation is consistent with physiological genu valgum, which is normal at age 4 years. 1 However, specific measurements should be documented:

• Measure the intercondylar distance to quantify the valgus deformity severity. 1
• Assess for limb asymmetry between the right and left legs, as asymmetry suggests pathological rather than physiological deformity and would change management. 1
• Document growth parameters including height velocity, as the child's height (100cm) and weight (12.5kg) appear appropriate for age. 1

Red Flags Requiring Investigation

Investigation is NOT routinely required for mild knocked knee, but biochemical testing should be obtained if any of the following are present: 1

• Short stature or poor growth velocity (not present in this case)
• Severe or progressive deformity
• Dental problems or spontaneous dental abscesses (suggesting X-linked hypophosphatemia) 2, 1
• Family history of metabolic bone disease 1

If red flags are present, obtain: serum phosphate, alkaline phosphatase, calcium, and PTH levels. 1

Radiographic Evaluation Decision

Standing anteroposterior radiographs of both lower extremities are indicated only when: 1

• The deformity appears moderate to severe clinically
• Asymmetry exists between limbs
• The child has short stature or poor growth velocity

This child does not meet criteria for radiographic evaluation based on the "mild" description provided. 1

Management Plan

Observation and reassurance are the only interventions needed. 3 Physiological genu valgum at age 4 has a favorable natural history with spontaneous resolution. 3, 4

• No bracing, orthotics, or physical therapy is indicated for physiological genu valgum
• Schedule follow-up if the deformity persists beyond age 7 years or worsens progressively 1
• Educate parents that two-thirds of children with physiological lower limb alignment variations remain asymptomatic long-term 3

Referral Indications

Orthopedic referral is indicated for: 1

• Substantial or progressive deformity
• Asymmetric deformity between limbs
• Persistence beyond age 7-8 years
• Associated short stature with biochemical abnormalities

Metabolic bone disease specialist referral is necessary if biochemical testing reveals abnormalities suggesting rickets or other metabolic conditions. 1

Critical Pitfalls to Avoid

• Do not assume all knocked knee is physiological in children with short stature, poor growth, or systemic symptoms - these require metabolic workup. 1
• Do not overlook asymmetry - this is a red flag for pathological causes including focal fibrocartilaginous dysplasia or epiphyseal osteochondroma. 1, 5
• Do not delay biochemical testing when clinical features suggest metabolic bone disease, as early treatment with active vitamin D and phosphate supplementation improves outcomes in conditions like X-linked hypophosphatemia. 2, 1
• Do not order radiographs for mild, symmetric genu valgum in a normally growing 4-year-old - this represents overinvestigation of a physiological condition. 1, 4