Treatment of Genu Varum (Bowing of Legs)
Initial Assessment: Distinguishing Physiologic from Pathologic Bowing
The primary management decision hinges on determining whether the bowing is physiologic (self-resolving) or pathologic (requiring intervention). Most children with bow legs have physiologic genu varum that resolves spontaneously by age 2-3 years without treatment 1, 2.
Clinical Screening Tool: The "Cover-Up Test"
Use the "cover-up test" to identify children at high risk for pathologic bowing (infantile tibia vara/Blount disease) who require radiographic evaluation 3:
- Negative test (physiologic bowing): Obvious valgus alignment of the proximal lower leg relative to the thigh—these children do not require X-rays and should be followed clinically for resolution 3
- Positive test (possible pathologic bowing): Neutral or varus alignment of the proximal lower leg—these children require standing radiographs of the entire lower limbs or specialist referral 3
The cover-up test has 100% sensitivity and 100% negative predictive value, meaning a negative test reliably excludes pathologic bowing 3.
Age-Based Follow-Up Protocol for Physiologic Genu Varum
For children with physiologic bowing (negative cover-up test), follow this monitoring schedule 1:
- Presenting before 18 months: Expect initial correction between 18-24 months, with resolution by 30 months of age 1
- Presenting between 18-23 months: Expect initial correction between 24-30 months, with resolution by 36 months of age 1
- Presenting at 24 months or older: Requires closer monitoring as physiologic bowing typically resolves by this age 1
Use regular well-child visits and fingerbreadth measurements of intercondylar distance to track progression 1. Children with physiologic bowing often walk earlier than average (10 months vs. 12-15 months) 1.
When to Obtain Radiographs and Specialist Referral
Order standing radiographs of the entire lower limbs if 2, 3:
- Positive cover-up test (neutral or varus alignment of proximal tibia) 3
- Persistence of bowing beyond expected resolution age (30-36 months depending on presentation age) 1
- Progressive worsening of deformity 1
- Unilateral bowing (asymmetric) 2
- Associated short stature or systemic symptoms 2
Pathologic Causes Requiring Specific Treatment
Metabolic Bone Disease (X-Linked Hypophosphatemia)
Consider X-linked hypophosphatemia (XLH) in children with persistent genu varum, especially with short stature and abnormal gait 4, 5. Biochemical screening should include serum phosphate, alkaline phosphatase, vitamin D levels, parathyroid hormone, and FGF23 4. Radiographs show partial fraying and irregularity of distal femoral and proximal tibial growth plates 4.
Medical treatment with phosphate supplementation and active vitamin D can improve bowing in XLH 6, 4. Maximize medical therapy for at least 12 months before considering surgery 6.
Surgical Indications for Pathologic Genu Varum
Surgery should be performed only after medical treatment has been optimized for at least 12 months 6. Consider surgical correction when 6:
- Persisting deformity (mechanical axis deviation Zone 2 or greater) despite optimized medical treatment 6
- Symptoms interfering with function 6
- Progressive joint instability 6
Surgical timing considerations 6:
Guided growth techniques (hemiepiphysiodesis with plates): Must be performed at least 2-3 years before skeletal maturity (age 14 in girls, age 16 in boys) to allow sufficient remaining growth potential 6. This technique corrects deformity at the physis before significant diaphyseal deformity develops, with success rates showing rapid correction of both varus and valgus deformities 6.
Osteotomy: Complications reduce when performed later in childhood or after skeletal maturity 6. Osteotomy provides acute or gradual correction in all three planes but carries a 29% recurrence rate and 57% complication rate, especially in young children with poor metabolic control 6.
Surgery should be performed by a surgeon with expertise in metabolic bone diseases 6.
Complications of Untreated Pathologic Genu Varum
Failure to treat pathologic genu varum leads to 4, 5:
- Abnormal gait and decreased mobility 4
- Progressive joint damage and early osteoarthritis 4
- Decreased growth velocity and disproportionate short stature (in metabolic causes) 4
Systemic Conditions Associated with Genu Varum
Evaluate for underlying systemic conditions when bowing is pathologic 2:
- Idiopathic tibia vara (Blount disease)—most common pathologic cause 2
- Achondroplasia 2
- Vitamin D-resistant rickets 2
- Renal osteodystrophy 2
- Osteogenesis imperfecta 2
- Focal fibrocartilaginous dysplasia (rare, usually requires no treatment) 2
Key Clinical Pitfalls to Avoid
- Do not routinely obtain radiographs in children under 3 years with physiologic bowing (negative cover-up test)—this exposes children to unnecessary radiation and is not cost-effective 3
- Do not delay evaluation in children with positive cover-up test—all children with positive tests require radiographic evaluation or specialist referral 3
- Do not perform surgery before maximizing medical therapy for 12 months in metabolic bone disease 6
- Do not use guided growth techniques in adolescents near skeletal maturity—insufficient remaining growth potential will prevent correction 6
- Measure actual femur length, not linear distance between femur ends, when bowing is present—this ensures accurate assessment and avoids misclassification 6