Genu Valgum

Overview

Definition

• Genu valgum is an angular deformity of the knee:
  • Apex pointing to the midline
  • Coronal plane deformity of the lower extremity
  • Characteristic compensatory circumduction gait
  • Becomes evident when toddler begins to walk
• Can be seen as a normal physiologic process during growth in healthy children:
  • Physiologic genu valgum: toddlers 2–6 years of age
  • Critical to differentiate between physiologic and pathologic genu valgum 
  • Can be related to hereditary, genetic, or metabolic bone disorders
• Colloquially known as “knock knees,” genu valgum is the Latin-derived term to describe the deformity. 

Classification

• Bilateral
• Unilateral
• Distinguished from genu varum 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

Epidemiology

• Generally presents between ages 3 and 10 years
• Present in 10% of schoolchildren 
• More common among overweight or obese schoolchildren
• Can be familial, associated with trauma, rheumatologic diseases, or metabolic bone disorders

Etiology

Bilateral genu valgum:

• Physiologic:
  • Presents in ages 2–6 years 
  • Accounts for majority of cases
• Adolescent idiopathic genu valgum: 
  • Typically bilateral
  • May be familial
• Metabolic (nutritional rickets)
• Renal osteodystrophy (renal rickets)
• Genetic/chromosomal disorders:
  • Down syndrome
  • Marfan syndrome
  • Neurofibromatosis
  • Hereditary multiple exostosis
  • Osteogenesis imperfecta
• Skeletal dysplasia:
  • Morquio syndrome
  • Spondyloepiphyseal dysplasia
  • Chondroectodermal dysplasia

Unilateral genu valgum:

• Physeal injury: 
  • Trauma
  • Infection
  • Vascular insult
• Fracture malunion:
  • Distal femur fracture
  • Proximal metaphyseal tibia fracture
• Poliomyelitis
• Benign tumors:
  • Fibrous dysplasia
  • Osteochondromas
  • Ollier disease

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 valgum alignment:
  • Defined by lateral displacement of the mechanical axis
  • Lateral femoral condyle and the lateral plateau of the tibia subjected to pathologic loading
  • Distal femur is the most common location of primary pathologic genu valgum.
  • Leads to inhibition of normal ossification of the epiphysis and the development of a shallow femoral sulcus (where the patella rests):
    • Propensity for patellar tilt and lateral patellar subluxation
    • Patellofemoral joint becomes unstable
  • Medial collateral ligaments become stretched 
  • Severe deformity leads to: 
    • Knee pain 
    • Tibial thrust during gait → progressive ligament laxity
    • Patient walks with a circumduction gait
  • Long-term effects:
    • Lateral meniscal tears
    • Tibiofemoral subluxation
    • Patellofemoral dislocation
    • Progressive joint laxity
    • Articular cartilage attrition
    • Arthrosis of anterior (patellofemoral) lateral compartments of the knee
    • Osteochondral fractures

Clinical Presentation

History

• Parents describe a knock-kneed appearance and abnormal gait.
• Family history of specific heritable conditions: 
  • Multiple exostosis
  • Osteogenesis imperfecta
  • Marfan syndrome
• Natural history of physiologic genu valgum:
  • Resolves by age 6
  • Lacks functional restrictions
  • Pain-free

Physical examination

• Angular deviation of the knee(s) in the coronal plane
• Changes may be symmetrical or asymmetrical.
• Physiologic genu valgum:
  • Generalized ligamentous laxity
  • ≤ 20 degrees of valgus angulation may be normal at 3–4 years of age.
  • Should resolve to ≤ 12 degrees of valgus angulation by age 7
• Evaluation of the gait: circumduction typical
• Leg-length evaluation important
• Screen for other signs of genetic syndromes.

Diagnosis

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

Diagnostic evaluation

• Physiologic genu valgum is a common normal variant in toddlers:
  • Asymptomatic and symmetric
  • Resolves by age 6–7 
• 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 valgum
• Indications for X-rays:
  • Asymmetrical genu valgum 
  • Excessive genu valgum
  • Patients beyond the age group for physiologic genu valgum 
  • Patients ＜ 10th percentile height for their age with genu valgum
  • 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 valgum shows lateral 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

Management

The majority of cases of genu valgum 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 valgum.
• Tibiofemoral angle is < 15 degrees.
• Child is < 6 years of age.

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 valgum 
  • Not effective for pathologic genu valgum

Surgical management

• Indicated in severe pathologic genu valgum
• Surgical options:
  • Guided growth with hemiepiphysiodesis or physeal tethering:
    • Indicated for > 15–20 degrees of valgus in children < 10 years of age 
    • 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.

Complications

• Due to failure to recognize pathologic genu valgum:
  • 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

Prognosis

• Most cases of physiologic genu valgum resolve spontaneously. 
• Results of cases of pathologic genu valgum 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.