Genu Varum

Genu varum is a deformation of the knee joint(s) that creates angulation of the lower limb(s) away from the midline in the coronal plane. Children ages 1–5 years are commonly affected. Many cases of genu varum are physiologic and will resolve with further growth. However, it is critical to differentiate between normal physiologic changes and pathologic disorders, as pathologic cases can have serious long-term consequences if not corrected. Clinical presentation includes characteristic outward bowing of the lower limbs accompanied by gait disturbances. Diagnosis is clinical but may require support with diagnostic imaging. Management is often supportive but may require surgical intervention.

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Overview

Definition

  • Genu varum is an angular deformity of the knee:
    • Apex pointing away from the midline
    • Coronal plane deformity of the lower extremity
    • Characteristic waddling gait
    • Becomes evident when toddler begins to walk
  • Common for toddlers to have physiologic genu varum: 
    • Common up to 3 years old
    • Generally symmetric and pain-free
    • Associated with tripping/intoeing
    • Generally self-correcting
    • Can be the result of intrauterine positioning
  • Pathologic genu varum: varus deformation that persists beyond the expected time frame because of an underlying condition:
    • Blount disease
    • Rickets
    • Skeletal dysplasia
  • Colloquially known as “bow-legged,” genu valgum is the Latin-derived term to describe the deformity.  

Classification

  • Bilateral
  • Unilateral (e.g., Blount disease)
  • Distinguished from genu valgum by the direction of angular deformity relative to the midline:
    • Genu varum: apex displaced away from the midline
    • Genu valgum: apex displaced toward the midline
Genu varum and valgum

Genu varum and genu valgum: note the difference in angulation in the coronal plane.

Image by Lecturio. License: CC BY-NC-SA 4.0

Epidemiology

  • Seen in children 2–5 years of age 
  • Present in 8% of schoolchildren 
  • More common among overweight or obese schoolchildren
  • More common in countries where malnutrition is usually seen

Etiology

  • Metabolic bone diseases:  
    • Rickets
    • Hyperparathyroidism
  • Asymmetric epiphysiodesis: 
    • Blount disease (tibia vara): 
      • Infantile
      • Juvenile
      • Adolescent
    • Trauma
    • Infection
    • Tumors
  • Skeletal dysplasias: 
    • Metaphyseal dysplasia
    • Achondroplasia
    • Pseudoachondroplasia
  • Digestive disorders: 
    • Celiac sprue
    • Inflammatory bowel disease
  • Disorder of bone/connective tissue fragility: 
    • Osteogenesis imperfecta
    • Ehlers–Danlos syndrome

Pathophysiology

  • Normal alignment:
    • Lower-extremity lengths are equal.
    • Mechanical axis bisects the knee in the anatomical position.
    • Balanced load on the medial and lateral compartments of the knee
    • Balanced load on the collateral ligaments
    • Patella centered in the femoral sulcus
  • Genu varum defined by medial displacement of the mechanical axis:
    • Medial femoral condyle and the medial plateau of the tibia subjected to pathologic loading
    • Leads to inhibition of normal ossification of the epiphysis
    • Lateral collateral ligaments become stretched.
    • Severe deformity leads to: 
      • Knee pain 
      • Lateral thrust during gait
      • Characteristic intoeing
      • Patient walks with a waddling gait
    • Long-term effects:
      • Medial meniscal tears
      • Tibiofemoral subluxation
      • Articular cartilage attrition
      • Arthrosis of medial compartment of the knee

Clinical Presentation

History

Parents describe a bow-legged appearance and abnormal gait.

Physical examination

  • Bowing of the legs away from the midline when the child stands upright
  • Observe in a weight-bearing position with feet together.
  • Bowing may be symmetrical or asymmetrical.
  • Measure intercondylar distance.
  • Waddling gait is typical.
Pathologic genu varum

Pathologic genu varum in a patient with osteomalacia

Image: “Genu varum” by Latifa Tahiri, et al. License: CC BY 2.0

Diagnosis

Diagnosis is primarily based on clinical examination. It is critical to differentiate between normal physiologic genu varum and a pathologic process.

Diagnostic evaluation

  • Physiologic genu varum:
    • Common normal variant in toddlers
    • Asymptomatic and symmetric
    • Resolves by age 2–3 years 
  • Symptomatic or unilateral genu valgum should be referred to an orthopedist.
  • Laboratory evaluation aims to uncover underlying syndrome or disorder:
    • Renal function
    • Vitamin/mineral levels
  • Bone densitometry may be appropriate if underlying nutritional/malabsorption/metabolic disorder is present.

Imaging

X-ray:

  • Not indicated in cases of physiologic genu varum
  • Indications for X-rays:
    • Asymmetrical genu varum 
    • Excessive genu varum
    • Patients beyond the age group for physiologic genu varum 
    • Patients < 10th percentile height for their age with genu varum
    • History of trauma involving the knee
    • Concern for infection
  • Standing anteroposterior (AP) radiography of the lower extremities:
    • Taken with patellae facing forward 
    • Allows visualization of true and apparent limb lengths and deformities
  • Mechanical axis determination:
    • Line drawn from the center of femoral head to center of ankle
    • Line should bisect the knee
    • Genu varum shows medial deviation of the axis toward or beyond the joint margin.
  • Deformity may be femoral, tibial, or both. 
  • AP radiography of wrist to determine bone age and remaining growth potential
X-ray of a child with genu varum

X-ray of a child with genu varum

Image: “ Pseudoachondroplasia in a four-year-old boy, who presented with genu vara and short stature” by Bhattacharya, K., et al. License: CC BY 4.0, cropped by Lecturio.

Management

The majority of cases of genu varum are physiologic and should resolve spontaneously; thus, they require only observation and expectant management.

Nonoperative management

Observation:

1st-line treatment, appropriate if:

  • Patient is within the age range for physiologic genu varum.
  • Spontaneous resolution by age 2–3

Medical management: 

  • Indicated in cases of underlying medical conditions and metabolic disorders:
    • Correct nutritional deficiencies.
    • Optimize bone formation and mineralization:
      • Vitamin D
      • Calcium
      • Bisphosphonates
  • Bracing:
    • Not necessary for physiologic genu varum 
    • Not effective for pathologic genu varum
  • Bracing may be used in early treatment of Blount disease.

Surgical management

  • Indicated in severe pathologic genu varum
  • Surgical options:
    • Guided growth with hemiepiphysiodesis or physeal tethering:
      • Indicated for severe varus in children with ≥ 2 years of growth potential 
      • Reversible and minimally invasive 
      • Extraperiosteally placed implants (plates and screws)
      • Implant serves as a tension band for gradual growth changes
    • Distal femoral varus osteotomy:
      •  Indicated in patients who are at or near skeletal maturity 
      • Risk of peroneal nerve injury mitigated by peroneal nerve release
  • Special surgical considerations in management of Blount disease

Complications

  • Due to failure to recognize pathologic genu varum:
    • Continued progression of unrecognized underlying medical illness
    • Gait disturbances
    • Premature arthritis
    • Chronic pain
  • Surgical complications:
    • Hardware failure is much less common with newer implants.
    • Physeal injuries due to implants: less common with guided-growth method
    • Overcorrection or undercorrection
    • Neurovascular injury (peroneal nerve injury with osteotomy) 
    • Infection
  • Most cases of physiologic genu varum resolve spontaneously by age 2–3 years.
  • Results of cases of pathologic genu varum using guided-growth techniques with close follow-up are generally positive.

Clinical Relevance

  • Rickets and osteomalacia: disorders of decreased bone mineralization. Rickets affects the cartilage of the epiphyseal growth plates in children, while osteomalacia affects the sites of bone turnover in children and adults. Although most cases of rickets and osteomalacia are due to vitamin D deficiency, other genetic and nutritional disorders, as well as medications, can cause these disorders.
  • Vitamin D deficiency: state of deficiency of the forms of vitamin D, which alters the homeostasis of calcium due to deficient absorption in the diet and reabsorption in the kidneys.

References

  1. Browner, B., Jupiter, J., Krettek, C., Anderson, P. (2020). Skeletal Trauma: Basic Science, Management, and Reconstruction. Philadelphia: Elsevier.
  2. Kliegman, R., et al. (2020). Nelson Textbook of Pediatrics. Philadelphia: Elsevier.
  3. Zitelli, B., McIntire, S., Nowalk, A. (2018). Zitelli and Davis’ Atlas of Pediatric Physical Diagnosis. Philadelphia: Elsevier.
  4. Murthy, D., & De Leucio, A. (2021). Blount disease. StatPearls. Retrieved June 24, 2021, from http://www.ncbi.nlm.nih.gov/books/NBK560923/

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