Harvey's Garden

Angular deformities of the lower extremities

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5 min read

Normal Physiologic Alignment & Progression

  • Birth to 18–24 months: Physiologic genu varum (bowlegs).
    • Symmetric bowing.
    • Max bowing occurs at ~6–12 months.
    • Normalizes to neutral alignment by 18–24 months.
  • 2 to 5 years: Physiologic genu valgum (knock-knees).
    • Alignment shifts to valgus; peaks at ~3–4 years of age.
  • 6 to 7 years to adulthood: Gradually resolves to normal adult alignment (~5–7° of valgus).

“Red Flags” Suggesting Pathologic Deformity

  • Unilateral or asymmetric presentation.
  • Severe or progressive angulation outside the typical age range (e.g., genu varum worsening after age 2; genu valgum persisting after age 7).
  • Associated short stature (<5th percentile for age).
  • Pain, limp, or abnormal gait (e.g., lateral thrust during stance phase).
  • Intercondylar distance (femoral) > 6 cm in genu varum.
  • Intermalleolar distance > 8 cm in genu valgum.
  • Concomitant systemic manifestations (e.g., craniotabes, rachitic rosary, dental abnormalities).

Genu Varum (Bowlegs)

Etiologies

  • Physiologic Genu Varum:
    • Bilateral, symmetric, painless; normal stature; self-corrects by age 2.
  • Blount Disease (Tibia Vara):
    • Pathologic disruption of the posteromedial proximal tibial physis.
    • Risk Factors: African descent, early walking (<1 year), childhood obesity.
    • Types:
      • Infantile (1–3 years): Often bilateral, severe progressive varus, medial tibial torsion.
      • Adolescent (>8 years): Unilateral, associated w/ rapid weight gain.
    • Imaging: Sharp, medial beaking of proximal tibial metaphysis, sloped epiphysis.
  • Nutritional Rickets:
    • Defective mineralization of osteoid secondary to Vitamin D deficiency.
    • Signs: Craniotabes, rachitic rosary (costochondral swelling), widened wrists, bowing.
    • Labs: ↓ / normal Ca, ↓↓ Phos, ↑↑ ALP, ↑ PTH, ↓ 25-OH Vit D.
    • Imaging: Metaphyseal fraying, cupping, and widening.
  • Skeletal Dysplasias:
    • E.g., Achondroplasia (FGFR3 mutation: rhizomelic limb shortening, macrocephaly, frontal bossing).
  • Post-Traumatic / Post-Infectious:
    • Physeal injury (Salter-Harris fractures) or osteomyelitis leading to asymmetric growth arrest.

Genu Valgum (Knock-Knees)

Etiologies

  • Physiologic Genu Valgum:
    • Symmetric, age 2–5, resolves spontaneously by age 7–8; intermalleolar distance < 8 cm.
  • Renal Osteodystrophy (“Renal Rickets”):
    • Chronic kidney disease (CKD) → impaired 1-alpha-hydroxylase → ↓ 1,25-(OH)2 Vit D + phosphate retention → secondary hyperparathyroidism.
    • Common cause of severe pathologic genu valgum in older children/adolescents.
  • Post-Traumatic (Cozen Phenomenon):
    • Valgus deformity following a proximal tibial metaphyseal fracture (transient asymmetric hypervascularity and overgrowth of medial physis).
  • Skeletal Dysplasias & Connective Tissue Disorders:
    • E.g., Ehlers-Danlos syndrome, Marfan syndrome, Morquio syndrome.

Diagnostic Workup

Initial / Physical Exam

  • Measure Intercondylar Distance (varum: knees apart with ankles touching).
  • Measure Intermalleolar Distance (valgum: ankles apart with knees touching).
  • Evaluate rotational profile: Assess for internal/external tibial torsion and femoral anteversion.
  • Gait analysis: Assess for lateral thrust (knee shifts laterally during stance phase → indicates Blount disease or ligamentous laxity).

Imaging

  • Full-Length Standing AP & Lateral Radiographs (hips to ankles, weight-bearing):
    • Indicated only if red flags are present (asymmetry, pain, age > 2 for varum, severe progression).
    • Measures mechanical axis deviation (MAD) and tibial-femoral angle.
    • Identifies metaphyseal beaking (Blount disease) or cupping/fraying (Rickets).

Laboratory Evaluation

  • Indicated if rickets, renal disease, or skeletal dysplasia suspected:
    • Serum Ca, Phos, ALP, Cr, BUN.
    • 25-OH Vit D (screen for nutritional deficiency).
    • 1,25-(OH)2 Vit D (if CKD or Vit D-dependent rickets suspected).
    • Intact PTH.

Differential Diagnostics

  • Physiologic Genu Varum vs. Blount Disease:
    • Physiologic: Resolves by 18–24 mo; diffuse bowing of femur and tibia; normal tibial metaphysis.
    • Blount: Progressive; localized to proximal medial tibia; medial metaphyseal beaking and stepping on XR.
  • Blount Disease vs. Nutritional Rickets:
    • Blount: Normal serum labs (Ca, Phos, ALP normal); isolated tibial physis deformity.
    • Rickets: Abnormal labs (↑ ALP, ↓ Phos); generalized skeletal involvement (widened wrists, rachitic rosary, diffuse fraying).
  • Physiologic Genu Valgum vs. Renal Osteodystrophy:
    • Physiologic: Peak age 3–4, normal labs, no systemic signs.
    • Renal Osteodystrophy: Older child/adolescent, azotemia (↑ Cr/BUN), ↑ Phos, ↓ Ca, ↑ PTH.

Management

Physiologic Varum / Valgum

  • Reassurance and Observation:
    • No orthotics, special shoes, or braces required (ineffective and unnecessary).
    • Follow-up clinically every 4–6 months to document expected resolution.

Pathologic Genu Varum

  • Infantile Blount Disease:
    • Initial: KAFO (Knee-Ankle-Foot Orthosis) brace if age < 3 years and early stage (Langenskiöld stage I–II).
    • Surgical: Proximal tibial realignment osteotomy if no response to bracing by age 4 or stage ≥ III.
  • Adolescent Blount Disease:
    • Bracing is ineffective.
    • Surgical: Guided growth (temporary hemiepiphysiodesis using 8-plates) if sufficient growth remains; corrective osteotomy if near skeletal maturity.
  • Nutritional Rickets:
    • Medical: High-dose oral Vitamin D (Ergocalciferol/Cholecalciferol) + supplemental calcium.
    • Skeletal deformity corrects spontaneously once remineralization occurs; surgery reserved for persistent deformities after metabolic normalization.

Pathologic Genu Valgum

  • Mild to Moderate (Growing Child):
    • Guided growth (medial hemiepiphysiodesis) to allow lateral side to catch up.
  • Severe / Skeletally Mature:
    • Corrective femoral/tibial osteotomy.
  • Renal Osteodystrophy:
    • Phosphate binders, Calcitriol, dietary phosphate restriction; optimize dialysis/renal transplant.

High-Yield USMLE Pearls

  • Timeline Rule: Bowlegs up to age 2, knock-knees from age 2 to 5, normal adult alignment by age 7.
  • Lateral thrust during gait is a pathognomonic clinical clue for Blount disease or severe ligamentous instability.
  • Never order radiographs or braces for an asymptomatic, normally growing 14-month-old with mild, symmetric bowlegs → select Reassurance/Observation.
  • Widened wrist physes + metaphyseal fraying/cupping on XR = Rickets; isolated proximal medial tibial beaking in an obese, early-walking toddler = Blount disease.

Graph View

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